Diamond Nitrogen-vacancy Research Articles

Laser-polarization-dependent spontaneous emission of the zero phonon line from single nitrogen–vacancy center in diamond

We investigate spontaneous emission properties and control of the zero phonon line (ZPL) from a diamond nitrogen–vacancy (NV) center coherently driven by a single elliptically polarized control field. We use the Schrödinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization-dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.

Creation of quantum entanglement with two separate diamond nitrogen vacancy centers coupled to a photonic molecule

We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.

Observing bulk diamond spin coherence in high-purity nanodiamonds

Nitrogen-vacancy (NV) centres in diamond are attractive for research straddling quantum information science, nanoscale magnetometry and thermometry. Whereas ultrapure bulk diamond NVs sustain the longest spin coherence times among optically accessible spins, nanodiamond NVs exhibit persistently poor spin coherence. Here we introduce high-purity nanodiamonds accommodating record-long NV coherence times, >60 μs, observed through universal dynamical decoupling. We show that the main contribution to decoherence comes from nearby nitrogen impurities rather than surface states. We protect the NV spin free precession, essential to d.c. magnetometry, by driving solely these impurities into the motional narrowing regime. This extends the NV free induction decay time from 440 ns, longer than that in type Ib bulk diamond, to 1.27 μs, which is comparable to that in type IIa (impurity-free) diamond. These properties allow the simultaneous exploitation of both high sensitivity and nanometre resolution in diamond-based emergent quantum technologies.

Suppression of electron spin decoherence of the diamond NV center by a transverse magnetic field

We demonstrate that the spin decoherence of nitrogen vacancy (NV) centers in diamond can be suppressed by a transverse magnetic field if the electron spin bath is the primary decoherence source. The NV spin coherence, created in ``a decoherence-free subspace,'' is protected by the transverse component of the zero-field splitting, increasing the spin-coherence time about twofold. The decoherence due to the electron spin bath is also suppressed at magnetic fields stronger than \ensuremath{\sim}25 G when applied parallel to the NV symmetry axis. Our method can be used to extend the spin-coherence time of similar spin systems for applications in quantum computing, field sensing, and other metrologies.

Hyperentanglement purification and concentration assisted by diamond NV centers inside photonic crystal cavities

Hyperentanglement has attracted much attention due to its fascinating applications in quantum communication. However, it is impossible to purify a pair of photon systems in a mixed hyperentangled state with errors in two degrees of freedom using linear optical elements only, far different from all the existing entanglement purification protocols in a degree of freedom (DOF) for quantum systems. Here, we investigate the possibility of purifying a spatial-polarization mixed hyperentangled Bell state with the errors in both the spatial-mode and polarization DOFs, resorting to the nonlinear optics of a nitrogen-vacancy (NV) center in a diamond embedded in a photonic crystal cavity coupled to a waveguide. We present the first hyperentanglement purification protocol for purifying a pair of two-photon systems in a mixed hyperentangled Bell state with the errors in two DOFs. We also propose an efficient hyperentanglement concentration protocol for a partially hyperentangled Bell pure state, which has the maximal success probability in principle. These two protocols are useful in long-distance quantum communication with hyperentanglement.

Achieving slow and fast light with high transmission by nanodiamond nitrogen-vacancy center coupling to photonic crystal cavity

Using a single diamond nitrogen-vacancy (NV) center embedded in a waveguide-coupled photonic crystal (PC) nanocavity and driven by a classical laser field, we investigate optical transmission and group delay characteristics of the hybrid system operating in the weak-coupling regime. It is found that double electromagnetically induced-transparency (EIT) transmission peaks and slow- and fast-light propagation inside the EIT-like windows can be realized with practical system parameters. The double-frequency transparency of the input light expands the frequency range of EIT and may improve the controllability of EIT in this composite PC-NV system. The present system also provides a way to achieve integrated photonic slow- and fast-light devices for applications requiring multiple EIT effect in a PC platform.

Diamond nitrogen-vacancy centers created by scanning focused helium ion beam and annealing

We demonstrate a method to create nitrogen-vacancy (NV) centers in diamond using focused helium ion microscopy. Near-surface NV centers can be created with spatial resolution below 0.6 μm. We studied the density, creation efficiency, and spectral linewidths at optical and microwave frequencies for NV centers produced using various helium ion implantation doses. The optical linewidths are narrower than those of similar nitrogen-vacancy centers produced using nitrogen ion implantation.

Laser-polarization-dependent and magnetically controlled optical bistability in diamond nitrogen-vacancy centers

Abstract We explore laser-polarization-dependent and magnetically controlled optical bistability (OB) in an optical ring cavity filled with diamond nitrogen-vacancy (NV) defect centers under optical excitation. The shape of the OB curve can be significantly modified in a new operating regime from the previously studied OB case, namely, by adjusting the intensity of the external magnetic field and the polarization of the control beam. The influences of the intensity of the control beam, the frequency detuning, and the cooperation parameter on the OB behavior are also discussed in detail. These results are useful in real experiments for realizing an all-optical bistate switching or coding element in a solid-state platform.

High-Sensitivity Magnetometry Based on Quantum Beats in Diamond Nitrogen-Vacancy Centers

We demonstrate an absolute magnetometer based on quantum beats in the ground state of nitrogen-vacancy centers in diamond. We show that, by eliminating the dependence of spin evolution on the zero-field splitting D, the magnetometer is immune to temperature fluctuation and strain inhomogeneity. We apply this technique to measure low-frequency magnetic field noise by using a single nitrogen-vacancy center located within 500 nm of the surface of an isotopically pure (99.99% 12C) diamond. The photon-shot-noise limited sensitivity achieves 38 nT/sqrt[Hz] for 4.45 s acquisition time, a factor of sqrt[2] better than the implementation which uses only two spin levels. For long acquisition times (>10 s), we realize up to a factor of 15 improvement in magnetic sensitivity, which demonstrates the robustness of our technique against thermal drifts. Applying our technique to nitrogen-vacancy center ensembles, we eliminate dephasing from longitudinal strain inhomogeneity, resulting in a factor of 2.3 improvement in sensitivity.

Propagation of magnetically controllable lasers and magneto-optic dual switching using nitrogen-vacancy centers in diamond

We study coherent laser-induced optical behaviors in weak twin-light propagation through strained diamond nitrogen-vacancy (NV) centers via switching on and off an external magnetic field. By numerically solving the coupled Bloch-Maxwell equations for NV center and field simultaneously in space and time, we address dynamic control of pulse propagation and magneto-optic dual switching in such a laser-driven NV center system. The proposed scheme may have applications in the design of magneto-optic switching and magneto-optic storage devices.

Engineering and quantum control of single spins in semiconductors

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Diamond NV centers for quantum computing and quantum networks

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Entanglement of electron spins and geometric phases in the diamond color center coupled to the P1 center

Impurity spins in semiconductors are potential quantum bits. Entanglement and topological phases are key resources in quantum computation. We prove that the coupled electron spins carried by a diamond nitrogen-vacancy color center (NV${}^{\ensuremath{-}}$) and a single substitutional nitrogen impurity (P1 center) are entangled in the immediate vicinity of the level anticrossing that appears in the Zeeman energy diagram at about 500 G. We also determine the Aharonov-Anandan, Berry, and marginal geometric phases that can be accumulated by the state vectors of this spin system when it is magnetically transported around a closed path. At the resonance where the gap between two energy levels is minimum, the geometric phases undergo discontinuities, and the entanglement of the two electron spins is maximal.

Flexible two-qubit controlled phase gate in a hybrid solid-state system

We propose a theoretical scheme for realizing {\deg}exible two-qubit controlled phase gate. A transmission line resonator is used to induce the coupling between nitrogen-vacancy (N-V) in diamond and superconducting qubit. The N-V center acts as control qubit and the superconducting qubit as target qubit. Through adjusting external flux, we obtain desired coupling between random superconducting qubit and transmission line resonator. Moreover, our protocol might be implemented via the current experimental technology.

Frontiers in diffraction unlimited optical methods for spin manipulation, magnetic field sensing and imaging using diamond nitrogen vacancy defects

AbstractThe nitrogen vacancy defect centre in diamond has attracted intense research interest owing to their appealing optical and electronic properties, which have laid the ground for new approaches for diffraction unlimited optical methods. In particular, the optical detected magnetic resonance of the electron spin of nitrogen vacancy centre at room temperature underpins many areas in nanophotonics, spintronics and quantum optics. This article reviews the recent development of super-resolution imaging and sensing nanoscopy based on this fascinating defect centre in diamond. These breakthroughs are presently indicating a new class of nanoscale sensors of tiny magnetic and electric fields at room temperature, as well as emerging fluorescent and magnetic probes for next generation nanoscopy and all-optical spin recording.

Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling.

Coupling of energy from quantum emitters to the plasmonic mode of V groove waveguides: A numerical study

This work is a theoretical investigation into the coupling of a single excited quantum emitter to the plasmon mode of a V groove waveguide. The V groove waveguide consists of a triangular channel milled in gold and the emitter is modeled as a dipole emitter, and could represent a quantum dot, nitrogen vacancy in diamond, or similar. In this work the dependence of coupling efficiency of emitter to plasmon mode is determined for various geometrical parameters of the emitter-waveguide system. Using the finite element method, the effect on coupling efficiency of the emitter position and orientation, groove angle, groove depth, and tip radius, is studied in detail. We demonstrate that all parameters, with the exception of groove depth, have a significant impact on the attainable coupling efficiency. Understanding the effect of various geometrical parameters on the coupling between emitters and the plasmonic mode of the waveguide is essential for the design and optimization of quantum dot–V groove devices.

Room temperature coherent control of defect spin qubits in silicon carbide

Electronic spins in semiconductors have been used extensively to explore the limits of external control over quantum mechanical phenomena. A long-standing goal of this research has been to identify or develop robust quantum systems that can be easily manipulated, for future use in advanced information and communication technologies. Recently, a point defect in diamond known as the nitrogen-vacancy centre has attracted a great deal of interest because it possesses an atomic-scale electronic spin state that can be used as an individually addressable, solid-state quantum bit (qubit), even at room temperature. These exceptional quantum properties have motivated efforts to identify similar defects in other semiconductors, as they may offer an expanded range of functionality not available to the diamond nitrogen-vacancy centre. Notably, several defects in silicon carbide (SiC) have been suggested as good candidates for exploration, owing to a combination of computational predictions and magnetic resonance data. Here we demonstrate that several defect spin states in the 4H polytype of SiC (4H-SiC) can be optically addressed and coherently controlled in the time domain at temperatures ranging from 20 to 300 kelvin. Using optical and microwave techniques similar to those used with diamond nitrogen-vacancy qubits, we study the spin-1 ground state of each of four inequivalent forms of the neutral carbon-silicon divacancy, as well as a pair of defect spin states of unidentified origin. These defects are optically active near telecommunication wavelengths, and are found in a host material for which there already exist industrial-scale crystal growth and advanced microfabrication techniques. In addition, they possess desirable spin coherence properties that are comparable to those of the diamond nitrogen-vacancy centre. This makes them promising candidates for various photonic, spintronic and quantum information applications that merge quantum degrees of freedom with classical electronic and optical technologies.

Diamond nitrogen-vacancy center as a probe of random fluctuations in a nuclear spin ensemble

New schemes that exploit the unique properties of nitrogen-vacancy (NV) centers in diamond are presently being explored as a platform for high-resolution magnetic sensing. Here we focus on the ability of a NV center to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we conduct comparative experiments where the NV spin evolves under the influence of surrounding ${}^{13}$C nuclei or, alternatively, in the presence of asynchronous alternating current fields engineered to emulate bath fluctuations. Our study reveals substantial differences that underscore the limitations of the semi-classical picture when interpreting and predicting the outcome of experiments designed to probe small nuclear spin ensembles. In particular, our study elucidates the NV center response to bath fluctuations under common pulse sequences, and explores a detection protocol designed to probe time correlations of the nuclear spin bath dynamics. Further, we show that the presence of macroscopic nuclear spin order is key to the emergence of semi-classical spin magnetometry.

Hybrid Nanocavity Resonant Enhancement of Color Center Emission in Diamond

Resonantly enhanced emission from the zero-phonon line of a diamond nitrogen-vacancy (NV) center in single crystal diamond is demonstrated experimentally using a hybrid whispering gallery mode nanocavity. A 900 nm diameter ring nanocavity formed from gallium phosphide, whose sidewalls extend into a diamond substrate, is tuned onto resonance at a low temperature with the zero-phonon line of a negatively charged NV center implanted near the diamond surface. When the nanocavity is on resonance, the zero-phonon line intensity is enhanced by approximately an order of magnitude, and the spontaneous emission lifetime of the NV is reduced by as much as 18%, corresponding to a 6.3X enhancement of emission in the zero photon line.Received 20 June 2011DOI:https://doi.org/10.1103/PhysRevX.1.011007This 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 Society