Multi-frequency composite pulse sequences for sensitivity enhancement in hexagonal boron nitride quantum sensor

Abstract

A negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has recently started to be used as a magnetic sensor.
However, VB- has magnetic resonance spectra broadened by hyperfine interactions, which decreases the signal contrast and thus degrades the magnetic field sensitivity. 
Here we propose multi-frequency composite pulse sequences to enhance the contrast of the measurement signal in the Rabi oscillation. 
We demonstrate that the sequence using five microwave frequencies enhances the signal contrast, improving the sensitivity by a factor of 2.3 compared to the conventional sequence.

Nitrogen isotope effects on boron vacancy quantum sensors in hexagonal boron nitride

“…The parameters obtained by this fitting are f −,0 = 2312 ± 1 MHz, C = 5.6 ± 0.3%, dν = 47 ± 3 MHz, and | (14N) A zz | = 43 ± 1 MHz. The obtained HFI parameter of 14 N spin is consistent with previous works 10,23,24,28) within a typical error of a few MHz. Generally, it is impossible to determine the sign of the HFI parameter from this fitting.…”

“…It degrades the sharpness/slope of the ODMR spectrum and makes it challenging to manipulate electron spins selectively to desired nuclear spin states. 24) It is also unfavorable for the magnetic field sensitivity, which is proportional to the slope of the ODMR spectrum (see SI). In the 15 N case, the increased occupancy and enhanced distance between resonance lines will help to reduce the overlap and sharpen ODMR spectra; thus, they are advantageous to improve magnetic field sensitivity and control fidelity.…”

“…Furthermore, the reduced overlap of individual resonance lines directly implies improved fidelity in electron spin manipulation selective to nuclear spin states (see SI). By applying operations with multi-frequency composite pulses, 24) it should be possible to excite most of the spectrum efficiently.…”