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Frontiers in Optics

Pursuing many-body dynamics of NV centers in diamond

Demitry Farfurnik, Y. Horowicz, Nir Alfasi, Sergei Masis, Yaron Kauffmann, E. Farchi, Yoav Romach, Yonatan Hovav, Eyal Buks, Nir Bar‐Gill

Published Jan 1, 2017• 0 citations
Publisher

Abstract

We describe experimental steps toward the observation of many-body dynamics in optically-addressable spin ensembles (NV centers) in diamond. We study the effect of electron irradiation using a 200 keV transmission electron microscope (TEM) on the conversion efficiency and the coherence times of various types of diamond samples with different initial nitrogen concentrations. Using fluorescence images obtained by confocal microscopy, we observe an order of magnitude improvement in the NV concentration (up to ~1011 NV/cm2), without any degradation in their coherence times of ~180 μs (for a Hahn-Echo experiment). We address the potential of this technique for studying many-body physics of ensembles of NV spins: our simulations show that by implementing a simple dynamical decoupling protocol, dipolar interactions could be distinguished from ordinary interactions with the spin-bath environment. These outcomes could contribute to the creation of non-classical spin states, e.g. for quantum sensing.

DOI
10.1364/fio.2017.jw4a.17

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We describe experimental steps toward the observation of many-body dynamics in optically-addressable spin ensembles (NV centers) in diamond. We study the effect of electron irradiation using a 200 keV transmission electron microscope (TEM) on the conversion efficiency and the coherence times of various types of diamond samples with different initial nitrogen concentrations. Using fluorescence images obtained by confocal microscopy, we observe an order of magnitude improvement in the NV concentration (up to ~1011 NV/cm2), without any degradation in their coherence times of ~180 μs (for a Hahn-Echo experiment). We address the potential of this technique for studying many-body physics of ensembles of NV spins: our simulations show that by implementing a simple dynamical decoupling protocol, dipolar interactions could be distinguished from ordinary interactions with the spin-bath environment. These outcomes could contribute to the creation of non-classical spin states, e.g. for quantum sensing.
The studies of many-body dynamics of interacting spin ensembles, as well as quantum sensing in solid state systems, are often limited by the need for high spin concentrations, along with efficient decoupling of the spin ensemble from its environment. In particular, for an ensemble of nitrogen-vacancy (NV) centers in diamond, high conversion efficiencies between nitrogen (P1) defects and NV centers are essential while maintaining long coherence times of an NV ensemble. In this work, we study the effect of electron irradiation on the conversion efficiency and the coherence time of various types of diamond samples with different initial nitrogen concentrations. The samples were irradiated using a 200 keV transmission electron microscope. Our study reveals that the efficiency of NV creation strongly depends on the initial conversion efficiency and on the initial nitrogen concentration. The irradiation of the examined samples exhibits an order of magnitude improvement in the NV concentration (up to ∼1011 NV/cm2), without degradation in their coherence time of ∼180 μs. We address the potential of this technique toward the study of many-body physics of NV ensembles and the creation of non-classical spin states for quantum sensing.
The study of quantum many-body spin physics in realistic solid-state platforms has been a long-standing goal in quantum and condensed-matter physics. We demonstrate separate steps required to reach this goal using nitrogen-vacancy (NV) centers in diamond. First, standard (TEM) electron irradiation is used for the enhancement of N to NV conversion efficiencies by over an order-of-magnitude. Second, robust pulsed and continuous dynamical decoupling (DD) techniques enable the preservation of arbitrary states of the ensemble. These combined efforts could lead to the desired interaction-dominated regime. Finally, we simulate the effects of continuous and pulsed microwave (MW) control on the resulting NV-NV many body dynamics in a realistic spin-bath environment. We emphasize that dominant interaction sources could be identified and decoupled by the application of proper pulse sequences, and the modification of such sequences could lead to the creation engineered interaction Hamiltonians. Such interaction Hamiltonians could pave the way toward the creation of non-classical states, e.g. spin-squeezed states, which were not yet demonstrated in the solid-state, and could eventually lead to magnetic sensing beyond the standard quantum limit (SQL).
Decoherence is the biggest bottleneck in all quantum technologies. For nitrogen-vacancy (NV) centers in diamond, the loss of coherence is caused by the electron and nuclear spin bath of the diamond lattice. Here, we demonstrate that the spin bath - that typically causes decoherence - entangles the spin states of the NV electron and the host 14^{14}14N nucleus. The many-body interaction between the 14^{14}14N nucleus - electron - bath spins at an energy level anti-crossing occurring for an applied magnetic field orientation perpendicular to the NV axis is responsible for this effect. This is observed experimentally in NV ensembles via electron spin-echo measurements, where the echo envelope is modulated at the frequency of a 14^{14}14N nuclear spin transition. Using numerical simulations, we show that the spin bath coupling to the NV centers is essential for observing this modulation. Due to the zero first-order Zeeman effect at the anti-crossing, the observed oscillations have long spin-echo coherence times, 2--3 times those at the parallel magnetic field orientation. The oscillation frequency is highly stable and robust against environmental fluctuations. These findings provide new opportunities for fundamental studies of many-body physics and quantum sensing.
Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( T2∗{T}_{2}^{* }T2∗​ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.
We systematically investigate the NV center creation and properties in bulk chemical vapor deposition (CVD) diamond, throughout growth, electron-beam irradiation, and annealing steps. We study diamond series grown with a varying nitrogen flow over 4 orders of magnitude, resulting in a broad range of single substitutional nitrogen (P1 center) densities from 0.2 to 20 ppm. We investigate in-situ P1 and NV creations, as well as NV charge states distributions. As the next step, we optimize electron-irradiation fluences for a fixed nitrogen concentration, with two different accelerated electron energies. We bring up a general approach to determine the optimal irradiation conditions, and discuss criteria for P1 to NV conversion ratios in the context of stable NV charge states. Through all these optimizations, we enhance the NV- concentration remarkably in our CVD diamond samples, without sacrificing their Hahn-echo coherence time T2. We achieve NV concentrations from 1 to 168 ppb with T2 from 549 to 45.5 µs respectively. This study shows a pathway to engineer targeted, optimized properties of NV-ensembles in bulk CVD diamonds for improved sensitivity.
Abstract A nitrogen vacancy (NV) center in diamond is a promising platform for the study of quantum sensing and quantum many-body physics. It is essential for such study to realize a system in which NV centers interact with one another. This requires the fabrication of highly concentrated NV centers, as the centers must exist within a few nanometers of one another. Only a few such samples have been fabricated, because the required irradiation of several-MV electron beams over long periods makes such sample preparation difficult. Here, highly concentrated NV ensembles ([NV] = 8.5 × 1018 cm-3) were created by narrowing the electron beam of a transmission electron microscope to generate large amounts of vacancies in highly concentrated nitrogen-doped CVD diamond ([N] = 8 × 1020 cm-3). This result reduces the difficulty of producing high-concentration NV ensembles and is expected to promote the development of many-body quantum physics.