Non-reciprocal coherent dynamics of a single spin under closed-contour interaction

TL;DR

This paper demonstrates a new method of controlling a single NV spin using closed-contour interaction, leading to phase-controlled interference and significant coherence time enhancement, with potential applications in quantum technologies.

Contribution

It introduces the experimental realization of coherent closed-contour interaction in a single NV spin, enabling phase-controlled interference and coherence protection.

Findings

Phase-controlled quantum interference fringes observed.

Nearly two orders of magnitude increase in coherence time.

Effective coherence protection at moderate drive strengths.

Abstract

Three-level quantum systems have formed a cornerstone of quantum optics since the discovery of coherent population trapping (CPT) and electromagnetically induced transparency. Key to these phenomena is quantum interference, which arises if two of the three available transitions are coherently driven at well-controlled amplitudes and phases. The additional coherent driving of the third available transition would form a closed-contour interaction (CCI) from which fundamentally new phenomena would emerge, including phase-controlled CPT and one atom interferometry. However, due to the difficulty in experimentally realising a fully coherent CCI, such aspects of three-level systems remain unexplored as of now. Here, we exploit recently developed methods for coherent driving of single Nitrogen-Vacancy (NV) electronic spins to implement highly coherent CCI driving. Our experiments reveal phase-controlled, single spin quantum interference fringes, reminiscent of electron dynamics on a triangular lattice, with the driving field phases playing the role of a synthetic magnetic flux. We find that for suitable values of this phase, CCI driving leads to efficient coherence protection of the NV spin, yielding a nearly two orders of magnitude improvement of the coherence time, even for moderate drive strengths <~1MHz. Our results establish CCI driving as a novel paradigm in coherent control of few-level systems that offers attractive perspectives for applications in quantum sensing or quantum information processing.