Single Spins In Diamond Research Articles

Detecting Spin-Bath Polarization with Quantum Quench Phase Shifts of Single Spins in Diamond

Detecting Spin-Bath Polarization with Quantum Quench Phase Shifts of Single Spins in Diamond

Nanoscale spin detection of copper ions using double electron-electron resonance at room temperature

We report the nanoscale spin detection and electron paramagnetic resonance (EPR) spectrum of copper (Cu$^{2+}$) ions via double electron-electron resonance with single spins in diamond at room temperature and low magnetic fields. We measure unexpectedly narrow EPR resonances with linewidths $\sim 2-3$ MHz from copper-chloride molecules dissolved in poly-lysine. We also observe coherent Rabi oscillations and hyperfine splitting from single Cu$^{2+}$ ions, which could be used for dynamic nuclear spin polarization and higher sensitivity of spin detection. We interpret and analyze these observations using both spin hamiltonian modeling of the copper-chloride molecules and numerical simulations of the predicted DEER response, and obtain a sensing volume $\sim (250 \text{nm})^3$. This work will open the door for copper-labeled EPR measurements under ambient conditions in bio-molecules and nano-materials.

Phase-sensitive quantum spectroscopy with high-frequency resolution

Classical sensors for spectrum analysis are widely used but lack micro- or nanoscale spatial resolution. On the other hand, quantum sensors, capable of working with nanoscale precision, do not provide precise frequency resolution over a wide range of frequencies. Using a single spin in diamond, we present a measurement protocol for quantum probes which enables full signal reconstruction on a nanoscale spatial resolution up to potentially 100\,GHz. We achieve $58\,\mathrm{nT/\sqrt{Hz}}$ amplitude and $0.095\,\mathrm{rad/\sqrt{Hz}}$ phase sensitivity and a relative frequency uncertainty of $10^{-12}$ for a $1.51\,\mathrm{GHz}$ signal within $10\,\mathrm{s}$ of integration. This technique opens the way to quantum spectrum analysis methods with potential applications in electron spin detection and nanocircuitry in quantum technologies.

Publisher's Note: Competition between electric field and magnetic field noise in the decoherence of a single spin in diamond [Phys. Rev. B 93 , 024305 (2016)

Received 13 June 2019DOI:https://doi.org/10.1103/PhysRevB.99.249903©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFluctuations & noiseOpen quantum systems & decoherenceQuantum information with solid state qubitsPhysical SystemsNitrogen vacancy centers in diamondCondensed Matter, Materials & Applied Physics

Experimental Observation of a Generalized Thouless Pump with a Single Spin.

Adiabatic cyclic modulation of a one-dimensional periodic potential will result in quantized charge transport, which is termed the Thouless pump. In contrast to the original Thouless pump restricted by the topology of the energy band, here we experimentally observe a generalized Thouless pump that can be extensively and continuously controlled. The extraordinary features of the new pump originate from interband coherence in nonequilibrium initial states, and this fact indicates that a quantum superposition of different eigenstates individually undergoing quantum adiabatic following can also be an important ingredient unavailable in classical physics. The quantum simulation of this generalized Thouless pump in a two-band insulator is achieved by applying delicate control fields to a single spin in diamond. The experimental results demonstrate all principal characteristics of the generalized Thouless pump. Because the pumping in our system is most pronounced around a band-touching point, this work also suggests an alternative means to detect quantum or topological phase transitions.

Quantum metrology with single spins in diamond under ambient conditions

AbstractThe detection of single quantum systems can reveal information that would be averaged out in traditional techniques based on ensemble measurements. The nitrogen-vacancy (NV) centers in diamond have shown brilliant prospects of performance as quantum bits and atomic sensors under ambient conditions, such as ultra-long coherence time, high fidelity control and readout of the spin state. In particular, the sensitivity of the NV center spin levels to external environmental changes makes it a versatile detector capable of measuring various physical quantities, such as temperature, strain, electric fields and magnetic fields. In this paper, we review recent progress in NV-based quantum metrology, and speculate on its future.

Submillihertz magnetic spectroscopy performed with a nanoscale quantum sensor.

Precise timekeeping is critical to metrology, forming the basis by which standards of time, length, and fundamental constants are determined. Stable clocks are particularly valuable in spectroscopy because they define the ultimate frequency precision that can be reached. In quantum metrology, the qubit coherence time defines the clock stability, from which the spectral linewidth and frequency precision are determined. We demonstrate a quantum sensing protocol in which the spectral precision goes beyond the sensor coherence time and is limited by the stability of a classical clock. Using this technique, we observed a precision in frequency estimation scaling in time T as T-3/2 for classical oscillating fields. The narrow linewidth magnetometer based on single spins in diamond is used to sense nanoscale magnetic fields with an intrinsic frequency resolution of 607 microhertz, which is eight orders of magnitude narrower than the qubit coherence time.

Experimental Demonstration of Uncertainty Relations for the Triple Components of Angular Momentum.

The uncertainty principle is considered to be one of the most striking features in quantum mechanics. In the textbook literature, uncertainty relations usually refer to the preparation uncertainty which imposes a limitation on the spread of measurement outcomes for a pair of noncommuting observables. In this work, we study the preparation uncertainty for the angular momentum, especially for spin-1/2. We derive uncertainty relations encompassing the triple components of angular momentum and show that, compared with the relations involving only two components, a triple constant 2/sqrt[3] often arises. Intriguingly, this constant is the same for the position and momentum case. Experimental verification is carried out on a single spin in diamond, and the results confirm the triple constant in a wide range of experimental parameters.

Experimental test of Born's rule by inspecting third-order quantum interference on a single spin in solids

As a fundamental postulate of quantum mechanics, Born's rule assigns probabilities to the measurement outcomes of quantum systems and excludes multi-order quantum interference. Here we report an experiment on a single spin in diamond to test Born's rule by inspecting the third-order quantum interference. The ratio of the third-order quantum interference to the second-order in our experiment is ceiled at the scale of $10^{-3}$, which provides a stringent constraint on the potential breakdown of Born's rule.

Wide-band nanoscale magnetic resonance spectroscopy using quantum relaxation of a single spin in diamond

We demonstrate a wide-band all-optical method of nanoscale magnetic resonance (MR) spectroscopy under ambient conditions. Our method relies on cross-relaxation between a probe spin, the electronic spin of a nitrogen-vacancy centre in diamond, and target spins as the two systems are tuned into resonance. By optically monitoring the spin relaxation time ($T_1$) of the probe spin while varying the amplitude of an applied static magnetic field, a frequency spectrum of the target spin resonances, a $T_1$-MR spectrum, is obtained. As a proof of concept, we measure $T_1$-MR spectra of a small ensemble of $^{14}$N impurities surrounding the probe spin within the diamond, with each impurity comprising an electron spin 1/2 and a nuclear spin 1. The intrinsically large bandwidth of the technique and probe properties allows us to detect both electron spin transitions -- in the GHz range -- and nuclear spin transitions -- in the MHz range -- of the $^{14}$N spin targets. The measured frequencies are found to be in excellent agreement with theoretical expectations, and allow us to infer the hyperfine, quadrupole and gyromagnetic constants of the target spins. Analysis of the strength of the resonances obtained in the $T_1$-MR spectrum reveals that the electron spin transitions are probed via dipole interactions, while the nuclear spin resonances are dramatically enhanced by hyperfine coupling and an electron-mediated process. Finally, we investigate theoretically the possibility of performing $T_1$-MR spectroscopy on nuclear spins without hyperfine interaction and predict single-proton sensitivity using current technology. This work establishes $T_1$-MR as a simple yet powerful technique for nanoscale MR spectroscopy, with broadband capability and a projected sensitivity down to the single nuclear spin level.

Detection of radio-frequency field with a single spin in diamond

Detection of a.c. magnetic field is consequential for many developments in physical and biological sciences, and various designs of magnetometer have been proposed recently. However, the large size of sensor and the extreme measurement conditions required strongly limit their application. It remains a challenge to reconstruct the vector of a.c. field with nanoscale spatial resolution using a single spin under ambient conditions. In this work, we choose the radio-frequency (RF) field as a typical case and realize the measurement of RF field based on a nitrogen-vacancy (NV) center in diamond. We build a solid sensor through measuring the effect of RF field on NV electron spin energy levels and the transition between them. Both of the phase and amplitude (including the transverse and longitudinal components) are measured by this new approach.

Competition between electric field and magnetic field noise in the decoherence of a single spin in diamond

We analyze the impact of electric field and magnetic field fluctuations in the decoherence of the electronic spin associated with a single nitrogen-vacancy (NV) defect in diamond by engineering spin eigenstates protected either against magnetic noise or against electric noise. The competition between these noise sources is analyzed quantitatively by changing their relative strength through modifications of the environment. This study provides significant insights into the decoherence of the NV electronic spin, which is valuable for quantum metrology and sensing applications.

Scanning Nanospin Ensemble Microscope for Nanoscale Magnetic and Thermal Imaging.

Quantum sensors based on solid-state spins provide tremendous opportunities in a wide range of fields from basic physics and chemistry to biomedical imaging. However, integrating them into a scanning probe microscope to enable practical, nanoscale quantum imaging is a highly challenging task. Recently, the use of single spins in diamond in conjunction with atomic force microscopy techniques has allowed significant progress toward this goal, but generalization of this approach has so far been impeded by long acquisition times or by the absence of simultaneous topographic information. Here, we report on a scanning quantum probe microscope which solves both issues by employing a nanospin ensemble hosted in a nanodiamond. This approach provides up to an order of magnitude gain in acquisition time while preserving sub-100 nm spatial resolution both for the quantum sensor and topographic images. We demonstrate two applications of this microscope. We first image nanoscale clusters of maghemite particles through both spin resonance spectroscopy and spin relaxometry, under ambient conditions. Our images reveal fast magnetic field fluctuations in addition to a static component, indicating the presence of both superparamagnetic and ferromagnetic particles. We next demonstrate a new imaging modality where the nanospin ensemble is used as a thermometer. We use this technique to map the photoinduced heating generated by laser irradiation of a single gold nanoparticle in a fluid environment. This work paves the way toward new applications of quantum probe microscopy such as thermal/magnetic imaging of operating microelectronic devices and magnetic detection of ion channels in cell membranes.

Entangled absorption of a single photon with a single spin in diamond.

Quantum entanglement, a key resource for quantum information science, is inherent in a solid. It has been recently shown that entanglement between a single optical photon and a single spin qubit in a solid is generated via spontaneous emission. However, entanglement generation by measurement is rather essential for quantum operations. We here show that the physics behind the entangled emission can be time reversed to demonstrate entangled absorption mediated by an inherent spin-orbit entanglement in a single nitrogen vacancy center in diamond. Optical arbitrary spin state preparation and complete spin state tomography reveal the fidelity of the entangled absorption to be 95%. With the entangled emission and absorption of a photon, materials can be spontaneously entangled or swap their quantum state based on the quantum teleportation scheme.

Two-Dimensional Nanoscale Imaging of Gadolinium Spins via Scanning Probe Relaxometry with a Single Spin in Diamond

Spin-labeling of molecules with paramagnetic ions is an important approach for determining molecular structure, however current ensemble techniques lack the sensitivity to detect few isolated spins. In this Letter, we demonstrate two-dimensional nanoscale imaging of paramagnetic gadolinium compounds using scanning relaxometry of a single nitrogen vacancy (NV) center in diamond. Gadopentetate dimeglumine attached to an atomic force microscope tip is controllably interacted with and detected by the NV center, by virtue of the fact that the NV exhibits fast relaxation in the fluctuating magnetic field generated by electron spin flips in the gadolinium. Using this technique, we demonstrate a reduction in the $T_1$ relaxation time of the NV center by over two orders of magnitude, probed with a spatial resolution of 20 nm. Our result exhibits the viability of the technique for imaging individual spins attached to complex nanostructures or biomolecules, along with studying the magnetic dynamics of isolated spins.

Addressing a single spin in diamond with a macroscopic dielectric microwave cavity

We present a technique for addressing single nitrogen-vacancy (NV) center spins in diamond over macroscopic distances using a tunable dielectric microwave cavity. We demonstrate optically detected magnetic resonance (ODMR) for a single negatively charged NV center (NV–) in a nanodiamond (ND) located directly under the macroscopic microwave cavity. By moving the cavity relative to the ND, we record the ODMR signal as a function of position, mapping out the distribution of the cavity magnetic field along one axis. In addition, we argue that our system could be used to determine the orientation of the NV– major axis in a straightforward manner.

Efficient route to high-bandwidth nanoscale magnetometry using single spins in diamond.

Nitrogen-vacancy (NV) center in diamond is a promising quantum metrology tool finding applications across disciplines. The spin sensor measures magnetic fields, electric fields and temperature with nano-scale precision and is fully operable under ambient conditions. Moreover, it achieves precision scaling inversely with total measurement time σB ∝ 1/T (Heisenberg scaling) rather than as the inverse of the square root of T, with the Shot-Noise limit. This scaling can be achieved by means of phase estimation algorithms (PEAs), in combination with single-shot read-out. Despite their accuracy, the range of applicability of PEAs is limited to sensing single frequencies with negligible temporal fluctuations. Nuclear Magnetic Resonance (NMR) signals from molecules often contain multifrequency components and sensing them using PEA is ruled out. Here we propose an alternative method for precision magnetometry in frequency multiplexed signals via compressive sensing (CS) techniques focusing on nanoscale NMR. We show that CS can provide for precision scaling approximately as σB ≈ 1/T, as well as for a 5-fold increase in sensitivity over dynamic-range gain, in addition to reducing the total number of resources required. We illustrate our method by taking model solid-state spectra of Glycine acquired under Magic Angle Spinning conditions.

Towards single-molecule NMR detection and spectroscopy using single spins in diamond

Nanomagnetometry using the nitrogen-vacancy (NV) centre in diamond has attracted a great deal of interest because of the combined features of room temperature operation, nanoscale resolution and high sensitivity. One of the important goals for nano-magnetometry is to be able to detect nanoscale nuclear magnetic resonance (NMR) in individual molecules. Our theoretical analysis shows how a single molecule at the surface of diamond, with characteristic NMR frequencies, can be detected using a proximate NV centre on a time scale of order seconds with nanometer precision. We perform spatio-temporal resolution optimisation and also outline paths to greater sensitivity. In addition, the method is suitable for application in low and relatively inhomogeneous background magnetic fields in contrast to both conventional liquid and solid state NMR spectroscopy.

Dual-channel lock-in magnetometer with a single spin in diamond

We present an experimental method to perform dual-channel lock-in magnetometry of time-dependent magnetic fields using a single spin associated with a nitrogen-vacancy (NV) color center in diamond. We incorporate multi-pulse quantum sensing sequences with phase estimation algorithms to achieve linearized field readout and constant, nearly decoherence-limited sensitivity over a wide dynamic range. Furthermore, we demonstrate unambiguous reconstruction of the amplitude and phase of the magnetic field. We show that our technique can be applied to measure random phase jumps in the magnetic field, as well as phase-sensitive readout of the frequency.

Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond

We demonstrate fluorescence thermometry techniques with sensitivities approaching 10 mK · Hz(-1/2) based on the spin-dependent photoluminescence of nitrogen vacancy (NV) centers in diamond. These techniques use dynamical decoupling protocols to convert thermally induced shifts in the NV center's spin resonance frequencies into large changes in its fluorescence. By mitigating interactions with nearby nuclear spins and facilitating selective thermal measurements, these protocols enhance the spin coherence times accessible for thermometry by 45-fold, corresponding to a 7-fold improvement in the NV center's temperature sensitivity. Moreover, we demonstrate these techniques can be applied over a broad temperature range and in both finite and near-zero magnetic field environments. This versatility suggests that the quantum coherence of single spins could be practically leveraged for sensitive thermometry in a wide variety of biological and microscale systems.