Isotope engineering for spin defects in van der Waals materials

Nat. Commun. 15, 104 (2024) · DOI: 10.1038/s41467-023-44494-3

License: CC BY 4.0.

Abstract

Spin defects in van der Waals materials offer a promising platform for advancing quantum technologies. Here, we propose and demonstrate a powerful technique based on isotope engineering of host materials to significantly enhance the coherence properties of embedded spin defects. Focusing on the recently-discovered negatively charged boron vacancy center ($\mathrm{V}_{\mathrm{B}}^{-}$) in hexagonal boron nitride (hBN), we grow isotopically purified h$^{10}$B$^{15}$N crystals. Compared to $\mathrm{V}_{\mathrm{B}}^{-}$ in hBN with the natural distribution of isotopes, we observe substantially narrower and less crowded $\mathrm{V}_{\mathrm{B}}^{-}$ spin transitions as well as extended coherence time $T_{2}$ and relaxation time $T_{1}$. For quantum sensing, $\mathrm{V}_{\mathrm{B}}^{-}$ centers in our h$^{10}$B$^{15}$N samples exhibit a factor of 4 (2) enhancement in DC (AC) magnetic field sensitivity. For additional quantum resources, the individual addressability of the $\mathrm{V}_{\mathrm{B}}^{-}$ hyperfine levels enables the dynamical polarization and coherent control of the three nearest-neighbor $^{15}$N nuclear spins. Our results demonstrate the power of isotope engineering for enhancing the properties of quantum spin defects in hBN, and can be readily extended to improving spin qubits in a broad family of van der Waals materials.

Figures

20 panels with data across 4 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 (c): ESR spectra of $\mathrm{V}_{\mathrm{B}}^{-}$ at $B_z \approx 87$ G: fluorescence (arb. units) against microwave frequency (MHz) for h$^{10}$B$^{15}$N (blue) and hBN$_{\mathrm{nat}}$ (orange), with error bars and the multi-peak Lorentzian fits (solid). The shaded simulated spectra of the print are not included. data.csv
• panel (c-inset-1): Inset of (c): ESR spectrum of h$^{10}$B$^{15}$N at $B_z = 0$ G, fluorescence (arb. units) against frequency (MHz), with error bars. The axis shows the printed window; the Source Data run from 3100 to 3900 MHz. data.csv
• panel (c-inset-2): Inset of (c): ESR spectrum of hBN$_{\mathrm{nat}}$ at $B_z = 0$ G, fluorescence (arb. units) against frequency (MHz), with error bars. The axis shows the printed window; the Source Data run from 3100 to 3900 MHz. data.csv

Fig. 2

• panel (a): Spin echo $T_2^{\mathrm{E}}$ measurements: normalized contrast $C(t)$ against time (ns) for sample S1 (h$^{10}$B$^{15}$N, triangles) and S4 (hBN$_{\mathrm{nat}}$, circles), with error bars and the dashed fit curves. data.csv
• panel (a-inset): Inset of (a): XY8 $T_2^{\mathrm{XY}}$ measurements, normalized contrast $C(t)$ against time (ns) for S1 (triangles) and S4 (circles), with error bars and the dashed fit curves. data.csv
• panel (b-1): Top of (b): spin relaxation time $T_1$ ($\times 10^{4}$ ns) for the six samples, S1 to S3 h$^{10}$B$^{15}$N (triangles) and S4 to S6 hBN$_{\mathrm{nat}}$ (circles), with error bars; the dashed line separates the two materials. data.csv
• panel (b-2): Bottom of (b): spin coherence times $T_2^{\mathrm{XY}}$ (red) and $T_2^{\mathrm{E}}$ (blue) in ns for the six samples, S1 to S3 h$^{10}$B$^{15}$N (triangles) and S4 to S6 hBN$_{\mathrm{nat}}$ (circles), with error bars; the dashed line separates the two materials. data.csv
• panel (c): Relaxation time $T_1$ (ms) against temperature (K) for h$^{10}$B$^{15}$N (triangles) and hBN$_{\mathrm{nat}}$ (circles), with error bars. data.csv
• panel (c-inset): Inset of (c): $T_1$ measurement at 10 K, normalized contrast $C(t)$ against time (ms) for h$^{10}$B$^{15}$N (triangles) and hBN$_{\mathrm{nat}}$ (circles), with error bars and the dashed fit curves. data.csv

Fig. 3

• panel (a): Right of (a): calculated excited state energy spectrum of $\mathrm{V}_{\mathrm{B}}^{-}$, energy (GHz) against magnetic field (G), 24 levels drawn as lines (numbered by energy at each field). data.csv
• panel (a-inset): Inset of (a): closeup of the calculated excited state levels around the anticrossing at 760 G, energy (GHz) against magnetic field (G), 24 levels as lines; the energy span is estimated, as the print labels only 0 GHz. data.csv
• panel (b): ESR spectra of the $|0\rangle \to |+1\rangle$ transition at the esLAC ($B_z \approx 760$ G) at laser powers 0.3, 5 and 10 mW: fluorescence (arb. units) against frequency (MHz), offset vertically as printed, with dashed best fits and dotted guide lines at the four hyperfine resonances. The 5 mW points are as printed; the Source Data differ slightly. data.csv
• panel (b-inset): Inset of (b): ESR spectrum of the $|0\rangle \to |-1\rangle$ transition at a laser power of about 10 mW, fluorescence (arb. units) against frequency (MHz), with the dashed best fit. data.csv
• panel (c): Extracted nuclear polarization $P(|\uparrow\rangle)$ against laser power (mW), with error bars and the dashed best fit. data.csv
• panel (c-inset): Inset of (c): $P(|\uparrow\rangle)$ against the magnetic field alignment angle $\theta$ (deg) relative to the c-axis of hBN, with error bars and the dashed best fit. data.csv
• panel (d): Depolarization dynamics of the $^{15}$N nuclear spins: $P(|\uparrow\rangle)$ against wait time $t$ ($\mu$s), with error bars and the dashed horizontal line as printed. data.csv
• panel (d-inset): Inset of (d): pulsed-ESR spectra at wait times $t = 2$ $\mu$s (diamonds) and 10 $\mu$s (circles), PL (arb. units) against frequency (MHz), with error bars and the dashed best fits. data.csv

Fig. 4

• panel (b): $^{15}$N nuclear spin resonance spectrum at 760 G: fluorescence (arb. units) against RF frequency (MHz), measured points with error bars and the simulated spectrum (dashed) with adjusted transverse hyperfine terms. data.csv
• panel (b-inset): Inset of (b): $^{15}$N nuclear spin resonance spectrum at 210 G, fluorescence (arb. units) against frequency (MHz), measured points with error bars and the simulated spectrum (dashed) as in the Source Data; the printed dashed curve sits about 1.6 MHz higher. data.csv
• panel (c): $^{15}$N nuclear spin Rabi oscillations: fluorescence (arb. units) against RF pulse time (ns), with error bars and the dashed fit $Ae^{-(t/T)^{\alpha}}\cos(2\pi t/\Omega)+c$. data.csv

Cite

Ruotian Gong et al. (12 authors). Isotope engineering for spin defects in van der Waals materials. Nat. Commun. 15, 104 (2024). https://doi.org/10.1038/s41467-023-44494-3

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