Coherent dynamics of strongly interacting electronic spin defects in hexagonal boron nitride

Abstract

Optically active spin defects in van der Waals materials are promising platforms for modern quantum technologies. Here we investigate the coherent dynamics of strongly interacting ensembles of negatively charged boron-vacancy ($${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ V B − ) centers in hexagonal boron nitride (hBN) with varying defect density. By employing advanced dynamical decoupling sequences to selectively isolate different dephasing sources, we observe more than 5-fold improvement in the measured coherence times across all hBN samples. Crucially, we identify that the many-body interaction within the $${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ V B − ensemble plays a substantial role in the coherent dynamics, which is then used to directly estimate the concentration of $${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ V B − . We find that at high ion implantation dosage, only a small portion of the created boron vacancy defects are in the desired negatively charged state. Finally, we investigate the spin response of $${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ V B − to the local charged defects induced electric field signals, and estimate its ground state transverse electric field susceptibility. Our results provide new insights on the spin and charge properties of $${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ V B − , which are important for future use of defects in hBN as quantum sensors and simulators.

Detection of Paramagnetic Spins with an Ultrathin van der Waals Quantum Sensor

“…In a photon-shot-noise-limited T 1 -relaxometry experiment, the signal-to-noise ratio scales as , SNR ∝ normalΓ 1 ext normalΓ 1 int scriptC I PL where Γ 1 int = 1/ T 1 int is the intrinsic relaxation rate in the absence of the target spin (assumed to satisfy Γ 1 int ≫Γ 1 ext ), C is the relative spin contrast, and I PL is the PL signal from one readout pulse. Currently, V B – defect ensembles exhibit inferior contrast and PL output compared to typical NV ensembles and so will need to be improved through material optimization (e.g., to increase defect creation yield, as currently only a small fraction of boron vacancies are in the desired negatively charged state) or photonics engineering to enhance collection. ,, On the other hand, the intrinsic relaxation time observed in this work for V B – in hBN nanopowders ( T 1 int ≈ 15–20 μs) is similar to that of NVs in nanodiamonds of comparable size of order 10 nm, which do not reach the longer relaxation times exhibited by NVs in bulk diamond but nevertheless have found widespread interest. Considering all these factors together, we believe hBN nanopowders can be improved as a sensing platform to detect submillimolar concentrations of paramagnetic ions and emerge as a viable alternative to nanodiamonds for T 1 relaxometry in this concentration regime with the potential of a lower production cost, making it appealing for applications such as high-sensitivity point-of-care diagnostics. , Note that for these applications the development of robust surface functionalization methods will be necessary …”

Quantum Sensing of Paramagnetic Spins in Liquids with Spin Qubits in Hexagonal Boron Nitride

“…They are relatively short due to the high doping density that we used to obtain high PL count rates. 47 In the presence of Gd 3+ ions (prepared by dissolving Gd(NO 3 ) 3 in water), we observe reduced T 1 relaxation times. The measured spin relaxation times are T 1 = 9.54 ± 0.32 μs for 1 M Gd 3+ ions and T 1 = 10.17 ± 0.50 μs for 0.5 M Gd 3+ ions (Figure 2d).…”

“…In DI water, the T 1,DI of Sensor 1 ( d = 6.4 nm) is measured to be 11.24 ± 0.17 μs, which is close to T 1 in air for this hBN nanosheet. They are relatively short due to the high doping density that we used to obtain high PL count rates . In the presence of Gd 3+ ions (prepared by dissolving Gd­(NO 3 ) 3 in water), we observe reduced T 1 relaxation times.…”

Sensing spin wave excitations by spin defects in few-layer-thick hexagonal boron nitride

“…In comparison with NV centers embedded in highly rigid, threedimensional (3D) diamond, spin defects contained in exfoliable, 2D materials exhibit improved compatibility with nanodevice integration, providing an attractive platform for implementing ultrasensitive quantum metrology measurements by exploiting the atomic length scale proximity between the spin sensors and objects of interest (20)(21)(22)(23). In the current state of the art, the local sensing of electrical, magnetic, and thermal flux arising from solid-state materials using spin defects in hBN has been experimentally demonstrated in both confocal and wide-field optical microscopy configurations (5,21,22,24), and the development of transformative approaches to revolutionize the current quantum technologies is under way (25)(26)(27)(28)(29).…”