cavsqueeze

Beyond-mean-field simulation of cavity-mediated spin squeezing (one-axis twisting) for solid-state clock-transition ensembles, and of squeezing by measurement of the spin population through the resonator. Developed for 171Yb3+:CaWO4 and applicable to any spin ensemble coupled to a resonator.

cavsqueeze implements

• the adiabatically eliminated Tavis-Cummings model with collective emission, collective thermal absorption, single-spin dephasing and coupling inhomogeneity (resonator.py);
• discretization of Gaussian, Lorentzian and Voigt lines into frequency classes with tail resolution (ensemble.py);
• a class-resolved second-order cumulant expansion in connected variables, whose cost is set by the number of classes rather than by N, so that N = 1e15 is no harder than N = 1e3, and which loses no precision to cancellation at large N because the means are subtracted analytically (cumulant.py), together with the raw-moment form used as a test reference (cumulant_raw.py); the solver can condition the ensemble on a continuous measurement of J_z through the resonator (Rates.meas, Rates.meas_eta);
• exact references: QuTiP master equation for distinguishable spins and the permutation-invariant Dicke solver PIQS (exact.py);
• pulse sequences: echo twist, Ramsey, twist-untwist readout, plain squeezed readout (protocols.py);
• far-detuned spectator spins propagated analytically, which removes the stiffness of heavy-tailed lines (ensemble.tail_resolved_classes, cumulant.evolve);
• an independent solver for cross-checking: discrete truncated Wigner trajectories (dtwa.py), which truncate the equations of motion rather than the statistics.

Installation

From PyPI:

pip install cavsqueeze          # core solver (numpy, scipy, matplotlib)
pip install cavsqueeze[exact]   # adds QuTiP for the exact reference solvers

Or from source, to run the tests:

git clone https://github.com/TaN-MM-Org/cavsqueeze
cd cavsqueeze
pip install -e .[test]
pytest tests              # validation testbench (about 2 minutes)

The test suite validates the cumulant solver against exact QuTiP and PIQS references, against closed-form limits, and against the independent discrete truncated Wigner solver; it runs in CI on every push and pull request.

Minimal example

import numpy as np
from cavsqueeze import from_hz, homogeneous
from cavsqueeze.protocols import optimal_squeezing
N = 1e10
p = from_hz(g_hz=1e6/np.sqrt(N), kappa_hz=1e4, Delta_hz=30e6, T=0.02, T2=0.15)
best = optimal_squeezing(p, homogeneous(N), 1e-6, 1e-2)
print(10*np.log10(best["xi2"]), "dB at", best["t"], "s")

Associated paper

The physics, the conventions and the validation of this package are described in: T. M. Mahim, M. M. Rahman, A. S. M. Mohsin, Synchronization sets the coherence and the squeezing limit of a spin ensemble in a cavity. The paper's companion repository, yb-cawo4-cavity-squeezing, contains the scripts, datasets and figures that reproduce the paper and is archived on Zenodo; this repository is the software's home for development, releases and support.

Contributing and support

Bug reports, questions and pull requests are welcome through GitHub issues; see CONTRIBUTING.md for the development setup and the testing requirements. Tagged releases are published to PyPI by CI.

License

Apache-2.0 (see LICENSE). Please cite the paper if you use this code; citation metadata is in CITATION.cff.