Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H45: Quantum Information with Ions, Photons and SpinsFocus

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Sponsoring Units: GQI DAMOP Chair: Philipp Schindler, Innsbruck University Room: 348 
Tuesday, March 15, 2016 2:30PM  3:06PM 
H45.00001: Parallel transport gates in a mixedspecies ion trap processor Invited Speaker: Jonathan Home Scaled up quantum information processors will require large numbers of parallel gate operations. For ion trap quantum processing, a promising approach is to perform these operations in separated regions of a multizone processing chip between which quantum information is transported either by distributed photonic entanglement or by deterministic shuttling of the ions through the array. However scaling the technology for controlling pulsed laser beams which address each of multiple regions appears challenging. I will describe recent work on the control of both beryllium and calcium ions by transporting ions through static laser beams \footnote{Leibfried et al. PRA 76:032324 (2007)}, \footnote{deClercq et al. arXiv:1509.06624 (2015)}. We have demonstrated both parallel individually addressed operations as well as sequences of operations. Work is in progress towards multiqubit gates, which requires good control of the ion transport velocity. We have developed a number of techniques for measuring and optimizing velocities in our trap, enabling significant improvements in performance \footnote{deClercq et al. arXiv:1509.07083 (2015)}. In addition to direct results, I will give an overview of our multispecies apparatus, including recent results on high fidelity multiqubit gates. [Preview Abstract] 
Tuesday, March 15, 2016 3:06PM  3:18PM 
H45.00002: Quantum information processing with longwavelength radiation David Murgia, Sebastian Weidt, Joseph Randall, Bjoern Lekitsch, Simon Webster, Tomas Navickas, Anton Grounds, Andrea Rodriguez, Anna Webb, Eamon Standing, Stuart Pearce, Ibrahim Sari, Kian Kiang, Hwanjit Rattanasonti, Michael Kraft, Winfried Hensinger To this point, the entanglement of ions has predominantly been performed using lasers. Using long wavelength radiation with static magnetic field gradients provides an architecture to simplify construction of a large scale quantum computer. The use of microwavedressed states protects against decoherence from fluctuating magnetic fields, with radiofrequency fields used for qubit manipulation. I will report the realisation of spinmotion entanglement using longwavelength radiation, and a new method to efficiently prepare dressedstate qubits and qutrits, reducing experimental complexity of gate operations. I will also report demonstration of ground state cooling using long wavelength radiation, which may increase twoqubit entanglement fidelity. I will then report demonstration of a highfidelity longwavelength twoion quantum gate using dressed states. Combining these results with microfabricated ion traps allows for scaling towards a large scale ion trap quantum computer, and provides a platform for quantum simulations of fundamental physics. I will report progress towards the operation of microchip ion traps with extremely high magnetic field gradients for multiion quantum gates. [Preview Abstract] 
Tuesday, March 15, 2016 3:18PM  3:30PM 
H45.00003: Controlledphase gate for photons based on stationary light Ivan Iakoupov, Johannes Borregaard, Anders S. S{\O}rensen We propose a controlledphase gate for optical photons based on an atomic ensemble coupled to a onedimensional waveguide. When an ensemble of $\Lambda$type atoms is subject to a standing wave control field, it creates a {\it stationary light} [1] effect where the ensemble develops a band gap for light propagation. For frequencies close to the band gap, the lightmatter interactions are enhanced due to the reduced group velocity of the light pulses. Changing the internal state of one of the atoms, such that it behaves as an absorbing twolevel atom instead of a transparent $\Lambda$type atom, can change the scattering properties of the whole ensemble, switching it from being completely transmissive to being completely reflective. To realize a controlledphase gate between photons, we store one of the photons inside the atomic ensemble (thereby changing the internal state of one of the atoms), scatter a second photon off the ensemble, and retrieve the first photon. Finally, we consider an application of the proposed controlledphase gate  a quantum repeater. \begin{thebibliography}{1} \bibitem{Bajcsy03} M. Bajcsy, A. S. Zibrov, M. D. Lukin, \textit{Nature} {\bf 426}, 638641 (2003). \end{thebibliography} [Preview Abstract] 
Tuesday, March 15, 2016 3:30PM  3:42PM 
H45.00004: Photonic Quantum Logic with Narrowband Light from Single Atoms Allison Rubenok, Annemarie Holleczek, Oliver Barter, Jerome Dilley, Peter B. R. NisbetJones, Gunnar LangfahlKlabes, Axel Kuhn, Chris Sparrow, Graham D. Marshall, Jeremy L. O'Brien, Konstantinos Poulios, Jonathan C. F. Matthews Atomcavity sources of narrowband photons are a promising candidate for the future development of quantum technologies. Likewise, integrated photonic circuits have established themselves as a forerunning contender in quantum computing, security, and communication. Here we report on recent achievements to interface these two technologies: Atomcavity sources coupled to integrated photonic circuits. Using narrow linewidth photons emitted from a single $^{87}Rb$ atom strongly coupled to a highfinesse cavity we demonstrate the successful operation of an integrated controlnot gate. Furthermore, we are able to verify the generation of postselected entanglement upon successful operation of the gate. We are able to see nonclassical correlations in detection events that are up to three orders of magnitude farther apart than the time needed for light to travel across the chip. Our hybrid approach will facilitate the future development of technologies that benefit from the advantages of both integrated quantum circuits and atomcavity photon sources. [Preview Abstract] 
Tuesday, March 15, 2016 3:42PM  3:54PM 
H45.00005: Scalable Boson Sampling with Noisy Components Tyler Keating, Joseph Slote, Gopikrishnan Muraleedharan, Ezequiel Carrasco, Ivan Deutsch The goal of a Boson Sampler is to efficiently and scalably sample from a probability distribution that cannot be simulated efficiently on a classical computer, thus violating the Extended ChurchTuring Thesis (ECTT). To properly falsify the ECTT, the physical device must do so even in the face of realistic noise. Scaling a Boson Sampler requires increasing quantities of a set of fixedsize components (beamsplitters, detectors, etc.), so it is natural to consider noise models that act on each component independently. We show that for any such model, the percomponent noise need only decrease polynomially to keep the sampling problem hard. In this sense, Boson Sampling with noise is scalable. However, the same result applies to a number of other quantum information systems, including universal circuitmodel quantum computers. Such devices are widely believed to require error correction in order to be truly scalable, even though polynomial reduction of percomponent errors would allow them to work without error correction. This belief is consistent with the stricter requirement that error rates should be not just polynomially small, but constant in problem size. We conclude that a more precise definition of scalability with noise is needed to properly evaluate Boson Samplers. [Preview Abstract] 
Tuesday, March 15, 2016 3:54PM  4:06PM 
H45.00006: Spin models and boson sampling Juan Jose Garcia Ripoll, Borja Peropadre, Alan AspuruGuzik Aaronson & Arkhipov showed that predicting the measurement statistics of random linear optics circuits (i.e. boson sampling) is a classically hard problem for highly nonclassical input states [1]. A typical bosonsampling circuit requires N single photon emitters and M photodetectors, and it is a natural idea to rely on fewlevel systems for both tasks. Indeed, we show that 2M twolevel emitters at the input and output ports of a general Mport interferometer interact via an XYmodel with collective dissipation and a large number of dark states that could be used for quantum information storage. More important is the fact that, when we neglect dissipation, the resulting longrange XY spinspin interaction is equivalent [2] to boson sampling under the same conditions that make boson sampling efficient. This allows efficient implementations of boson sampling using quantum simulators & quantum computers. [1] S. Aaronson, A. Arkhipov, Proc. of the 43rd annual ACM symposium on Theory of computing (ACM, 2011) 333342 [2] arXiv:1509.02703 [Preview Abstract] 
Tuesday, March 15, 2016 4:06PM  4:18PM 
H45.00007: Experimental fault tolerant universal quantum gates with solidstate spins under ambient conditions. Xing Rong Quantum computation provides great speedup over classical counterpart for certain problems, such as quantum simulations, prime factoring and database searching. One of the challenges for realizing quantum computation is to execute precise control of the quantum system in the presence of noise. Recently, high fidelity control of spinqubits has been achieved in several quantum systems. However, control of the spinqubits with the accuracy required by the fault tolerant quantum computation under ambient conditions remains exclusive. Here we demonstrate a universal set of logic gates in nitrogenvacancy centers with an average singlequbit gate fidelity of 0.99995 and two qubit gate fidelity of 0.992. These high control fidelities have been achieved in the C naturally abundant diamonds at room temperature via composite pulses and optimal control method. This experimental implementation of quantum gates with fault tolerant control fidelity sets an important step towards the faulttolerant quantum computation under ambient conditions. [Preview Abstract] 
Tuesday, March 15, 2016 4:18PM  4:30PM 
H45.00008: Universal Superadiabatic Geometric Quantum Gates in NitrogenVacancy Centers Hui Yan, Zhengtao Liang, Shiliang Zhu We propose a scheme to implement a universal set of quantum gates based on geometric phases and superadiabatic quantum control. The proposed quantum gates consolidate the advantages of both strategies for robust and fast. The diamond nitrogenvacancy center system is adopted as a typical example to illustrate the scheme. We show those gates can be realized in a simple twolevel configuration by appropriately controlling the amplitude, phase and frequency of just one microwave field. The robust and fast features are confirmed by comparing the fidelities of the proposed superadiabatic geometric phase gate with three other kinds of phase gates. [Preview Abstract] 
Tuesday, March 15, 2016 4:30PM  4:42PM 
H45.00009: Nonlinear optical effects and HongOuMandel interference in cavity quantum electrodynamics Imran M. Mirza, Steven J. van Enk Pure quantum interference among single photons is one of the key ingredients to perform linear optics quantum computation (LOQC). The HongOuMandel interference (HOMI) [C. K. Hong, Z. Y. Ou and L. Mandel, Phys. Rev. Lett. 59, (18), 20442046 (1987)] i.e. complete destructive interference between two identical and indistinguishable photons simultaneously entering input ports of a 50/50 beam splitter, is a wellknown example in this context. In this talk, I'll present our theoretical study of HOMI in a coupled JaynesCummings array. In particular and by applying quantum jump/trajectory formalism, I'll focus on how partial quantum interference between two photons survive both nonlinearities produced by twolevel emitter and spectral filtering due to optical cavities in our coupled cavity array setup [Imran M. Mirza and Steven J. van Enk, Opt. Comm. 343, 172177 (2015)]. Along with LOQC, this work is crucial from the perspective of exploiting coupled cavity arrays to store single photons reliably (without altering their temporal and spectral traits) [Imran M. Mirza, Steven J. van Enk and Jeff Kimble, JOSA B, 10, 26402649, (2013)]. [Preview Abstract] 
Tuesday, March 15, 2016 4:42PM  4:54PM 
H45.00010: Saving entangled photons from sudden death in a singlemode fiber  Interplay of decoherence and dynamical decoupling. Manish K. Gupta, Chenglong You, Hwang Lee, Jonathan P. Dowling We study the dynamics of decoherence in an optical fiber for the case of entangled photons. Such a study will allow us to increase the physical length of fiber for the transmission of entangled photon from the sources such as SPDC. We analytically derive the model for decoherence of entangled state photons in a singlemode fiber. We also show that entanglement lifetime can be increased with open loop control technique called dynamical decoupling. [Preview Abstract] 
Tuesday, March 15, 2016 4:54PM  5:06PM 
H45.00011: Restoring photon indistinguishability via pulse and continuouswave control of solidstate quantum emitters. Herbert F. Fotso, Adrian E. Feiguin, David D. Awschalom, Viatcheslav V. Dobrovitski Interference of indistinguishable photons is a central element of many protocols for entangling distant qubits in quantum networks. In spite of great progress [1,2,3] in development and applications of solidstate quantum emitters, the entanglement rate remains severely limited. One of the major obstacles is the photon indistinguishability which is greatly reduced by the uncontrollable slow drift of the qubit emission frequency. We investigate several pulsebased and continuouswave control protocols which suppress the spectral diffusion. We confirm, using both analytics and direct numerical simulations, that these protocols effectively keep the emission at a set target frequency, and explicitly show that the indistinguishability of the emitted photons is restored by the control. We also compare several pulsebased protocols with different pulse timings, and discuss how they affect the emission line and the photon properties. Considering the nitrogenvacancy centers in diamonds as a convenient example, we demonstrate that both pulsebased and continuouswave controls can boost the success rate of the longrange entanglement. [1]B. Hensen et al., Nature 526, 682 (2015). [2]B. B. Buckley et al., Science 330, 1212 (2010). [3]W. B. Gao et al., Nature Comm. 4, 2744 (2013). [Preview Abstract] 
Tuesday, March 15, 2016 5:06PM  5:18PM 
H45.00012: Optimizing Adiabaticity in NMR Jonathan Vandermause, Chandrasekhar Ramanathan We demonstrate the utility of Berry's superadiabatic formalism for numerically finding control sequences that implement quasiadiabatic unitary transformations. Using an iterative interaction picture, we design a shortcut to adiabaticity that reduces the time required to perform an adiabatic inversion pulse in liquid state NMR. We also show that it is possible to extend our scheme to two or more qubits to find adiabatic quantum transformations that are allowed by the control algebra, and demonstrate a twoqubit entangling operation in liquid state NMR. We examine the pulse lengths at which the fidelity of these adiabatic transitions break down and compare with the quantum speed limit. [Preview Abstract] 
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