Room-temperature hybrid 2D-3D quantum spin system for enhanced magnetic sensing and many-body dynamics

Abstract

Advances in hybrid quantum systems and their precise control are pivotal for developing advanced quantum technologies. Two-dimensional (2D) materials with optically accessible spin defects have emerged as a promising platform for building integrated quantum spin systems due to their exceptional flexibility and scalability. However, experimentally realizing such systems and demonstrating their superiority remains challenging. Here, we present a hybrid spin system operating under ambient conditions, integrating boron vacancy (V_B^-) spins in 2D hexagonal boron nitride flakes with a single nitrogen vacancy (NV) center in 3D single-crystal diamonds. This combined system achieves full controllability and exhibits enhanced performance for nanoscale magnetic sensing, including an improved dynamic range. Moreover, we investigate the rich many-body spin dynamics within the hybrid system, which enables us to estimate the concentration of V_B^- spins. This work provides a critical foundation for advancing the development of 2D-3D integrated quantum spin systems.

Figures (4)

• Figure 1: Optical and microwave addressability of NV and V${\rm{_{B}^{-}}}$ spins.a Schematic of the experimental configuration for spin manipulation and the atomic structures of NV and V${\rm{_{B}^{-}}}$ centers. The diamond with the transferred hBN flakes is placed upside down onto a gold film microwave stripline. b Simplified energy level diagram of NV and V${\rm{_{B}^{-}}}$ spins, illustrating optical transitions between the ground state (GS) and the excited state (ES). $D_{\rm{NV}}$ and $D_{\rm{V_{B}^{-}}}$ denote the zero-field splitting parameters. Transition frequencies: $f_-$($m_{s} = -1 \leftrightarrow m_{s} = 0$) and $f_+$($m_{s} = +1 \leftrightarrow m_{s} = 0$). c Top left: Normalized photoluminescence spectra of NV and V${\rm{_{B}^{-}}}$ centers excited with 532 nm laser at room temperature. The shaded regions indicate the fluorescence collected using short-pass (SP) or long-pass (LP) filter. Bottom left $\&$ right: Confocal PL images of NV and V${\rm{_{B}^{-}}}$ spins obtained without a filter (bottom left), with a 758 nm SP filter (top right), and with a 785 nm LP filter (bottom right). d Continuous-wave (CW) ODMR spectra and Rabi oscillations of NV (blue) and V${\rm{_{B}^{-}}}$ (red) spins. Left: CW ODMR spectra obtained under simultaneous MW driving, optical pumping, and readout. Right: Rabi oscillations for the $m_{s} = -1 \leftrightarrow m_{s} = 0$ transition, measured using a variable-length MW pulse following optical excitation.
• Figure 2: Hybrid magnetic sensing. ODMR spectra of NV and V${\rm{_{B}^{-}}}$ spins at magnetic fields of approximately 50 mT (a) and 93 mT (b), where the magnetic field is aligned along the NV axis ($B$$_{\rm{NV}}$) or the V${\rm{_{B}^{-}}}$ axis ($B_{\rm{V_{B}^{-}}}$), respectively. c Overlap $\left | \alpha \right | ^{2}$ of each spin level for NV (dashed lines) and V${\rm{_{B}^{-}}}$ spins (solid lines) with $\left | 0 \right \rangle _{z}$ as a function of the magnetic field, where $B$ is at an angle of 54.7$^{\circ}$ to the NV or V${\rm{_{B}^{-}}}$ axis. Upper panel: Calculated results for the ES. Lower panel$:$ Calculated results for the GS.
• Figure 3: Characterization of NV-V${\rm{_{B}^{-}}}$ coupling strength and V${\rm{_{B}^{-}}}$ concentration.a ODMR spectra of NV-1 and V${\rm{_{B}^{-}}}$ spins measured at 15.9 mT (upper panel) and 24.8 mT (lower panel), with the magnetic field aligned along the NV-1 axis. b Longitudinal relaxation rate (1/$T_{1}$) of NV-1 as a function of the transition frequencies, $f_{+}$. The data are fitted using the equation $1/{T_{1}^{\rm{other}}}+{b^{2}}{{\Gamma}/({\Delta^{2}+\Gamma^{2}})}$, with fitted values of $\Gamma/2\uppi$$\sim$ 160 MHz and $1/{T_{1}^{\rm{other}}}$$\sim$ 0.24. The inset shows $T_{1}$ measurements of NV-1, where the $T_{1}$ signal is obtained by subtracting two consecutive measurements: one with a $\uppi$ pulse and one without. At 15.9 mT, $T_{1}$ = 1.38(0.13) ms; at 24.8 mT, $T_{1}$ = 3.47(0.38) ms. c Summary of coupling strengths for NV centers under various hBN samples. d Measured fluorescence counts of different hBN samples versus estimated V${\rm{_{B}^{-}}}$ concentration. The data are fitted using a linear function with a slope of 6.86(1.06).
• Figure 4: Probing many-body dynamics through a single spin probe.a Schematic of fluctuating signal $\left(\delta B \right)^{2}$ measurement using a nearby NV center, where $\left(\delta B \right)^{2}$ is produced by flip-flops between the V${\rm{_{B}^{-}}}$ spins. b Measurements of fluctuating (waiting 50 $\upmu$s) and polarized (waiting 1 $\upmu$s) magnetic field from V${\rm{_{B}^{-}}}$ spins. The upper panel is the DEER pulse sequence, and the lower panel shows the measurement results. The coherence time $T_2$ of the NV center is $\sim$2.6 $\upmu$s, and the measurements were performed at 37.5 mT. c Variation of DEER decay rates with NV depths for fully driving and not driving V${\rm{_{B}^{-}}}$ spins, where the fluorescence-estimated V${\rm{_{B}^{-}}}$ density is $\sim$0.01 $\rm{nm^{-2}}$. The orange dots represent experimental results obtained with a 50 $\upmu$s waiting time. d Simulated DEER signals for varying NV coherence times and polarization degrees of the V${\rm{_{B}^{-}}}$ spins.