Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond

Abstract

We demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to $77$ K suppresses longitudinal spin relaxation $T_1$ effects and DD microwave pulses are used to increase the transverse coherence time $T_2$ from $\sim 0.7$ ms up to $\sim 30$ ms. We extend previous work of single-axis (CPMG) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We identify that the optimal control scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of AC magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states

Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiation

“…Furthermore, the achieved concentration of ∼ 10 15 NV/cm 3 corresponds to NV-NV dipolar coupling of ∼ 50 Hz. By repeating the irradiation process on isotopically pure 12 C samples, where ∼ 30 ms coherence times can be achieved using optimized dynamical decoupling [13], the NV-NV interaction dominated regime could be reached, opening an avenue for the study of many-body spin dynamics with available samples and processing techniques [10][11][12].…”

“…While this realistic scheme is expected to be limited in terms of the resulting NV-NV interaction strength, with the use of proper dynamical decoupling protocols [13], the NV-NV interactiondominated regime could still be reached. Moreover, the resulting enhancement in the conversion efficiency could make NV ensemble sensors vastly smaller and therefore more practical for magnetic [1,3,7], thermal [8], and electric [9] sensing.…”

“…The sensitivity of magnetic sensing grows as the square-root of the number of spins [1,3], thus enhanced NV concentrations could improve magnetometric sensitivities. Furthermore, enhanced NV concentrations could lead to strong NV-NV couplings, which together with long coherence times, achieved using a proper dynamical decoupling protocol [13], could pave the way toward the study of many-body dynamics in the NV-NV interaction-dominated regime [10][11][12]. However, nitrogen defects not associated with vacancies (P1 centers) create randomly fluctuating magnetic fields that cause decoherence of the quantum state of the NV ensemble [14,15].…”

Measurement-device-independent quantum key distribution with nitrogen vacancy centers in diamond

“…5, we have plotted the key rate for our proposed scheme at two different values of coherence time. At T 2 = 100 ms, which is the typical coherence time of electron spins [37], we outperform the no-QM system by nearly one order of magnitude at distances around 400 km. We can extend the window over which our NV-center-based scheme outperforms MDI-QKD if we increase the coherence time by one order of magnitude.…”

High-sensitivity spin-based electrometry with an ensemble of nitrogen-vacancy centers in diamond

“…Additional coherent control on either the surrounding electron [55,56] or nuclear spins [57][58][59] in diamond would further improve the sensitivity by reducing the broadening of the transition linewidth. Microwave field inhomogeneities that are typically more problematic for pulsed techniques would benefit from recently proposed methodologies for generating robust pulse sequences [60]. Other promising directions for spin-based sensing involve all-optical techniques in diamond for electrometry [61].…”