Spin-Dependent Charge-State Conversion in NV Ensembles Mediated by Electron Tunneling

TL;DR

This study demonstrates that excitation at 575 nm induces spin-dependent NV0 emission via electron tunneling, enabling enhanced spin contrast and improved sensitivity in NV-based quantum sensing.

Contribution

It reveals a new excitation wavelength that leverages spin-dependent charge conversion, improving signal utilization in NV center sensing.

Findings

Excitation at 575 nm produces NV0 through spin-selective tunneling.

NV0 emission can carry spin contrast when excited at 575 nm.

Using this method enhances the sensitivity of NV-based measurements.

Abstract

The nitrogen-vacancy (NV) center in diamond enables optical initialization and readout of its electronic spin, forming the basis of a wide range of quantum sensing and metrology applications. A central challenge in such measurements is the coexistence of two charge states, NV- and NV0: While detection protocols rely on the spin-dependent properties of NV-, fluorescence from NV0 does not carry useful contrast and is typically removed as background, reducing the available signal. Here, we show that the origin of NV0 emission depends strongly on the excitation wavelength in nitrogen-containing diamond. Using ensembles of NV centers with varying nitrogen concentrations, we compare excitation at the NV0 zero-phonon line (ZPL) at 575 nm with the commonly used 532 nm. We find that excitation at 575 nm generates NV0 predominantly through spin-selective tunneling from the excited state of NV- to nearby nitrogen donors, such that the NV0 emission follows the spin polarization of NV-. As a result, the NV0 fluorescence contributes to the measurable spin contrast, allowing the full fluorescence signal to be used for detection. This result opens opportunities for improved sensitivity in NV-based sensing applications.