Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session J4: Quantum Information Theory |
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Chair: Ivan Deutsch, University of New Mexico Room: 554AB |
Wednesday, May 25, 2016 2:00PM - 2:12PM |
J4.00001: A loophole-free Bell test and the route to larger quantum networks Andreas Reiserer, Bas Hensen, Hannes Bernien, Anaïs Dréau, Norbert Kalb, Machiel Blok, Tim Taminiau, Ronald Hanson The nitrogen-vacancy (NV) center in diamond gives access to few-qubit nuclear-spin registers with exceptional coherence properties. Entanglement between remote registers can be established via a joint measurement of single photons that are each entangled with the electron spin of one NV center. The entanglement protocol is thus probabilistic but heralded, which has allowed us to perform the first loophole-free test of Bell’s inequality using two NV centers at a distance of 1.3km. Extending the size of the network requires control over additional qubits at each node. To this end, we use nuclear spins that are controlled via the hyperfine interaction with the electronic spin. I will present our recent experimental results, where we keep a qubit locally in a single nuclear spin or in a decoherence-protected two-spin state while applying a sequence of optical pulses on the electronic spin that generates remote entanglement. Our results open perspectives toward the purification of remote entanglement and toward larger quantum networks. [Preview Abstract] |
Wednesday, May 25, 2016 2:12PM - 2:24PM |
J4.00002: Physical randomness sources for loophole-free Bell tests Morgan W. Mitchell We describe the strategy and physics used to select unpredictable measurement settings in the loophole-free Bell tests reported in [Hensen et al. Nature 2015, Giustina et al. PRL 2015, and Shalm et al. PRL 2015]. We demonstrate direct measurements of laser phase diffusion, a process driven by spontaneous emission, rigorous bounds on the effect of other, less-trusted contributions, and exponential predictability reduction by randomness extraction. As required for the cited experiments, we show the six-sigma bound for the predictability of the basis choices is below 0.001{\%}. C. Abellan et al, PRL 2015. [Preview Abstract] |
Wednesday, May 25, 2016 2:24PM - 2:36PM |
J4.00003: Highly efficient Bell state purification and GHZ preparation and purification Stefan Krastanov, Liang Jiang We investigate novel protocols for entanglement purification with Bell states. Employing genetic algorithms for the design of the purification circuit, we obtain shorter circuits giving higher success rates and better final fidelities than what is available in the literature. We generalize these circuits in order to prepare GHZ states from Bell pairs and to subsequently purify these GHZ states. We provide new threshold estimates for codes using these GHZ states for fault-tolerant stabilizer measurements. [Preview Abstract] |
Wednesday, May 25, 2016 2:36PM - 2:48PM |
J4.00004: A Narrow-Linewidth Atomic Line Filter for Free Space Quantum Key Distribution under Daytime Atmospheric Conditions Justin Brown, David Woolf, Joel Hensley Quantum key distribution can provide secure optical data links using the established BB84 protocol, though solar backgrounds severely limit the performance through free space. Several approaches to reduce the solar background include time-gating the photon signal, limiting the field of view through geometrical design of the optical system, and spectral rejection using interference filters. Despite optimization of these parameters, the solar background continues to dominate under daytime atmospheric conditions. We demonstrate an improved spectral filter by replacing the interference filter ($\Delta\nu\sim$50 GHz) with an atomic line filter ($\Delta\nu\sim1$ GHz) based on optical rotation of linearly polarized light through a warm Rb vapor. By controlling the magnetic field and the optical depth of the vapor, a spectrally narrow region can be transmitted between crossed polarizers. We find that the transmission is more complex than a single peak and evaluate peak transmission as well as a ratio of peak transmission to average transmission of the local spectrum. We compare filters containing a natural abundance of Rb with those containing isotopically pure $^{87}$Rb and $^{85}$Rb. A filter providing $>95\%$ transmission and $\Delta\nu\sim$1.1 GHz is achieved. [Preview Abstract] |
Wednesday, May 25, 2016 2:48PM - 3:00PM |
J4.00005: Statistical Quadrature Evolution for Continuous-Variable Quantum Key Distribution Laszlo Gyongyosi, Sandor Imre We propose a statistical quadrature evolution (SQE) method for multicarrier continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD protocol utilizes Gaussian subcarrier quantum continuous variables (CV) for information transmission. The SQE framework provides a minimal error estimate of the quadratures of the CV quantum states from the discrete, measured noisy subcarrier variables. We define a method for the statistical modeling and processing of noisy Gaussian subcarrier quadratures. We introduce the terms statistical secret key rate and statistical private classical information, which quantities are derived purely by the statistical functions of our method. We prove the secret key rate formulas for a multiple access multicarrier CVQKD. The framework can be established in an arbitrary CVQKD protocol and measurement setting, and are implementable by standard low-complexity statistical functions, which is particularly convenient for an experimental CVQKD scenario. [Preview Abstract] |
Wednesday, May 25, 2016 3:00PM - 3:12PM |
J4.00006: Robust quantum state transfer with suppressed parametric noise Mengzhen Zhang, Changling Zou, Liang Jiang For opto-electro-mechanical transducers, there are undesirable parametric processes that introduce parametric noise, which will limit the fidelity of the transferred quantum state \footnote{R. W. Andrews, R. W. Peterson, T. P. Purdy, K. Cicak, R. W. Simmonds, C. A. Regal & K. W. Lehnert, Nature Physics \textbf{10}, 321-326 (2014)}. To overcome this imperfection, we propose a quantum state transfer scheme with squeezed input states and measurement dependent compensation to eliminate the parametric noise from the quantum state transfer. Besides parametric noise, we also investigate the sensitivity of our scheme to thermal noise, signal frequency detuning and imperfect impedance matching, and show a good quantum state fidelity and applicability to quantum state transfer. [Preview Abstract] |
Wednesday, May 25, 2016 3:12PM - 3:24PM |
J4.00007: Realizing quantum advantage without entanglement in single-photon states Alejandra Maldonado Trapp, Pablo Solano, Anzi Hu, CHARLES W. CLARK Quantum discord expresses quantum correlations beyond those associated with entanglement.\footnote{K Modi, {\em et al., Rev. Mod. Phys. } \bf{84}, 1655 (2012)}. Although it has been extensively studied theoretically, quantum discord has yet to become a standard tool in experimental studies of correlation. We propose a class of experiments in which quantum correlations are present in the absence of entanglement, and are best understood in terms of quantum discord.. These utilize X-states of two qubits, which correspond to the polarization and the optical path of a single photon within a Mach-Zehnder interferometer. We show how to produce states with diverse measures of discord and entanglement, including the case of discord without entanglement. With these states we show how a classical random variable $K$ can be encoded by Alice and decoded by Bob. Using our previous results \footnote{A. Maldonado-Trapp, {\em et al., Quantum Inf. Process} \bf{14} 1947 (2015)} we analytically study the correlations between the spin and path qubits and its relation with the information about $K$ that can be decoded by Bob using local measurements with or without two-qubit gate operations.\footnote{M. Gu, {\em et al., Nature Phys. }\bf{8}, 671 (2012)} [Preview Abstract] |
Wednesday, May 25, 2016 3:24PM - 3:36PM |
J4.00008: Universal holonomic quantum computing with cat-codes Victor V. Albert, Chi Shu, Stefan Krastanov, Chao Shen, Ren-Bao Liu, Zhen-Biao Yang, Robert J. Schoelkopf, Mazyar Mirrahimi, Michel H. Devoret, Liang Jiang Universal computation of a quantum system consisting of superpositions of well-separated coherent states of multiple harmonic oscillators can be achieved by three families of adiabatic holonomic gates. The first gate consists of moving a coherent state around a closed path in phase space, resulting in a relative Berry phase between that state and the other states. The second gate consists of “colliding” two coherent states of the same oscillator, resulting in coherent population transfer between them. The third gate is an effective controlled-phase gate on coherent states of two different oscillators. Such gates should be realizable via reservoir engineering of systems which support tunable nonlinearities, such as trapped ions and circuit QED. [Preview Abstract] |
Wednesday, May 25, 2016 3:36PM - 3:48PM |
J4.00009: Fidelity of adiabatic holonomic quantum gates Vladimir Malinovsky, Sergey Rudin During last few years non-Abelian geometric phases are attracting increasing interest due to possible experimental applications in quantum computation. Here we discuss universal set of holonomic quantum gates using the geometric phase that the qubit wave function acquires after a cyclic evolution. The proposed scheme utilizes ultrafast pulses and provides a possibility to substantially suppress transient population of the ancillary states. Fidelity of the holonomic quantum gates in the presence of dephasing and dissipation is discussed. Example of electron spin qubit system in the InGaN/GaN, GaN/AlN quantum dot is considered in details. [Preview Abstract] |
Wednesday, May 25, 2016 3:48PM - 4:00PM |
J4.00010: Exploiting Symmetry for Quantum Error Suppression Yunseong Nam, Reinhold Bl\"umel In light of recent experimental progress in quantum computing, the time is ripe to discuss quantum computer hardware optimization. Taking the digital/analog hybrid nature of quantum computers into account, choosing a proper processor architecture for a given quantum algorithm becomes crucial in making quantum computing a practical reality. As a first step in this direction, we investigate the robustness of quantum adders with respect to naturally occurring hardware defects and errors. In particular, we compare the robustness of the ripple-carry adder to that of the quantum Fourier adder. We show that, surprisingly, when used in Shor's algorithm, the quantum Fourier adder may well be more robust than the ripple-carry adder. We present a noise suppression scheme, called symmetric noise, applicable to the quantum Fourier architecture, that, measured in terms of fidelity, results in an order-of-magnitude performance boost. [Preview Abstract] |
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