Correlated noise enhances coherence and fidelity in coupled qubits

TL;DR

This paper demonstrates that correlated environmental noise can actually improve coherence and fidelity in coupled qubits, challenging the common view that noise is solely detrimental to quantum systems.

Contribution

It introduces a model incorporating noise correlation into quantum dynamics and shows how correlation can enhance entanglement fidelity and purity.

Findings

Correlation increases fidelity of Bell states.

Environmental correlation can be probed via Bell state evolution.

Correlated noise can be beneficial for quantum communication.

Abstract

It is generally assumed that environmental noise arising from thermal fluctuations is detrimental to preserving coherence and entanglement in a quantum system. In the simplest sense, dephasing and decoherence are tied to energy fluctuations driven by coupling between the system and the normal modes of the bath. Here, we explore the role of noise correlation in an open-loop model quantum communication system whereby the ``sender'' and the ``receiver'' are subject to local environments with various degrees of correlation or anticorrelation. We introduce correlation within the spectral density by solving a multidimensional stochastic differential equations and introduce these into the Redfield equations of motion for the system density matrix. We find that correlation can enhance both the fidelity and purity of a maximally entangled (Bell) state. Moreover, by comparing the evolution of different initial Bell states, we show that one can effectively probe the correlation between two local environments. These observations may be useful in the design of high-fidelity quantum gates and communication protocols.