Performance of rotation-symmetric bosonic codes in the presence of random telegraph noise

TL;DR

This paper investigates how rotation-symmetric bosonic codes perform under random telegraph noise, analyzing non-Markovian effects, and demonstrating their robustness in quantum error correction amidst complex noise environments.

Contribution

It provides a detailed analysis of non-Markovian behavior in bosonic modes affected by RTN and evaluates the robustness of RSB codes under such noise, including multiple fluctuators.

Findings

Non-Gaussian states exhibit unbounded non-Markovianity measure.

RSB codes' non-Markovianity grows linearly with code symmetry.

Error correction performance remains above break-even in most parameter regimes.

Abstract

Decoherence in quantum devices, such as qubits and resonators, is often caused by bistable fluctuators modeled as random telegraph noise (RTN), leading to significant dephasing. We analyze the impact of individual and multiple fluctuators on a bosonic mode in continuous variable systems, identifying non-Markovian behavior governed by two timescales: the fluctuator switching rate ($\xi$) and coupling strength ($\nu$). Using the Breuer-Piilo-Laine (BLP) measure, we show that for Gaussian states, squeezing and thermal fluctuations do not enhance non-Markovianity. In contrast, for non-Gaussian states, the measure becomes unbounded. For rotation-symmetric bosonic (RSB) codes, known for their error correction advantages, non-Markovianity grows linearly with code symmetry. We evaluate the performance of RSB codes under simultaneous loss and RTN dephasing. For a teleportation-based Knill error-correction circuit, the codes perform robustly in the Markovian limit. In the non-Markovian regime, the performance depends on the time the error correction is performed for a given codeword. The average gate fidelity of the error-corrected state in this case exhibits oscillations as a function of time due to the oscillatory nature of the dephasing function of the RTN noise; however, for most of the parameter ranges, the values stay above the break-even point. Extending to multiple fluctuators that produce $1/f$ noise, we observe that non-Markovianity decays with increasing fluctuator count, while the performance of RSB codes remains effective with increasing number of fluctuators.