qcsys

S. R. Jha, S. Chowdhury, M. Hays, J. A. Grover, W. D. Oliver

Docs: equs.github.io/qcsys

Community Discord: discord.gg/frWqbjvZ4s

Built on JAX, qcsys presents a scalable way to assemble and simulate systems of quantum circuits.

Installation

Installing from source (recommended)

Recommended: As this is a rapidly evolving project, we recommend installing the latest version of qcsys from source as follows:

pip install git+https://github.com/EQuS/qcsys.git

After installing qcsys, update the jaxquantum dependency to its latest version from source:

pip install git+https://github.com/EQuS/jaxquantum.git

Installing from source in editable mode (recommended for developers)

If you are interested in contributing to the package, please clone this repository and install this package in editable mode after changing into the root directory of this repository:

pip install -e ".[dev]"

This will also install extras from the dev flag, which can be useful when developing the package. Since this is installed in editable mode, the package will automatically be updated after pulling new changes in the repository.

After installing qcsys, update the jaxquantum dependency to its latest version from source:

pip install git+https://github.com/EQuS/jaxquantum.git

Installing from PyPI (not recommended)

qcsys is also published on PyPI. Simply run the following code to install the package:

pip install qcsys

For more details, please visit the getting started > installation section of our docs.

An Example

Here's an example on how to use qcsys:

import qcsys as qs


# Devices ----


_, Ec_a, El_a = qs.calculate_lambda_over_four_resonator_zpf(3, 50)

resonator = qs.Resonator.create(
    10,
    {"Ec": Ec_a, "El": El_a},
    N_pre_diag=10,
)


Ec_q = 1
El_q = 0.5
Ej_q = 8

qubit = qs.Fluxonium.create(
    25,
    {"Ec": Ec_q, "El": El_q, "Ej": Ej_q, "phi_ext": 0.47},
    use_linear=False,
    N_pre_diag=100,
)

# System ----

g_rq = 0.3

devices = [resonator, qubit]
r_indx = 0
q_indx = 1
Ns = [device.N for device in devices]

a0 = qs.promote(resonator.ops["a"], r_indx, Ns)
a0_dag = qs.promote(resonator.ops["a_dag"], r_indx, Ns)

q0 = qs.promote(qubit.ops["a"], q_indx, Ns)
q0_dag = qs.promote(qubit.ops["a_dag"], q_indx, Ns)

couplings = []
couplings.append(-g_rq * (a0 - a0_dag) @ (q0 - q0_dag))

system = qs.System.create(devices, couplings=couplings)
system.params["g_rq"] = g_rq

Es, kets = system.calculate_eig()

# chi ----
χ_e = Es[1:, 1] - Es[:-1, 1]
χ_g = Es[1:, 0] - Es[:-1, 0]
χ = χ_e - χ_g

# kerr ----
# kerr[0,n] = (E(n+2, g) - E(n+1, g)) - (E(n+1, g) - E(n, g))
# kerr[1,n] = (E(n+2, e) - E(n+1, e)) - (E(n+1, e) - E(n, e))
K_g = (Es[2:, 0] - Es[1:-1, 0]) - (Es[1:-1, 0] - Es[0:-2, 0])
K_e = (Es[2:, 1] - Es[1:-1, 1]) - (Es[1:-1, 1] - Es[0:-2, 1])

χ, K_g, K_e

Acknowledgements & History

Core Devs: Shantanu A. Jha, Shoumik Chowdhury

This package was initially developed in early 2023 to aid in the design of a superconducting circuit device made for bosonic quantum error correction. This package was also briefly announced to the world at APS March Meeting 2023. Since then, this package has been open sourced and developed while conducting research in the Engineering Quantum Systems Group at MIT with invaluable advice from Prof. William D. Oliver.

Citation

Thank you for taking the time to try our package out. If you found it useful in your research, please cite us as follows:

@software{jha2024jaxquantum,
  author = {Shantanu R. Jha and Shoumik Chowdhury and Max Hays and Jeff A. Grover and William D. Oliver},
  title  = {An auto differentiable and hardware accelerated software toolkit for quantum circuit design, simulation and control},
  url    = {https://github.com/EQuS/jaxquantum, https://github.com/EQuS/bosonic, https://github.com/EQuS/qcsys},
  version = {0.1.0},
  year   = {2024},
}

S. R. Jha, S. Chowdhury, M. Hays, J. A. Grover, W. D. Oliver. An auto differentiable and hardware accelerated software toolkit for quantum circuit design, simulation and control (2024), in preparation.

Contributions & Contact

This package is open source and, as such, very open to contributions. Please don't hesitate to open an issue, report a bug, request a feature, or create a pull request. We are also open to deeper collaborations to create a tool that is more useful for everyone. If a discussion would be helpful, please email [email protected] to set up a meeting.