Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing

Nat. Commun. 14, 5089 (2023) · DOI: 10.1038/s41467-023-40473-w

License: CC BY 4.0.

Abstract

Negatively-charged boron vacancy centers ($V_B^-$) in hexagonal Boron Nitride (hBN) are attracting increasing interest since they represent optically-addressable qubits in a van der Waals material. In particular, these spin defects have shown promise as sensors for temperature, pressure, and static magnetic fields. However, their short spin coherence time limits their scope for quantum technology. Here, we apply dynamical decoupling techniques to suppress magnetic noise and extend the spin coherence time by two orders of magnitude, approaching the fundamental $T_1$ relaxation limit. Based on this improvement, we demonstrate advanced spin control and a set of quantum sensing protocols to detect radiofrequency signals with sub-Hz resolution. The corresponding sensitivity is benchmarked against that of state-of-the-art NV-diamond quantum sensors. This work lays the foundation for nanoscale sensing using spin defects in an exfoliable material and opens a promising path to quantum sensors and quantum networks integrated into ultra-thin structures.

Figures

16 panels with data across 3 figures. Each panel page shows the plot, its columns and its files; each data.csv begins with a header naming the paper, the panel, the source, the license and the provenance route.

Fig. 1

• panel (e): ODMR spectrum of the $|0\rangle \rightarrow |-1\rangle$ transition: baseline-subtracted contrast (arb. u., $\times 10^{-3}$) against ODMR frequency (GHz). Circles are the data points, dotted lines the single Gaussian functions fitted to them and the solid line their sum. data.csv
• panel (f): Rabi oscillations for four MW powers (37, 33, 28 and 23 dBm): contrast against MW pulse duration $t_p$ (ns), data points with a fitted curve through each trace. The traces are stacked as printed: 33, 28 and 23 dBm are shifted down by 0.05, 0.10 and 0.14. The printed contrast axis carries no numbers. data.csv
• panel (f-inset): Inset of panel (f): Rabi frequency $\nu_R$ (MHz) against the square root of the microwave power, $\sqrt{P}$ ($\sqrt{\mathrm{W}}$), for the four MW powers, with the linear fit through the origin. data.csv
• panel (g): $T_1$ measurement: normalized contrast against time $\tau$ ($\mu$s, log axis), measured with the recovery pulse sequence. Circles are the data points and the line is the mono-exponential fit. data.csv
• panel (h): Spin-echo $T_2$ measurement: normalized contrast against time $\tau$ ($\mu$s, log axis). Circles are the data points; the line, labelled $T_2$ decay in the print, is the fit of a stretched exponential decay with a damped oscillation superimposed. data.csv

Fig. 2

• panel (a): Decoherence curves under CPMG decoupling with $N$ = 1, 4, 16, 64, 300, 600, 800 and 1000 $\pi$-pulses: normalized contrast against pulse sequence duration $t_s$ (s, log axis). Coloured dots are data points and solid lines their fits. Black squares with a dotted line are the $T_1$ measurement and its fit. data.csv
• panel (a-inset): Inset of panel (a): coherence time $T_2$ ($\mu$s) against the number of $\pi$-pulses $N$ used in each CPMG experiment, eight points with the power-function fit $f(N) = a \times N^{s}$. data.csv
• panel (b): Rotating-frame spin-lattice relaxation: normalized contrast against spinlock duration $t_{SL}$ (s, log axis). Blue circles and the solid line are the $T_{1\rho}$ data and fit; black squares and the dotted line are the $T_1$ measurement and its fit. data.csv

Fig. 3

• panel (b): RF sensing with an XY8-2 sequence: baseline-subtracted contrast (%) against interpulse delay $\tau$ (ns, logarithmic axis as printed) for $\nu_{RF}$ = 16 MHz (squares) and 18 MHz (circles). The lines are the $(\mathrm{sinc})^2$ fits. data.csv
• panel (c): Lineshape for XY8-1, XY8-2, XY8-3 and XY8-4 sequences at $\nu_{RF}$ = 16 MHz: baseline-subtracted contrast (%) against interpulse delay $\tau$ (ns), dots with fitted lines. The traces are stacked as printed: XY8-2, XY8-3 and XY8-4 are shifted down by 0.25, 0.40 and 0.52. data.csv
• panel (e): Spinlock RF sensing: baseline-subtracted contrast (%) against spinlock amplitude $\Omega/(2\pi)$ (MHz) for $\nu_{RF}$ = 17 MHz (circles) and 20 MHz (squares), with Lorentzian fits (lines). The three lowest-amplitude points of each series lie outside the printed frame. data.csv
• panel (f): Dependence of the lineshape on the spinlock duration at $\nu_{RF}$ = 16 MHz: baseline-subtracted contrast (%) against spinlock amplitude $\Omega/(2\pi)$ (MHz) for $t_{SL}$ = 0.1, 0.5, 1, 3 and 6 $\mu$s, dots with Lorentzian fits (lines). The traces are stacked as printed, shifted down by 0.07, 0.13, 0.21 and 0.33. data.csv
• panel (h): Time-domain CASR signal: contrast (arb. units) against measurement time $t_m$ (s) over the 2 s measurement. data.csv
• panel (h-inset): Inset of panel (h): the first 4 ms of the CASR signal, contrast (arb. units) against $t_m$ (ms), points joined by a line. The red curve the print draws through the oscillation is not reproduced. data.csv
• panel (i): Fourier transform of the CASR signal: $|\mathrm{FFT}|$ ($\times 10^{-4}$) against relative frequency $\Delta\nu$ (Hz), over the printed frequency window. data.csv
• panel (i-inset): Inset of panel (i): zoom on the peak, $|\mathrm{FFT}|$ ($\times 10^{-4}$) against relative frequency $\Delta\nu$ (Hz). Dots are the data points and the red line is the Lorentzian line fit. data.csv

Cite

Roberto Rizzato et al. (15 authors). Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing. Nat. Commun. 14, 5089 (2023). https://doi.org/10.1038/s41467-023-40473-w

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