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arXiv:2210.04171 · Physical Review Applied

Nitrogen-Vacancy Singlet-Manifold Ionization Energy

Sigal A. Wolf, Idan Meirzada, Galya Haim, Nir Bar‐Gill

Published Mar 23, 2023• 9 citations
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Abstract

The singlet states of the negatively charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be in the range 1.91--2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and nitrogen-vacancy charge state differentiation, along with simulations based on the nitrogen-vacancy's master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved readout methods.

DOI
10.1103/physrevapplied.19.034076

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The singlet states of the negatively charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be in the range 1.91--2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and nitrogen-vacancy charge state differentiation, along with simulations based on the nitrogen-vacancy's master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved readout methods.
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Spectroscopy of photoionization from the 1E^1E1E singlet state in nitrogen−-−vacancy centers in diamond
The 1E−1A1^1E-^1A_11E−1A1​ singlet manifold of the negatively charged nitrogen vacancy (NV−)(NV^-)(NV−) center in diamond plays a central role in the quantum information and quantum sensing applications of the NV−NV^-NV− center. However, the energy of this manifold within the diamond bandgap and with respect to the 3A2−3E^3A_2-^3E3A2​−3E triplet manifold has not been measured directly. Using field-quenching effects on photoluminescence (PL) spectra, we report on the energy gap between the 1E−1A1^1E-^1A_11E−1A1​ singlet manifold and the 3A2^3A_23A2​ and 3E^3E3E ground and excited triplet states of the NV−NV^-NV− as a function of excitation wavelength and power, temperature, and applied magnetic field in a heavily nitrogen-doped sample. Increased PL and decreased zero-phonon line width from the NV0NV^0NV0 were observed in the presence of an applied magnetic field, indicating ionization from the long-lived 1E^1E1E singlet state. A temperature-dependent ionization threshold between 532 nm and 550 nm was found, locating the singlet states within the diamond band gap.
The 1E^{1}E1E--1A1^{1}A_{1}1A1​ singlet manifold of the negatively charged nitrogen vacancy ($\mathrm{N}{V}^{\ensuremath{-}}$) center in diamond plays a central role in its quantum-information and quantum-sensing applications. However, the energy gap between the 1E^{1}E1E singlet state and diamond band edges or the 3A2^{3}A_{2}3A2​--3E^{3}E3E triplet manifold has not been measured directly. Using the magnetic-field quenching effect on the $\mathrm{N}{V}^{\ensuremath{-}}$ photoluminescence (PL) spectra, we measure these energy gaps as a function of temperature, applied magnetic field, excitation wavelength, and excitation power in a heavily nitrogen-doped sample. Increased PL and decreased zero-phonon line width from the NV0\mathrm{N}{V}^{0}NV0 center were observed in the presence of an applied magnetic field, indicating ionization from the long-lived 1E^{1}E1E singlet state. A temperature-dependent ionization threshold between 532 and 550 nm was found, locating the singlet states within the diamond band gap.
The vast research conducted on nitrogen-vacancy (NV) centers in diamond in recent years opened the door for a wide range of NV based applications. However, some properties of the NV center dynamics and energy levels remain unknown. In this work, we propose a charge-conversion pulsed sequence scheme for locating the NV center singlet manifold energy level, by multicolor excitation using a tunable laser. We present two approaches for readout, photoinduced current and NV0{\mathrm{NV}}^{0}NV0 population, and discuss their efficiency for different regimes in the relevant spectrum.
We utilize nonlinear absorption to design all-optical protocols that improve both charge-state initialization and spin readout for the nitrogen-vacancy (NV) center in diamond. Nonmonotonic variations in the equilibrium charge state as a function of visible and near-infrared optical power are attributed to competing multiphoton absorption processes. In certain regimes, multicolor illumination enhances the steady-state population of the NV's negative charge state above 90%. At higher NIR intensities, selective ionization of the singlet manifold facilitates a protocol for spin-to-charge conversion that dramatically enhances the spin readout fidelity. We demonstrate a sixfold increase in the signal-to-noise ratio for single-shot spin measurements and demonstrate a pathway towards single-shot electron spin readout at room temperature.
The readout of negatively charged nitrogen-vacancy centre electron spins is essential for applications in quantum computation, metrology and sensing. Conventional readout protocols are based on the detection of photons emitted from nitrogen-vacancy centres, a process limited by the efficiency of photon collection. We report on an alternative principle for detecting the magnetic resonance of nitrogen-vacancy centres, allowing the direct photoelectric readout of nitrogen-vacancy centres spin state in an all-diamond device. The photocurrent detection of magnetic resonance scheme is based on the detection of charge carriers promoted to the conduction band of diamond by two-photon ionization of nitrogen-vacancy centres. The optical and photoelectric detection of magnetic resonance are compared, by performing both types of measurements simultaneously. The minima detected in the measured photocurrent at resonant microwave frequencies are attributed to the spin-dependent ionization dynamics of nitrogen-vacancy, originating from spin-selective non-radiative transitions to the metastable singlet state.