A defect in diamond with millisecond-scale spin relaxation time at room temperature

Abstract

Spin defects in diamond are promising platforms for quantum sensing. The longest electron spin relaxation times ($T_1$) at room temperature for solid-state defects are observed in nitrogen vacancy centers in diamond, which can reach 6.67 ms, and substitutional nitrogen ("P1 centers") in diamond, which exhibit a $T_1$ of 2 ms. No other solid-state defect has exhibited millisecond-scale spin relaxation times at room temperature thus far. Here, we characterize the spin properties of the WAR5 defect in diamond with pulsed electron spin resonance. The observed $T_1$ is one of the longest for solid-state spin defects: 0.97(27) ms at room temperature and 14.38(19) min at 4 K. The observed coherence time ($T_2$) is 246(7) $μ$s, which can be extended to 6.49(34) ms at 4 K with dynamical decoupling. Furthermore, we demonstrate optical spin polarization with a range of wavelengths from 405 nm to 500 nm and propose potential zero-phonon line candidates.

Figures (15)

• Figure 1: (a) Pulsed ESR spectrum of the WAR5 sample at 4 K with the magnetic field aligned to $\langle111\rangle$. Optical polarization with 455 nm shows the WAR5 peak at 242.95 mT ($m_s=0\leftrightarrow+1$ transition). The set of three peaks centered at 243.38 mT originates from NV centers in the same sample, with their characteristic hyperfine splitting due to $^{14}$N nuclei. (b) WAR5 ESR as a function of the angle between the crystal axes and the magnetic field. ESR spectra including the NV peaks are shown in gray. WAR5 transitions are extracted from multi-Lorentzian fits and plotted in black. Blue lines are fits to the WAR5 Hamiltonian with g-factor and zero-field splitting as free parameters. All transitions are corrected to the same resonance frequency, 9.696 GHz. (c) Saturation recovery on WAR5 at 4 K. Exponential fit gives $T_1$ = 14.38(19) min.
• Figure 2: (a) Coherence of WAR5 under dynamical decoupling using the CPMG sequence with number of $\pi$-pulses, $N_\pi$ = 1, 2, 4, …, 1024 (purple to red) at 4 K. For 1024 $\pi$-pulses, $T_{2,\rm{CPMG}}$ = 6.49(34) ms. (b) $T_{2,\rm{CPMG}}$ as a function of $N_\pi$. The solid line is a fit to the data points yielding a scaling power of 0.507(6), which shows that $T_{2,\rm{CPMG}}$ scales as $\sqrt{N_\pi}$. (c) Temperature dependence of $T_1$ measured using saturation recovery. The solid line is a fit to the data with Eq. \ref{['eq:T1']}, excluding the room-temperature measurement. The dotted and dashed gray lines correspond to the direct and Orbach components of the fitted curve, respectively.
• Figure 3: Optical spin polarization of WAR5 at 10 K. (a) Spin polarization as a function of the polarization time for optical and thermal polarization. 50 mW of optical power is used. The solid curves are biexponential fits, which yield time constants of 55(4) s, 2.3(1) min, and 16.3(1.8) min for 455 nm, 405 nm, and thermal polarization, respectively. The shorter timescale is attributed to spectral diffusion. (b) Optical spin polarization as a function of wavelength with 10 mW of optical power. Spins are polarized for 2 min, which corresponds to a thermal polarization baseline of 0.4%. Broadband and narrowband measurements correspond to 20 nm and $\lesssim1$ nm spectral bandwidths, respectively. The discontinuity at 501 nm is from switching bandpass filters. Error bars are standard errors from averaging 5 measurements. The shaded region is a guide for the eye to indicate the absorption spectrum of WAR5.
• Figure 4: Atomic and electronic structure of OV$^0$. (a) Energy levels of OV$^0$, including both triplet (spin = 1) and singlet (spin = 0) states. (b) Atomic configurations and Kohn-Sham levels of the triplet states, including the $^3A_2$ ground state ($C_{3v}$ symmetry), $^3A^{\prime\prime}$ metastable state ($C_s$ symmetry), and $^3E$ excited state. (c) Atomic configurations and Kohn-Sham levels of the $^1A^\prime$ singlet state. Carbon atoms are denoted in gray and oxygen in red. Green and blue shaded bands indicate the valence band and conduction band, respectively. (d) Configuration coordinate diagram of the $^3A_2$ and the $^3E$ states. The horizontal axis represents the generalized coordinate $Q$, and the difference in $Q$ indicates the difference between the ground state and excited state geometries. The absorption, emission, and zero-phonon line energies are denoted as $E_\text{abs}$, $E_\text{em}$, and $E_\text{ZPL}$, respectively, and the Huang-Rhys factor as HR.
• Figure A1: Schematic diagram of the home-built pulsed ESR setup. Dashed gray lines denote synchronization channels.