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ABSTRACT: eap/ We demonstrate a fiber-optical switch that operates with a few hundred pho-tons per switching pulse. The light-light interaction is mediated by laser-cooled atoms. The required strong interaction between atoms and light is achieved by simultaneously confining photons and atoms inside the microscopic hollow core of a single-mode photonic-crystal fiber.
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ABSTRACT: Hybrid quantum devices, where dissimilar quantum systems are combined to attain qualities not available with either system alone, may enable far-reaching control in quantum measurement, sensing, and information processing. A paradigmatic example is trapped ultra-cold atoms, which offer excellent quantum coherent properties, coupled to nanoscale solid-state systems, which allow for strong interactions. We demonstrate a deterministic interface between a single trapped rubidium atom and a nanoscale photonic crystal cavity. Precise control over the atom's position allows us to probe the cavity near-field with a resolution below the diffraction limit, and to observe large atom-photon coupling. This approach may enable the realization of integrated, strongly coupled quantum nano-optical circuits.
Science 04/2013; · 31.20 Impact Factor
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ABSTRACT: Magnetic imaging is a powerful tool for probing biological and physical systems. However, existing techniques either have poor spatial resolution compared to optical microscopy and are hence not generally applicable to imaging of sub-cellular structure (for example, magnetic resonance imaging), or entail operating conditions that preclude application to living biological samples while providing submicrometre resolution (for example, scanning superconducting quantum interference device microscopy, electron holography and magnetic resonance force microscopy). Here we demonstrate magnetic imaging of living cells (magnetotactic bacteria) under ambient laboratory conditions and with sub-cellular spatial resolution (400 nanometres), using an optically detected magnetic field imaging array consisting of a nanometre-scale layer of nitrogen-vacancy colour centres implanted at the surface of a diamond chip. With the bacteria placed on the diamond surface, we optically probe the nitrogen-vacancy quantum spin states and rapidly reconstruct images of the vector components of the magnetic field created by chains of magnetic nanoparticles (magnetosomes) produced in the bacteria. We also spatially correlate these magnetic field maps with optical images acquired in the same apparatus. Wide-field microscopy allows parallel optical and magnetic imaging of multiple cells in a population with submicrometre resolution and a field of view in excess of 100 micrometres. Scanning electron microscope images of the bacteria confirm that the correlated optical and magnetic images can be used to locate and characterize the magnetosomes in each bacterium. Our results provide a new capability for imaging bio-magnetic structures in living cells under ambient conditions with high spatial resolution, and will enable the mapping of a wide range of magnetic signals within cells and cellular networks.
Nature 04/2013; 496(7446):486-9. · 36.28 Impact Factor
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ABSTRACT: We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n[over ¯]_{x}=n[over ¯]_{y}=0.01, n[over ¯]_{z}=8) even for a trap beam waist as small as w=900 nm. The small atomic wave packet with δx=δy=24 nm and δz=270 nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces.
Physical Review Letters 03/2013; 110(13):133001. · 7.37 Impact Factor
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ABSTRACT: Topology plays a central role in ensuring the robustness of a wide variety of physical phenomena. Notable examples range from the current-carrying edge states associated with the quantum Hall and the quantum spin Hall effects to topologically protected quantum memory and quantum logic operations. Here we propose and analyse a topologically protected channel for the transfer of quantum states between remote quantum nodes. In our approach, state transfer is mediated by the edge mode of a chiral spin liquid. We demonstrate that the proposed method is intrinsically robust to realistic imperfections associated with disorder and decoherence. Possible experimental implementations and applications to the detection and characterization of spin liquid phases are discussed.
Nature Communications 03/2013; 4:1585. · 7.40 Impact Factor
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ABSTRACT: We propose and analyze a novel mechanism for long-range spin-spin
interactions in diamond nanostructures. The interactions between electronic
spins, associated with nitrogen-vacancy centers in diamond, are mediated by
their coupling via strain to the vibrational mode of a diamond mechanical
nanoresonator. This coupling results in phonon-mediated effective spin-spin
interactions that can be used to generate squeezed states of a spin ensemble.
We show that spin dephasing and relaxation can be largely suppressed, allowing
for substantial spin squeezing under realistic experimental conditions. Our
approach has implications for spin-ensemble magnetometry, as well as
phonon-mediated quantum information processing with spin qubits.
01/2013;
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ABSTRACT: We theoretically study the dynamic polarization of lattice nuclear spins in
GaAs double quantum dots containing two electrons. In our prior work [Phys.
Rev. Lett. 104, 226807 (2010)] we identified three regimes of long-term
dynamics, including the build up of a large difference in the Overhauser fields
across the dots, the saturation of the nuclear polarization process associated
with formation of so-called "dark states," and the elimination of the
difference field. In particular, when the dots are different sizes we found
that the Overhauser field becomes larger in the smaller dot. Here we present a
detailed theoretical analysis of these problems including a systematic
description of the polarization dynamics and the development of a new numerical
method to efficiently simulate semiclassical-central-spin problems. When
nuclear spin noise is included, the results agree with our prior work
indicating that large difference fields and dark states are stable
configurations, while the elimination of the difference field is unstable;
however, in the absence of noise we find all three steady states are achieved
depending on parameters. These results are in good agreement with dynamic
nuclear polarization experiments in double quantum dots.
12/2012;
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ABSTRACT: We propose and analyze a physical system that naturally admits two-dimensional topological nearly flat bands. Our approach utilizes an array of three-level dipoles (effective S=1 spins) driven by inhomogeneous electromagnetic fields. The dipolar interactions produce arbitrary uniform background gauge fields for an effective collection of conserved hard-core bosons, namely, the dressed spin flips. These gauge fields result in topological band structures, whose band gap can be larger than the corresponding bandwidth. Exact diagonalization of the full interacting Hamiltonian at half-filling reveals the existence of superfluid, crystalline, and supersolid phases. An experimental realization using either ultracold polar molecules or spins in the solid state is considered.
Physical Review Letters 12/2012; 109(26):266804. · 7.37 Impact Factor
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ABSTRACT: We propose to use subwavelength confinement of light associated with the near field of plasmonic systems to create nanoscale optical lattices for ultracold atoms. Our approach combines the unique coherence properties of isolated atoms with the subwavelength manipulation and strong light-matter interaction associated with nanoplasmonic systems. It allows one to considerably increase the energy scales in the realization of Hubbard models and to engineer effective long-range interactions in coherent and dissipative many-body dynamics. Realistic imperfections and potential applications are discussed.
Physical Review Letters 12/2012; 109(23):235309. · 7.37 Impact Factor
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ABSTRACT: We present a detailed theoretical analysis of a weakly driven multimode
optomechanical system, in which two optical modes are strongly and
near-resonantly coupled to a single mechanical mode via a three-wave mixing
interaction. We calculate one- and two-time intensity correlations of the two
optical fields and compare them to analogous correlations in atom-cavity
systems. Nonclassical photon correlations arise when the optomechanical
coupling $g$ exceeds the cavity decay rate $\kappa$, and we discuss signatures
of one- and two-photon resonances as well as quantum interference. We also find
a long-lived correlation that decays slowly with the mechanical decay rate
$\gamma$, reflecting the heralded preparation of a single phonon state after
detection of a photon. Our results provide insight into the quantum regime of
multimode optomechanics, with potential applications for quantum information
processing with photons and phonons.
10/2012;
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ABSTRACT: The detection of ensembles of spins under ambient conditions has
revolutionized the biological, chemical, and physical sciences through magnetic
resonance imaging and nuclear magnetic resonance. Pushing sensing capabilities
to the individual-spin level would enable unprecedented applications such as
single molecule structural imaging; however, the weak magnetic fields from
single spins are undetectable by conventional far-field resonance techniques.
In recent years, there has been a considerable effort to develop nanoscale
scanning magnetometers, which are able to measure fewer spins by bringing the
sensor in close proximity to its target. The most sensitive of these
magnetometers generally require low temperatures for operation, but measuring
under ambient conditions (standard temperature and pressure) is critical for
many imaging applications, particularly in biological systems. Here we
demonstrate detection and nanoscale imaging of the magnetic field from a single
electron spin under ambient conditions using a scanning nitrogen-vacancy (NV)
magnetometer. Real-space, quantitative magnetic-field images are obtained by
deterministically scanning our NV magnetometer 50 nanometers above a target
electron spin, while measuring the local magnetic field using dynamically
decoupled magnetometry protocols. This single-spin detection capability could
enable single-spin magnetic resonance imaging of electron spins on the nano-
and atomic scales and opens the door for unique applications such as mechanical
quantum state transfer.
09/2012;
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L. M. Pham,
D. Le Sage,
P. L. Stanwix,
T. K. Yeung,
D. Glenn,
A. Trifonov,
P. Cappellaro,
P. R. Hemmer, M. D. Lukin,
H. Park,
A. Yacoby,
R. L. Walsworth
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ABSTRACT: We demonstrate a method of imaging spatially varying magnetic fields using a
thin layer of nitrogen-vacancy (NV) centers at the surface of a diamond chip.
Fluorescence emitted by the two-dimensional NV ensemble is detected by a CCD
array, from which a vector magnetic field pattern is reconstructed. As a
demonstration, AC current is passed through wires placed on the diamond chip
surface, and the resulting AC magnetic field patterns are imaged using an
echo-based technique with sub-micron resolution over a 140 \mu m x 140 \mu m
field of view, giving single-pixel sensitivity ~100 nT/\sqrt{Hz}. We discuss
ongoing efforts to further improve sensitivity and potential bioimaging
applications such as real-time imaging of activity in functional, cultured
networks of neurons.
07/2012;
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ABSTRACT: We demonstrate preferential orientation of nitrogen-vacancy (NV) color
centers along two of four possible crystallographic axes in diamonds grown by
chemical vapor deposition on the {100} face. We identify the relevant growth
regime and present a possible explanation of this effect. We show that
preferential orientation provides increased optical read-out contrast for NV
multi-spin measurements, including enhanced AC magnetic field sensitivity, thus
providing an important step towards high fidelity multi-spin-qubit quantum
information processing, sensing and metrology.
07/2012;
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ABSTRACT: We describe how strong resonant interactions in multimode optomechanical systems can be used to induce controlled nonlinear couplings between single photons and phonons. Combined with linear mapping schemes between photons and phonons, these techniques provide a universal building block for various classical and quantum information processing applications. Our approach is especially suited for nano-optomechanical devices, where strong optomechanical interactions on a single photon level are within experimental reach.
Physical Review Letters 07/2012; 109(1):013603. · 7.37 Impact Factor
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ABSTRACT: We investigate dissipative phase transitions in an open central spin system. In our model the central spin interacts coherently with the surrounding many-particle spin environment and is subject to coherent driving and dissipation. We develop analytical tools based on a self-consistent Holstein-Primakoff approximation that enable us to determine the complete phase diagram associated with the steady states of this system. It includes first- and second-order phase transitions, as well as regions of bistability, spin squeezing, and altered spin-pumping dynamics. Prospects of observing these phenomena in systems such as electron spins in quantum dots or nitrogen-vacancy centers coupled to lattice nuclear spins are briefly discussed.
Physical Review A 07/2012; 86:012116. · 2.88 Impact Factor
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ABSTRACT: We study the driven-dissipative dynamics of photons interacting with an array
of micromechanical membranes in an optical cavity. Periodic membrane driving
and phonon creation result in an effective photon-number conserving non-unitary
dynamics, which features a steady state with long-range photonic coherence. If
the leakage of photons out of the cavity is counteracted by incoherent driving
of the photonic modes, we show that the system undergoes a dynamical phase
transition to the state with long-range coherence. A minimal system, composed
of two micromechanical membranes in a cavity, is studied in detail, and it is
shown to be a realistic setup where the key processes of the driven-dissipative
dynamics can be seen.
06/2012;
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P C Maurer,
G Kucsko,
C Latta,
L Jiang,
N Y Yao,
S D Bennett,
F Pastawski,
D Hunger,
N Chisholm,
M Markham,
D J Twitchen,
J I Cirac, M D Lukin
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ABSTRACT: Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. We demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 second at room temperature. The qubit consists of a single (13)C nuclear spin in the vicinity of a nitrogen-vacancy color center within an isotopically purified diamond crystal. The long qubit memory time was achieved via a technique involving dissipative decoupling of the single nuclear spin from its local environment. The versatility, robustness, and potential scalability of this system may allow for new applications in quantum information science.
Science 06/2012; 336(6086):1283-6. · 31.20 Impact Factor
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ABSTRACT: We study the implementation of quantum state transfer protocols in phonon
networks, where in analogy to optical networks, quantum information is
transmitted through propagating phonons in extended mechanical resonator arrays
or phonon waveguides. We describe how the problem of a non-vanishing thermal
occupation of the phononic quantum channel can be overcome by implementing
optomechanical multi- and continuous mode cooling schemes to create a 'cold'
frequency window for transmitting quantum states. In addition, we discuss the
implementation of phonon circulators and switchable phonon routers, which rely
on strong coherent optomechanical interactions only, and do not require strong
magnetic fields or specific materials. Both techniques can be applied and
adapted to various physical implementations, where phonons coupled to spin or
charge based qubits are used for on-chip networking applications.
05/2012;
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ABSTRACT: We study theoretically the measurement of a mechanical oscillator using a
single two level system as a detector. In a recent experiment, we used a single
electronic spin associated with a nitrogen vacancy center in diamond to probe
the thermal motion of a magnetized cantilever at room temperature {Kolkowitz et
al., Science 335, 1603 (2012)}. Here, we present a detailed analysis of the
sensitivity limits of this technique, as well as the possibility to measure the
zero point motion of the oscillator. Further, we discuss the issue of
measurement backaction in sequential measurements and find that although
backaction heating can occur, it does not prohibit the detection of zero point
motion. Throughout the paper we focus on the experimental implementation of a
nitrogen vacancy center coupled to a magnetic cantilever; however, our results
are applicable to a wide class of spin-oscillator systems. Implications for
preparation of nonclassical states of a mechanical oscillator are also
discussed.
05/2012;
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ABSTRACT: The nitrogen-vacancy defect centre in diamond has potential applications in nanoscale electric and magnetic-field sensing, single-photon microscopy, quantum information processing and bioimaging. These applications rely on the ability to position a single nitrogen-vacancy centre within a few nanometres of a sample, and then scan it across the sample surface, while preserving the centre's spin coherence and readout fidelity. However, existing scanning techniques, which use a single diamond nanocrystal grafted onto the tip of a scanning probe microscope, suffer from short spin coherence times due to poor crystal quality, and from inefficient far-field collection of the fluorescence from the nitrogen-vacancy centre. Here, we demonstrate a robust method for scanning a single nitrogen-vacancy centre within tens of nanometres from a sample surface that addresses both of these concerns. This is achieved by positioning a single nitrogen-vacancy centre at the end of a high-purity diamond nanopillar, which we use as the tip of an atomic force microscope. Our approach ensures long nitrogen-vacancy spin coherence times (∼75 µs), enhanced nitrogen-vacancy collection efficiencies due to waveguiding, and mechanical robustness of the device (several weeks of scanning time). We are able to image magnetic domains with widths of 25 nm, and demonstrate a magnetic field sensitivity of 56 nT Hz(-1/2) at a frequency of 33 kHz, which is unprecedented for scanning nitrogen-vacancy centres.
Nature Nanotechnology 04/2012; 7(5):320-4. · 27.27 Impact Factor
