Squeezed comb states

TL;DR

This paper characterizes the squeezed comb, a finite superposition of squeezed coherent states, as a practical quantum error-correcting code with specific robustness properties against damping and diffusion noise in continuous-variable quantum systems.

Contribution

It provides a detailed analysis of the squeezed comb states, their phase space features, and their noise robustness, offering insights into their suitability for quantum error correction.

Findings

Squeezed comb states are more robust against damping noise.

Finite squeezed combs approximate ideal Gottesman-Kitaev-Preskill codes.

Noise robustness depends on encoding parameters.

Abstract

Continuous-variable codes are an expedient solution for quantum information processing and quantum communication involving optical networks. Here we characterize the squeezed comb, a finite superposition of equidistant squeezed coherent states on a line, and its properties as a continuous-variable encoding choice for a logical qubit. The squeezed comb is a realistic approximation to the ideal code proposed by Gottesman, Kitaev, and Preskill [Phys. Rev. A 64, 012310 (2001)], which is fully protected against errors caused by the paradigmatic types of quantum noise in continuous-variable systems: damping and diffusion. This is no longer the case for the code space of finite squeezed combs, and noise robustness depends crucially on the encoding parameters. We analyze finite squeezed comb states in phase space, highlighting their complicated interference features and characterizing their dynamics when exposed to amplitude damping and Gaussian diffusion noise processes. We find that squeezed comb state are more suitable and less error-prone when exposed to damping, which speaks against standard error correction strategies that employ linear amplification to convert damping into easier-to-describe isotropic diffusion noise.