Anticrossing Spin Dynamics of Diamond Nitrogen-Vacancy Centers and All-Optical Low-Frequency Magnetometry

Abstract

We investigate the photo-induced spin dynamics of single nitrogen-vacancy (NV) centres in diamond near the electronic ground state level anti-crossing (GSLAC), which occurs at an axial magnetic field around 1024 G. Using optically detected magnetic resonance spectroscopy, we first find that the electron spin transition frequency can be tuned down to 100 kHz for the 14 NV centre, while for the 15 NV centre the transition strength vanishes for frequencies below about 2 MHz owing to the GSLAC level structure. Using optical pulses to prepare and readout the spin state, we observe coherent spin oscillations at 1024 G for the 14 NV, which originate from spin mixing induced by residual transverse magnetic fields. This effect is responsible for limiting the smallest observable transition frequency, which can span two orders of magnitude from 100 kHz to tens of MHz depending on the local magnetic noise. A similar feature is observed for the 15 NV centre at 1024 G. As an application of these findings, we demonstrate all-optical detection and spectroscopy of externally-generated fluctuating magnetic fields at frequencies from 8 MHz down to 500 kHz, using a 14 NV centre. Since the Larmor frequency of most nuclear spin species lies within this frequency range near the GSLAC, these results pave the way towards all-optical, nanoscale nuclear magnetic resonance spectroscopy, using longitudinal spin cross-relaxation.

Spin-strain interaction in nitrogen-vacancy centers in diamond

“…The method, inspired by the experiment of Ref. 46, requires a finite magnetic field along the NV axis, which tunes the system to the ground-state level anticrossing (GSLAC) where the | − 1e and |0e electronic states are approximately degenerate, B z ≈ B g ≡ D/γ e ≈ 1024 G. In that setting, mechanical stress can induce strong mixing of the spin eigenstates of the coupled electron-nuclear system via the coupling-strength parameters g 25 and g 26 . In turn, the spin dynamics governed by this mixing can be detected in a time-resolved fashion, via photoluminescence-based optical readout of the NV spin system.…”

“…2: instead of two electron spin levels crossing at B z = B g , there are six levels, with two level pairs showing hyperfine-induced anticrossings. We focus on the case when the N atom of the NV center is an 14 N; the analysis can be generalized straightforwardly for the 15 N case 46,48 .…”

High precision single qubit tuning via thermo-magnetic field control

“…For CR spectroscopy it is desirable to implement small changes in frequency as this defines the maximum possible spectral resolution of the technique. We compare with our current mechanical control setup, with a 400 nm axial step size; around the ground state level anti-crossing (GSLAC) [26] this step corresponds to a smallest NV frequency change of 65 kHz. For the temperature control setup described here 0.01 • C steps in the magnet temperature were pos-sible, corresponding to a change of 26 kHz.…”

Microwave-free nuclear magnetic resonance at molecular scales

“…A T 1 -NMR spectrum recorded using evolution times τ =1 μs (reference) and τ =20 μs is shown in Fig. 3b and reveals three main features, labelled A, B and C. The first two dips (A and B) are seen only for τ =20 μs and correspond to the cross-relaxation resonances with 1 H. The third dip, (C), exhibiting a far stronger decay, which is also visible at short time τ =1 μs, corresponds to the intrinsic feature discussed above36.…”