Southwest Quantum Information and TechnologyFifteenth Annual Meeting, February 21-23, 2013
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All Abstracts | Poster Abstracts | Talk Abstracts 1. Unitary Transformations in a Large Hilbert SpaceBrian Anderson, University of Arizona (Session 2 : Thursday from 3:15 - 3:45) Abstract. Quantum systems with Hilbert space dimension greater than two (qudits) provide an alternative to qubits as carriers of quantum information, and may prove advantageous for quantum information tasks if good laboratory tools for qudit manipulation and readout can be developed. We have implemented a protocol for arbitrary unitary transformations in the 16 dimensional hyperfine ground manifold of Cesium 133 atoms, using phase modulated rf and microwave magnetic fields to drive the atomic evolution. Our phase modulation waveforms are designed numerically using a variant of the highly efficient GRAPE algorithm. The fidelity of the resulting transformations is verified experimentally through randomized benchmarking, which indicates an average fidelity better than 97% across a sample of random unitaries. Our toolbox for quantum control is in principle applicable for a broad class of physical systems, such as large spins or anharmonic oscillators. 2. Ultrafast Quantum Process Tomography via Continuous Measurement and Convex OptimizationCharles Baldwin, University of New Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. Quantum process tomography (QPT) is an essential tool to diagnose the implementation of a dynamical map. However, the standard protocol is extremely resource intensive. For a Hilbert space of dimension d, it requires d^2 different input preparations followed by state tomography via the estimation of the expectation values of d^2-1 orthogonal observables. We show that when the process is nearly unitary, we can dramatically improve the efficiency and robustness of QPT through a collective continuous measurement protocol on an ensemble of identically prepared systems. Given the measurement history we obtain the process matrix via a convex program that optimizes a desired cost function. We study two estimators: least-squares and compressive sensing. Both allow rapid QPT due to the condition of complete positivity of the map; this is a powerful constraint to force the process to be physical and consistent with the data. We apply the method to a real experimental implementation, where optimal control is used to perform a unitary map on a d=8 dimensional system of hyperfine levels in cesium atoms, and obtain the measurement record via Faraday spectroscopy of a laser probe. 3. Squeezing of Spin Waves in Atomic EnsemblesBen Baragiola, Center for Quantum Information and Control, University of New Mexico (Session 10 : Saturday from 2:00 - 2:30) Abstract. Squeezing the collective spin of an atomic ensemble via QND measurement is based on the interaction between a cloud of atoms and a laser probe. When the shot noise resolution of the laser probe is below the projection noise fluctuations of the atoms, the resulting backaction can reduce the uncertainty for a collective atomic observable. Most current models of this process rely on idealized one-dimensional plane wave approximations of the underlying light-matter interaction, which are not appropriate for describing a real system consisting of a cigar-shaped cold atomic cloud in dipole trap interacting with a probe laser. We extend such models from first principles to include spatial dependence of both the light and of the atomic ensemble and apply it to QND spin squeezing for large-spin alkali atoms. The model includes spin waves, diffraction, paraxial modes, and optical pumping, derived by a full master equation description. We find that to optimally mode-match for spin squeezing one must consider not only collective scattering into the forward modes of the field, but also the effects of local decoherence from spatially-varying diffuse photon scattering. Surprisingly, in certain circumstances such local decoherence can be less destructive to spin squeezing than previously thought from phenomenological models. 4. Using postselection to control ground state quantum beats in Cavity QEDPablo Barberis-Blostein, Universidad Nacional Autonoma de Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. Pablo Barberis-Blostein (Universidad Nacional Autonoma de Mexico) Howard Carmichael (University of Auckland) Luis Orozco (University of Maryland) Andres Cimmarusti (University of Maryland) Ground state quantum beats observed in the second order intensity correlation from a continuously driven atomic ensemble inside a two mode optical cavity are subject to a frequency shift and decoherence. While driving the cavity with light of linear polarization ($\pi$ transitions) the second order autocorrelation function is measured in the undriven mode (orthogonal polarization): a first photon detection prepares a superposition of atomic ground-state Zeeman sublevels and the second measures the ground state beats. Between these two detections, the atoms can become excited and return to the ground state, emitting most of the photons into modes other than the cavity modes. Depending on the drive strength this process can happen several times. Each time there is a relative phase advance between the Zeeman sublevels. The information of this phase advance and its associated decoherence is then leaked into the modes that are not the cavity modes, which form the environment. It is possible to get information about the number of photons leaked into the environment by monitoring the driven mode. Here we propose a scheme to manipulate the loss of amplitude of the beats (decoherence) and the beat frequency shift, by postselecting on the basis of information gathered through measurement of the driven cavity mode. This proposal is a new strategy compared with controlling the decoherence and light shift through turning off the driven field. Work supported by CONACYT, NSF and the Marsden Fund of the RSNZ. 5. Oscillator-Field Model of OptomechanicsRyan Behunin, Los Alamos National Laboratory (Session 3 : Thursday from 5:00 - 7:00) Abstract. We present a microphysics model for the kinematics and dynamics of optomechanics describing the coupling between an optical field, modeled here by a massless scalar field, with the internal and mechanical degrees of freedom of a moveable mirror. Instead of implementing boundary conditions on the field we introduce an internal degree of freedom and its dynamics to describe the mirror's reflectivity. Depending on parameter values, the internal degrees of freedom of the mirror in this model captures a range of its optical activities, from those exhibiting broadband reflective properties to those reflecting only in a narrow band. After establishing the model we show how appropriate parameter choices lead to other well-known optomechanical models including those of Barton & Calogeracos [1], Law [2] and Golestanian & Kardar [3]. As a simple illustrative application we derive classical radiation pressure cooling from this model. Our microphysics model can be connected to the common descriptions of a moving mirror coupled to radiation pressure (e.g., with Nx coupling, where N is the photon number and ),x is the mirror displacement) making explicit the underlying assumptions made in these phenomenological models. Our model is also applicable to the lesser explored case of small N, which existing models based on side-band approximations [4] cannot cope with. Interestingly, we also find that slow moving mirrors in our model can be described by the ubiquitous Brownian motion model of quantum open systems. The scope of applications of this model ranges from a full quantum mechanical treatment of radiation pressure cooling and quantum entanglement between macroscopic mirrors to the backreaction of Hawking radiation on black hole evaporation in a moving mirror analog. [1] G. Barton and A. Calogeracos, Ann. Phys. 238, 227 (1995). A. Calogeracos and G. Barton, Ann. Phys. 238, 268 (1995). [2] C. K. Law, Phys. Rev. A 51, 2537 (1995). [3] R. Golestanian and M. Kardar, Phys. Rev. Lett. 78, 3421 (1997); Phys. Rev. A 58, 1713 (1998) [4] H. J. Kimble, Yuri Levin, Andrey B. Matsko, Kip S. Thorne, and Sergey P. Vyatchanin, Phys. Rev. D 65, 022002 (2001) 6. Cavity integrated surface ion trap for enhanced light collectionFrancisco Benito, Sandia National Laboratories - University of New Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. Cavity integrated surface ion trap for enhanced light collectionFrancisco Benito, Matthew Blain, Chin-wen Chou, Craig Clark, Mike Descour, Ray Haltli, Edwin Heller, Jon Sterk, Boyan Tabakov, Chris Tigges, Peter Maunz, Daniel Stick Sandia National Laboratories Center for Quantum Information and Control, University of New Mexico, MSC 07-4220, Albuquerque, NM 87131-0001 The scalable distribution of coherent information in a quantum network is a prerequisite for the creation of a quantum repeater for secure long-distance communication and a large scale quantum information processor. Ion trap systems allow the faithful storage and manipulation of qubits encoded in the energy levels of trapped ions, which can be interfaced with photonic qubits that can be easily transmitted to connect remote quantum systems. Single photons transmitted from two remote sites, each entangled with one quantum memory, can be used to generate entanglement between the two distant quantum memories [1]. In order to make this photon mediated entanglement efficient a strong interaction between atomic and photonic qubits is necessary. This can be realized by integrating an ion trap with an optical cavity and employing the Purcell effect for enhancing the light collection. We present progress towards integrating a 1 mm optical cavity with a micro-fabricated surface ion trap. The plano-concave cavity is oriented normal to the chip surface where the planar mirror is attached underneath the trap chip. The linear ion trap allows ions to be shuttled in and out of the cavity mode. The Purcell enhancement of spontaneous emission into the cavity mode will allow us to collect up to 12% of the emitted photons, enabling remote entanglement generation much faster than the qubit coherence time. Moehring, D. L., Maunz, P., Olmschenk, S., Younge, K. C., Matsukevich, D. N., Duan, L. M., & Monroe, C. (2007). Entanglement of single-atom quantum bits at a distance. Nature, 449(7158), 68-71. This work was supported by Sandia's Laboratory Directed Research and Development (LDRD) and the Intelligence Advanced Research Projects Activity (IARPA). Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 7. Adaptive gate-set tomographyRobin Blume-Kohout, Sandia National Laboratories (Session 7a : Friday from 4:00 - 4:30) Abstract. Quantum information hardware needs to be characterized and calibrated. This is the job of quantum state and process tomography, but standard tomographic methods have an Achilles heel: to characterize an unknown process, they rely on a set of absolutely calibrated measurements. Many technologies (e.g., solid-state qubits) admit only a single native measurement basis, and other bases are measured using unitary control. So tomography becomes circular -- tomographic protocols are using gates to calibrate themselves! Gate-set tomography confronts this problem head-on and resolves it by treating gates relationally. We abandon all assumptions about what a given gate operation does, and characterize entire universal gate sets from the ground up using only the observed statistics of an [unknown] 2-outcome measurement after various strings of [unknown] gate operations. The accuracy and reliability of the resulting estimates depend critically on which gate strings are used, and benefits greatly from adaptivity. We demonstrate gate-set tomography and quantify the accuracy with which the individual gates can be estimated. 8. Experimental signatures of quantum annealingSergio Boixo, University of Southern California, Information Sciences Institute (Session 11 : Saturday from 3:30 - 4:00) Abstract. Quantum annealing is a general strategy for solving optimization problems with the aid of quantum adiabatic evolution. How effective is rapid decoherence in precluding quantum effects in a quantum annealing experiment, and will engineered quantum annealing devices effectively perform classical thermalization when coupled to a decohering thermal environment? Using the D-Wave machine, we report experimental results for a simple problem which takes advantage of the fact that for quantum annealing the measurement statistics are determined by the energy spectrum along the quantum evolution, while in classical thermalization they are determined by the spectrum of the final Hamiltonian only. We establish an experimental signature which is consistent with quantum annealing, and at the same time inconsistent with classical thermalization, in spite of a decoherence timescale which is orders of magnitude shorter than the adiabatic evolution time. For larger and more difficult problems, we compare the measurements statistics of the D-Wave machine to large-scale numerical simulations of simulated annealing and simulated quantum annealing, implemented through classical and quantum Monte Carlo simulations. For our test cases the statistics of the machine are - within calibration uncertainties - indistinguishable from a simulated quantum annealer with suitably chosen parameters, but significantly different from a classical annealer. 9. Quantum simulation and many-body physics with hundreds of trapped ionsJohn Bollinger, National Institute of Standards and Technology (Session 1 : Thursday from 8:30 - 9:15) Abstract. Many different quantum information protocols have been demonstrated with small linear chains of ions in rf (Paul) traps. I will describe our efforts to extend some of the techniques developed with small linear chains of ions to larger two-dimensional crystals of hundreds of ions formed in a Penning trap [1]. Our qubit (or spin) is the 124 GHz electron spin-flip transition in the ground state of Be+ in the 4.5 Tesla magnetic field of the trap. We control the spins with an effective transverse magnetic field obtained with 124 GHz microwaves [2]. By employing spin-dependent optical dipole forces, we engineer long-range Ising interactions (both ferromagnetic and anti-ferromagnetic) between the ion qubits [3]. We benchmark the interactions through measurements of mean-field spin precession [4]. I will describe the types of Ising interactions we can readily implement and discuss the prospects for simulating the transverse Ising model with hundreds of qubits. [1] T. Mitchell, J. J. Bollinger, D. Dubin, X. Huang, W. M. Itano, and R. Baughman, Science 282, 1290 (1998). [2] M. J. Biercuk, H. Uys, A. P. VanDevender, N. Shiga, W. M. Itano, and J. J. Bollinger, Quantum Information and Computation 9, 920 (2009). [3] K. Kim, M.-S. Chang, R. Islam, S. Korenblit, L.-M. Duan, and C. Monroe, Phys. Rev. Lett. 103, 120502 (2009). [4] J. W. Britton, B. C. Sawyer, A. C. Keith, C.-C. J. Wang, J. K. Freericks, H. Uys, M. J. Biercuk, and J. J. Bollinger, Nature 484, 489 (2012). 10. Instantaneous Quantum Circuits for Ising ModelsGavin Brennen, Macquarie University (Session 1 : Thursday from 10:15 - 11:00) Abstract. Statistical Mechanics has provided us with straightforward recipes to compute various physical quantities that can be experimentally probed on an interacting many-body system. But more often than not, the application of these recipes is computationally inefficient, as can be seen from very idealised systems. It may be expected that quantum algorithms could help in this regard. I will describe a scheme for measuring complex temperature partition functions of Ising models which, through appropriate Wick rotations, can be analytically continued to yield estimates for real ones. Notably, the kind of state preparations and measurements involved in this application can in principle be made "instantaneous", i.e. independent of the system size or the parameters being simulated. The estimation error is analysed numerically and analytically and shown to be compatible with prior art using larger depth quantum circuits. Also I'll describe some results on when the algorithm yields approximation scales with multiplicative rather than additive error which could have application in other contexts as well. Finally the dual problem concerning the BQP-hardness of computing partition functions for classical ferromagnetic and consistent Ising models in 2D a high but not perfect accuracy will be described. 11. Exploring adiabatic quantum computing trajectories via optimal controlConstantin Brif, Sandia National Laboratories (Session 6a : Friday from 2:00 - 2:30) Abstract. Adiabatic quantum computation (AQC) employs a slow change of the Hamiltonian, which helps keeping the system in the instantaneous ground state. When the evolution time is finite, dynamic trajectories corresponding to different forms of time-dependent control function(s) will result in different degrees of adiabaticity (quantified as the average ground state population during evolution). We employ optimal control methods to search for control functions that achieve the target final state while simultaneously maximizing the degree of adiabaticity. Exploring properties of optimal AQC trajectories in model systems elucidates dynamic mechanisms that minimize unwanted excitations from the ground state. 12. Magic state distillation with noisy Clifford gatesPeter Brooks, California Institute of Technology (Session 7b : Friday from 5:00 - 5:30) Abstract. A promising method for achieving universal fault-tolerant quantum computation is to supplement Clifford operations, which are sufficient for error correction but not a universal basis, with copies of certain single-qubit states called magic states. High-fidelity copies of these states can be prepared from noisy copies using state distillation protocols which use only Clifford gates. This process can proceed to arbitrarily high fidelity, assuming that the Clifford gates are perfect. In practice, imperfect Clifford operations will both reduce the efficiency of distillation and limit the achievable fidelity of the distilled state. This will be particularly relevant to quantum computation where the noise from Clifford operations is substantial, which will likely be the case with early demonstrations of fault-tolerant quantum computing. Recently, a number of interesting proposals have been made for more efficient state distillation protocols which use fewer ancillas to achieve a given error rate. We analyze and compare the efficiency and success probability for magic state distillation under these various proposals, taking into account the presence of imperfect Clifford operations. 13. Reliable transport through a microfabricated X-junction surface-electrode ion trap*Kenton Brown, Georgia Tech Research Institute (Session 3 : Thursday from 5:00 - 7:00) Abstract. At the heart of most ion-based quantum information processing and simulation efforts is an RF-Paul trap to confine the ion qubits. There is increasing need for complex trapping geometries that can hold larger numbers of ions beyond single linear chains. As part of GTRI's ongoing trap development effort, we have demonstrated reliable, uncooled transport of ions through a surface electrode X-junction. Through careful modeling of the junction potentials, including modeling of non-ideal effects seen during trap characterization, we reduced the transport heating sufficiently to allow for more than 60 round trip transports of an ion through the junction without cooling. These results open up the possibility of ion swapping and transport through multi-junction arrays without continual ion cooling. In addition to presenting these results, we will describe GTRI's next generation junction design that addresses confinement and control limitations observed in the first generation junction. Combined with a novel transport and storage structure, the new junction trap should be able to hold dozens of ions in separate wells and combine them as needed for gate operations. This material is based upon work supported by the Georgia Tech Research Institute and the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA) under U.S. Army Research Office (ARO) contract W911NF081-0315. 14. Quantum Technology Taken to its LimitsTommaso Calarco, University of Ulm (Session 2 : Thursday from 3:45 - 4:30) Abstract. The full power of quantum coherence has not yet been tapped for everyday technological applications. The exquisite level of control of current atomic physics experiments may enable this, for instance in the field of quantum communication and quantum computing - but scalable quantum information processing requires extremely precise operations. Quantum optimal control theory allows to design the evolution of realistic systems in order to attain the best possible performance that is allowed by the laws of quantum mechanics. I will present a range of its applications to a variety of quantum technologies, and discuss its use in probing the ultimate limits to the speed, fidelity and size of the corresponding quantum processes. 15. Quantum Control: A Circuit-Based ClassificationCarlton Caves, University of New Mexico (Session 2 : Thursday from 2:15 - 2:45) Abstract. Control of the behavior of quantum systems, to make them do what we want them to do, instead of just what comes naturally, is fundamental to quantum information science. I will discuss a classification scheme that divides control and feedback techniques into three types: measurement-based control and feedback; coherent control and feedback; and quantum (noncommutative) control and feedback. The classification is based on how these techniques are represented in quantum-circuit diagrams and will be illustrated by examples. 16. Accurate quantum Z rotations with less magicChris Cesare, Center for Quantum Information and Control, Department of Physics and Astronomy, University of New Mexico (Session 7b : Friday from 4:30 - 5:00) Abstract. We present quantum protocols for executing arbitrarily accurate pi/2^k rotations of a qubit about its Z axis. Unlike reduced instruction set computing (RISC) protocols which use a two-step process of synthesizing high- fidelity "magic" states from which T = Z(pi/4) gates can be teleported and then compiling a sequence of adaptive stabilizer operations and T gates to approximate Z(pi/2^k), our complex instruction set computing (CISC) protocol distills magic states for the Z(pi/2^k) gates directly. Replacing this two-step process with a single step results in substantial reductions in the number of gates needed. The key to our construction is a family of shortened quantum Reed-Muller codes of length 2^(k+2)-1, whose distillation threshold shrinks with k but is greater than 0.85% for k <= 6. CC was supported in part by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 17. Cavity-enhanced non-demolition measurements for atom counting and spin squeezingZilong Chen, JILA and Department of Physics, University of Colorado at Boulder (Session 10 : Saturday from 2:30 - 3:00) Abstract. Cavity-enhanced probing of an atomic ensemble is an important tool for precision metrology. In particular, high resolution, non-destructive atom counting increases measurement or sensing bandwidth, and mitigates noise aliasing (Dick effect) in an atomic sensor. Achieving high resolution atom counting while preserving coherence can generate conditionally spin squeezed states that has phase sensitivity below the standard quantum limit. In recent years, there has been much interest in cavity-enhanced measurements for the above metrological applications. We consider fundamental measurement imprecision and scalings for cavity-enhanced measurements. As a particular example, we will discuss fundamental squeezing limits in Rb-87 for the clock and stretched hyperfine transitions, taking into account the multilevel structure. We will also discuss our experimental squeezing on the Rb-87 clock transition and give an outlook on current efforts to squeeze using the Rb-87 cycling transition. References: [1] Zilong Chen, Justin G. Bohnet, Joshua M. Weiner, Kevin C. Cox, and James K. Thompson, arXiv:1211.0723 [2] Zilong Chen, Justin G. Bohnet, Shannon R. Sankar, Jiayan Dai, and James K. Thompson, Phys. Rev. Lett. 106, 133601 (2011) 18. Reflective Parabolic Ion Trap for Efficient Ion Photon CollectionChen-Kuan Chou, University of Washington (Session 3 : Thursday from 5:00 - 7:00) Abstract. Single trapped ion qubit is an excellent candidate for quantum computation and information due to its low decoherence, ease of control and detection, and ability to couple to a photon, the flying qubit. Efficiently coupling ion fluorescence into a single-mode fiber is the most challenging part in remote entangled ion qubit state generation. To address this issue, we developed an ion trap combining a reflective parabolic surface with trap electrodes. This parabolic trap design covers a solid angle close to 2 Pi, and allows precise ion placement at the focal point of the parabola. We measured approximately 39% fluorescence collection with this mirror. With the advantage of producing a collimated photon beam, we expect to couple the ion fluorescence into a single-mode fiber in a straightforward way. The improved collection efficiency will make the loophole-free Bell inequality test possible with two remotely entangled ions approximately 1 km apart. 19. Towards a robust cavity QED apparatus for control of quantum beats.Andres Cimmarusti, Joint Quantum Institute (Session 3 : Thursday from 5:00 - 7:00) Abstract. Andres D. Cimmarusti1, Burkley D. Patterson1, Wanderson M. Pimenta1,2, Luis A. Orozco1 1Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, College Park, MD, USA We present our new cavity QED apparatus for control of ground state quantum beats in Rb. We obtain our continuous cold atomic beam from a steerable, high flux Low Velocity Intense Source (LVIS) of Rb [1]. The atoms travel perpendicularly to the axis of the cavity and couple to its TEM00 mode. Our Fabry-Perot cavity has improved finesse for the same atom-field coupling strength. We have a dual isotope setup to handle 85Rb and 87Rb. Our detection system relies on the separation between the two polarization modes of the cavity. The Birefringence due to the vacuum chamber windows and the mirrors of the cavity is challenging, but we use low stress-optic coefficient windows to mitigate it. The preparation of the coherences that generate the quantum beats requires careful control of the magnetic field. For this purpose, we implement in vacuo three-axis magnetometry. RF/Microwave antennas allow the possibility to excite the coherences with low frequency electromagnetic fields. These hardware improvements will yield a more robust and versatile experimental apparatus to continue exploring light matter interaction in cavity QED. Work supported by NSF from USA and FAPEMIG from Brazil [1] Z. T. Lu, K. L. Corwin, M. J. Renn, M. H. Anderson, E. A. Cornell, and C. E. Wieman, Phys. Rev. Lett. 77, 3331 (1996). 20. Fast and strong feedback for control of quantum beats in a cavity QED system.Andres Cimmarusti, Joint Quantum Institute (Session 3 : Thursday from 5:00 - 7:00) Abstract. Andres D. Cimmarusti1, Burkley D. Patterson1, Christopher A. Schroeder1, Wanderson M. Pimenta1,2, Luis A. Orozco1, Pablo Barberis-Blostein3 and Howard J. Carmichael4 1Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, College Park, MD, USA Second order correlations studies reveal the generation of quantum beats from a coherent ground-state superposition created by conditional measurements on the undriven mode of a two-mode cavity QED system. Continuous drive of the system induces amplitude decoherence and frequency shifts in the beats due to the intrinsic phase diffusion process as a consequence of successive interruptions from Rayleigh scattering. Our results show we can stop this decoherence process and prevent phase shifts on the Larmor precesion, by implementing a fast and strong feedback protocol: The detection of a phtoton triggers a switch to turn down or off the drive, the systen then evolves in the dark for a pre-set time until the drive returns. The revived quantum beat shows phase accumulation only from Larmor precession and can exhibit an amplitude scaling of more than a factor of two with respect to continuous drive. Work supported by NSF, USA; CONACYT, Mexico; The Marsden Fund of the Royal Society of New Zealand; and FAPEMIG of Brazil. 21. Characterization of novel surface ion trap structures for quantum information processingCraig Clark, Sandia National Laboratory (Session 3 : Thursday from 5:00 - 7:00) Abstract. Craig Clark, Matthew Blain, Francisco Benito, Chin-wen Chou, Mike Descour, Rob Ellis, Ray Haltli, Edwin Heller, Shanalyn Kemme, Jon Sterk, Boyan Tabakov, Chris Tigges, Peter Maunz, Daniel Stick Sandia National Laboratories Center for Quantum Information and Control, University of New Mexico, MSC 07-4220, Albuquerque, NM 87131-0001 Segmented surface electrode ion traps are one of the most mature platforms among candidates for scalable quantum information processing. At Sandia National Laboratories we design, fabricate, and test such traps. Here we describe our characterization of a linear trap with integrated diffractive optic elements for collecting light into multi-mode fibers. In this trap, micro-motion is minimized, the effect of the dielectric is characterized, and the light collection efficiency is assessed by single photon counting. We also report progress towards long range compensation of stray electric fields in a trap with a ring geometry. This should allow us to trap a circular crystal of equally spaced ions tangentially confined by their mutual Coulomb repulsion. Finally, we report on initial testing of a trap structure with vastly improved in-plane optical access. In this structure in-plane beams can be focused to less than 8 microns while keeping a distance of at least 5 beam radii to the trap structure. This work was supported by Sandia's Laboratory Directed Research and Development (LDRD) and the Intelligence Advanced Research Projects Activity (IARPA). Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 22. Is building a superconducting quantum computer actually feasible?Andrew Cleland, University of California - Santa Barbara (Session 4 : Friday from 8:30 - 9:15) Abstract. There has recently been tremendous progress in the performance of superconducting quantum circuits, especially in single qubit T1 and T2 coherence times, as well as in quantum measurement. Simple implementations of quantum algorithms have also been demonstrated. Are these advances sufficient to consider actually building a quantum computer? I will argue that the answer is (probably) affirmative, although such an effort would still be faced with many challenges, including how to achieve high-fidelity tune-up, control, and measurement of large numbers of qubits. A highly fault-tolerant approach is also needed; I will describe the surface code architecture, which provides what may be the most fault-tolerant scheme that includes topologically-protected logical operations. I will outline the basic principles and operation of this scheme, as well as prospects for the medium and long-term future of this area of research. 23. Quantum trajectories for an arbitrary quantum system probed by a travelling wave non-Gaussian fieldJoshua Combes, The University of New Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. Quantum trajectories are a description of the continuous in time evolution of a quantum system undergoing a continuous in time ancilla coupled measurement. Until recently most quantum trajectory analysis was for Gaussian fields be they vacuum, coherent, squeezed, thermal or some combination thereof (see e.g. Wiseman and Milburn's Book). Using Gardiner and Collett's input-ouput theory I describe how to derive the quantum trajectories associated with an itinerant non-Gaussian probe prepared in any superposition and or mixture of: Fock statesa or coherent statesb. We focus on the trajectories associated with direct (photon counting), homodyne, and heterodyne detection. Finally I present some progress towards incorporating and then generalizing Shen, Fan and coworkers scattering matrix calculations into standard input-output theory for arbitrary fieldsc, coupled with our results this allows for the correct description of heralded state preparation of itinerant modes. a Joint work with Ben Baragiola b Joint work with John Gough, Hendra Nurdin, and Matt James c Joint work with Chris Cesare 24. Single shot quantum state estimation via continuous measurement in a strong back-action regimeRobert Cook, University of New Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. Quantum state reconstruction is a fundamental task in quantum information science. The standard approach employs many projective measurements on a series of identically prepared systems in order to collect sufficient statistics of an informationally complete set of observables. An alternative procedure is to reconstruct quantum state by performing weak continuous measurement collectively on an ensemble, while simultaneously applying time varying controls [1]. For known dynamics, the measurement history determines the initial state. In current implementations [2,3] the shot noise of the probe dominates over projection noise so that measurement-induced backaction is negligible. We generalize this to the regime where quantum backaction is significant, even for a small number of particles. Using the framework of quantum filtering theory, we model the reconstruction of the state of a qubit through collective spin measurement via the Faraday interaction and magnetic field controls, and develop a maximum-likelihood estimate. We present numerical results indicating that our estimates have an average fidelity of reconstruction that approaches an optimum bound. [1] A. Silberfarb and I. H. Deutsch, Phys. Rev. Lett. 95, 030402 (2005). [2] C. A. Riofrío et al., J. Phys. B: At. Mol. Opt. Phys. 44, 154007 (2011). [3] A. Smith et al., Arxiv:1208.5015 (2012). 25. Quantum information processing with trapped electrons and superconducting electronicsNikos Daniilidis, University of California, Berkeley (Session 3 : Thursday from 5:00 - 7:00) Abstract. We describe a quantum information processing (QIP) architecture based on single trapped electrons and superconducting electronics. The electron spins function as quantum memory elements, and the electron motion is used to couple the electrons to microwave circuits. To achieve this, we propose a parametric coupling mechanism which utilizes the non-linearity of the electrostatic potential of a sharp electrode placed 10 μm from a single trapped electron. This mechanism allows parametric coupling rates higher than 350 kHz for electrons with trap frequency of 300 MHz, coupled to a 7 GHz resonant circuit. We discuss state transfer and entangling operations between distant electrons, as well as between electrons and superconducting qubits, e.g. transmon qubits. The coupling to high frequency superconducting electronics enables initialization as well as state read-out of the electron motion. In addition, the manifold of the ground and the first excited state of the electron motion can be mapped onto its spin using an oscillating magnetic field, completing all requirements for quantum computing with the electron spin. We estimate that all involved operations can be carried out with fidelities higher than 0.996, enabling fault-tolerant quantum computing. 26. Optimally Shaped Gates for Trapped Ion ChainsShantanu Debnath, Joint Quantum Institute/ University of Maryland (Session 3 : Thursday from 5:00 - 7:00) Abstract. We perform entangling phase gates between selective pairs of qubits in a chain of trapped atomic 171Yb+ ions through a coupling to multiple motional modes. We accomplish this by coherently manipulating and coupling the qubits to collective transverse modes of motion using Raman beat notes between frequency comb lines of a 355nm pulsed laser[1]. We optimally shape the phase and amplitude of Raman beat notes to implement robust gates that can operate at nearly any beat note detuning from the modes. We demonstrate a five-segment scheme[2] to entangle two Qubits with full control and high fidelity as compared to single segment gate. We extend this scheme to selectively entangle pairs of Qubits in a chain of 3 or more using shaped pulses and individual optical addressing that can be extended to much large number of Qubits. This work was supported by grants from the U.S. Army Research Office with funding from IARPA, the DARPA OLE program, and the MURI Hybrid Quantum Circuits program; and the NSF Physics Frontier Center at JQI. [1] D. Hayes et al., Phys. Rev. Lett 104, 140501 (2010). [2] S.-L. Zhu et al., Europhys. Lett., 73 (4), pp. 485-491 (2006). 27. The Kibble-Zurek mechanism in ion chainsAdolfo Del Campo, Los Alamos National Laboratory (Session 3 : Thursday from 5:00 - 7:00) Abstract. Structural defects in ion crystals can be formed during a linear quench of the transverse trapping frequency across the mechanical instability from a linear chain to the zigzag structure. The density of defects after the sweep can be conveniently described by the Kibble-Zurek mechanism [1,2]. In particular, the number of kinks in the zigzag ordering can be derived from a time-dependent Ginzburg-Landau equation for the order parameter, here the zigzag transverse size, under the assumption that the ions are continuously laser cooled. In a linear Paul trap the transition becomes inhomogeneous, the charge density being larger in the center and more rarefied at the edges. During the linear quench the mechanical instability is first crossed in the center of the chain, and a front, at which the mechanical instability is crossed during the quench, is identified which propagates along the chain from the center to the edges. If the velocity of this front is smaller than the sound velocity, the dynamics becomes adiabatic even in the thermodynamic limit and no defect is produced. Otherwise, the nucleation of kinks is reduced with respect to the case in which the charges are homogeneously distributed, leading to a new scaling of the density of kinks with the quenching rate. The analytical predictions are verified numerically by integrating the Langevin equations of motion of the ions, in presence of a time-dependent transverse confinement. The non-equilibrium dynamics of an ion chain in a Paul trap constitutes an ideal scenario to test the inhomogeneous extension of the Kibble-Zurek mechanism [3], and has recently led to its demonstration in the laboratory [4]. Journal-refs: [1] A. del Campo, G. De Chiara, G. Morigi, M. B. Plenio, A. Retzker, Phys. Rev. Lett. 105, 075701 (2010) [2] G. De Chiara, A. del Campo, G. Morigi, M. B. Plenio, A. Retzker, New J. Phys. 12, 115003 (2010) [3] A. del Campo, T. W. B. Kibble, W. H. Zurek, J. Phys.: Condens. Matter, 2013 (accepted). [4] K. Pyka, J. Keller, H. L. Partner, R. Nigmatullin, T. Burgermeister, D.-M. Meier, K. Kuhlmann, A. Retzker, M. B. Plenio, W. H. Zurek, A. del Campo, T. E. Mehlstäubler, arXiv:1211.7005. 28. Measurement-based quantum computation is contextualRaouf Dridi. Co-author: Robert Raussendorf, University of British Columbia, Department of Physics and Astronomy, 6224 Agricultural Road, Vancouver, BC, V6T 1Z1 Canada (Session 3 : Thursday from 5:00 - 7:00) Abstract. Anders and Browne [1] have converted a specific (state dependent) proof of the Kochen-Specker Theorem [2] due to Mermin [3] into a measurement based quantum computation (MBQC). Here we show that any measurement-based quantum computation (with two settings and two outcomes per measurement) which deterministically computes a nonlinear Boolean function is contextual. The result continues to hold for slightly probabilistic computations. Furthermore, building on [4], we use the language of Grothendieck topologies and sheaves on sites to describe contextuality in quantum mechanics and its role in MBQC. In this framework, Mermin's simple proof of Kochen-Specker theorem is captured nicely and quickly as an amalgamation problem. [1] J. Anders and D.E. Browne, Phys. Rev. Lett. 102, 050502 (2009). [2] S. Kochen, and E.P. Specker, J. Math. Mech. 17, 59 (1967). [3] N. D. Mermin, Rev. Mod. Phys. 65, 803 (1993). [4] S. Abramsky and A. Brandenburger, New J. Phys 13 (2011) 113036. 29. Direct-to-Toffoli Magic-state DistillationBryan Eastin, Northrop Grumman Corporation (Session 3 : Thursday from 5:00 - 7:00) Abstract. In recently proposed quantum computing architectures, approximately 90% of the required resources are consumed during the distillation of single-qubit magic-states for use in performing Toffoli gates. I describe how the overhead for magic-state distillation can be reduced by merging distillation with the implementation of Toffoli gates. The resulting routines distill single-qubit magic-states directly to Toffoli ancillae, each of which can be used without further magic to perform a Toffoli gate. 30. Graph Equitable Partitioning in Quantum Many-Body PhysicsDavid Feder, University of Calgary (Session 7c : Friday from 4:00 - 4:30) Abstract. The Hamiltonian for bosonic and fermionic particles hopping on lattices can be interpreted as the adjacency matrix of an undirected, weighted graph, usually with self-loops. The properties of these quantum many-body systems can therefore be analyzed in terms of graph theory. For example, the simple graph for non-interacting distinguishable particles is the Cartesian product of each particle's adjacency matrix; if these particles become indistinguishable, the graph 'collapses' via a graph equitable partition. Under various circumstances, equitable partitioning can allow for a more efficient determination of the eigenstates (and therefore the properties) of physically interesting quantum many-body systems. I will focus in particular on the ground states of the Bose and Fermi Hubbard models. 31. Adiabatic Quantum Computation with Rydberg AtomsAndrew Ferdinand, University of New Mexico (Session 3 : Thursday from 5:00 - 7:00) Abstract. We are developing, both theoretically and experimentally, a neutral atom qubit approach to adiabatic quantum computing (AQC). The approach uses an array of trapped Cs atoms with the qubits encoded in hyperfine ground state manifold of each atom. The entangling mechanism between qubits is mediated through the electric-dipole coupling of highly excited Rydberg states. With the laser fields off resonant from a Rydberg state, the ground state of the atoms are dressed with the Rydberg state and allow a continuous tunable interaction between qubits. Rydberg dressing of the ground states in conjunction with well developed single atom manipulation techniques allow all the necessary tools for our instance of AQC. We will develop this experimental capability to generate a two-qubit adiabatic evolution aimed specifically toward demonstrating quantum annealing in an two-spin Ising spin chain as a proof of principle experiment. Studying this two-qubit problem will test the immunity of our approach to AQC from noise processes in the control interactions as well as dissipation mechanisms associated with the trapping. We are developing our theoretical and experimental capabilities through key collaborations with the University of Wisconsin and the University of New Mexico. 32. Minimax quantum tomography: the ultimate bounds on accuracyChris Ferrie, Center for Quantum Information and Control, University of New Mexico (Session 7a : Friday from 4:30 - 5:00) Abstract. There are many methods for quantum state tomography (e.g., linear inversion, maximum likelihood, Bayesian mean...). But none of them is clearly "the most accurate" for data of finite size N. Even the upper limits on accuracy are as yet unknown, which makes it difficult to say that a given method is "accurate enough". We address this problem here by (i) calculating the minimum achievable error for single-qubit tomography with N Pauli measurements, (ii) finding "minimax" estimators that achieve this bound, and (iii) comparing the performance of known estimators. 33. Continuous measurement procedures via weak probe interactionsJan Florjanczyk, University of Southern California (Session 3 : Thursday from 5:00 - 7:00) Abstract. It is known that given any measurement, one can construct a sequence of weak measurements that converge to it without the use of ancilla (Oreshkov, Brun, '05). This procedure relies on constructing a 1-dimensional random walk from the weak measurement operators where the ends of the walk converge to the two strong measurement operators desired. We study possible realizations of a such a procedure when the weak measurement is effectuated via weak interaction of a probe with the system in question. We give restrictions on the interaction Hamiltonians that yield such a random walk via differential conditions on the (weak measurement) step operators. We also study, in detail, the case where the probe and system are both qubits which interact via a diagonal Hamiltonian. We describe the procedure for preparing and measuring the probe qubit which yields any diagonal measurement operators on the system qubit. Our results hold in the limit of continuous monitoring via the probe. 34. Atom trapping in the large-angle diffraction pattern behind a pinhole for quantum computingTravis Frazer, California Polytechnic State University, San Luis Obispo (Session 3 : Thursday from 5:00 - 7:00) Abstract. We are seeking to solve one of the few remaining problems in the field of neutral atom quantum computing, the issue of scalability. To do this, we plan to utilize the diffraction pattern of laser light shining through an array of pinholes. The diffraction pattern of each pinhole consists of localized bright and dark spots, which we have previously shown computationally to be effective dipole traps for neutral atoms. We propose to bring the atoms together and apart by changing the angles of incidence of two incoming laser beams. We are currently investigating both experimentally and computationally how the diffraction pattern changes for large angles of incidence, measuring the projection of the diffraction pattern, and building an experimental setup to physically implement these traps. We will present the computational and experimental results of our work. This work was performed in collaboration with Danielle May, Sara Monahan, David Roberts, Jason Schray, Glen D. Gillen, and Katharina Gillen-Christandl (PI). We acknowledge helpful discussions with Thomas D. Gutierrez, Ivan H. Deutsch, and Marianna Safronova. This work was supported by the National Science Foundation Grant No. PHY-0855524. 35. Thermodynamics and Quantum Correlations in Trapped Ion CrystalsManuel Gessner, University of California, Berkeley (Session 3 : Thursday from 5:00 - 7:00) Abstract. Crystals of trapped ions exhibit a broad variety of physical phenomena ranging from fundamental quantum effects with applications for quantum information theory to mesoscopic physics at the border to the classical regime. In our current experiments we are investigating the melting dynamics of larger ion crystals and the distribution and transport of energy in such systems. In another experiment in the quantum regime, we are aiming at detecting the signatures of nonclassical system-environment correlations in the dynamics of an open quantum system. We present a theoretical scheme which does not require control over the environment and that can be carried out by local operations on the open system only. 36. Recovering quantum secrets via classical channelsVlad Gheorghiu, Institute for Quantum Information Science at the University of Calgary (Session 3 : Thursday from 5:00 - 7:00) Abstract. Quantum secret sharing is an important multipartite cryptographic protocol in which a quantum state (secret) is shared among a set of n players. The secret is distributed in such a way that it can only be recovered by certain authorized subsets of players acting collaboratively. The recovery procedure assumes that all players are interconnected through quantum channels, or, equivalently, that the players are allowed to perform non-local quantum operations. However, for practical applications, the consumption of quantum communication resources such as entanglement or quantum channels needs to minimized. We provide a novel scheme in which quantum communication is replaced by local operations and classical communication (LOCC). Our protocol is based on embedding a classical maximum distance separable (MDS) code into a quantum error correcting code and employing the properties of the latter. Our scheme is appealing for real-world scenarios where the implementation of two-qubit gates is challenging. We illustrate the results by simple examples. Our methods constitute a first step towards attacking the important problem of decoding quantum error correcting codes by LOCC. *Collaboration with Barry C. Sanders. We acknowledge support from the Natural Sciences and Engineering Research Council (NSERC) of Canada and from Pacific Institute for Mathematical Sciences (PIMS).37. Linear Density Matrix Estimation from Homodyne Measurements: Uncertainty ComparisonScott Glancy, National Institute of Standards and Technology (Boulder) (Session 3 : Thursday from 5:00 - 7:00) Abstract. co-authors: Katelyn Weber and Emmanuel Knill In the 1990s, researchers developed linear estimators of photon number basis density matrix elements from homodyne detection data. This estimator uses a "pattern function" of the measured quadrature / phase pair, where the expectation value of the pattern function is equal to the desired density matrix element. Thus the estimate is linear and unbiased, but may result in unphysical density matrix estimates. Because the estimate is linear, we can use Hoeffding's Inequality to give uncertainty bounds. In this poster, we revisit the pattern function estimator and compare its results with the maximum likelihood estimates. We find that there exists a trade-off: the maximum likelihood estimates have lower variance but higher bias, which makes error difficult to quantify, while the pattern function estimates have higher variance but low bias, which allows for easy quantification of error. The pattern function estimates require much less computation and may be advantageous when computing power is limited but a large data set is available. 38. Robust quantum gates via sequential convex programmingMatthew Grace, Sandia National Laboratories (Session 3 : Thursday from 5:00 - 7:00) Abstract. Resource tradeoffs can often be established by solving an appropriate robust optimization problem for a variety of scenarios involving constraints on optimization variables and uncertainties. Using an approach based on sequential convex programming, we demonstrate that a substantial fidelity robustness is obtainable against uncertainties while simultaneously using limited resources of control amplitude and bandwidth. What is required is a specific knowledge of the range and character of the uncertainties, a process referred to in the control theory literature as "uncertainty modeling." Using a general one-qubit model for illustrative simulations of a controlled qubit, we generate robust controls for a universal gate set. Our results demonstrate that, even for this simple model, there exist a rich variety of control design possibilities. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 39. Improved approximation of realistic errors and its effect on quantum error-correcting circuitsMauricio Gutierrez, Georgia Institute of Technology (Session 3 : Thursday from 5:00 - 7:00) Abstract. The Gottesman-Knill theorem allows for the efficient classical simulation of stabilizer circuits. Although not enough for universal quantum computation, these circuits can give important insights on the performance of stabilizer-based error codes and correction schemes. Errors in these circuits are commonly modeled as depolarizing channels by inserting Pauli gates randomly throughout the circuit [1]. In previous work we have proposed expanding this error model to include all operations allowed within the stabilizer formalism, namely Clifford gates and measurements in the Pauli bases followed by conditional operations. The latter addition allows us to simulate non-unital channels and to better approximate errors due to spontaneous emission [2]. Here we present our work examining if the xpanded error model still holds a considerable improvement over the depolarizing channels in the context of whole quantum error-correcting circuits. We compare the performance of several error-correcting procedures in the presence of realistic error channels with their performance in the presence of their approximate error channels. These results will show if the improvement in error approximation at the physical layer yields substantial improvements in the precision of the error at the logical level. [1] A.M. Steane, Phys. Rev. A 68, 042322 (2003) [2] M. Gutierrez, L. Svec, A. Vargo, K.R. Brown. arXiv:1207.0046 40. Transforming AKLT-like states to Graph-States (universal resources for measurement based quantum computation)Poya Haghnegahdar, University of British Columbia (Session 3 : Thursday from 5:00 - 7:00) Abstract. Finding (physical) states which can serve as universal resources for measurement-based-quantum-computation (MBQC) is one of challenges of implementation for this model of quantum computing. Recently, Wei et al. have shown that the AKLT state on a 2-D Honeycomb lattice (HC) can be used as a universal resource for MBQC. This is done by observing that a typical 2-D HC lattice can be transformed (encoded) into a graph-state, which is then known to be a universal resource. The method that is used to perform this transformation however, is a specific procedure, which nonetheless need not be unique or in any way intended to be special. In a recent work, Darmawan et. al. have shown that using the same method, an entire phase of matter around the AKLT point can be transformed into useful graph-states. We expand upon these works by presenting a generalization of the previously used method that can be applied to AKLT-like states of any spin, in any spatial dimension (the present method only works for spin <=3/2). That is, we produce the map between the question of universality to a percolation problem for all such cases. In addition we investigate the robustness of this method in the presence of a particular class of noise. 41. Adiabatic Quantum Computation with Neutral CesiumAaron Hankin, University of New Mexico (Session 11 : Saturday from 4:00 - 4:30) Abstract. We are implementing a new platform for adiabatic quantum computation (AQC) [1] based on trapped neutral atoms whose coupling is mediated by the dipole-dipole interactions of Rydberg states. Ground state cesium atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism [2,3], thereby providing the requisite entangling interactions. As a benchmark we study a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model. [1] E. Farhi, et al. Science 292, 472 (2000) [2] S. Rolston, et al. Phys. Rev. A, 82, 033412 (2010) [3] T. Keating, et al. arXiv:1209.4112 (2012) 42. Surface studies for reduction of anomalous heating in ion trapsDustin Hite, National Institute of Standards and Technology (Session 3 : Thursday from 5:00 - 7:00) Abstract. Motional heating of trapped ions is a major obstacle to their use as quantum bits in a scalable quantum information processor. The detailed physical origin of this heating is not well understood, but experimental evidence suggests that it is caused by electric-field noise emanating from the surface of the trap electrodes. In this work, we detail our efforts to implement surface science techniques to help elucidate the origin of this problem, and to mitigate its effects. We find that an in-situ electrode-cleaning treatment of Ar-ion-beam bombardment results in a room-temperature heating rate that is reduced by more than two orders of magnitude, surpassing the performance of many cryogenic traps. We also report findings that in-situ evaporation of gold films on surface-contaminated electrodes does not reduce the heating rate, due to a growth mode that leaves the contaminants exposed at the surface. Finally, we detail progress of a novel, LIGA-fabricated, stylus ion trap that is engineered for single-ion probing of proximal surfaces, allowing for quick-turnaround heating-rate measurements from surfaces of various materials systems. This work was supported by IARPA, ARO contract No. EAO139840, ONR, and the NIST Quantum Information Program. *Collaborators (in alphabetical order): C. L. Arrington, E. Baca, K. R. Brown, J. J. Coleman, Y. Colombe, P. S. Finnegan, A. E. Hollowell, R. Jordens, J. D. Jost, D. Leibfried, K. S. McKay, D. P. Pappas, A. M. Rowen, U. Warring, A. C. Wilson, and D. J. Wineland. 43. A family of finite geometry codes in quantum key expansionKung-Chuan Hsu, University of Southern California (Session 3 : Thursday from 5:00 - 7:00) Abstract. Quantum key distribution (QKD) generates a common secret key to be securely shared between two distant parties. With the aid of an entanglement-assisted quantum error correcting code (EAQECC), QKD can be made to expand a common key rather than to generate one, in which case the process is known as quantum key expansion (QKE). Based on good EAQECCs, the performance of QKE is judged by the key rate, which is the rate of key expansion. In our work, we examined closely the families of codes constructed from finite geometry (FG), especially those with low density parity check (LDPC) matrices, and their use in QKE. We simulated QKE with one set of FG LDPC codes where the noise model is a depolarizing channel, and we observed that the performance is highly correlated with the block error rates of the codes. As a result, we proposed an improved version of the QKE protocol. Based on the simulation of QKE with this new protocol, we selected the codes, which are from the set of FG LDPC codes considered, that perform well for various channel error regions. 44. Scalable Quantum Networking of Trapped Ion QubitsIsmail Inlek, Joint Quantum Institute, University of Maryland (Session 3 : Thursday from 5:00 - 7:00) Abstract. Trapped atomic ions are standard qubits for the production of entangled states for applications in QIS and metrology. Trapped ions can exhibit very long coherence times, while strong local interactions can be gated by external fields for the operation of entangling quantum logic gates. However, transferring quantum information over remote distances in a scalable fashion relies on the juxtaposition of fast ion/photonic interfaces with local gate operations. We report progress on these fronts with an experiment that combines remote and local entanglement protocols between three ions in two separate traps for the generation of both local and remote correlations. In related work, we are utilizing fast imaging optics to collect photons from trapped ions and push towards 10-100 Hz entangling rates between distant trapped ion qubits using a two-photon interference protocol. Importantly, this is several times faster than the observed coherence times of the qubits, a prerequisite for scaling to larger networks. These developments hold promise for scaling trapped ion qubits for applications in quantum communication and computation networks. This work was supported by grants from the U.S. Army Research Office with funding from IARPA, the DARPA OLE program, and the MURI Hybrid Quantum Circuits program; and the NSF Physics Frontier Center at JQI. 45. Quantum many-body problems for identical particles: |