Models#
qpdk.models contains frequency-domain circuit models for the QPDK
components, built on SAX, together with
the analytical helpers used to design them. Install them with
pip install qpdk[models].
SAX models
Transmon, fluxonium, flipmon and unimon circuits, bare or coupled to a resonator.
Quarter- and half-wave transmission-line resonators and their coupled variants.
Straight and ring couplers between CPW lines.
Interdigital and plate capacitors, meander inductors and lumped-element resonators.
Single junctions and SQUIDs.
Straights, bends, tapers, launchers, airbridges, bumps, TSVs, rectangles and generic N-port blocks.
Opens, shorts, series and shunt elements and ideal LC resonators.
Helper functions
Effective permittivity, characteristic impedance and propagation of CPW and microstrip lines.
Conversions between circuit energies, capacitances and inductances, and unimon spectra.
Transmon frequency and anharmonicity, dispersive shifts, Purcell decay, linewidths and dephasing.
Closed-form estimates for resonators, couplers and inductors.
SAX models#
Frequency-domain models returning S-parameter dictionaries (sax.SDict). Pass them to sax.circuit() to simulate netlists, or call them directly with a frequency array f.
Qubits#
Transmon, fluxonium, flipmon and unimon circuits, bare or coupled to a resonator.
LC resonator model for a double-island transmon qubit. |
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LC resonator model for a double-island transmon qubit with bounding box ports. |
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Model for a double-island transmon qubit coupled to a quarter-wave resonator. |
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LC resonator model for a double-pad transmon qubit. |
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LC resonator model for a double-island transmon qubit with bounding box ports. |
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Model for a double-island transmon qubit coupled to a quarter-wave resonator. |
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LC resonator model for a flipmon qubit. |
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LC resonator model for a flipmon qubit with bounding box ports. |
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Model for a flipmon qubit coupled to a quarter-wave resonator. |
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S-parameter model for a fluxonium qubit. |
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Coupled fluxonium qubit model. |
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S-parameter model for a fluxonium qubit with bounding box ports. |
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Model for a fluxonium qubit coupled to a quarter-wave resonator. |
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Model for a transmon qubit coupled to a quarter-wave resonator. |
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LC resonator model for a shunted transmon qubit. |
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Coupled transmon qubit model. |
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Model for a transmon qubit coupled to a quarter-wave resonator. |
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SAX model for a capacitively coupled unimon qubit. |
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LC resonator model for an Xmon style transmon qubit. |
double_island_transmon#
- qpdk.models.double_island_transmon(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a double-island transmon qubit.
A double-island transmon has two superconducting islands connected by Josephson junctions, with both islands floating (not grounded). This is modeled as an ungrounded parallel LC resonator.
The qubit frequency is approximately:
\[f_\text{q} \approx \frac{1}{2\pi} \sqrt{8 E_\text{J} E_\text{C}} - E_\text{C}\]For the LC model, the resonance frequency is:
\[f_\text{r} = \frac{1}{2\pi\sqrt{LC}}\]Use
ec_to_capacitance()andej_to_inductance()to convert from qubit Hamiltonian parameters.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (FloatArrayLike) – Total capacitance \(C_\Sigma\) of the qubit in Farads.
inductance (FloatArrayLike) – Josephson inductance \(L_\text{J}\) in Henries.
ground_capacitance (FloatArrayLike) – Parasitic capacitance to ground \(C_\text{g}\) at each port in Farads.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.double_island_transmon() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
double_island_transmon_with_bbox#
- qpdk.models.double_island_transmon_with_bbox(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a double-island transmon qubit with bounding box ports.
This model is the same as
double_island_transmon().- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
ground_capacitance (FloatArrayLike)
(Source code, svg, pdf, png)
qpdk.models.double_island_transmon_with_bbox() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
double_island_transmon_with_resonator#
- qpdk.models.double_island_transmon_with_resonator(f=5000000000.0, qubit_capacitance=1e-13, qubit_inductance=1e-09, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)[source]#
Model for a double-island transmon qubit coupled to a quarter-wave resonator.
This model is identical to
qubit_with_resonator()but the qubit is set to floating.
(Source code, svg, pdf, png)
qpdk.models.double_island_transmon_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
double_pad_transmon#
- qpdk.models.double_pad_transmon(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a double-pad transmon qubit.
Physically the
double_island_transmon()model, with ports renamed toleft_padandright_padto match the layout cell ports.- Returns:
S-parameters dictionary with ports left_pad and right_pad.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
ground_capacitance (FloatArrayLike)
double_pad_transmon_with_bbox#
- qpdk.models.double_pad_transmon_with_bbox(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)#
LC resonator model for a double-island transmon qubit with bounding box ports.
This model is the same as
double_island_transmon().- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
ground_capacitance (FloatArrayLike)
(Source code, svg, pdf, png)
qpdk.models.double_pad_transmon_with_bbox() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
double_pad_transmon_with_resonator#
- qpdk.models.double_pad_transmon_with_resonator(f=5000000000.0, qubit_capacitance=1e-13, qubit_inductance=1e-09, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)#
Model for a double-island transmon qubit coupled to a quarter-wave resonator.
This model is identical to
qubit_with_resonator()but the qubit is set to floating.
(Source code, svg, pdf, png)
qpdk.models.double_pad_transmon_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
flipmon#
- qpdk.models.flipmon(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a flipmon qubit.
This model is identical to
double_island_transmon().- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
ground_capacitance (FloatArrayLike)
(Source code, svg, pdf, png)
qpdk.models.flipmon() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
flipmon_with_bbox#
- qpdk.models.flipmon_with_bbox(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a flipmon qubit with bounding box ports.
This model is the same as
flipmon().- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
ground_capacitance (FloatArrayLike)
(Source code, svg, pdf, png)
qpdk.models.flipmon_with_bbox() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
flipmon_with_resonator#
- qpdk.models.flipmon_with_resonator(f=5000000000.0, qubit_capacitance=1e-13, qubit_inductance=1e-09, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)[source]#
Model for a flipmon qubit coupled to a quarter-wave resonator.
This model is identical to
qubit_with_resonator()but the qubit is set to floating.
(Source code, svg, pdf, png)
qpdk.models.flipmon_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
fluxonium#
- qpdk.models.fluxonium(f=5000000000.0, capacitance=1e-14, josephson_inductance=1e-08, superinductance=5e-07, ground_capacitance=0.0)[source]#
S-parameter model for a fluxonium qubit.
A fluxonium qubit consists of a Josephson junction shunted by a large superinductance and a capacitor. In the linear regime, this is modeled as a parallel LCL circuit.
For an accurate microwave model reflecting the real physical layout, the circuit is treated as ungrounded (floating) with optional symmetric parasitic capacitances connecting both ends to ground [NLS+19].
Note
The total shunt capacitance capacitance should include the pads, junction capacitance, and parasitic meander capacitance. Spurious array self-resonance (SR) modes can be phenomenologically modeled by adding to the shunt capacitance or using a multimode model.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (float) – Total shunt capacitance \(C_\Sigma\) in Farads.
josephson_inductance (float) – Josephson inductance \(L_\text{J}\) in Henries.
superinductance (float) – Superinductance \(L_\text{s}\) in Henries.
ground_capacitance (float) – Parasitic capacitance to ground \(C_\text{g}\) at each port in Farads.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.fluxonium() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
fluxonium_coupled#
- qpdk.models.fluxonium_coupled(f=5000000000.0, capacitance=1e-14, josephson_inductance=1e-08, superinductance=5e-07, ground_capacitance=0.0, coupling_capacitance=1e-14, coupling_inductance=0.0)[source]#
Coupled fluxonium qubit model.
This model adds a coupling network to the fluxonium model.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (float) – Total shunt capacitance \(C_\Sigma\) in Farads.
josephson_inductance (float) – Josephson inductance \(L_\text{J}\) in Henries.
superinductance (float) – Superinductance \(L_\text{s}\) in Henries.
ground_capacitance (float) – Parasitic capacitance to ground \(C_\text{g}\) in Farads.
coupling_capacitance (float) – Coupling capacitance \(C_\text{c}\) in Farads.
coupling_inductance (float) – Coupling inductance \(L_\text{c}\) in Henries.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.fluxonium_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
fluxonium_with_bbox#
- qpdk.models.fluxonium_with_bbox(f=5000000000.0, capacitance=1e-14, josephson_inductance=1e-08, superinductance=5e-07, ground_capacitance=0.0)[source]#
S-parameter model for a fluxonium qubit with bounding box ports.
This model is the same as
fluxonium().
(Source code, svg, pdf, png)
qpdk.models.fluxonium_with_bbox() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
fluxonium_with_resonator#
- qpdk.models.fluxonium_with_resonator(f=5000000000.0, capacitance=1e-14, josephson_inductance=1e-08, superinductance=5e-07, ground_capacitance=0.0, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)[source]#
Model for a fluxonium qubit coupled to a quarter-wave resonator.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (float) – Total shunt capacitance \(C_\Sigma\) in Farads.
josephson_inductance (float) – Josephson inductance \(L_\text{J}\) in Henries.
superinductance (float) – Superinductance \(L_\text{s}\) in Henries.
ground_capacitance (float) – Parasitic capacitance to ground \(C_\text{g}\) in Farads.
resonator_length (float) – Length of the quarter-wave resonator in µm.
resonator_cross_section (str) – Cross-section specification for the resonator.
coupling_capacitance (float) – Coupling capacitance between qubit and resonator in Farads.
- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.fluxonium_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
qubit_with_resonator#
- qpdk.models.qubit_with_resonator(f=5000000000.0, qubit_capacitance=1e-13, qubit_inductance=1e-09, qubit_grounded=False, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)[source]#
Model for a transmon qubit coupled to a quarter-wave resonator.
This model corresponds to the layout function
transmon_with_resonator().The model combines: - A transmon qubit (LC resonator) - A quarter-wave coplanar waveguide resonator - A coupling capacitor connecting the qubit to the resonator
The qubit can be either: - A double-island transmon (
qubit_grounded=False): both islands floating - A shunted transmon (qubit_grounded=True): one island groundedUse
ec_to_capacitance()andej_to_inductance()to convert from qubit Hamiltonian parameters (\(E_\text{C}\), \(E_\text{J}\)) to circuit parameters.Note
This function is not JIT-compiled because it depends on
straight_shorted(), which internally uses cpw_parameters for transmission line modeling.- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
qubit_capacitance (float) – Total capacitance \(C_\Sigma\) of the qubit in Farads. Convert from charging energy using
ec_to_capacitance().qubit_inductance (float) – Josephson inductance \(L_\text{J}\) in Henries. Convert from Josephson energy using
ej_to_inductance().qubit_grounded (bool) – If True, the qubit is a shunted transmon (grounded). If False, it is a double-island transmon (ungrounded).
resonator_length (float) – Length of the quarter-wave resonator in µm.
resonator_cross_section (str) – Cross-section specification for the resonator.
coupling_capacitance (float) – Coupling capacitance between qubit and resonator in Farads. Use
coupling_strength_to_capacitance()to convert from qubit-resonator coupling strength \(g\).
- Returns:
- S-parameters dictionary with ports
o1(resonator input) and
o2(qubit ground or floating).
- S-parameters dictionary with ports
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.qubit_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
shunted_transmon#
- qpdk.models.shunted_transmon(f=5000000000.0, capacitance=1e-13, inductance=7e-09, ground_capacitance=0.0)[source]#
LC resonator model for a shunted transmon qubit.
A shunted transmon has one island grounded and the other island connected to the junction. This is modeled as a grounded parallel LC resonator.
The qubit frequency is approximately:
\[f_\text{q} \approx \frac{1}{2\pi} \sqrt{8 E_\text{J} E_\text{C}} - E_\text{C}\]For the LC model, the resonance frequency is:
\[f_\text{r} = \frac{1}{2\pi\sqrt{LC}}\]Use
ec_to_capacitance()andej_to_inductance()to convert from qubit Hamiltonian parameters.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (FloatArrayLike) – Total capacitance \(C_\Sigma\) of the qubit in Farads.
inductance (FloatArrayLike) – Josephson inductance \(L_\text{J}\) in Henries.
ground_capacitance (FloatArrayLike) – Parasitic capacitance to ground \(C_\text{g}\) at the floating port in Farads.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.shunted_transmon() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
transmon_coupled#
- qpdk.models.transmon_coupled(f=5000000000.0, capacitance=1e-13, inductance=1e-09, grounded=False, ground_capacitance=0.0, coupling_capacitance=1e-14, coupling_inductance=0.0)[source]#
Coupled transmon qubit model.
This model extends the basic transmon qubit by adding a coupling network consisting of a parallel capacitor and/or inductor. This can represent capacitive or inductive coupling between qubits or between a qubit and a readout resonator.
The coupling network is connected in series with the LC resonator:
- For capacitive coupling (common for qubit-resonator coupling):
Set
coupling_capacitanceto the coupling capacitor valueSet
coupling_inductance=0.0
- For inductive coupling (common for flux-tunable coupling):
Set
coupling_inductanceto the coupling inductor valueSet
coupling_capacitance=0.0(or small value)
Use
coupling_strength_to_capacitance()to convert from the qubit-resonator coupling strength \(g\) to the coupling capacitance.- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (FloatArrayLike) – Total capacitance \(C_\Sigma\) of the qubit in Farads.
inductance (FloatArrayLike) – Josephson inductance \(L_\text{J}\) in Henries.
grounded (bool) – If True, the qubit is a shunted transmon (grounded). If False, it is a double-pad transmon (ungrounded).
ground_capacitance (FloatArrayLike) – Parasitic capacitance to ground \(C_\text{g}\) in Farads.
coupling_capacitance (FloatArrayLike) – Coupling capacitance \(C_\text{c}\) in Farads.
coupling_inductance (FloatArrayLike) – Coupling inductance \(L_\text{c}\) in Henries.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.transmon_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
transmon_with_resonator#
- qpdk.models.transmon_with_resonator(f=5000000000.0, qubit_capacitance=1e-13, qubit_inductance=1e-09, qubit_grounded=False, resonator_length=5000.0, resonator_cross_section='cpw', coupling_capacitance=1e-14)[source]#
Model for a transmon qubit coupled to a quarter-wave resonator.
This model is identical to
qubit_with_resonator().
(Source code, svg, pdf, png)
qpdk.models.transmon_with_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
unimon_coupled#
- qpdk.models.unimon_coupled(f=5000000000.0, arm_length=3000.0, cross_section='cpw', junction_capacitance=5e-15, junction_inductance=-7e-09, coupling_capacitance=1e-14)[source]#
SAX model for a capacitively coupled unimon qubit.
The unimon is modeled as a closed system of two shorted quarter-wave CPW resonators connected by a Josephson junction. Interaction with the qubit is provided via a single coupling capacitor connected to one of the arms.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
arm_length (float) – Length of each quarter-wave resonator arm in µm.
cross_section (str) – Cross-section specification for the CPW arms.
junction_capacitance (float) – Junction capacitance \(C_\text{J}\) in Farads.
junction_inductance (float) – Junction inductance \(L_\text{J}\) in Henries.
coupling_capacitance (float) – Coupling capacitance \(C_\text{c}\) in Farads.
- Returns:
S-parameters dictionary with a single port
o1.- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.unimon_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
xmon_transmon#
- qpdk.models.xmon_transmon(f=5000000000.0, capacitance=1e-13, inductance=7e-09)[source]#
LC resonator model for an Xmon style transmon qubit.
An Xmon transmon is typically shunted, so this model wraps
shunted_transmon().- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
- Parameters:
f (FloatArrayLike)
capacitance (FloatArrayLike)
inductance (FloatArrayLike)
(Source code, svg, pdf, png)
qpdk.models.xmon_transmon() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Resonators#
Quarter- and half-wave transmission-line resonators and their coupled variants.
Model for a quarter-wave coplanar waveguide resonator coupled to a probeline. |
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S-parameter model for a simple transmission line resonator. |
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Model for a coplanar waveguide resonator coupled to a probeline. |
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S-parameter model for a half-wave resonator (open at both ends). |
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S-parameter model for a quarter-wave resonator (shorted at one end). |
quarter_wave_resonator_coupled#
- qpdk.models.quarter_wave_resonator_coupled(f=5000000000.0, length=4000.0, coupling_gap=20.0, coupling_straight_length=200.0, cross_section='cpw', cross_section_non_resonator='cpw')[source]#
Model for a quarter-wave coplanar waveguide resonator coupled to a probeline.
- Parameters:
cross_section (CrossSectionSpec) – The cross-section of the CPW.
f (FloatArrayLike) – Frequency in Hz at which to evaluate the S-parameters.
length (float) – Total length of the resonator in μm.
coupling_gap (float) – Gap between the resonator and the probeline in μm.
coupling_straight_length (float) – Length of the coupling section in μm.
cross_section_non_resonator (CrossSectionSpec | None) – Cross-section of the coupling waveguide. If
None, usescross_section.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.quarter_wave_resonator_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
resonator#
- qpdk.models.resonator(f=5000000000.0, length=4000.0, cross_section='cpw')[source]#
S-parameter model for a simple transmission line resonator.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
resonator_coupled#
- qpdk.models.resonator_coupled(f=5000000000.0, length=4000.0, coupling_gap=20.0, coupling_straight_length=200.0, cross_section='cpw', cross_section_non_resonator='cpw', open_start=True, open_end=False)[source]#
Model for a coplanar waveguide resonator coupled to a probeline.
- Parameters:
cross_section (CrossSectionSpec) – The cross-section of the CPW.
f (FloatArrayLike) – Frequency in Hz at which to evaluate the S-parameters.
length (float) – Total length of the resonator in μm.
coupling_gap (float) – Gap between the resonator and the probeline in μm.
coupling_straight_length (float) – Length of the coupling section in μm.
cross_section_non_resonator (CrossSectionSpec | None) – Cross-section of the coupling waveguide. If
None, usescross_section.open_start (bool) – If True, adds an electrical open at the start.
open_end (bool) – If True, adds an electrical open at the end.
- Returns:
S-parameters dictionary with 4 ports.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.resonator_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
resonator_half_wave#
- qpdk.models.resonator_half_wave(f=5000000000.0, length=4000.0, cross_section='cpw')[source]#
S-parameter model for a half-wave resonator (open at both ends).
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.resonator_half_wave() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
resonator_quarter_wave#
- qpdk.models.resonator_quarter_wave(f=5000000000.0, length=4000.0, cross_section='cpw')[source]#
S-parameter model for a quarter-wave resonator (shorted at one end).
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.resonator_quarter_wave() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Couplers#
Straight and ring couplers between CPW lines.
S-parameter model for two coupled coplanar waveguides in a ring configuration. |
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S-parameter model for two coupled coplanar waveguides, |
coupler_ring#
- qpdk.models.coupler_ring(f=5000000000.0, length_x=20.0, gap=16, cross_section='cpw')[source]#
S-parameter model for two coupled coplanar waveguides in a ring configuration.
The implementation is the same as straight coupler for now.
TODO: Fetch coupling capacitance from a curved simulation library.
- Parameters:
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.coupler_ring() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
coupler_straight#
- qpdk.models.coupler_straight(f=5000000000.0, length=10, gap=16, cross_section='cpw', cross_section_non_resonator=None, resonator_offset=0.0)[source]#
S-parameter model for two coupled coplanar waveguides,
coupler_straight().- Parameters:
f (ArrayLike) – Array of frequency points in Hz
length (int | float) – Physical length of coupling section in µm
gap (int | float) – Gap between the coupled waveguides in µm
cross_section (CrossSectionSpec) – The cross-section of the CPW.
cross_section_non_resonator (CrossSectionSpec | None) – Optional cross section of the upper bus.
resonator_offset (float) – Lower trace layout offset in µm; the legacy model retains the full nominal coupling length.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
o2──────▲───────o3 │gap o1──────▼───────o4
(Source code, svg, pdf, png)
qpdk.models.coupler_straight() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Capacitors and inductors#
Interdigital and plate capacitors, meander inductors and lumped-element resonators.
Interdigital capacitor Sax model. |
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Lumped-element LC resonator SAX model. |
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Meander inductor SAX model. |
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Plate capacitor Sax model. |
interdigital_capacitor#
- qpdk.models.interdigital_capacitor(*, f=5000000000.0, fingers=4, finger_length=20.0, finger_gap=2.0, thickness=5.0, cross_section='cpw')[source]#
Interdigital capacitor Sax model.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
fingers (int) – Total number of fingers (must be >= 2)
finger_length (float) – Length of each finger in μm
finger_gap (float) – Gap between adjacent fingers in μm
thickness (float) – Thickness of fingers in μm
cross_section (CrossSectionSpec) – Cross-section specification
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.interdigital_capacitor() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
lumped_element_resonator#
- qpdk.models.lumped_element_resonator(*, f=5000000000.0, fingers=20, finger_length=20.0, finger_gap=2.0, finger_thickness=5.0, n_turns=15, sheet_inductance=4e-13, cross_section='meander_inductor_cross_section', grounded=False)[source]#
Lumped-element LC resonator SAX model.
Combines an interdigital capacitor and a meander inductor in parallel to form an LC resonator. The resonance frequency is:
\[f_\text{r} = \frac{1}{2\pi\sqrt{LC}}\]where \(C\) is computed from the interdigital capacitor geometry using
interdigital_capacitor_capacitance_analytical()and \(L\) is computed from the meander inductor geometry usingmeander_inductor_inductance_analytical().The inductor section uses the width and gap derived from the cross_section to ensure consistent RF behavior across the meander. The vertical spacing between meander runs is set to twice the etch gap to prevent overlap of the etched regions.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
fingers (int) – Number of interdigital capacitor fingers.
finger_length (float) – Length of each capacitor finger in µm.
finger_gap (float) – Gap between adjacent capacitor fingers in µm.
finger_thickness (float) – Width of each capacitor finger in µm.
n_turns (int) – Number of horizontal meander inductor runs (must be odd to match the cell geometry where the path spans left-to-right bus bars).
sheet_inductance (float) – Sheet inductance per square in H/□.
cross_section (CrossSectionSpec) – Cross-section specification. Used for substrate permittivity and to determine inductor wire width and gap.
grounded (bool) – If True, one port of the resonator is grounded.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.lumped_element_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
meander_inductor#
- qpdk.models.meander_inductor(*, f=5000000000.0, n_turns=5, turn_length=200.0, cross_section='meander_inductor_cross_section', wire_gap=None, sheet_inductance=4e-13)[source]#
Meander inductor SAX model.
Computes the inductance from the meander geometry and returns S-parameters of an equivalent lumped inductor.
The model extracts the center conductor width and gap from the provided cross-section. The vertical pitch is calculated as:
\[p = w + \text{wire gap}\]where \(w\) is the center conductor width. Without an explicit
wire_gap, the gap defaults to twice the etch-section width so that the etched regions of adjacent meander runs do not overlap and interfere with the characteristic impedance of each other, or to \(w\) for cross-sections without an etch section such as a plain microstrip.- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
n_turns (int) – Number of horizontal meander runs.
turn_length (float) – Length of each horizontal run in µm.
cross_section (CrossSectionSpec) – Cross-section specification for the meander wire. Used to determine the wire width and the gap between runs.
wire_gap (float | None) – Optional explicit gap between adjacent meander runs in µm. If None (default), it is inferred from the cross-section the same way the meander inductor cell does it. An explicit gap is used as is, whether or not the cross-section defines an etch section, and must be positive.
sheet_inductance (float) – Sheet inductance per square in H/□.
- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.meander_inductor() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
plate_capacitor#
- qpdk.models.plate_capacitor(*, f=5000000000.0, length=26.0, width=5.0, gap=7.0, cross_section='cpw')[source]#
Plate capacitor Sax model.
- Parameters:
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.plate_capacitor() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Josephson junctions#
Single junctions and SQUIDs.
Josephson junction (RCSJ) small-signal Sax model. |
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DC SQUID small-signal Sax model in the zero-screening limit. |
josephson_junction#
- qpdk.models.josephson_junction(*, f=5000000000.0, ic=1e-06, capacitance=5e-15, resistance=10000.0, ib=0.0)[source]#
Josephson junction (RCSJ) small-signal Sax model.
Linearized RCSJ model consisting of a bias-dependent Josephson inductance in parallel with capacitance and resistance.
Valid in the superconducting (zero-voltage) state and for small AC signals.
Default capacitance taken from [SFS+15].
See [McC68] for details.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
ic (Float) – Critical current \(I_\text{c}\) in Amperes
capacitance (Float) – Junction capacitance \(C\) in Farads
resistance (Float) – Shunt resistance \(R\) in Ohms
ib (Float) – DC bias current \(I_\text{b}\) in Amperes (\(\|I_\text{b}\| < I_\text{c}\))
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.josephson_junction() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
squid_junction#
- qpdk.models.squid_junction(*, f=5000000000.0, ic_tot=2e-06, asymmetry=0.0, capacitance=1e-14, resistance=5000.0, ib=0.0, flux=0.0)[source]#
DC SQUID small-signal Sax model in the zero-screening limit.
Treats the DC SQUID as a single effective RCSJ whose critical current is tunable by an external magnetic flux. Assumes negligible loop geometric inductance.
See [KYG+07] and [Tin15] for details on asymmetric SQUIDs and effective Josephson inductance.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
ic_tot (Float) – Total critical current sum \(I_{\text{c}1} + I_{\text{c}2}\) in Amperes
asymmetry (Float) – Junction asymmetry \((I_{\text{c}1} - I_{\text{c}2}) / I_{\text{c,tot}}\)
capacitance (Float) – Total SQUID capacitance \(C_1 + C_2\) in Farads
resistance (Float) – Total SQUID shunt resistance \(R_1 || R_2\) in Ohms
ib (Float) – DC bias current \(I_\text{b}\) in Amperes
flux (FloatArrayLike) – External magnetic flux \(\Phi_{\text{ext}}\) in Webers
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.squid_junction() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Waveguides and interconnects#
Straights, bends, tapers, launchers, airbridges, bumps, TSVs, rectangles and generic N-port blocks.
S-parameter model for a superconducting CPW airbridge. |
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S-parameter model for a circular bend, wrapped to |
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S-parameter model for a circular bend, wrapped to |
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S-parameter model for an Euler bend, wrapped to |
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S-parameter model for an Euler bend, wrapped to |
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S-parameter model for an S-bend, wrapped to |
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S-parameter model for an indium bump, wrapped to |
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S-parameter model for a launcher, effectively a straight section followed by a taper. |
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NxN junction model using tee components. |
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S-parameter model for a rectangular section, wrapped to |
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S-parameter model for a straight coplanar waveguide. |
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S-parameter model for a straight coplanar waveguide. |
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S-parameter model for a straight waveguide with open ends. |
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S-parameter model for a straight microstrip transmission line. |
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S-parameter model for a straight waveguide with one open end. |
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S-parameter model for a straight waveguide with one shorted end. |
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S-parameter model for a cross-section taper using linear interpolation. |
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S-parameter model for a through-silicon via (TSV), wrapped to |
airbridge#
- qpdk.models.airbridge(f=5000000000.0, cpw_width=10.0, bridge_width=8.0, airgap_height=3.0, loss_tangent=1.2e-08)[source]#
S-parameter model for a superconducting CPW airbridge.
The airbridge is modeled as a lumped lossy shunt admittance to ground (shunt capacitance plus dielectric loss) across the CPW at the bridge location.
Ports
o1ando2are the CPW reference planes immediately either side of the bridge, both referenced to \(Z_0 = 50\,\Omega\). The bridge footprint adds no transmission line length, so the two reference planes coincide. The landing pads of the layout cell (e1ande2, on theAB_VIAlayer) contact the ground plane and are not RF ports of this model.Parallel plate capacitor model is as done in [CMK+14] The default value for the loss tangent \(\tan\,\delta\) is also taken from there.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
cpw_width (Float) – Width of the CPW center conductor in µm.
bridge_width (Float) – Width of the airbridge in µm.
airgap_height (Float) – Height of the airgap in µm.
loss_tangent (Float) – Dielectric loss tangent of the supporting layer/residues.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.airbridge() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
bend_circular#
- qpdk.models.bend_circular(f=5000000000.0, length=1000, cross_section='cpw')[source]#
S-parameter model for a circular bend, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.bend_circular() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
bend_circular_all_angle#
- qpdk.models.bend_circular_all_angle(f=5000000000.0, length=1000, cross_section='cpw')[source]#
S-parameter model for a circular bend, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.bend_circular_all_angle() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
bend_euler#
- qpdk.models.bend_euler(f=5000000000.0, length=1000, cross_section='cpw')[source]#
S-parameter model for an Euler bend, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.bend_euler() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
bend_euler_all_angle#
- qpdk.models.bend_euler_all_angle(f=5000000000.0, length=1000, cross_section='cpw')[source]#
S-parameter model for an Euler bend, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.bend_euler_all_angle() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
bend_s#
- qpdk.models.bend_s(f=5000000000.0, length=None, size=(20.0, 3.0), npoints=99, cross_section='cpw')[source]#
S-parameter model for an S-bend, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float | None) – Physical length in µm. When omitted, it is derived from
size.size (Size) – Layout S-bend extent in µm.
npoints (int | Array) – Number of points used to discretize the layout Bézier curve; a scalar array (as gdsfactoryplus model binding emits) is accepted.
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.bend_s() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
indium_bump#
- qpdk.models.indium_bump(f=5000000000.0, bump_height=10.0)[source]#
S-parameter model for an indium bump, wrapped to
straight().TODO: add a constant loss channel for indium bumps.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
bump_height (float) – Physical height (length) of the indium bump in µm.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.indium_bump() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
launcher#
- qpdk.models.launcher(f=5000000000.0, straight_length=200.0, taper_length=100.0, cross_section_big=<function launcher_cross_section_big>, cross_section_small='cpw')[source]#
S-parameter model for a launcher, effectively a straight section followed by a taper.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
straight_length (Float) – Length of the straight section in µm.
taper_length (Float) – Length of the taper section in µm.
cross_section_big (CrossSectionSpec) – Cross-section for the wide section.
cross_section_small (CrossSectionSpec) – Cross-section for the narrow section.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
nxn#
- qpdk.models.nxn(f=5000000000.0, west=1, east=1, north=1, south=1)[source]#
NxN junction model using tee components.
This model creates an N-port divider/combiner by chaining 3-port tee junctions. All ports are connected to a single node.
- Parameters:
- Returns:
S-parameters dictionary with ports o1, o2, …, oN.
- Return type:
sax.SDict
- Raises:
ValueError – If total number of ports is not positive.
(Source code, svg, pdf, png)
qpdk.models.nxn() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
rectangle#
- qpdk.models.rectangle(f=5000000000.0, length=1000, cross_section='cpw')[source]#
S-parameter model for a rectangular section, wrapped to
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.rectangle() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight#
- qpdk.models.straight(f=5000000000.0, length=10.0, cross_section='cpw')[source]#
S-parameter model for a straight coplanar waveguide.
Wraps
sax.models.rf.coplanar_waveguide(), extracting the physical dimensions from the given cross_section and the PDK layer stack.Computes S-parameters analytically using conformal-mapping CPW theory following Simons [Sim01] (ch. 2) and the Qucs-S CPW model (Qucs technical documentation, §12.4). Conductor thickness corrections use the first-order model of Gupta, Garg, Bahl, and Bhartia [GGBB96].
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (FloatArrayLike) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight_all_angle#
- qpdk.models.straight_all_angle(f=5000000000.0, length=10.0, cross_section='cpw')[source]#
S-parameter model for a straight coplanar waveguide.
Same as
straight().- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight_all_angle() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight_double_open#
- qpdk.models.straight_double_open(f=5000000000.0, length=10.0, cross_section='cpw')[source]#
S-parameter model for a straight waveguide with open ends.
Note
Ports
o1ando2are internally open-circuited and should not be used. They are provided to match the number of ports in the layout component.- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight_double_open() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight_microstrip#
- qpdk.models.straight_microstrip(f=5000000000.0, length=1000, width=10.0, h=500.0, t=0.2, ep_r=11.45, tand=0.0)[source]#
S-parameter model for a straight microstrip transmission line.
Wraps
sax.models.rf.microstrip(), mapping the qpdk parameter names to the upstream model.Computes S-parameters analytically using the Hammerstad-Jensen [HJ80] closed-form expressions for effective permittivity and characteristic impedance, as described in Pozar [MP12] (ch. 3, §3.8). Conductor thickness corrections follow Gupta et al. [GGBB96] (§2.2.4).
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
length (Float) – Physical length in µm.
width (Float) – Strip width in µm.
h (Float) – Substrate height in µm.
t (Float) – Conductor thickness in µm (default 0.2 µm = 200 nm).
ep_r (Float) – Relative permittivity of the substrate (default 11.45 for Si).
tand (Float) – Dielectric loss tangent (default 0 — lossless).
- Returns:
S-parameters dictionary.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight_microstrip() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight_open#
- qpdk.models.straight_open(f=5000000000.0, length=10.0, cross_section='cpw')[source]#
S-parameter model for a straight waveguide with one open end.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight_open() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
straight_shorted#
- qpdk.models.straight_shorted(f=5000000000.0, length=10.0, cross_section='cpw')[source]#
S-parameter model for a straight waveguide with one shorted end.
This may be used to model a quarter-wave coplanar waveguide resonator.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section (CrossSectionSpec) – The cross-section of the waveguide.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.straight_shorted() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
taper_cross_section#
- qpdk.models.taper_cross_section(f=5000000000.0, length=10, cross_section1='cpw', cross_section2='cpw', npoints=100)[source]#
S-parameter model for a cross-section taper using linear interpolation.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
length (Float) – Physical length in µm
cross_section1 (CrossSectionSpec) – Cross-section for the start of the taper.
cross_section2 (CrossSectionSpec) – Cross-section for the end of the taper.
npoints (int) – Number of segments to divide the taper into for simulation. Clamped to a minimum of one segment. Ignored when both cross-sections have identical dimensions.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.taper_cross_section() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
tsv#
- qpdk.models.tsv(f=5000000000.0, via_height=1000.0)[source]#
S-parameter model for a through-silicon via (TSV), wrapped to
straight().TODO: add a constant loss channel for TSVs.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
via_height (float) – Physical height (length) of the TSV in µm.
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.tsv() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Generic circuit elements#
Opens, shorts, series and shunt elements and ideal LC resonators.
Electrical short 2-port connection Sax model. |
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LC resonator Sax model with capacitor and inductor in parallel. |
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Coupled LC resonator Sax model. |
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Return the reflection coefficient of an ideal one-port open. |
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Return two isolated ports with ideal open reflections. |
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Two-port series impedance Sax model. |
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Return the reflection coefficient of an ideal one-port short. |
|
Electrical short 2-port connection Sax model. |
|
Two-port shunt admittance Sax model. |
electrical_short_2_port#
- qpdk.models.electrical_short_2_port(f=5000000000.0)[source]#
Electrical short 2-port connection Sax model.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.electrical_short_2_port() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
lc_resonator#
- qpdk.models.lc_resonator(f=5000000000.0, capacitance=1e-13, inductance=1e-09, grounded=False, ground_capacitance=0.0)[source]#
LC resonator Sax model with capacitor and inductor in parallel.
The resonance frequency is given by:
If grounded=True, a 2-port short is connected to port o2:
Optional ground capacitances Cg can be added to both ports:
\[f_\text{r} = \frac{1}{2 \pi \sqrt{LC}}\]For theory and relation to superconductors, see [Gao08].
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (FloatArrayLike) – Capacitance of the resonator in Farads.
inductance (FloatArrayLike) – Inductance of the resonator in Henries.
grounded (bool) – If True, add a 2-port ground to the second port.
ground_capacitance (FloatArrayLike) – Parasitic capacitance to ground Cg at each port in Farads.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.lc_resonator() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
lc_resonator_coupled#
- qpdk.models.lc_resonator_coupled(f=5000000000.0, capacitance=1e-13, inductance=1e-09, grounded=False, ground_capacitance=0.0, coupling_capacitance=1e-14, coupling_inductance=0.0)[source]#
Coupled LC resonator Sax model.
This model extends the basic LC resonator by adding a coupling network consisting of a parallel capacitor and inductor connected in series to one port of the LC resonator.
The resonance frequency of the main LC resonator is given by:
\[f_\text{r} = \frac{1}{2 \pi \sqrt{LC}}\]The coupling network modifies the effective coupling to the resonator.
Where \(L_\text{c}\) and \(C_\text{c}\) are the coupling inductance and capacitance, respectively.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
capacitance (FloatArrayLike) – Capacitance of the main resonator in Farads.
inductance (FloatArrayLike) – Inductance of the main resonator in Henries.
grounded (bool) – If True, the resonator is grounded.
ground_capacitance (FloatArrayLike) – Parasitic capacitance to ground Cg at each port in Farads.
coupling_capacitance (FloatArrayLike) – Coupling capacitance in Farads.
coupling_inductance (FloatArrayLike) – Coupling inductance in Henries.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.lc_resonator_coupled() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
open#
- qpdk.models.open(f=5000000000.0)[source]#
Return the reflection coefficient of an ideal one-port open.
- Parameters:
f (FloatArrayLike)
- Return type:
SDict
(Source code, svg, pdf, png)
qpdk.models.open() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
open_2_port#
- qpdk.models.open_2_port(f=5000000000.0)[source]#
Return two isolated ports with ideal open reflections.
- Parameters:
f (FloatArrayLike)
- Return type:
SDict
(Source code, svg, pdf, png)
qpdk.models.open_2_port() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
series_impedance#
- qpdk.models.series_impedance(f=5000000000.0, z=0.0, z0=50.0)[source]#
Two-port series impedance Sax model.
See [MP12] (Ch. 4, Table 4.1, Table 4.2, Problem 4.11) for the S-parameter derivation.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
z (ComplexArrayLike) – Complex impedance in Ohms.
z0 (float) – Reference characteristic impedance in Ohms.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.series_impedance() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
short#
- qpdk.models.short(f=5000000000.0)[source]#
Return the reflection coefficient of an ideal one-port short.
- Parameters:
f (FloatArrayLike)
- Return type:
SDict
(Source code, svg, pdf, png)
qpdk.models.short() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
short_2_port#
- qpdk.models.short_2_port(f=5000000000.0)#
Electrical short 2-port connection Sax model.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz
- Returns:
S-parameters dictionary
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.short_2_port() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
shunt_admittance#
- qpdk.models.shunt_admittance(f=5000000000.0, y=0.0, z0=50.0)[source]#
Two-port shunt admittance Sax model.
See [MP12] (Ch. 4, Table 4.1, Table 4.2, Problem 4.11) for the S-parameter derivation.
- Parameters:
f (FloatArrayLike) – Array of frequency points in Hz.
y (ComplexArrayLike) – Complex admittance in Siemens.
z0 (float) – Reference characteristic impedance in Ohms.
- Returns:
S-parameters dictionary with ports o1 and o2.
- Return type:
sax.SDict
(Source code, svg, pdf, png)
qpdk.models.shunt_admittance() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Other#
Model the meander by its total CPW electrical length. |
resonator_meander#
- qpdk.models.resonator_meander(f=5000000000.0, length=3700.0, cross_section='cpw')[source]#
Model the meander by its total CPW electrical length.
Bends are approximated as straight CPW of equal length. The layout’s meander count, bend specification, and end-bend setting do not alter this electrical model, matching the pre-section whole-device model.
- Returns:
Two-port SAX S-parameters for the meander path.
- Parameters:
f (FloatArrayLike)
length (float)
cross_section (CrossSectionSpec)
- Return type:
SDict
(Source code, svg, pdf, png)
qpdk.models.resonator_meander() S-parameters for \(f\in[1,10]\,\text{GHz}\).#
Helper functions#
Analytical formulas, parameter conversions and Hamiltonians used to build and design with the SAX models above.
Transmission-line parameters#
Effective permittivity, characteristic impedance and propagation of CPW and microstrip lines.
Effective permittivity of a CPW on a finite-height substrate. |
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Compute complex effective permittivity and characteristic impedance for a CPW. |
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Apply conductor thickness correction to CPW ε_eff and Z₀. |
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Characteristic impedance of a CPW. |
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Characteristic impedance of a CPW defined by a layout cross-section. |
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Effective permittivity of a microstrip line. |
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Conductor thickness correction for a microstrip line. |
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Characteristic impedance of a microstrip line. |
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Complex propagation constant of a quasi-TEM transmission line. |
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S-parameters of a uniform transmission line (ABCD→S conversion). |
cpw_epsilon_eff#
- qpdk.models.cpw_epsilon_eff(w, s, h, ep_r)[source]#
Effective permittivity of a CPW on a finite-height substrate.
\[\begin{split}\begin{aligned} k_0 &= \frac{w}{w + 2s} \\ k_1 &= \frac{\sinh(\pi w / 4h)}{\sinh\bigl(\pi(w + 2s) / 4h\bigr)} \\ q_1 &= \frac{K(k_1^2)/K(1 - k_1^2)}{K(k_0^2)/K(1 - k_0^2)} \\ \varepsilon_{\mathrm{eff}} &= 1 + \frac{q_1(\varepsilon_r - 1)}{2} \end{aligned}\end{split}\]where \(K\) is the complete elliptic integral of the first kind in the parameter convention (\(m = k^2\)).
References
Simoons, Eq. 2.37; Ghione & Naldi
- Parameters:
w (FloatArrayLike) – Centre-conductor width (m).
s (FloatArrayLike) – Gap to ground plane (m).
h (FloatArrayLike) – Substrate height (m).
ep_r (FloatArrayLike) – Relative permittivity of the substrate.
- Returns:
Effective permittivity (dimensionless).
- Return type:
cpw_parameters#
- qpdk.models.cpw_parameters(width, gap, *, tand=None)[source]#
Compute complex effective permittivity and characteristic impedance for a CPW.
Uses the JAX-jittable functions from
sax.models.rfwith the PDK layer stack (substrate height, conductor thickness, material permittivity).Dielectric loss is included via the filling factor \(q\) and the provided tand:
\[\varepsilon_{\text{eff, complex}} = \varepsilon_{\text{eff}} \left( 1 - j q \frac{\varepsilon_\text{r}}{\varepsilon_{\text{eff}}} \tan \delta \right)\]where \(q = (\varepsilon_{\text{eff}} - 1) / (\varepsilon_\text{r} - 1)\).
Conductor thickness corrections follow Gupta, Garg, Bahl & Bhartia [GGBB96] (§7.3, Eqs. 7.98-7.100).
- Parameters:
- Returns:
(ep_eff, z0)— complex effective permittivity (dimensionless) and characteristic impedance (Ω).- Return type:
cpw_thickness_correction#
- qpdk.models.cpw_thickness_correction(w, s, t, ep_eff)[source]#
Apply conductor thickness correction to CPW ε_eff and Z₀.
First-order correction from Gupta, Garg, Bahl & Bhartia
\[\begin{split}\begin{aligned} \Delta &= \frac{1.25\,t}{\pi} \left(1 + \ln\frac{4\pi w}{t}\right) \\ k_e &= k_0 + (1 - k_0^2)\,\frac{\Delta}{2s} \\ \varepsilon_{\mathrm{eff},t} &= \varepsilon_{\mathrm{eff}} - \frac{0.7\,(\varepsilon_{\mathrm{eff}} - 1)\,t/s} {K(k_0^2)/K(1-k_0^2) + 0.7\,t/s} \\ Z_{0,t} &= \frac{30\pi} {\sqrt{\varepsilon_{\mathrm{eff},t}}\; K(k_e^2)/K(1-k_e^2)} \end{aligned}\end{split}\]References
Gupta, Garg, Bahl & Bhartia, §7.3, Eqs. 7.98-7.100
- Parameters:
w (FloatArrayLike) – Centre-conductor width (m).
s (FloatArrayLike) – Gap to ground plane (m).
t (FloatArrayLike) – Conductor thickness (m).
ep_eff (FloatArrayLike) – Uncorrected effective permittivity.
- Returns:
(ep_eff_t, z0_t)— thickness-corrected effective permittivity and characteristic impedance (Ω).- Return type:
cpw_z0#
- qpdk.models.cpw_z0(w, s, ep_eff)[source]#
Characteristic impedance of a CPW.
\[Z_0 = \frac{30\pi}{\sqrt{\varepsilon_{\mathrm{eff}}} K(k_0^2)/K(1 - k_0^2)}\]References
Simons, Eq. 2.38. Note that our \(w\) and \(s\) correspond to Simons’ \(s\) and \(w\).
- Parameters:
w (FloatArrayLike) – Centre-conductor width (m).
s (FloatArrayLike) – Gap to ground plane (m).
ep_eff (FloatArrayLike) – Effective permittivity (see
cpw_epsilon_eff()).
- Returns:
Characteristic impedance (Ω).
- Return type:
cpw_z0_from_cross_section#
- qpdk.models.cpw_z0_from_cross_section(cross_section, f=None)[source]#
Characteristic impedance of a CPW defined by a layout cross-section.
- Parameters:
cross_section (CrossSectionSpec) – A gdsfactory cross-section specification.
f (ArrayLike | None) – Frequency array (Hz). Used only to determine the output shape; the impedance is frequency-independent in the quasi-static model.
- Returns:
Characteristic impedance broadcast to the shape of f (Ω).
- Return type:
microstrip_epsilon_eff#
- qpdk.models.microstrip_epsilon_eff(w, h, ep_r)[source]#
Effective permittivity of a microstrip line.
Uses the Hammerstad-Jensen formula as given in Pozar.
\[\varepsilon_{\mathrm{eff}} = \frac{\varepsilon_r + 1}{2} + \frac{\varepsilon_r - 1}{2} \left(\frac{1}{\sqrt{1 + 12h/w}} + 0.04(1 - w/h)^2 \Theta(1 - w/h)\right)\]where the last term contributes only for narrow strips (\(w/h < 1\)).
References
Hammerstad & Jensen; Pozar, Eqs. 3.195-3.196.
- Parameters:
w (FloatArrayLike) – Strip width (m).
h (FloatArrayLike) – Substrate height (m).
ep_r (FloatArrayLike) – Relative permittivity of the substrate.
- Returns:
Effective permittivity (dimensionless).
- Return type:
microstrip_thickness_correction#
- qpdk.models.microstrip_thickness_correction(w, h, t, ep_r, ep_eff)[source]#
Conductor thickness correction for a microstrip line.
Uses the widely-adopted Schneider correction as presented in Pozar and Gupta et al.
\[\begin{split}\begin{aligned} w_e &= w + \frac{t}{\pi} \ln\frac{4e}{\sqrt{(t/h)^2 + (t/(wPI + 1.1tPI))^2}} \\ \varepsilon_{\mathrm{eff},t} &= \varepsilon_{\mathrm{eff}} - \frac{(\varepsilon_r - 1)\,t/h} {4.6\,\sqrt{w/h}} \end{aligned}\end{split}\]Then the corrected \(Z_0\) is computed with the effective width \(w_e\) and corrected \(\varepsilon_{\mathrm{eff},t}\).
References
Pozar, §3.8; Gupta, Garg, Bahl & Bhartia
- Parameters:
w (FloatArrayLike) – Strip width (m).
h (FloatArrayLike) – Substrate height (m).
t (FloatArrayLike) – Conductor thickness (m).
ep_r (FloatArrayLike) – Relative permittivity of the substrate.
ep_eff (FloatArrayLike) – Uncorrected effective permittivity.
- Returns:
(w_eff, ep_eff_t, z0_t)— effective width (m), thickness-corrected effective permittivity, and characteristic impedance (Ω).- Return type:
microstrip_z0#
- qpdk.models.microstrip_z0(w, h, ep_eff)[source]#
Characteristic impedance of a microstrip line.
Uses the Hammerstad-Jensen approximation as given in Pozar.
\[\begin{split}\begin{aligned} Z_0 = \begin{cases} \displaystyle\frac{60}{\sqrt{\varepsilon_{\mathrm{eff}}}} \ln\!\left(\frac{8h}{w} + \frac{w}{4h}\right) & w/h \le 1 \\[6pt] \displaystyle\frac{120\pi} {\sqrt{\varepsilon_{\mathrm{eff}}}\, \bigl[w/h + 1.393 + 0.667\ln(w/h + 1.444)\bigr]} & w/h \ge 1 \end{cases} \end{aligned}\end{split}\]References
Hammerstad & Jensen; Pozar, Eqs. 3.197-3.198.
- Parameters:
w (FloatArrayLike) – Strip width (m).
h (FloatArrayLike) – Substrate height (m).
ep_eff (FloatArrayLike) – Effective permittivity (see
microstrip_epsilon_eff()).
- Returns:
Characteristic impedance (Ω).
- Return type:
propagation_constant#
- qpdk.models.propagation_constant(f, ep_eff, tand=0.0, ep_r=1.0)[source]#
Complex propagation constant of a quasi-TEM transmission line.
For the general lossy case
\[\gamma = \alpha_d + j\,\beta\]where the dielectric attenuation is
\[\alpha_d = \frac{\pi f}{C_{M_S}} \frac{\varepsilon_r}{\sqrt{\varepsilon_{\mathrm{eff}}}} \frac{\varepsilon_{\mathrm{eff}} - 1} {\varepsilon_r - 1} \tan\delta\]and the phase constant is
\[\beta = \frac{2\pi f}{C_{M_S}}\,\sqrt{\varepsilon_{\mathrm{eff}}}\]For a superconducting line (\(\tan\delta = 0\)) the propagation is purely imaginary: \(\gamma = j\beta\).
References
Pozar, §3.8
- Parameters:
f (FloatArrayLike) – Frequency (Hz).
ep_eff (FloatArrayLike) – Effective permittivity.
tand (FloatArrayLike) – Real dielectric loss tangent (default 0 — lossless).
ep_r (FloatArrayLike) – Substrate relative permittivity (only needed when
tand > 0).
- Returns:
Complex propagation constant \(\gamma\) (1/m).
- Return type:
transmission_line_s_params#
- qpdk.models.transmission_line_s_params(gamma, z0, length, z_ref=None)[source]#
S-parameters of a uniform transmission line (ABCD→S conversion).
The ABCD matrix of a line with characteristic impedance \(Z_0\), propagation constant \(\gamma\), and length \(\ell\) is:
\[\begin{split}\begin{aligned} \begin{pmatrix} A & B \\ C & D \end{pmatrix} = \begin{pmatrix} \cosh\theta & Z_0\sinh\theta \\ \sinh\theta / Z_0 & \cosh\theta \end{pmatrix}, \quad \theta = \gamma\ell \end{aligned}\end{split}\]Converting to S-parameters referenced to \(Z_{\mathrm{ref}}\)
\[\begin{split}\begin{aligned} S_{11} &= \frac{A + B/Z_{\mathrm{ref}} - CZ_{\mathrm{ref}} - D}{ A + B/Z_{\mathrm{ref}} + CZ_{\mathrm{ref}} + D} \\ S_{21} &= \frac{2}{A + B/Z_{\mathrm{ref}} + CZ_{\mathrm{ref}} + D} \end{aligned}\end{split}\]When
z_refisNonethe reference impedance defaults toz0(matched case), giving \(S_{11} = 0\) and \(S_{21} = e^{-\gamma\ell}\).References
Pozar, Table 4.2
- Parameters:
gamma (ComplexLike) – Complex propagation constant (1/m).
z0 (ComplexLike) – Characteristic impedance (Ω).
length (FloatArrayLike) – Physical length (m).
z_ref (ComplexLike | None) – Reference (port) impedance (Ω). Defaults to
z0.
- Returns:
(S11, S21)— complex S-parameter arrays.- Return type:
Qubit parameters#
Conversions between circuit energies, capacitances and inductances, and unimon spectra.
Convert coupling strength \(g\) to coupling capacitance \(C_\text{c}\). |
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Return the capacitance seen by charge moving between the two pads, in F. |
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Build a linearized transmon circuit from the stored two-pad Palace matrix. |
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Convert charging energy \(E_\text{C}\) to total capacitance \(C_\Sigma\). |
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Convert Josephson energy \(E_\text{J}\) to Josephson inductance \(L_\text{J}\). |
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Convert inductive energy \(E_\text{L}\) to geometric inductance of one arm \(L\). |
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Convert Josephson energy \(E_\text{J}\) to Josephson inductance \(L_\text{J}\). |
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Join inner and top pads with an ideal wire, then add a linearized junction. |
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Return the complete static readout coupon as a JAX SAX model. |
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Return the three-electrode electrostatic coupon as a JAX SAX model. |
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Compute the lowest energy eigenvalues of the unimon Hamiltonian. |
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Compute the qubit transition frequency and anharmonicity of the unimon. |
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Build the unimon Hamiltonian matrix in the harmonic-oscillator basis. |
coupling_strength_to_capacitance#
- qpdk.models.coupling_strength_to_capacitance(g_ghz, c_sigma, c_r, f_q_ghz, f_r_ghz)[source]#
Convert coupling strength \(g\) to coupling capacitance \(C_\text{c}\).
In the dispersive limit (\(g \ll f_\text{q}, f_\text{r}\)), the coupling strength can be related to a coupling capacitance via:
\[g \approx \frac{1}{2} \frac{C_\text{c}}{\sqrt{C_\Sigma C_\text{r}}} \sqrt{f_\text{q} f_\text{r}}\]Solving for \(C_\text{c}\):
\[C_\text{c} = \frac{2g}{\sqrt{f_\text{q} f_\text{r}}} \sqrt{C_\Sigma C_\text{r}}\]See [KKY+19, Sav23] for details.
- Parameters:
g_ghz (ArrayLike) – Coupling strength in GHz.
c_sigma (ArrayLike) – Total qubit capacitance in Farads.
c_r (ArrayLike) – Total resonator capacitance in Farads.
f_q_ghz (ArrayLike) – Qubit frequency in GHz.
f_r_ghz (ArrayLike) – Resonator frequency in GHz.
- Returns:
Coupling capacitance in Farads.
- Return type:
Example
>>> C_c = coupling_strength_to_capacitance( ... g_ghz=0.1, ... c_sigma=100e-15, # 100 fF ... c_r=50e-15, # 50 fF ... f_q_ghz=5.0, ... f_r_ghz=7.0, ... ) >>> print(f"{C_c * 1e15:.2f} fF")
double_pad_transmon_capacitance#
- qpdk.models.double_pad_transmon_capacitance(*, pad_width=250.0, pad_height=400.0, pad_gap=20.0, ground_clearance=200.0)[source]#
Return the capacitance seen by charge moving between the two pads, in F.
Both pads float inside a 300 um wide coplanar ground frame on silicon. Dimensions are in um. The stored Palace matrix includes pad-to-pad and pad-to-ground fields;
differential_capacitance()combines them for equal and opposite pad charges.The junction and neighbouring devices are omitted. Add the junction’s capacitance in parallel before computing \(E_\text{C}=e^2/(2C)\). Dimensions outside the stored grid return NaN. Supports JIT, vmap and grad.
double_pad_transmon_fem_model#
- qpdk.models.double_pad_transmon_fem_model(*, inductance, junction_capacitance=0.0)[source]#
Build a linearized transmon circuit from the stored two-pad Palace matrix.
Supply the Josephson inductance in H and additional junction capacitance in F. The returned JAX model accepts frequency in Hz,
z_refin ohms, andpad_width,pad_height,pad_gap,ground_clearancein um. Itsleft_padandright_padports both reference the finite ground frame. All pad-to-ground and mutual capacitances are retained.This describes small oscillations, not the nonlinear qubit spectrum. No readout, feedline, package lid or backside ground is included. See
junction_model()for the circuit convention.
ec_to_capacitance#
- qpdk.models.ec_to_capacitance(ec_ghz)[source]#
Convert charging energy \(E_\text{C}\) to total capacitance \(C_\Sigma\).
The charging energy is related to capacitance by:
\[E_\text{C} = \frac{e^2}{2 C_\Sigma}\]where \(e\) is the electron charge.
- Parameters:
ec_ghz (ArrayLike) – Charging energy in GHz.
- Returns:
Total capacitance in Farads.
- Return type:
Example
>>> C = ec_to_capacitance(0.2) # 0.2 GHz (200 MHz) charging energy >>> print(f"{C * 1e15:.1f} fF") # ~96 fF
ej_to_inductance#
- qpdk.models.ej_to_inductance(ej_ghz)[source]#
Convert Josephson energy \(E_\text{J}\) to Josephson inductance \(L_\text{J}\).
The Josephson energy is related to inductance by:
\[E_\text{J} = \frac{\Phi_0^2}{4 \pi^2 L_\text{J}} = \frac{(\hbar / 2e)^2}{L_\text{J}}\]This is equivalent to:
\[L_\text{J} = \frac{\Phi_0}{2 \pi I_\text{c}}\]where \(I_\text{c}\) is the critical current and \(\Phi_0\) is the magnetic flux quantum.
- Parameters:
ej_ghz (ArrayLike) – Josephson energy in GHz.
- Returns:
Josephson inductance in Henries.
- Return type:
Example
>>> L = ej_to_inductance(20.0) # 20 GHz Josephson energy >>> print(f"{L * 1e9:.2f} nH") # ~1.0 nH
el_to_arm_inductance#
- qpdk.models.el_to_arm_inductance(el_ghz)[source]#
Convert inductive energy \(E_\text{L}\) to geometric inductance of one arm \(L\).
The total inductive energy \(E_\text{L}\) of the unimon is related to the geometric inductance of its two arms (in series) by:
\[E_\text{L} = \frac{\Phi_0^2}{4 \pi^2 \cdot 2 L} = \frac{(\hbar / 2e)^2}{2 L}\]Solving for the inductance \(L\) of a single arm:
\[L = \frac{\Phi_0^2}{8 \pi^2 E_\text{L}}\]- Parameters:
el_ghz (ArrayLike) – Inductive energy in GHz.
- Returns:
Geometric inductance of one arm in Henries.
- Return type:
Example
>>> L = el_to_arm_inductance(5.0) # 5 GHz inductive energy >>> print(f"{L * 1e9:.2f} nH")
el_to_inductance#
- qpdk.models.el_to_inductance(ej_ghz)#
Convert Josephson energy \(E_\text{J}\) to Josephson inductance \(L_\text{J}\).
The Josephson energy is related to inductance by:
\[E_\text{J} = \frac{\Phi_0^2}{4 \pi^2 L_\text{J}} = \frac{(\hbar / 2e)^2}{L_\text{J}}\]This is equivalent to:
\[L_\text{J} = \frac{\Phi_0}{2 \pi I_\text{c}}\]where \(I_\text{c}\) is the critical current and \(\Phi_0\) is the magnetic flux quantum.
- Parameters:
ej_ghz (ArrayLike) – Josephson energy in GHz.
- Returns:
Josephson inductance in Henries.
- Return type:
Example
>>> L = ej_to_inductance(20.0) # 20 GHz Josephson energy >>> print(f"{L * 1e9:.2f} nH") # ~1.0 nH
flipmon_ideal_bond_model#
- qpdk.models.flipmon_ideal_bond_model(*, inductance, junction_capacitance=0.0)[source]#
Join inner and top pads with an ideal wire, then add a linearized junction.
Supply the Josephson inductance in H and additional junction capacitance in F. The returned JAX model accepts the same geometry and frequency arguments as
flipmon_unbonded_model(). Its ports areinner_padandouter_ring, both referenced to chip ground.The ideal wire preserves capacitance to ground but adds no bump field or inductance. This reduction has no finite-bump validation and describes small oscillations, not the nonlinear qubit spectrum. See
junction_model()for the circuit convention.
flipmon_readout_coupon_model#
- qpdk.models.flipmon_readout_coupon_model()[source]#
Return the complete static readout coupon as a JAX SAX model.
The ports include a separate unbonded top pad in addition to
island_a,island_b,readoutandfeedline. Each port references chip ground. The returned model acceptspad_length,pad_offset,feedline_gapandcoupling_lengthin um, frequencyfin Hz andz_refin ohms.The feedline ends are cut open and the entire readout conductor shares one potential. This does not describe a shorted resonator mode. Adding it to a distributed circuit would duplicate route and ground capacitance. No driven/eigenmode or resonance validation is implied.
- Returns:
Jittable five-port static coupon model; out-of-grid inputs return NaN.
- Return type:
Model
flipmon_unbonded_model#
- qpdk.models.flipmon_unbonded_model()[source]#
Return the three-electrode electrostatic coupon as a JAX SAX model.
inner_pad,outer_ringandtop_padremain separate ports, all referenced to the two chip ground frames. The coupon has two 300 um silicon chips and 0.2 um metal. It omits the junction and bonding bump. The returned model acceptschip_gap,alignment,inner_radiusandtop_radiusin um, frequencyfin Hz andz_refin ohms. Alignment shifts the top pad horizontally while ground frames stay fixed. Dimensions outside the stored grid return NaN.- Returns:
Jittable three-port model retaining all Maxwell capacitances.
- Return type:
Model
unimon_energies#
- qpdk.models.unimon_energies(ec_ghz=1.0, el_ghz=5.0, ej_ghz=10.0, phi_ext=3.141592653589793, n_max=30, n_levels=5)[source]#
Compute the lowest energy eigenvalues of the unimon Hamiltonian.
Diagonalises the Hamiltonian returned by
unimon_hamiltonian()and returns then_levelslowest eigenvalues, shifted so that the ground state energy is zero.- Parameters:
ec_ghz (float) – Charging energy \(E_\text{C}\) in GHz.
el_ghz (float) – Inductive energy \(E_\text{L}\) in GHz.
ej_ghz (float) – Josephson energy \(E_\text{J}\) in GHz.
phi_ext (float) – External flux \(\varphi_{\text{ext}}\) in radians.
n_max (int) – Basis truncation, see
unimon_hamiltonian().n_levels (int) – Number of lowest energy levels to return.
- Returns:
Array of shape
(n_levels,)with energies in GHz, referenced to the ground state.- Return type:
Example
>>> energies = unimon_energies(ec_ghz=1.0, el_ghz=5.0, ej_ghz=10.0) >>> f_01 = float(energies[1]) # qubit frequency in GHz >>> alpha = float(energies[2] - 2 * energies[1]) # anharmonicity
unimon_frequency_and_anharmonicity#
- qpdk.models.unimon_frequency_and_anharmonicity(ec_ghz=1.0, el_ghz=5.0, ej_ghz=10.0, phi_ext=3.141592653589793, n_max=30)[source]#
Compute the qubit transition frequency and anharmonicity of the unimon.
The qubit frequency is
\[f_{01} = E_1 - E_0\]and the anharmonicity is
\[\alpha = (E_2 - E_1) - (E_1 - E_0) = E_2 - 2 E_1\](since \(E_0 = 0\) after shifting).
- Parameters:
- Returns:
Tuple of (frequency_ghz, anharmonicity_ghz).
- Return type:
Example
>>> f01, alpha = unimon_frequency_and_anharmonicity( ... ec_ghz=1.0, el_ghz=5.0, ej_ghz=10.0 ... ) >>> print(f"f_01 = {f01:.3f} GHz, alpha = {alpha:.3f} GHz")
unimon_hamiltonian#
- qpdk.models.unimon_hamiltonian(ec_ghz=1.0, el_ghz=5.0, ej_ghz=10.0, phi_ext=3.141592653589793, n_max=30)[source]#
Build the unimon Hamiltonian matrix in the harmonic-oscillator basis.
The effective single-mode unimon Hamiltonian is
\[\hat{H} = 4 E_\text{C} \hat{n}^2 + \tfrac{1}{2} E_\text{L} (\hat{\varphi} - \varphi_{\text{ext}})^2 - E_\text{J} \cos\hat{\varphi}\]Energy Scales and Physics: - \(E_\text{J}\): The Josephson energy of the single non-linear junction. - \(E_\text{C}\): The effective charging energy. The large geometric capacitance
of the CPW resonator means this is lower than typical transmons.
\(E_\text{L}\): The inductive energy provided by the CPW resonator shunting the junction. The unimon operates in the regime \(E_\text{L} \sim E_\text{J}\).
Similarities to Fluxonium: The effective single-mode circuit model of the unimon is mathematically identical to a fluxonium qubit. The inductive shunt (provided by the CPW resonators) guarantees there are no isolated superconducting islands, making the unimon intrinsically immune to dephasing caused by low-frequency \(1/f\) charge noise.
Phase and Charge Operators: Because the unimon is inductively shunted, its potential energy features a quadratic term \(\tfrac{1}{2} E_\text{L} \hat{\varphi}^2\), meaning the potential is not \(2\pi\)-periodic. Thus, the phase operator \(\hat{\varphi}\) must be treated as an extended, non-compact variable. Consequently, the conjugate charge variable \(n\) is continuous, rather than taking discrete integer values as it does for a transmon.
Note on this implementation: The Hamiltonian is represented in the eigenbasis of the harmonic part \(4 E_\text{C} \hat{n}^2 + \tfrac{1}{2} E_\text{L} \hat{\varphi}^2\), truncated to \(2 n_{\max} + 1\) states, with \(\hat{\varphi} = \varphi_\text{zpf} (\hat{a} + \hat{a}^\dagger)\), \(\hat{n} = \tfrac{i}{2 \varphi_\text{zpf}} (\hat{a}^\dagger - \hat{a})\) and \(\varphi_\text{zpf} = (2 E_\text{C} / E_\text{L})^{1/4}\). \(\cos\hat{\varphi}\) is evaluated from the eigendecomposition of the truncated \(\hat{\varphi}\).
- Parameters:
ec_ghz (float) – Charging energy \(E_\text{C}\) in GHz.
el_ghz (float) – Inductive energy \(E_\text{L}\) in GHz.
ej_ghz (float) – Josephson energy \(E_\text{J}\) in GHz.
phi_ext (float) – External flux bias \(\varphi_{\text{ext}}\) in radians (reduced flux-quantum units). The optimal operating point is \(\pi\).
n_max (int) – Basis truncation; Hilbert-space dimension is \(2 n_{\max} + 1\).
- Returns:
A
(2*n_max+1, 2*n_max+1)Hermitian matrix (in GHz).- Return type:
Perturbation theory#
Transmon frequency and anharmonicity, dispersive shifts, Purcell decay, linewidths and dephasing.
Compute the dispersive shift numerically. |
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Compute the coupling strength from a target dispersive shift. |
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Convert \(E_\text{J}\) and \(E_\text{C}\) to qubit frequency and anharmonicity. |
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Estimate measurement-induced dephasing rate. |
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Estimate the Purcell decay rate of a transmon through a resonator. |
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Compute resonator linewidth from external quality factor. |
dispersive_shift#
- qpdk.models.dispersive_shift(ω_t_ghz, ω_r_ghz, α_ghz, g_ghz)[source]#
Compute the dispersive shift numerically.
Evaluates the second-order dispersive shift for a transmon coupled to a resonator. Uses the analytical formula derived from perturbation theory (without the rotating wave approximation) [BGGW21, KYG+07]:
\[\chi = \frac{2g^2}{\Delta - \alpha} - \frac{2g^2}{\Delta} - \frac{2g^2}{\omega_\text{t} + \omega_\text{r} + \alpha} + \frac{2g^2}{\omega_\text{t} + \omega_\text{r}}\]where \(\Delta = \omega_\text{t} - \omega_\text{r}\). The first two terms give the rotating-wave-approximation (RWA) contribution
\[\chi_\text{RWA} = \frac{2 \alpha g^2}{\Delta(\Delta - \alpha)}\]and the last two are corrections from the counter-rotating terms.
All parameters are in GHz, and the returned value is also in GHz.
- Parameters:
ω_t_ghz (float | TypeAliasForwardRef('ArrayLike')) – Transmon frequency in GHz.
ω_r_ghz (float | TypeAliasForwardRef('ArrayLike')) – Resonator frequency in GHz.
α_ghz (float | TypeAliasForwardRef('ArrayLike')) – Transmon anharmonicity in GHz (positive value).
g_ghz (float | TypeAliasForwardRef('ArrayLike')) – Coupling strength in GHz.
- Returns:
Dispersive shift \(\chi\) in GHz.
- Return type:
Example
>>> χ = dispersive_shift(5.0, 7.0, 0.2, 0.1) >>> print(f"χ = {χ * 1e3:.2f} MHz")
dispersive_shift_to_coupling#
- qpdk.models.dispersive_shift_to_coupling(χ_ghz, ω_t_ghz, ω_r_ghz, α_ghz)[source]#
Compute the coupling strength from a target dispersive shift.
Inverts the dispersive shift relation to find the coupling strength \(g\) required to achieve a desired \(\chi\). Uses only the dominant rotating-wave term [KYG+07]:
\[g \approx \sqrt{\frac{-\chi\,\Delta\,(\Delta - \alpha)}{2\alpha}}\]where \(\Delta = \omega_\text{t} - \omega_\text{r}\).
Note
The expression under the square root may be negative when the sign of the target \(\chi\) is inconsistent with the detuning and anharmonicity (e.g., positive \(\chi\) with \(\Delta < 0\)). In that case the absolute value is taken so that the returned coupling strength is always real and non-negative, but the caller should verify self-consistency via
dispersive_shift().- Parameters:
χ_ghz (float | TypeAliasForwardRef('ArrayLike')) – Target dispersive shift in GHz (typically negative).
ω_t_ghz (float | TypeAliasForwardRef('ArrayLike')) – Transmon frequency in GHz.
ω_r_ghz (float | TypeAliasForwardRef('ArrayLike')) – Resonator frequency in GHz.
α_ghz (float | TypeAliasForwardRef('ArrayLike')) – Transmon anharmonicity in GHz (positive value; the physical anharmonicity of a transmon is negative, but following the Hamiltonian convention used throughout this module, \(\alpha\) is taken as positive).
- Returns:
Coupling strength \(g\) in GHz.
- Return type:
Example
>>> g = dispersive_shift_to_coupling(-0.001, 5.0, 7.0, 0.2) >>> print(f"g = {g * 1e3:.1f} MHz")
ej_ec_to_frequency_and_anharmonicity#
- qpdk.models.ej_ec_to_frequency_and_anharmonicity(ej_ghz, ec_ghz)[source]#
Convert \(E_\text{J}\) and \(E_\text{C}\) to qubit frequency and anharmonicity.
Uses the standard transmon approximations [KYG+07]:
\[\begin{split}\begin{aligned} \omega_\text{q} &\approx \sqrt{8 E_\text{J} E_\text{C}} - E_\text{C} \\ \alpha &\approx E_\text{C} \end{aligned}\end{split}\]Note
The physical anharmonicity of a transmon is negative (\(\alpha = -E_\text{C}\)), but the Hamiltonian convention used in this module and in pymablock takes \(\alpha\) as positive.
- Parameters:
- Returns:
Tuple of
(ω_q_ghz, α_ghz).- Return type:
Example
>>> ω_q, α = ej_ec_to_frequency_and_anharmonicity(20.0, 0.2) >>> print(f"ω_q = {ω_q:.2f} GHz, α = {α:.1f} GHz")
measurement_induced_dephasing#
- qpdk.models.measurement_induced_dephasing(χ_ghz, κ_ghz, n_bar)[source]#
Estimate measurement-induced dephasing rate.
During dispersive readout, photons in the resonator cause additional dephasing of the qubit [BGGW21, GBS+06]:
\[\Gamma_\phi = \frac{8 \chi^2 \bar{n}}{\kappa}\]where \(\bar{n}\) is the mean photon number in the resonator.
- Parameters:
- Returns:
Measurement-induced dephasing rate in GHz.
- Return type:
Example
>>> Γ_φ = measurement_induced_dephasing(-0.001, 0.001, 5.0) >>> print(f"Γ_φ = {Γ_φ * 1e6:.1f} kHz")
purcell_decay_rate#
- qpdk.models.purcell_decay_rate(g_ghz, ω_t_ghz, ω_r_ghz, κ_ghz)[source]#
Estimate the Purcell decay rate of a transmon through a resonator.
The Purcell effect limits qubit lifetime when coupled to a lossy resonator. In the dispersive regime [BGGW21, HSJ+08]:
\[\gamma_\text{Purcell} = \kappa \left(\frac{g}{\Delta}\right)^2\]where \(\kappa\) is the resonator decay rate and \(\Delta = \omega_\text{t} - \omega_\text{r}\).
- Parameters:
g_ghz (float | TypeAliasForwardRef('ArrayLike')) – Coupling strength in GHz.
ω_t_ghz (float | TypeAliasForwardRef('ArrayLike')) – Transmon frequency in GHz.
ω_r_ghz (float | TypeAliasForwardRef('ArrayLike')) – Resonator frequency in GHz.
κ_ghz (float | TypeAliasForwardRef('ArrayLike')) – Resonator linewidth (decay rate) in GHz.
- Returns:
Purcell decay rate in GHz.
- Return type:
Example
>>> γ = purcell_decay_rate(0.1, 5.0, 7.0, 0.001) >>> T_purcell = 1 / (γ * 1e9) >>> print(f"T_Purcell = {T_purcell * 1e6:.0f} µs")
resonator_linewidth_from_q#
- qpdk.models.resonator_linewidth_from_q(ω_r_ghz, q_ext)[source]#
Compute resonator linewidth from external quality factor.
Converts external quality factor to linewidth (half-linewidth at half-maximum) [GFB+08, MP12]:
\[\kappa = \frac{\omega_\text{r}}{Q_\text{ext}}\]- Parameters:
- Returns:
Resonator linewidth \(\kappa\) in GHz.
- Return type:
Example
>>> κ = resonator_linewidth_from_q(7.0, 10_000) >>> print(f"κ = {κ * 1e6:.1f} kHz")
Component helpers#
Closed-form estimates for resonators, couplers and inductors.
Look up Palace coupling capacitance between two parallel CPWs. |
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Analytical formula for meander inductor inductance. |
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Calculate the resonance frequency of a quarter- or half-wave CPW resonator. |
cpw_cpw_coupling_capacitance#
- qpdk.models.cpw_cpw_coupling_capacitance(f, length, gap, cross_section)[source]#
Look up Palace coupling capacitance between two parallel CPWs.
The uniform sheet dataset supplies mutual capacitance per length. Values outside its width, outer-slot and inter-trace-gap domain return NaN. Its inner ground strip has width
max(gap - 2 * cpw_gap, 0), matching the etch masks ofcoupler_straight. Dielectric half-space scaling accounts for cross-section permittivity; kinetic inductance, thickness and fringing are omitted.- Parameters:
f (FloatArrayLike) – Frequency array in Hz.
length (ArrayLike) – The coupling length in µm.
gap (ArrayLike) – The gap between the two center conductors in µm.
cross_section (CrossSectionSpec) – The cross-section of the CPW.
- Returns:
The total coupling capacitance in Farads.
- Return type:
Note
Raises
ValueErrorviaget_cpw_dimensions()if the cross-section has no section with ‘etch’ in its name, so the CPW gap cannot be determined, or if the conductor width or etch gap is not positive.
meander_inductor_inductance_analytical#
- qpdk.models.meander_inductor_inductance_analytical(n_turns, turn_length, wire_width, wire_gap, sheet_inductance, thickness=None)[source]#
Analytical formula for meander inductor inductance.
The total inductance is the sum of geometric and kinetic contributions:
\[L_{\text{total}} = L_\text{g} + L_\text{k}\]The geometric inductance \(L_\text{g}\) is calculated by summing the self-inductances of all horizontal segments and the mutual inductances between all pairs of parallel segments, following [CSD+23]:
\[L_\text{g} = N L_\text{s} + 2 \sum_{k=1}^{N-1} (N-k) (-1)^k L_\text{m}(k p)\]where \(N\) is the number of turns and \(p\) is the pitch.
The kinetic inductance \(L_\text{k}\) is calculated from the sheet inductance \(L_\square\):
\[L_\text{k} = L_\square \cdot \frac{\ell_{\text{total}}}{w}\]- Parameters:
n_turns (int) – Number of horizontal meander runs.
turn_length (float) – Length of each horizontal run in µm.
wire_width (float) – Width of the meander wire in µm.
wire_gap (float) – Gap between adjacent meander runs in µm.
sheet_inductance (float) – Sheet inductance per square in H/□.
thickness (float | None) – Thickness of the metal film in µm. If None, it is fetched from the PDK technology parameters.
- Returns:
Total inductance in Henries.
- Return type:
resonator_frequency#
- qpdk.models.resonator_frequency(*, length, epsilon_eff=None, media=None, cross_section='cpw', is_quarter_wave=True)[source]#
Calculate the resonance frequency of a quarter- or half-wave CPW resonator.
\[\begin{split}\begin{aligned} f &= \frac{v_\text{p}}{4L} \text{(quarter-wave resonator)} \\ f &= \frac{v_\text{p}}{2L} \text{(half-wave resonator)} \end{aligned}\end{split}\]The phase velocity is \(v_\text{p} = c_0 / \sqrt{\varepsilon_{\text{eff}}}\).
See [MP12, Sim01] for details.
- Parameters:
length (float) – Length of the resonator in μm.
epsilon_eff (float | None) – Effective permittivity. If
None(default), computed from cross_section usingcpw_parameters().media (Any) – Deprecated. Use epsilon_eff or cross_section instead.
cross_section (CrossSectionSpec) – Cross-section specification (used only when epsilon_eff and media are not provided).
is_quarter_wave (bool) – If True, calculates for a quarter-wave resonator; if False, for a half-wave resonator. default is True.
- Returns:
Resonance frequency in Hz.
- Return type:
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