Quantum memories at finite temperature

TL;DR

This paper reviews the progress in developing passive quantum memories capable of preserving quantum information at finite temperatures, highlighting theoretical principles and key examples from recent research.

Contribution

It provides a comprehensive, pedagogical overview of self-correcting quantum memories, analyzing major examples and recent advances in overcoming no-go theorems.

Findings

Analysis of 2D, 3D, and higher-dimensional quantum memories

Identification of key principles for self-correction

Summary of recent experimental and theoretical milestones

Abstract

To use quantum systems for technological applications we first need to preserve their coherence for macroscopic timescales, even at finite temperature. Quantum error correction has made it possible to actively correct errors that affect a quantum memory. An attractive scenario is the construction of passive storage of quantum information with minimal active support. Indeed, passive protection is the basis of robust and scalable classical technology, physically realized in the form of the transistor and the ferromagnetic hard disk. The discovery of an analogous quantum system is a challenging open problem, plagued with a variety of no-go theorems. Several approaches have been devised to overcome these theorems by taking advantage of their loopholes. Here we review the state-of-the-art developments in this field in an informative and pedagogical way. We give the main principles of self-correcting quantum memories and we analyze several milestone examples from the literature of two-, three- and higher-dimensional quantum memories.