Controlling dephasing of coupled qubits via shared-bath coherence

TL;DR

This paper demonstrates that the decoherence of coupled qubits can be significantly reduced or eliminated by leveraging the quantum coherence of a shared environment, with specific distances between qubits playing a crucial role.

Contribution

It introduces a method to control qubit dephasing by exploiting shared-bath coherence, showing how environmental quantum effects can be used to enhance qubit coherence.

Findings

Dephasing rates are reduced at specific inter-qubit distances.

Shared bath coherence enables control of decoherence absent in independent baths.

The effect is demonstrated with quantum dots interacting via phonons.

Abstract

The interaction of a quantum system with its environment limits its coherence time. This, in particular, restricts the utility of qubits in quantum information processing applications. In this paper, we show that the decoherence of a coupled qubit system can be minimized, or even eliminated, by exploiting the quantum coherence of the bath itself. We investigate the dephasing in a system of two spatially separated, electronically decoupled qubits, with direct or mediated coupling, interacting with a shared bath. For illustration, we treat F\"orster or cavity-mediated coupling between semiconductor quantum dots interacting with acoustic phonons. Using the rigorous method of Trotter's decomposition with cumulant expansion, we demonstrate a reduction in the dephasing rates at specific distances between the dots. The control of dephasing with distance is a coherent effect of the shared bath and is absent for independent baths. It can be understood in terms of phonon-assisted transitions between the entangled qubit states of the coupled system.