Abstract
We introduce and demonstrate a scheme for eliminating the inhomogeneous dephasing of a collective quantum state. The scheme employs off-resonant fields that continuously dress the collective state with an auxiliary sensor state, which has an enhanced and opposite sensitivity to the same source of inhomogeneity. We derive the optimal conditions under which the dressed state is fully protected from dephasing when using either one or two dressing fields. The latter provides better protection, circumvents qubit phase rotation, and suppresses the sensitivity to drive noise. We further derive expressions for all residual, higher-order sensitivities. We experimentally study the scheme by protecting a collective excitation of an atomic ensemble, where inhomogeneous dephasing originates from thermal motion. Using photon storage and retrieval, we demonstrate complete suppression of inhomogeneous dephasing and, consequently, a prolonged memory time. Our scheme may be applied to eliminate motional dephasing in other systems, improving the performance of quantum gates and memories with neutral atoms. It is also generally applicable to various gas, solid, and engineered systems, where sensitivity to variations in time, space, or other domains limits possible scale-up of the system.
- Received 23 April 2020
- Revised 1 October 2020
- Accepted 23 November 2020
DOI:https://doi.org/10.1103/PhysRevX.11.011008
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Progress in quantum information processing relies in part on maintaining quantum state coherence among the various parts of the system. Unfortunately, decoherence readily arises because of variations in these systems, such as different external fields, temperatures, and engineering imperfections. While some mechanisms have been proposed to mitigate decoherence, they either work only at discrete, predetermined times or are incompatible with other system requirements. Here, we propose and demonstrate an alternative approach for providing continuous protection against such decoherence.
Our scheme relies on admixing the quantum state with an auxiliary “sensor state,” a separate quantum state that has an opposite and enhanced sensitivity to the source of inhomogeneity. By fine tuning the mixing of these states with a carefully modulated laser, we produce a composite state that is insensitive to environmental noise.
Experimentally, we apply our scheme to mitigating motional dephasing—a prominent decoherence mechanism in atomic vapors, where quantum information is lost as a result of random velocities of the thermal atoms—and show that we can preserve the original imprinted phase even though the atoms continue to move randomly. Importantly, no efficient protocol for this problem has been demonstrated to date.
