Electron Spin Of Nitrogen-vacancy Center Research Articles

Preparing highly entangled states of nanodiamond rotation and NV center spin

A nanodiamond with an embedded nitrogen-vacancy (NV) center is one of the experimental systems that can be coherently manipulated within current technologies. Entanglement between NV center electron spin and mechanical rotation of the nanodiamond plays a fundamental role in building a quantum network connecting these microscopic and mesoscopic degrees of motions. Here we present a protocol to asymptotically prepare a highly entangled state of the total quantum angular momentum and electron spin by adiabatically boosting the external magnetic field.

Electron Induced Nanoscale Nuclear Spin Relaxation Probed by Hyperpolarization Injection.

We report on experiments that quantify the role of a central electronic spin as a relaxation source for nuclear spins in its nanoscale environment. Our strategy exploits hyperpolarization injection from the electron as a means to controllably probe an increasing number of nuclear spins in the bath and subsequently interrogate them with high fidelity. Our experiments are focused on a model system of a nitrogen vacancy center electronic spin surrounded by several hundred ^{13}C nuclear spins. We observe that the ^{13}C transverse spin relaxation times vary significantly with the extent of hyperpolarization injection, allowing the ability to measure the influence of electron-mediated relaxation extending over several nanometers. These results suggest interesting new means to spatially discriminate nuclear spins in a nanoscale environment and have direct relevance to dynamic nuclear polarization and quantum sensors and memories constructed from hyperpolarized nuclei.

Using Weak Measurements to Synthesize Projective Measurement of Nonconserved Observables of Weakly Coupled Nuclear Spins

Projective quantum measurement is fundamental for quantum technologies. Here we propose a method for construction of projective measurement of nonconserved quantity of nuclear spin via a weakly coupled auxiliary electron spin. The key idea is to apply suitable quantum control on the electron to construct a weak quantum nondemolition (QND) measurement on the nuclear spin and then cascade a sequence of such measurements into a projective one. We identify a set of tunable parameters to select the QND observables and control the strength of the weak QND measurement. We also find that the QND measurement can be stabilized against realistic experimental control errors. As a demonstration of our method, we design projective measurement on a ${}^{13}\mathrm{C}$ nuclear spin weakly coupled to a nitrogen-vacancy center electron spin in diamond.

A home-made portable device based on Arduino Uno for pulsed magnetic resonance of NV centers in diamond

We describe the realization of a homemade and portable setup to perform experiments of pulsed magnetic resonance of nitrogen-vacancy (NV) centers in diamonds. The system is fully implemented by using an Arduino Uno board equipped with an AVR microcontroller that is used as a transistor-transistor logic pulse sequencer to drive precise laser and microwave pulses with a resolution of 62.5 ns. The equipment is assembled with low-cost modules on a printed circuit board and placed in a compact box with a volume of 20 × 40 × 10 cm3. The detection system is based on a switched integrator and a photodiode in the vicinity of a diamond substrate and read by oversampling the analog-to-digital converter of Arduino Uno. We characterize a CVD diamond sample by performing the pulsed optically detected magnetic resonance and we show the possibility to perform a coherent manipulation of the electron spin of NV centers by driving Rabi oscillations up to 6 MHz with microwave powers within 1 W. We demonstrate different pulse sequences to study electron spin relaxation and dephasing. Finally, we propose additional modules and an antenna to perform the multifrequency manipulation of the electron spin by microwave and radio-frequency pulses. Compared to the previous studies, our system results in a low-cost setup with significantly reduced complexity, which finds application as a learning module for science education and enables a wider audience to access the magnetic resonance in diamond.

Coherent electrical control of a single electron spin in diamond nitrogen-vacancy centers

The nitrogen-vacancy (NV) color center quantum system in diamond has shown great application potential in the fields of solid-state quantum computing and quantum precision measurement because of its unique advantages such as single-spin addressing and manipulation and long quantum coherence time at room temperature. The precise manipulation technology of single spin is particularly important for the development of the application of NV center. The common spin manipulation methods used in NV center quantum system are to drive and manipulate the electron spin by resonant alternating magnetic field. In recent years, the electrical control of quantum spin has attracted extensive attention. In this paper, the use of alternating electric field to control the electron spin of NV center has been studied. The alternating electric field generated by the electrode successfully drives the Rabi oscillation of the NV center spin between the $\Delta m_s=\pm2$ magnetic-dipole forbidden energy levels of $|m_s=-1\rangle$ and $|m_s=+1\rangle$. Further studies show that the frequency of the electrically driven Rabi oscillation is controlled by the power of the driven electric field and independent of the resonant frequency of the electric field. The combination of spin electric control and magnetic control technology can realize the full manipulation of the direct transition between the three spin energy levels of NV center, thus promoting the development of the research and applications of NV quantum system in the fields of quantum simulation, quantum computing, precision measurement of electromagnetic field and so on.

Optomechanical interface between telecom photons and spin quantum memory

Quantum networks enable a broad range of practical and fundamental applications spanning distributed quantum computing to sensing and metrology. A cornerstone of such networks is an interface between telecom photons and quantum memories. Here we demonstrate a novel approach based on cavity optomechanics that utilizes the susceptibility of spin qubits to strain. We use it to control electron spins of nitrogen-vacancy centers in diamond with photons in the 1550 nm telecommunications wavelength band. This method does not involve qubit optical transitions and is insensitive to spectral diffusion. Furthermore, our approach can be applied to solid-state qubits in a wide variety of materials, expanding the toolbox for quantum information processing.

Anisotropic electron-nuclear interactions in a rotating quantum spin bath

The interaction between a central qubit spin and a surrounding bath of spins is critical to spin-based solid-state quantum sensing and quantum information processing. Spin-bath interactions are typically strongly anisotropic, and rapid physical rotation has long been used in solid-state nuclear magnetic resonance to simulate motional averaging of anisotropic interactions, such as dipolar coupling between nuclear spins. Here, we show that the interaction between electron spins of nitrogen-vacancy centers and a bath of $^{13}\mathrm{C}$ nuclear spins in a diamond rotated at up to 300 000 rpm introduces decoherence into the system via frequency modulation of the nuclear spin Larmor precession. The presence of an off-axis magnetic field necessary for averaging of the dipolar coupling leads to a rotational dependence of the electron-nuclear hyperfine interaction, which cannot be averaged out with experimentally achievable rotation speeds. Our findings offer new insights into the use of physical rotation for quantum control with implications for quantum systems having motional and rotational degrees of freedom that are not fixed.

High-fidelity single-shot readout of single electron spin in diamond with spin-to-charge conversion

High fidelity single-shot readout of qubits is a crucial component for fault-tolerant quantum computing and scalable quantum networks. In recent years, the nitrogen-vacancy (NV) center in diamond has risen as a leading platform for the above applications. The current single-shot readout of the NV electron spin relies on resonance fluorescence method at cryogenic temperature. However, the spin-flip process interrupts the optical cycling transition, therefore, limits the readout fidelity. Here, we introduce a spin-to-charge conversion method assisted by near-infrared (NIR) light to suppress the spin-flip error. This method leverages high spin-selectivity of cryogenic resonance excitation and flexibility of photoionization. We achieve an overall fidelity > 95% for the single-shot readout of an NV center electron spin in the presence of high strain and fast spin-flip process. With further improvements, this technique has the potential to achieve spin readout fidelity exceeding the fault-tolerant threshold, and may also find applications on integrated optoelectronic devices.

Controllable and shortcut-based population transfers with a composite system of a nitrogen-vacancy electron spin and microwave photons

Optimal population transfer is of critical importance for quantum information processing. Here an efficient scheme is proposed for implementing controllable and shortcut-based population transfers with a nitrogen-vacancy (NV) electron spin and cavity photons. The electron spin is placed inside a setup of circuit quantum electrodynamics (QED). Under a suitable magnetic field bias, the ground state of electron spin constitutes an effective triplet. By means of the quantized cavity field and classical drivings, we obtain a $$\Delta $$ -configuration interaction within a composite three-state system. Based on the adjustable Rabi couplings, the shortcut-based population transfers can be performed controllably. Moreover, compared with the adiabatic counterparts, the operations assisted by counter-diabatic drivings need much shorter times and then are less susceptible to decoherence effects. Our scheme provides a promising avenue toward optimized transfer operations on NV center electron spins in circuit QED.

Cluster correlation expansion for studying decoherence of clock transitions in spin baths

The clock transitions (CTs) of central spins have long coherence times because their frequency fluctuations vanish in the linear order of external field noise (such as Overhauser fields from nuclear spin baths). Therefore, CTs are useful for quantum technologies. Also, the quadratic dependence of frequencies on noises makes the CT decoherence an interesting physics problem. Thus we are motivated to study the decoherence of CTs. We consider noise from spin baths, which is one of the most relevant mechanisms of qubit decoherence. Various quantum many-body methods have been developed to study the decoherence of a central spin in spin baths. In particular, the cluster-correlation expansion (CCE) systematically accounts for the many-body correlations that cause the central spin decoherence. However, the CCE can not be straightforwardly applied to CTs in spin baths, for the expansion may fail to converge due to the effective long-range interactions resulting from the quadratic term of the noise (e.g., the second-order interaction mediated by hyperfine interactions for a nuclear spin bath). In this work, we develop a modified CCE method to tackle this class of decoherence problems. By diagonalizing the central spin Hamiltonian for each bath eigenstate of the hyperfine interaction, we find that the effects of long-range interactions are absorbed as fluctuations of central spin eigenenergies in the form of single-spin correlations. We apply the method to two specific systems, namely, nitrogen vacancy center electron spins in near zero magnetic field and singlet-triplet transition of two electrons in a double quantum dot. The numerical simulation shows that the modified CCE converges rapidly for the CTs.

System for the remote control and imaging of MW fields for spin manipulation in NV centers in diamond

Nitrogen-vacancy (NV) centers in diamond have been used as platforms for quantum information, magnetometry and imaging of microwave (MW) fields. The spatial distribution of the MW fields used to drive the electron spin of NV centers plays a key role for these applications. Here, we report a system for the control and characterization of MW magnetic fields used for the NV spin manipulation. The control of the MW field in the vicinity of a diamond surface is mediated by an exchangeable lumped resonator, coupled inductively to a MW planar ring antenna. The characterization of the MW fields in the near-field is performed by an FFT imaging of Rabi oscillations, by using an ensemble of NV centers. We have found that the Rabi frequency over a lumped resonator is enhanced 22 times compared to the Rabi frequency without the presence of the lumped resonator. Our system may find applications in quantum information and magnetometry where a precise and controlled spin manipulation is required, showing NV centers as good candidates for imaging MW fields and characterization of MW devices.

Strong polarization of individual nuclear spins weakly coupled to nitrogen-vacancy color centers in diamond

We experimentally demonstrate high degree of polarization of 13C nuclear spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We combine coherent microwave excitation pulses with optical illumination to provide controlled relaxation and achieve a polarity-tunable, fast nuclear polarization of degree higher than 85% at room temperature for remote 13C nuclear spins exhibiting hyperfine interaction strength with NV centers of the order of 600 kHz. We show with the aid of numerical simulation that the anisotropic hyperfine tensor components naturally provide a route to control spin mixing parameter so that highly efficient nuclear polarization is enabled through careful tuning of nuclear quantization axis by external magnetic field. We further discuss spin dynamics and wide applicability of this method to various target 13C nuclear spins around the NV center electron spin. The proposed control method demonstrates an efficient and versatile route to realize, for example, high-fidelity spin register initialization and quantum metrology using nuclear spin resources in solids.

Coherent quantum control of nitrogen-vacancy center spins near 1000 kelvin

Quantum coherence control usually requires low temperature environments. Even for nitrogen-vacancy center spins in diamond, a remarkable exception, the coherence signal is limited to about 700 K due to the quench of the spin-dependent fluorescence at a higher temperature. Here we overcome this limit and demonstrate quantum coherence control of the electron spins of nitrogen-vacancy centers in nanodiamonds at temperatures near 1000 K. The scheme is based on initialization and readout of the spins at room temperature and control at high temperature, which is enabled by pulse laser heating and rapid diffusion cooling of nanodiamonds on amorphous carbon films. Using the diamond magnetometry based on optically detected magnetic resonance up to 800 K, we observe the magnetic phase transition of a single nickel nanoparticle at about 615 K. This work enables nano-thermometry and nano-magnetometry in the high-temperature regime.

Spin dynamics characteristics of nitrogen vacancy spins in diamond films using enhanced Raman shift with spin microscopy

The diamond films were deposited on a Si substrate with chemical vapor deposition MCVD using methane-hydrogen gas. Raman active phonon and sp2/sp3 ratio in diamond/Si(100) films were investigated by Raman spectra in the difference scattering configurations. Furthermore, the Raman scattering spectrum of diamond/Si(100) hetero-junction was measured with different thickness to investigate the spin dynamics of nitrogen vacancy spins. The Fluorescence scanning microscopy indicated that nitrogen vacancy center electron spin was coupled to the host nitrogen nuclear spin by the electron spin resonance. The strong peak of 1332 cm−1 displayed the F2g symmetry of diamond, while the broad E2g mode peak of 1550 cm−1 was a broad band G mode, and 1150 cm−1 peak corresponded to the nano-diamond and disordered graphitic carbon form with disordered SP2 hybridization. The Raman spectra of the diamond films were observed as a function of the residual stress, crystal size and their orientation. The peaks of 1132 cm−1 and 1480 cm−1 were associated with hydrogen bonding. The transport of diamond exhibited sp3 spin related effect. The diamond/Si(100) PDOS is the results of spin-related couple of sp3, p and d orbital hybridization. The spin dynamics was achieved by the orbital competition, strong crystal field and charge order.

AC magnetic field sensing using continuous-wave optically detected magnetic resonance of nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in diamond can be used as highly sensitive quantum sensors for detecting magnetic fields at room temperature. Pulsed optically detected magnetic resonance (ODMR) is typically used to detect AC magnetic fields, but can only be implemented after careful calibration that involves aligning an external static magnetic field, measuring continuous-wave (CW) ODMR, determining the Rabi frequency, and setting the microwave phase. In contrast, CW-ODMR can be simply implemented by continuous application of a green CW laser and a microwave field, and can be used to detect DC or low-frequency (kHz-range) AC magnetic fields. We report a method that uses NV centers and CW-ODMR to detect high-frequency (MHz-range) AC magnetic fields. This method fully utilizes spin-1 properties of electron spins of NV centers. Unlike conventional methods, the proposed method does not require a pulse sequence; this greatly simplifies the procedure and apparatus needed for implementation. A sensitivity of 2.5 μT/Hz is found for our present experimental apparatus, the sensitivity of which is currently limited by inhomogeneous broadening and low measurement contrast of samples used and by the low collection efficiency of the optical setup, both of which could be improved in the future. Thus, this simple alternative to existing AC magnetic field sensors paves the way for the development of a practical and feasible quantum sensor.

Dephasing mechanisms of diamond-based nuclear-spin memories for quantum networks

We probe dephasing mechanisms within a quantum network node consisting of a single nitrogen-vacancy centre electron spin that is hyperfine coupled to surrounding $^{13} \text{C}$ nuclear-spin quantum memories. Previous studies have analysed memory dephasing caused by the stochastic electron-spin reset process, which is a component of optical internode entangling protocols. Here, we find, by using dynamical decoupling techniques and exploiting phase matching conditions in the electron-nuclear dynamics, that control infidelities and quasi-static noise are the major contributors to memory dephasing induced by the entangling sequence. These insights enable us to demonstrate a 19-fold improved memory performance which is still not limited by the electron reinitialization process. We further perform pump-probe studies to investigate the spin-flip channels during the optical electron spin reset. We find that spin-flips occur via decay from the meta-stable singlet states with a branching ratio of 8(1):1:1, in contrast with previous work. These results allow us to formulate straightforward improvements to diamond-based quantum networks and similar architectures.

Robust nano-fabrication of an integrated platform for spin control in a tunable microcavity

Coupling nitrogen-vacancy (NV) centers in diamonds to optical cavities is a promising way to enhance the efficiency of diamond-based quantum networks. An essential aspect of the full toolbox required for the operation of these networks is the ability to achieve the microwave control of the electron spin associated with this defect within the cavity framework. Here, we report on the fabrication of an integrated platform for the microwave control of an NV center electron spin in an open, tunable Fabry–Pérot microcavity. A critical aspect of the measurements of the cavity’s finesse reveals that the presented fabrication process does not compromise its optical properties. We provide a method to incorporate a thin diamond slab into the cavity architecture and demonstrate the control of the NV center spin. These results show the promise of this design for future cavity-enhanced NV center spin-photon entanglement experiments.

Time-optimal control for hybrid systems based on the nitrogen-vacancy center

Fast and high fidelity quantum control is the key technology of quantum computing. The hybrid system composed of the nitrogen-vacancy center and nearby Carbon-13 nuclear spin is expected to solve this problem. The nitrogen-vacancy center electron spin enables fast operations for its strong coupling to the control field, whereas the nuclear spins preserve the coherence for their weak coupling to the environment. In this paper, we describe a strategy to achieve time-optimal control of the Carbon-13 nuclear spin qubit by alternating controlling the nitrogen-vacancy center electron spin as an actuator. We transform the qubit gate operation into a switched system. By using the maximum principle, we study the minimum time control of the switched system and obtain the time-optimal control of the qubit gate operation. We show that the X gate and Y gate operations are within 10 μs while the fidelity reaches 0.995.

Robust Quantum-Network Memory Using Decoherence-Protected Subspaces of Nuclear Spins

The realization of a network of quantum registers is an outstanding challenge in quantum science and technology. We experimentally investigate a network node that consists of a single nitrogen-vacancy center electronic spin hyperfine coupled to nearby nuclear spins. We demonstrate individual control and readout of five nuclear spin qubits within one node. We then characterize the storage of quantum superpositions in individual nuclear spins under repeated application of a probabilistic optical internode entangling protocol. We find that the storage fidelity is limited by dephasing during the electronic spin reset after failed attempts. By encoding quantum states into a decoherence-protected subspace of two nuclear spins, we show that quantum coherence can be maintained for over 1000 repetitions of the remote entangling protocol. These results and insights pave the way towards remote entanglement purification and the realization of a quantum repeater using nitrogen-vacancy center quantum-network nodes.Received 9 March 2016DOI:https://doi.org/10.1103/PhysRevX.6.021040This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasOpen quantum systems & decoherenceQuantum memoriesPhysical SystemsNitrogen vacancy centers in diamondQuantum Information

Efficient signal processing for time-resolved fluorescence detection of nitrogen-vacancy spins in diamond

Room-temperature fluorescence detection of the nitrogen-vacancy center electronic spin typically has low signal to noise, requiring long experiments to reveal an averaged signal. Here, we present a simple approach to analysis of time-resolved fluorescence data that permits an improvement in measurement precision through signal processing alone. Applying our technique to experimental data reveals an improvement in signal to noise equivalent to a 14% increase in photon collection efficiency. We further explore the dependence of the signal to noise ratio on excitation power, and analyze our results using a rate equation model. Our results provide a rubric for optimizing fluorescence spin detection, which has direct implications for improving precision of nitrogen-vacancy-based sensors.