pennylane-toroidal-noise 0.1.0

Toroidal dephasing noise channel for PennyLane — spectral-gap suppression on T² lattices

pennylane-toroidal-noise

Toroidal dephasing noise channel for PennyLane.

Qubits on a toroidal lattice experience reduced dephasing because the lattice Laplacian's spectral gap filters low-frequency noise. This plugin provides ToroidalDephasing — a drop-in replacement for qml.PhaseDamping that models this suppression.

Installation

pip install pennylane-toroidal-noise

Usage

import pennylane as qml
from pennylane_toroidal_noise import ToroidalDephasing

dev = qml.device("default.mixed", wires=1)

@qml.qnode(dev)
def circuit(gamma):
    qml.Hadamard(wires=0)
    ToroidalDephasing(gamma, grid_n=12, wires=0)
    return qml.expval(qml.PauliX(0))

# Compare: more coherence preserved than plain PhaseDamping
circuit(0.5)  # ~0.99 (vs ~0.87 for PhaseDamping)

How it works

The effective dephasing probability is suppressed by the spectral gap of the cycle graph C_n:

gamma_eff = gamma * lambda_1 / (lambda_1 + alpha)

where lambda_1 = 2 - 2*cos(2*pi/n) is the smallest nonzero eigenvalue of the n-vertex cycle graph Laplacian (also the spectral gap of the n x n torus).

grid_n	suppression (alpha=1)
4	1.5x
8	2.7x
12	4.7x
32	27x

Parameters

Parameter	Type	Default	Description
gamma	float	—	Bare dephasing probability in [0, 1]
grid_n	int	12	Side length of the toroidal lattice
alpha	float	1.0	Coupling strength (larger = stronger filtering)
wires	int	—	Wire the channel acts on

Rust companion

A pure-Rust implementation is also available: toroidal-noise

Reference

S. Cormier, "Toroidal Logit Bias," Zenodo, 2026. DOI: 10.5281/zenodo.18516477

License

MIT