Quantum information protocols utilizing atomic ensembles require preparation of a coherent spin state (CSS) of the ensemble as an important starting point. We investigate the magneto-optical resonance method for characterizing a spin state of cesium atoms in a paraffin coated vapor cell. Atoms in a constant magnetic field are subject to an off-resonant laser beam and an RF magnetic field. The spectrum of the Zeeman sub-levels, in particular the weak quadratic Zeeman effect, enables us to measure the spin orientation, the number of atoms, and the transverse spin coherence time. Notably the use of 894nm pumping light on the D1-line, ensuring the state F=4, m_F=4 to be a dark state, helps us to achieve spin orientation of better than 98%. Hence we can establish a CSS with high accuracy which is critical for the analysis of the entangled states of atoms.
The characterization of the quantum ensemble is a fundamental issue in quantum information theory and foundations. The ensemble is also useful for various quantum information processing. To characterize the quantum ensemble, in this article, we generalize the coherence measure of a state to the quantum ensemble. Exploiting the fidelity and affinity between the ensemble, we propose a quantumness quantifier for the quantum ensemble. It is shown that the proposed quantifier satisfies the necessary axioms of a bonafide measure of quantumness. Finally, we compute the quantumness of a few well-known…
Nitrogen-vacancy (NV) centers in diamond are suitable sensors of high-sensitivity magnetometry which have attracted much interest in recent years. Here, we demonstrate sensitivity-enhanced ensembles magnetometry via adaptively complete transitions overlapping with a bias magnetic field equally projecting onto all existing NV orientations. Under such conditions, the spin transitions corresponding to different NV orientations are completely overlapped which will bring about an obviously improved photoluminescence contrast. And we further introduce particle swarm optimization into the calibration…
Improved constraints on exotic spin-dependent interactions are established at the micrometer scale by a magnetometer with ensembles of nitrogen-vacancy (NV) centers in diamond. A thin layer of NV electronic spin ensembles is utilized as the sensor, and a lead sphere is taken as the source of the nucleons. The exotic spin-dependent interactions are explored by detecting the possible effective magnetic fields by the sensor. Stringent bounds on an exotic parity-odd spin- and velocity-dependent interaction are set within the force range from 5 to 500 $μ$m. The upper limit of the corresponding coup…
Robust gigahertz-range ac magnetometry with an ensemble of NV centers in diamond using concatenated continuous dynamical decoupling
Ulm University（乌尔姆大学）；Racah Institute of Physics, The Hebrew University of Jerusalem（拉卡物理研究所，耶路撒冷希伯来大学）；Advanced Materials Laboratory, Sumitomo Electric Industries Ltd.（住友电工株式会社先进材料实验室）；Quantum Materials and Applications Research Center, National Institutes for Quantum Science and Technology（量子科学和技术研究院量子材料与应用程序研究中心）；Faculty of Pure and Applied Sciences, University of Tsukuba（筑波大学理工学部）
Insufficiency of Pure-State Ensembles in Characterizing Transformations of Entangled States under LOCC
School of Information Science and Engineering, Shandong University（山东大学信息科学与工程学院）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）
We study gradient magnetometry with an ensemble of atoms with arbitrary spin. We calculate precision bounds for estimating the gradient of the magnetic field based on the quantum Fisher information. For quantum states that are invariant under homogeneous magnetic fields, we need to measure a single observable to estimate the gradient. On the other hand, for states that are sensitive to homogeneous fields, a simultaneous measurement is needed, as the homogeneous field must also be estimated. We prove that for the cases studied in this paper, such a measurement is feasible. We present a method t…
We present a new magnetometry method integrating an ensemble of nitrogen-vacancy (NV) centers in a single-crystal diamond with an extended dynamic range for monitoring the fast changing magnetic-field. The NV-center spin resonance frequency is tracked using a closed-loop frequency locked technique with fast frequency hopping to achieve a 10 kHz measurement bandwidth, thus, allowing for the detection of fast changing magnetic signals up to 0.723 T/s.This technique exhibits an extended dynamic range subjected to the working bandwidth of the microwave source. This extended dynamic range can reach…
Ensembles of nitrogen-vacancy (NV) centers in diamonds are widely utilized for magnetometry, magnetic-field imaging and magnetic-resonance detection. They have not been used for magnetometry at zero ambient field because Zeeman sublevels lose first-order sensitivity to magnetic fields as they are mixed due to crystal strain or electric fields. In this work, we realize a zero-field (ZF) magnetometer using polarization-selective microwave excitation in a 12C-enriched HPHT crystal sample. We employ circularly polarized microwaves to address specific transitions in the optically detected magnetic …
Differential magnetometry with partially flipped Dicke states
University of the Basque Country UPV/EHU（巴斯克地区大学）；Universitat de València（瓦伦西亚大学）；CSIC（西班牙国家研究委员会）；Donostia International Physics Center DIPC（多诺斯蒂亚国际物理中心）；IKERBASQUE, Basque Foundation for Science（伊卡巴斯基克，巴斯克科学基金会）；HUN-REN Wigner Research Centre for Physics（匈牙利研究与教育网络维格纳物理研究中心）
Ensembles of nitrogen-vacancy (NV) centers in diamond are widely used as AC magnetometers. While such measurements are usually performed using standard (XY) dynamical decoupling (DD) protocols at room temperature, we study the sensitivities achieved by utilizing various DD protocols, for measuring magnetic AC fields at frequencies in the 10-250 kHz range, at room temperature and 77 K. By performing measurements on an isotopically pure $^{12}$C sample, we find that the Carr-Purcell-Meiboom-Gill (CPMG) protocol, which is not robust against pulse imperfections, is less efficient for magnetometry …
We investigate the quantum dynamics of an atomic mixture composed of two multi-atom ensembles. Each ensemble is driven separately by a coherent laser field, respectively, and dampens via the interactions with the environmental vacuum electromagnetic field reservoir. We find that, due to the photon exchange among the two components, long-time excitation oscillations appear, which may be significantly longer than the inverse lifetime of a single emitter. Furthermore, few-atom "jumps" to the excited state occur as a function of the parameter characterizing the inter-component interactions around …
Magnetic field sensors that exploit quantum effects have shown that they can outperform classical sensors in terms of sensitivity enabling a range of novel applications in future, such as a brain machine interface. Negatively charged nitrogen-vacancy (NV) centers in diamond have emerged as a promising high sensitivity platform for measuring magnetic fields at room temperature. Transferring this technology from laboratory setups into products and applications, the total size of the sensor, the overall power consumption, and the costs need to be reduced and optimized. Here, we demonstrate a fibe…
We study the problem of determining the photon number statistics of an unknown quantum state by simultaneously measuring conjugate quadratures with double homodyne detectors. Classically, the sum of the squared outputs of the two homodyne detectors is proportional to the intensity (thus the photon number) of the input light. Quantum mechanically, due to vacuum noise, the above photon number measurement is intrinsically noisy. We quantify the information gain in a single-shot measurement and discuss potential applications of this technology in quantum key distribution. We also show that the pho…
We reported a compact squeezed light source consisting of an diode laser near resonant on 87Rb optical D1 transition and an warm Rubidium vapor cell. The -4dB vacuum squeezing at 795 nm via nonlinear magneto-optical rotation was observed when applying the magnetic field orthogonal to the propagation direction of the light beam. This compact squeezed light source can be potentially utilized in the quantum information protocols such as quantum repeater and memory, and quantum metrology such as atomic magnetometer.
An accurate measurement of the bunching of photons in the fluorescent emission from an ultracold ensemble of thermal 87Rb atoms in a steady-state magneto-optical trap is presented. Time-delayed-intensity-interferometry (TDII) performed with a 5-nanosecond time resolution yielded a second-order intensity correlation function that has the ideal value of 2 at zero delay, and that shows coherent Rabi oscillations of upto 5 full periods - much longer than the spontaneous emission lifetime of the excited state of Rb. The oscillations are damped out by ~150ns, and thereafter, as expected from a therm…
Ensembles of nitrogen-vacancy centers in diamond are a highly promising platform for high-sensitivity magnetometry, whose efficacy is often based on efficiently generating and monitoring magnetic-field dependent infrared fluorescence. Here we report on an increased sensing efficiency with the use of a 532-nm resonant confocal cavity and a microwave resonator antenna for measuring the local magnetic noise density using the intrinsic nitrogen-vacancy concentration of a chemical-vapor deposited single-crystal diamond. We measure a near-shot-noise-limited magnetic noise floor of 200 pT/$\sqrt{\tex…
We propose to employ a recurrent neural network to estimate a fluctuating magnetic field from continuous optical Faraday rotation measurement on an atomic ensemble. We show that an encoder-decoder architecture neural network can process measurement data and learn an accurate map between recorded signals and the time-dependent magnetic field. The performance of this method is comparable to Kalman filters while it is free of the theory assumptions that restrict their application to particular measurements and physical systems.
Many important physical processes have dynamics that are too complex to completely model analytically. Optimisation of such processes often relies on intuition, trial-and-error, or the construction of empirical models. Machine learning based on artificial neural networks has emerged as an efficient means to develop empirical models of complex systems. We implement a deep artificial neural network to optimise the magneto-optic cooling and trapping of neutral atomic ensembles. Cold atomic ensembles have become commonplace in laboratories around the world, however, many-body interactions give ris…
High-contrast absorption magnetometry in the visible to near-infrared range with nitrogen-vacancy ensembles
Fraunhofer Institute for Applied Solid State Physics IAF（弗劳恩霍夫应用固态物理研究所）；TECNALIA, Basque Research and Technology Alliance (BRTA)（巴斯克研究与技术联盟 TECNALIA）；College of Staten Island (CUNY)（史泰登岛学院（CUNY））；National Institutes for Quantum Science and Technology (QST)（量子科学技术研究开发机构）；Department of Materials Science, Tohoku University（东北大学材料科学系）
Solid-state spin systems including nitrogen-vacancy (NV) centers in diamond constitute an increasingly favored quantum sensing platform. However, present NV ensemble devices exhibit sensitivities orders of magnitude away from theoretical limits. The sensitivity shortfall both handicaps existing implementations and curtails the envisioned application space. This review analyzes present and proposed approaches to enhance the sensitivity of broadband ensemble-NV-diamond magnetometers. Improvements to the spin dephasing time, the readout fidelity, and the host diamond material properties are ident…
A simplified theory for the wavepackets of the photons emitted during the read process of a quantum memory formed by cold atoms is provided. We arrive at analytical expressions for the single- and double-photon emissions, evidencing superradiant features in both cases. In the two-photon case, both photons are emitted in the same spatiotemporal mode, characterizing a superradiant emission of a Fock state of light with two excitations. Experiments confirm the theoretical predictions with a satisfactory agreement.
Macroscopic quantum phenomena such as lasers, Bose-Einstein condensates, superfluids, and superconductors are of great importance in foundations and applications of quantum mechanics. In particular, quantum superposition of a large number of spins in solids is highly desirable for both quantum information processing and ultrasensitive magnetometry. Spin ensembles in solids, however, have rather short collective coherence time (typically less than microseconds). Here we demonstrate that under realistic conditions it is possible to maintain macroscopic quantum superposition of a large spin ensem…
We describe here the construction and characterization of a high-resolution optical magnetometer to measure the full vector magnetic field on an ultrathin layer near the surface of the device. This solid-state device is based on quantum sensors created by a layer of nitrogen-vacancy (NV) centers less than 20 nm below the surface of an ultrapure diamond. This ensemble of nanosensors provides a versatile device capable of mapping magnetic fields and surface current densities with a sub-micrometer resolution and high sensitivity, making it suitable for many applications. Here, we show a custom-bu…
