Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session B6: Quantum Information and Quantum Computing |
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Chair: Dietrich Leibfried, National Institute of Standards and Technology Room: Arboretum IV-V |
Wednesday, May 26, 2010 10:30AM - 10:42AM |
B6.00001: Using and Extending Randomized Benchmarks for Trapped-Ion Quantum Computing Adam Meier, Emanuel Knill Randomized benchmarking is a procedure that extracts a ``typical'' error probability for an experimental quantum computer. This number describes the failure rate of a typical gate in the middle of a long computation and is a worthwhile figure of merit for quantum control demonstrations. I will present a practical, systematic approach to randomized benchmarking using examples from planned experiments in ion traps. I will discuss ways to extend the data analysis to reveal information about individual gates. Finally, I will look at the simplifying assumptions made regarding the error models and randomness of the experimental gates and how they could be generalized. This work has been done in collaboration with K. Brown, D. Hanneke, and J. Home. [Preview Abstract] |
Wednesday, May 26, 2010 10:42AM - 10:54AM |
B6.00002: Microwave pulse driven quantum algorithms with ultracold polar molecules in an electric field Philippe Pellegrini, La\"etitia Bomble, Mich\`ele Desouter-Lecomte We theoretically investigated the possibility of running complex microwave pulse driven logical operations on a register of quantum bits (qubits) encoded in rovibrational levels of ultracold polar molecules in an electric field. Using optimal control theory, microwave pulses are designed to perform specific universal logic gates such as the controlled NOT or Toffoli gates. Simulations with highly polar molecules like NaCs or LiCs show that logic gates involving 2 or 3 qubits can be run in a time scale of a few tens of microseconds and with a fidelity as high as 99\%. The use of both the vibration and the rotation of the dimers facilitates the manipulation of the qubits and opens new possibilities for the realization of a scalable quantum computer. [Preview Abstract] |
Wednesday, May 26, 2010 10:54AM - 11:06AM |
B6.00003: Implementation of an attack scheme on a practical QKD system Antia Lamas-Linares, Qin Liu, Ilja Gerhardt, Vadim Makarov, Christian Kurtsiefer We report on an experimental implementation of an attack of a practical quantum key distribution system [1], based on a vulnerability of single photon detectors [2]. An intercept/resend-like attack has been carried out which revealed 100\% of the raw key generated between the legitimate communication partners. No increase of the error ratio was observed, which is usually considered a reliable witness for any eavesdropping attempt. We also present an experiment which shows that this attack is not revealed by key distribution protocols probing for eavesdroppers by testing a Bell inequality {[3]}, and discuss implications for practical quantum key distribution.\\[4pt] [1] I. Marcikic, A. Lamas-Linares, C. Kurtsiefer, Appl. Phys. Lett. 89, 101122 (2006); {[2]} V. Makarov, New J. Phys. 11, 065003 (2009); {[3]} A. Ling et al., Phys. Rev. A 78, 020301(R), (2008) [Preview Abstract] |
Wednesday, May 26, 2010 11:06AM - 11:18AM |
B6.00004: Environment-induced bound entanglement Julio T. Barreiro, P. Schindler, O. Guehne, T. Monz, M. Chwalla, V. Nebendahl, M. Hennrich, R. Blatt Entanglement, the most powerful physical resource for quantum information, has been conjectured to decay, under the influence of decoherence, into a seemingly unprofitable form, known as bound entanglement. Bound entangled states have several applications, but most importantly, they underline our understanding of multiparticle entanglement and its dynamics under decohering environments. Here, we present our experiments with trapped calcium ions showing the existence of bound entanglement in nature. By embedding an entangled and multipartite distillable quantum state of four qubits in a locally dephasing environment (via spontaneous decay), we observe a transition into full separability via bound entanglement. To our knowledge, our work is the first to experimentally explore such multiparticle entanglement dynamics. [Preview Abstract] |
Wednesday, May 26, 2010 11:18AM - 11:30AM |
B6.00005: Decoherence Effects in a Light Storage Experiment Jin Wang This investigation develops a model that shows the effects of decoherence originating from both dephasing and population relaxation on rubidium vapor in the EIT regime. This investigation quantifies the effect of decoherence on the large Faraday rotation, susceptibility, transmission, population and coherence relationships of the system. The model derived in this investigation is in excellent agreement with experimental results. The total decoherence rate for the experiment has been found by fitting the experimental data to the model. This investigation also includes a discussion of other types of experiments that this model could be adapted to such as Dipole Induced Transmission (DIT) and the detection of single atoms. [Preview Abstract] |
Wednesday, May 26, 2010 11:30AM - 11:42AM |
B6.00006: Coherence freeze in an optical lattice investigated via two-dimensional pump-probe spectroscopy Samansa Maneshi, Chao Zhuang, Christopher Paul, Luciano Cruz, Aephraim Steinberg Motivated by our observation of fast echo decay and a surprising coherence freeze, we have developed a two-dimensional pump-probe spectroscopy technique for vibrational states of ultracold $^{85}$Rb atoms in a 1D optical lattice to gain information on the memory dynamics of the system. In the 1D lattice, transverse motion of atoms through an inhomogeneous distribution of lattice depths gives rise to many frequency trajectories. We use pump-probe spectroscopy to characterize the probability distribution of these trajectories, and show that the inferred distribution, unlike a naive microscopic model of the lattice, correctly predicts the main features of the observed echo decay. Such techniques should be broadly useful for understanding (and subsequently correcting) decoherence in quantum information systems. [Preview Abstract] |
Wednesday, May 26, 2010 11:42AM - 11:54AM |
B6.00007: Telecom wavelength photons from a long-lived quantum memory Alexander G. Radnaev, Yaroslav O. Dudin, Ran Zhao, Stewart D. Jenkins, Alex Kuzmich, Brian Kennedy We report frequency up and down conversion of light between (telecom) 1367 nm and (rubidium) 795 nm wavelengths with efficiency in excess of 50{\%} using non-degenerate and non-collinear four-wave mixing in a cold rubidium vapor. We have integrated the conversion scheme with a long lived quantum memory and verified quantum correlations of the memory and telecom field by measuring the quality of retrieved single photons. [Preview Abstract] |
Wednesday, May 26, 2010 11:54AM - 12:06PM |
B6.00008: Fundamental bounds and performance tests for the storage or transmission of quantum light Norbert Lutkenhaus, Hauke Haseler, Nathan Killoran In advanced quantum communication protocols, we require the ability to store light in a way which preserves the imprinted quantum information, a task which cannot be done with classical protocols. We propose benchmarks based on the idea that a quantum communication experiment is successful only if it operates in a quantum regime, that is, it outperforms any classical transmission strategy. Current criteria suffer from a gap between theory, which typically prescribes testing using a continuous distribution of test states, and experiment, which can test only a finite set of states. Our benchmark approach avoids this. One of our new benchmarks is based on weak coherent states with just three phase settings and homodyne detection. This benchmark has optimal strength reaching that of the continuous set of test states and avoids the need of costly tomographic reconstruction of the output states. As further simplification, for phase- randomized lasers, one coherent test state is sufficient to implement our test. As an extension, we consider the problem of quantitative performance, providing estimates for quantum throughput of the tested devices. [Preview Abstract] |
Wednesday, May 26, 2010 12:06PM - 12:18PM |
B6.00009: Tailored State Preparation for Solid-State Quantum Memory Jingyun Fan, Elizabeth Goldschmidt, Sergey Polyakov, Sarah Beavan, Alan Migdall Rare earth ion-doped crystals are promising candidates for ensemble-based quantum memory because they are solid-state systems with narrow optical transitions and seconds-scale coherence times. We are using one such material, Pr3+:YSO, to generate single photons and implement a quantum memory protocol. A major challenge associated with rare earth ion-doped crystals is the large inhomogeneous broadening of the optical transition. We report experimental progress using spectral hole-burning techniques to create a narrow absorbing feature on a background emptied of absorbers that acts as an inhomogeneously narrow ensemble for quantum memory applications. We also describe a narrow spectral filter generated via spectral hole-burning that can separate fields a few MHz apart with 15 dB extinction. This filter is necessary due to the few MHz splitting of the hyperfine ground states that we use for the quantum memory. Finally, we develop a model of spectral hole-burning in rare earth ion-doped crystals and use it to perform a computational optimization of our state preparation scheme. We find that the optimal parameters of our spectral hole-burning sequence are experimentally accessible and flexible. [Preview Abstract] |
Wednesday, May 26, 2010 12:18PM - 12:30PM |
B6.00010: Light shift compensated quantum memories Yaroslav O. Dudin, Ran Zhao, Stewart D. Jenkins, Brian Kennedy, Alex Kuzmich Quantum telecommunication could provide secure long-distance data transfer. Direct transmission losses in optical fiber scale exponentially with distance. The quantum repeater protocol allows one to reach polynomial scaling of the communication rate with distance. The quantum repeater relies on long-lived quantum memory elements. Here we report on our recent progress in extending the lifetime of quantum memory based on an ensemble of cold rubidium atoms confined in an optical lattice. Previously observed coherence times ($\sim $ 7 ms) were limited by ac Stark broadening of the ground state hyperfine transition. Two different light shift compensation schemes based on two photon transitions and magnetically-dressed optical potentials are reported. We reach $\sim $1/3 second lifetimes for stored classical light pulses and similar values for single quanta. [Preview Abstract] |
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