QPDK — Superconducting Quantum RF Process Design Kit#

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QPDK is an open-source process design kit (PDK) for superconducting quantum RF applications built on gdsfactory. It provides a library of parametric quantum circuit components (transmon qubits, CPW resonators, Josephson junctions, etc.), analytical S-parameter models, routing utilities, and test-chip examples.

QPDK gives researchers, engineers, and students a scriptable, version-controlled foundation to go from concept to GDSII in minutes.

Key Features#

  • Rich component library — Transmons, fluxonium, unimon qubits, CPW resonators, interdigital capacitors, SQUID junctions, launchers, bump bonds, TSVs, and more.

  • Parametric & composable — Combine Python functions (@gf.cell) into hierarchical designs or define full chips in YAML.

  • Analytical circuit models — Fast, differentiable S-parameter simulations powered by SAX and JAX.

  • Automated routing — CPW-aware routing strategies with auto-tapers for complex layouts, and DoRoutes.

  • KLayout integration — Layer definitions, technology files, and cross sections for immediate visual inspection.

  • Regression-tested — GDS regression tests, netlist checks, and model validation.

  • Notebook-driven workflows — Jupyter notebooks for frequency modeling, tolerance analysis, parameter extraction, pulse-level simulation, and optimization.

  • GDSFactory+ integration — Seamlessly design, verify, and validate chips with the enhanced commercial extension. Includes access to 43+ foundry PDKs, graphical layout and schematic editors directly in VSCode, an AI assistant, and comprehensive verification tools (DRC, LVS, Connectivity checks).

Notable Components#

QPDK ships with a broad set of ready-to-use superconducting circuit components. Browse all the components in the documentation.

Qubits#

Transmon

Fluxonium

Double-pad capacitively shunted qubit

Superinductance-shunted qubit

Transmon

Fluxonium

Unimon

SQUID Junction

Resonator-embedded junction qubit

Superconducting quantum interference device

Unimon

SQUID Junction

Passive Components#

CPW Resonator

Interdigital Capacitor

Meandering coplanar waveguide resonator

Finger-style lumped-element capacitor

CPW Resonator

Interdigital Capacitor

Composite Components#

Transmon with Resonator & Probeline — Qubit cell with coupled resonator and probeline section:

Transmon with Resonator and Probeline

Sample Test Chips#

QPDK includes some complete, tapeout-ready test chip examples that demonstrate real-world design workflows.

Qubit Test Chip#

A four-transmon test chip with coupled readout resonators, probeline routing, flux lines, and launchers. Defined entirely in YAML.

Qubit Test Chip

Filled Qubit Test Chip#

The same qubit test chip with magnetic vortex trapping holes filling the ground plane and chip edges.

Filled Qubit Test Chip

Resonator Test Chip#

A 16-resonator characterization chip with systematically varied CPW widths and gaps across two probelines. Ideal for extracting loss tangents and kinetic inductance. Also check the notebook demonstrating network model simulations and fabrication tolerance Monte Carlo.

Resonator Test Chip

Quick Start#

import gdsfactory as gf
from qpdk import PDK

PDK.activate()

# Create a transmon qubit
from qpdk.cells.transmon import double_pad_transmon

qubit = double_pad_transmon(pad_size=(250, 400), pad_gap=15)
qubit.plot()

# Build a complete test chip from YAML
from gdsfactory.read import from_yaml
from qpdk import tech

chip = from_yaml(
    "qpdk/samples/qubit_test_chip.pic.yml",
    routing_strategies=tech.routing_strategies,
)
chip.show()  # Opens in KLayout

Examples & Notebooks#

  • PDK cells in the documentation — Collection of all available geometries.

  • qpdk/samples/ — Example layouts and simulations including qubit test chips, resonator arrays, routing demos, and 3D export.

  • notebooks/ — Jupyter notebooks covering:

    • Resonator frequency modeling and S-parameter analysis

    • Circuit simulation with SAX

    • Monte Carlo fabrication tolerance analysis

    • Hamiltonian parameter extraction with scqubits

    • Pulse-level quantum gate simulation with QuTiP

    • Capacitor geometry optimization with Optuna

    • Dispersive shift calculation with Pymablock

    • Transmon design optimization with NetKet

  • gsim example notebooks — Electromagnetic simulation examples using Palace and Meep with gdsfactory.

Installation#

We recommend using uv for package management. just is used for project-specific recipes.

Installation for Users#

Install the package with:

uv pip install qpdk

Or with pip:

pip install qpdk

Optional dependencies for the analytical models and simulation tools (SAX, scqubits, JAX) can be installed with:

uv pip install qpdk[models]

KLayout Technology Installation#

To use the PDK in KLayout (for viewing GDS files with correct layers and technology settings), install the technology files:

python -m qpdk.install_tech

[!NOTE] After installation, restart KLayout to ensure the new technology appears.

Installation for Contributors#

For contributors, please follow the installation and development workflow instructions.

Project Structure#

qpdk/                   Core Python package
  cells/                Component definitions (transmons, resonators, capacitors, …)
  models/               Analytical models, mostly S-parameters
  samples/              Example layouts and complete test chips
  klayout/              KLayout technology files
  tech.py               Layer stack, cross sections, routing strategies
tests/                  Regression, integration and unit tests
notebooks/              Jupyter notebooks for design and simulation workflows
docs/                   Sphinx documentation (HTML + PDF)

Documentation#

Contributing#

We welcome contributions of all sizes: new components, improved models, bug fixes, documentation, and notebook tutorials. Please see the contributing guide to get started.

Support#

For commercial support, training, and custom PDK development, please visit gdsfactory+ (gdsfactory.com/plus).

License#

QPDK is released under the MIT License.