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Fuchs, G. D.; Burkard, G.; Klimov, P. V.; Awschalom, D. D. |
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Title |
A quantum memory intrinsic to single nitrogen–vacancy centres in diamond |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
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Volume |
7 |
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10 |
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789-793 |
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fromIPMRAS |
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A quantum memory, composed of a long-lived qubit coupled to each processing qubit, is important to building a scalable platform for quantum information science. These two qubits should be connected by a fast and high-fidelity operation to store and retrieve coherent quantum states. Here, we demonstrate a room-temperature quantum memory based on the spin of the nitrogen nucleus intrinsic to each nitrogen–vacancy (NV) centre in diamond. We perform coherent storage of a single NV centre electronic spin in a single nitrogen nuclear spin using Landau–Zener transitions across a hyperfine-mediated avoided level crossing. By working outside the asymptotic regime, we demonstrate coherent state transfer in as little as 120 ns with total storage fidelity of 88±6%. This work demonstrates the use of a quantum memory that is compatible with scaling as the nitrogen nucleus is deterministically present in each NV centre defect. |
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RPLAB @ gujma @ |
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823 |
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Hosseini, M.; Campbell, G.; Sparkes, B. M.; Lam, P. K.; Buchler, B. C. |
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Title |
Unconditional room-temperature quantum memory |
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Journal Article |
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Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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7 |
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10 |
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794-798 |
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fromIPMRAS |
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Just as classical information systems require buffers and memory, the same is true for quantum information systems. The potential that optical quantum information processing holds for revolutionizing computation and communication is therefore driving significant research into developing optical quantum memory. A practical optical quantum memory must be able to store and recall quantum states on demand with high efficiency and low noise. Ideally, the platform for the memory would also be simple and inexpensive. Here, we present a complete tomographic reconstruction of quantum states that have been stored in the ground states of rubidium in a vapour cell operating at around 80 °C. Without conditional measurements, we show recall fidelity up to 98% for coherent pulses containing around one photon. To unambiguously verify that our memory beats the quantum no-cloning limit we employ state-independent verification using conditional variance and signal-transfer coefficients. |
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RPLAB @ gujma @ |
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824 |
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Vishveshwara, Smitha |
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Title |
Topological qubits: A bit of both |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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7 |
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450–451 |
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fromIPMRAS |
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'Standard' qubits have been implemented in diverse physical systems. Now, so-called topological qubits are coming into the limelight, and could potentially be used for decoherence-free quantum computing. Coupling these two types of qubit might enable devices that exploit the virtues of both. |
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RPLAB @ gujma @ |
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825 |
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Biercuk, Michael J. |
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Title |
A quantum spectrum analyser |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
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525–526 |
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fromIPMRAS |
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Noise filters based on so-called dynamical decoupling pulse sequences can suppress decoherence in quantum systems. Turning this idea on its head now provides a new technique for studying the noise itself. |
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RPLAB @ gujma @ |
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826 |
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Grinolds, M. S.; Maletinsky, P.; Hong, S.; Lukin, M. D.; Walsworth, R. L.; Yacoby, A. |
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Title |
Quantum control of proximal spins using nanoscale magnetic resonance imaging |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
9 |
Pages |
687-692 |
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fromIPMRAS |
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Quantum control of individual spins in condensed-matter systems is an emerging field with wide-ranging applications in spintronics, quantum computation and sensitive magnetometry. Recent experiments have demonstrated the ability to address and manipulate single electron spins through either optical or electrical techniques. However, it is a challenge to extend individual-spin control to nanometre-scale multi-electron systems, as individual spins are often irresolvable with existing methods. Here we demonstrate that coherent individual-spin control can be achieved with few- nanometre resolution for proximal electron spins by carrying out single-spin magnetic resonance imaging (MRI), which is realized using a scanning-magnetic-field gradient that is both strong enough to achieve nanometre spatial resolution and sufficiently stable for coherent spin manipulations. We apply this scanning-field-gradient MRI technique to electronic spins in nitrogen-vacancy (NV) centres in diamond and achieve nanometre resolution in imaging, characterization and manipulation of individual spins. For NV centres, our results in individual-spin control demonstrate an improvement of nearly two orders of magnitude in spatial resolution when compared with conventional optical diffraction-limited techniques. This scanning-field-gradient microscope enables a wide range of applications including materials characterization, spin entanglement and nanoscale magnetometry. |
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RPLAB @ gujma @ |
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827 |
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Dada, Adetunmise C.; Leach, Jonathan; Buller, Gerald S.; Padgett, Miles J.; Andersson, Erika |
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Title |
Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
9 |
Pages |
677-680 |
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fromIPMRAS |
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Abstract |
Quantum entanglement plays a vital role in many quantum-information and communication tasks. Entangled states of higher-dimensional systems are of great interest owing to the extended possibilities they provide. For example, they enable the realization of new types of quantum information scheme that can offer higher-information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems (see ref. and references therein). Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher-dimensional entangled systems are used. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalized to d-dimensional systems up to d=12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum, generated through spontaneous parametric down-conversion, and manipulated using computer-controlled holograms. |
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RPLAB @ gujma @ |
Serial |
828 |
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Bylander, Jonas; Gustavsson, Simon; Yan, Fei; Yoshihara, Fumiki; Harrabi, Khalil; Fitch, George; Cory, David G.; Nakamura, Yasunobu; Tsai, Jaw-Shen; Oliver, William D. |
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Title |
Noise spectroscopy through dynamical decoupling with a superconducting flux qubit |
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Journal Article |
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Year |
2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
7 |
Pages |
565-570 |
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fromIPMRAS |
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Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1=12μs. We first demonstrate that dynamical decoupling improves the coherence time T2 in this system up to the T2=2T1 limit (pure dephasing times exceeding 100μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20MHz, observing a 1/fα distribution with α<1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence. |
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RPLAB @ gujma @ |
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829 |
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Author |
Baumert, Thomas |
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Title |
Quantum technology: Wave packets get a kick |
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Journal Article |
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2011 |
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Nature Physics |
Abbreviated Journal |
Nat. Phys. |
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Volume |
7 |
Issue |
5 |
Pages |
373-374 |
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fromIPMRAS |
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Intense femtosecond pulses of infrared light can manipulate molecules. It is now shown that such control even extends to making different molecular eigenstates interfere with each other in a way never considered before -- a potential tool for optically engineered chemical reactions and for ultrafast information encoding and manipulation. |
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RPLAB @ gujma @ |
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830 |
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Bozyigit, D.; Lang, C.; Steffen, L.; Fink, J. M.; Eichler, C.; Baur, M.; Bianchetti, R.; Leek, P. J.; Filipp, S.; da Silva, M. P.; Blais, A.; Wallraff, A. |
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Antibunching of microwave-frequency photons observed in correlation measurements using linear detectors |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
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Volume |
7 |
Issue |
2 |
Pages |
154-158 |
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fromIPMRAS |
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At optical frequencies the radiation produced by a source, such as a laser, a black body or a single-photon emitter, is frequently characterized by analysing the temporal correlations of emitted photons using single-photon counters. At microwave frequencies, however, there are no efficient single-photon counters yet. Instead, well-developed linear amplifiers allow for efficient measurement of the amplitude of an electromagnetic field. Here, we demonstrate first- and second-order correlation function measurements of a pulsed microwave-frequency single-photon source integrated on the same chip with a 50/50 beam splitter followed by linear amplifiers and quadrature amplitude detectors. We clearly observe single-photon coherence in first-order and photon antibunching in second-order correlation function measurements of the propagating fields. |
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RPLAB @ gujma @ |
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835 |
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Kumar, Sushil; Wang I. Chan, Chun; Hu, Qing; Reno, John L. |
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A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB |
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Journal Article |
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2011 |
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Nature Physics |
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Nat. Phys. |
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7 |
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Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~ω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9ω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser. |
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RPLAB @ gujma @ |
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836 |
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