Harnessing symmetry-protected topological order for quantum memories

TL;DR

This paper investigates how symmetry-protected topological order in spin chains can be used for quantum memories, focusing on the effects of disorder and interactions on the stability of stored quantum information.

Contribution

It demonstrates the potential of using an $XZX$ cluster Hamiltonian for encoding and analyzes the impact of many-body interactions and disorder on quantum memory stability.

Findings

Edge state stability varies with disorder realization.

Classical information stability depends on encoding direction.

Low interactions and high disorder favor quantum memory fidelity.

Abstract

Spin chains with symmetry-protected edge modes are promising candidates to realize intrinsically robust physical qubits that can be used for the storage and processing of quantum information. In any experimental realization of such physical systems, weak perturbations in the form of induced interactions and disorder are unavoidable and can be detrimental to the stored information. At the same time, the latter may in fact be beneficial; for instance by deliberately inducing disorder which causes the system to localize. In this work, we explore the potential of using an $XZX$ cluster Hamiltonian to encode quantum information into the local edge modes and comprehensively investigate the influence of both many-body interactions and disorder on their stability over time, adding substance to the narrative that many-body localization may stabilize quantum information. We recover the edge state at each time step, allowing us to reconstruct the quantum channel that captures the locally constrained out of equilibrium time evolution. With this representation in hand, we analyze how well classical and quantum information are preserved over time as a function of disorder and interactions. We find that the performance of the edge qubits varies dramatically between disorder realizations. Whereas some show a smooth decoherence over time, a sizeable fraction are rapidly rendered unusable as memories. We also find that the stability of the classical information -- a precursor for the usefulness of the chain as a quantum memory -- depends strongly on the direction in which the bit is encoded. When employing the chain as a genuine quantum memory, encoded qubits are most faithfully recovered for low interaction and high disorder.