We demonstrate a planar ion-exfoliation/dry etching fabrication-process for high-optical-quality single-crystal-diamond membranes. The process allows patterning of an array of 200 nm-thick membranes with millimeter-to-micrometer dimensions and exfoliation of the thin films from a single-crystal diamond sample via a parallel fabrication process. The optical properties of the films are measured using transmission microscopy, Raman and fluorescence spectroscopy. The process yields a measured nitrogen-vacancy emission spectra having the zero-phonon line (ZPL) peak of negatively charged centers in an unshifted spectral position suggesting high quality crystalline material. (c) 2012 Elsevier B.V. All rights reserved.

We present a mass fabrication method of diamond nanoscale slabs by alternating plasma etching and mask deposition. These slabs support NV- spins with long coherence times and are suitable for a range of nanophotonic devices.

Frequency standards based on atomic states, such as Rb or Cs vapors, or single trapped ions, are the most precise measures of time. Here we introduce a complementary device based on spins in a solid-state system - the nitrogen-vacancy defect in single crystal diamond. We show that this system has comparable stability to portable atomic standards and is readily incorporable as a chip-scale device. Using a pulsed spin-echo technique, we anticipate an Allan deviation of {\sigma}_y =1E-12 ({\tau})^(-1/2) with current photoluminescence detection methods and posit exceeding 1E-14 with improved diamond material processing and nanophotonic engineering.

Photonic entanglement interconversion between time-bin and polarization bases has application to quantum communication, computation and memories. We characterize hybrid-basis entanglement between a pair photons obtained through such interconversion and show that non-classical correlations persist.

We investigate the sensitivity of a recently proposed method for precision measurement [Phys. Rev. Lett. 106, 140502 (2011)], focusing on an implementation based on solid-state spin systems. The scheme amplifies a quantum sensor response to weak external fields by exploiting its coupling to spin impurities in the environment. We analyze the limits to the sensitivity due to decoherence and propose dynamical decoupling schemes to increase the spin coherence time. The sensitivity is also limited by the environment spin polarization; therefore we discuss strategies to polarize the environment spins and present a method to extend the scheme to the case of zero polarization. The coherence time and polarization determine a figure of merit for the environment's ability to enhance the sensitivity compared to echo-based sensing schemes. This figure of merit can be used to engineer optimized samples for high-sensitivity nanoscale magnetic sensing, such as diamond nanocrystals with controlled impurity density.

The electronic spin associated with the nitrogen vacancy (NV) color center in diamond is an excellent candidate for a solid-state qubit functioning as a quantum register or sensor. However, the lack of thin film technologies for crystalline diamond with low impurity levels hampers the development of photonic interfaces to such diamond-based qubits. We present a method for manufacturing slabs of diamond of 200 nm thickness and several microns in extent from high-purity single crystal chemical vapor deposition diamond. We measure spin coherence times approaching 100 mu s and observe increased photoluminescence collection from shallow implant NV centers in these slabs. We anticipate these slabs to be appealing as quantum memory nodes in hybrid diamond nanophotonic systems.

Semiconductor nanoparticles host a number of paramagnetic point defects and impurities, many of them adjacent to the surface, whose response to external stimuli could help probe the complex dynamics of the particle and its local, nanoscale environment. Here, we use optically detected magnetic resonance in a nitrogen-vacancy (NV) center within an individual diamond nanocrystal to investigate the composition and spin dynamics of the particle-hosted spin bath. For the present sample, a ∼45 nm diamond crystal, NV-assisted dark-spin spectroscopy reveals the presence of nitrogen donors and a second, yet-unidentified class of paramagnetic centers. Both groups share a common spin lifetime considerably shorter than that observed for the NV spin, suggesting some form of spatial clustering, possibly on the nanoparticle surface. Using double spin resonance and dynamical decoupling, we also demonstrate control of the combined NV center-spin bath dynamics and attain NV coherence lifetimes comparable to those reported for bulk, Type Ib samples. Extensions based on the experiments presented herein hold promise for applications in nanoscale magnetic sensing, biomedical labeling, and imaging.

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.

We describe a method to enhance the sensitivity of precision measurements that takes advantage of the environment of a quantum sensor to amplify the response of the sensor to weak external perturbations. An individual qubit is used to sense the dynamics of surrounding ancillary qubits, which are in turn affected by the external field to be measured. The resulting sensitivity enhancement is determined by the number of ancillas that are coupled strongly to the sensor qubit; it does not depend on the exact values of the coupling strengths and is resilient to many forms of decoherence. The method achieves nearly Heisenberg-limited precision measurement, using a novel class of entangled states. We discuss specific applications to improve clock sensitivity using trapped ions and magnetic sensing based on electronic spins in diamond.

Optical nanocavities enable a strong interaction between single photons and single emitters. An appealing application is the construction of a quantum interface for photonic and solid state qubits. Since the material of the solid state qubit is often different from the nanocavity, there has been considerable interest in combining the two in a hybrid architecture. We describe our recent development of such a hybrid interface based a Gallium Phosphide photonic crystal nanocavity that is scanned and deterministically coupled to single emitters on a surface. The technique is used to couple the cavity to the nitrogen vacancy center in diamond, an emitter system with optically accessible electron spins and the ability to transfer electronic spin states to nuclear spins.

The development of material-processing techniques that can be used to generate optical diamond nanostructures containing a single-color center is an important problem in quantum science and technology. In this work, we present the combination of ion implantation and top-down diamond nanofabrication in two scenarios: diamond nanopillars and diamond nanowires. The first device consists of a ‘shallow’ implant (∼20 nm) to generate nitrogen-vacancy (NV) color centers near the top surface of the diamond crystal prior to device fabrication. Individual NV centers are then mechanically isolated by etching a regular array of nanopillars in the diamond surface. Photon anti-bunching measurements indicate that a high yield (>10%) of the devices contain a single NV center. The second device demonstrates ‘deep’ (∼1 μm) implantation of individual NV centers into diamond nanowires as a post-processing step. The high single-photon flux of the nanowire geometry, combined with the low background fluorescence of the ultrapure diamond, allowed us to observe sustained photon anti-bunching even at high pump powers.

A fundamental limit to existing optical techniques for measurementand manipulation of spin degrees of freedom is set by diffraction, which does not allow spins separated by less than about a quarter of a micrometre to be resolved using conventional far-field optics. Here, we report an efficient far-field optical technique that overcomes the limiting role of diffraction, allowing individual electronic spins to be detected, imaged and manipulated coherently with nanoscale resolution. The technique involves selective flipping of the orientation of individual spins, associated with nitrogen-vacancy centres in room-temperature diamond, using a focused beam of light with intensity vanishing at a controllable location, which enables simultaneous single-spin imaging and magnetometry at the nanoscale with considerably less power than conventional techniques. Furthermore, by inhibiting spin transitions away from the laser intensity null, selective coherent rotation of individual spins is realized. This technique can be extended to subnanometre dimensions, thus enabling applications in diverse areas ranging from quantum information science to bioimaging.

We experimentally demonstrate over 2 orders of magnitude increase in the room-temperature coherence time of nitrogen-vacancy centers in diamond by implementing decoupling techniques. We show that equal pulse spacing decoupling performs just as well as nonperiodic Uhrig decoupling and also allows us to take advantage of revivals in the echo to explore the longest coherence times. At short times, we can extend the coherence of particular quantum states out from T2*=2.7  μs out to an effective T2>340  μs. For preserving arbitrary states we show the experimental importance of using pulse sequences that compensate the imperfections of individual pulses for all input states through judicious choice of the phase of the pulses. We use these compensated sequences to enhance the echo revivals and show a coherence time of over 1.6 ms in ultrapure natural abundance 13C diamond.

Magnetic resonance imaging can characterize and discriminate among tissues using their diverse physical and biochemical properties. Unfortunately, submicrometer screening of biological specimens is presently not possible, mainly due to lack of detection sensitivity. Here we analyze the use of a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. We examine the ability of such a sensor to probe the fluctuations of the “classical” dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample. We identify detection protocols that appropriately take into account the quantum character of the sensor and find a signal-to-noise ratio compatible with realistic experimental parameters. Through various example calculations we illustrate different kinds of image contrast. In particular, we show how to exploit the comparatively long nuclear spin correlation times to reconstruct a local, high-resolution sample spectrum.

We report on the use of a single nitrogen-vacancy (NV) center to probe fluctuating ac magnetic fields. Using engineered currents to induce random changes in the field amplitude and phase, we show that stochastic fluctuations reduce the NV center sensitivity and, in general, make the NV response field-dependent. We also introduce two modalities to determine the field spectral composition, unknown a priori in a practical application. One strategy capitalizes on the generation of ac-field-induced coherence "revivals" while the other approach uses the time-tagged fluorescence intensity record from successive NV observations to reconstruct the ac field spectral density. These studies are relevant for magnetic sensing in scenarios where the field of interest has a nontrivial, stochastic behavior, such as sensing unpolarized nuclear spin ensembles at low static magnetic fields.