Depolarizing noise linked to simpler Gaussian channel for better quantum codes
A depolarizing choir sings in Gaussian harmony
Information Theory
Summary
Quantum computers need to handle noise, which can cause errors in processing. The paper studies a specific type of noise called depolarizing noise on quantum bits, finding that when many noisy qubits are considered together, their behavior resembles a simpler kind of noise found in light particles. This discovery helps improve strategies to protect quantum information by using easier-to-optimize code for that simpler noise, which then translates into better codes against the original noise. This improves our understanding of how to build more reliable quantum communication systems.
What this means in practice
- •For quantum communication engineers: Design more efficient quantum error-correcting codes by using Gaussian channel models to improve data transmission over noisy quantum links.
- •For quantum hardware developers: Optimize quantum device calibration protocols by understanding noise as Gaussian-like, leading to better noise mitigation techniques.
Authors
Rabsan Galib Ahmed, Sujeet Bhalerao, Sungjai Lee, Felix Leditzky, Debbie Leung, Luke Schaeffer, Graeme Smith
Abstract
We study the noise threshold for positive quantum capacity for the qubit depolarizing channel. We explore analytically the action of the qubit depolarizing channel on the symmetric subspaces of the input qubits, in the limit of asymptotically many uses of the channel. We observe the emergence of a bosonic Gaussian channel. Furthermore, the codes previously developed for the depolarizing channel can be translated to codes for the emergent Gaussian channel, and it is easier to further optimize these codes for the simpler emergent Gaussian channel. Translating these codes back to the depolarizing channel leads to extremely good input states for the coherent information of the depolarizing channel producing new lower bounds on the noise threshold for positive capacity. In addition to improved lower bounds on the threshold, this newly found link between depolarizing noise and Gaussian channels offers a novel perspective contributing to our understanding of these symmetric codes.