Spin Coherence During Optical Excitation of a Single NV Center in Diamond

TL;DR

This study investigates the preservation of quantum spin coherence in a single NV center in diamond during optical excitation, demonstrating high fidelity in spin state preservation despite orbital transitions, which is promising for quantum control.

Contribution

It provides the first quantitative analysis of spin decoherence during optical excitation using quantum process tomography, revealing high process fidelity and potential for quantum control applications.

Findings

Spin coherence is largely preserved during optical excitation.

Quantum process fidelity during excitation is approximately 0.87.

Extrapolated fidelity at excitation is about 0.95.

Abstract

We examine the quantum spin state of a single nitrogen-vacancy (NV) center in diamond at room temperature as it makes a transition from the orbital ground-state (GS) to the orbital excited-state (ES) during non-resonant optical excitation. While the fluorescence read-out of NV-center spins relies on conservation of the longitudinal spin projection during optical excitation, the question of quantum phase preservation has not been examined. Using Ramsey measurements and quantum process tomography, we establish limits on NV center spin decoherence induced during optical excitation. Treating the optical excitation and ES spin precession as a quantum process, we measure a process fidelity of F=0.87\pm0.03, which includes ES spin dephasing during measurement. Extrapolation to the moment of optical excitation yields F\approx0.95. This result demonstrates that ES spin interactions may be used as a resource for quantum control because the quantum spin state can survive incoherent orbital transitions.