Coherent population trapping of a single nuclear spin under ambient conditions

TL;DR

This paper demonstrates room-temperature coherent population trapping of a single nuclear spin in diamond, using a controlled relaxation scheme to achieve dark state formation and multiple resonances, advancing quantum control in solid-state systems.

Contribution

It introduces a novel method for CPT of a nuclear spin at room temperature using controlled relaxation, enabling new quantum control and metrology applications.

Findings

Successful CPT of a single nuclear spin at ambient conditions.

Observation of multiple dark resonances due to constructive interference.

Controlled relaxation enhances quantum state preparation capabilities.

Abstract

Coherent control of quantum systems has far-reaching implications in quantum engineering. In this context, coherent population trapping (CPT) involving dark resonances has played a prominent role, leading to a wealth of major applications including laser cooling of atoms and molecules, optical magnetometry, light storage and highly precise atomic clocks. Extending CPT methods to individual solid-state quantum systems has been only achieved in cryogenic environments for electron spin impurities and superconducting circuits. Here, we demonstrate efficient CPT of a single nuclear spin in a room temperature solid. To this end, we make use of a three-level system with a $\Lambda$-configuration in the microwave domain, which consists of nuclear spin states addressed through their hyperfine coupling to the electron spin of a single nitrogen-vacancy defect in diamond. Dark state pumping requires a relaxation mechanism which, in atomic systems, is simply provided by spontaneous emission. In this work, the relaxation process is externally controlled through incoherent optical pumping and separated in time from consecutive coherent microwave excitations of the nuclear spin $\Lambda$-system. Such a pumping scheme with controlled relaxation allows us (i) to monitor the sequential accumulation of population into the dark state and (ii) to reach a new regime of CPT dynamics for which periodic arrays of dark resonances can be observed, owing to multiple constructive interferences. This work offers new prospects for quantum state preparation, information storage in hybrid quantum systems and metrology.