Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session M5: Quantum Information Methods |
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Chair: Emily Edwards, JQI and University of Maryland Room: A705 |
Thursday, June 16, 2011 8:00AM - 8:12AM |
M5.00001: Experimental repetitive quantum error correction Julio T. Barreiro, P. Schindler, T. Monz, V. Nebendahl, D. Nigg, M. Chwalla, M. Hennrich, R. Blatt The computational power of a quantum processor can only be unleashed if errors during a quantum computation can be controlled and corrected for. Quantum error correction works if imperfections of quantum gate operations and measurements are below a certain threshold and corrections can be applied repeatedly. We have realized the first implementation of multiple quantum error correction steps for phase-flip errors on qubits encoded with trapped ions. Errors are corrected without measurement by a quantum feedback algorithm employing high-fidelity gate operations and a reset technique for the auxiliary qubits. Up to three consecutive consecutive correction steps are realized and the behavior of the algorithm for different noise environments is analyzed. [Preview Abstract] |
Thursday, June 16, 2011 8:12AM - 8:24AM |
M5.00002: Arbitrary Ultrafast Manipulation of a Trapped Ion Qubit Jonathan Mizrahi, Wesley C. Campbell, Crystal Senko, Chris Monroe We demonstrate ultrafast spin flips of a trapped ion, using pulses from a mode-locked laser to drive Raman transitions between hyperfine qubit levels [1]. The laser's large bandwidth and intensity allow an individual pulse to coherently transfer more than 50\% population in about 10 ps. Furthermore, the large intensity allows us to be far detuned from resonance, which makes spontaneous emission and AC Stark shift negligible. Complete control over the quantum state can be accomplished by splitting the pulse into two halves and varying the relative delay and intensity to drive x- or z-rotations of variable angle. This amounts to full SU(2) control of the qubit in tens of picoseconds. We plan to use this to implement proposals for motional gates which can be performed much faster than the trap period [2,3]. [1] W.C. Campbell et al., PRL 105, 090502 (2010). [2] J.J. Garcia-Ripoll et al., PRL 91, 157901 (2003). [3] L.-M. Duan, PRL 93, 100502 (2004). [Preview Abstract] |
Thursday, June 16, 2011 8:24AM - 8:36AM |
M5.00003: Fast Quantum Gates Using Dynamical and Geometrical Phase Vladimir Malinovsky, Patrick Hawkins, Svetlana Malinovskaya We propose and analyze an experimentally feasible scheme to design universal set of quantum gates utilizing dynamical and geometrical phases accumulated by a qubit during the excitation. Our scheme provides a possibility to employ strong femtosecond pulses while keeping all advantages of the Rabi solution regime. We design fast quantum gates (picosecond time scale) by choosing proper parameters of the chirped pulses as a way to control nonadiabatic coupling and to satisfy the adiabaticity conditions. We also demonstrate a possibility to control the dynamical and geometrical phases by controlling the relative phase between excitation pulses applied in the Raman configuration. Proposed Hadamard and phase-shift gates allow us to construct a universal set of single qubit gates by controlling the effective pulse area, relative phase and two-photon detuning. Implementation of a controlled-NOT gate based on the proposed excitation scheme is also discussed. [Preview Abstract] |
Thursday, June 16, 2011 8:36AM - 8:48AM |
M5.00004: Long-range quantum gates using external symmetry breaking Hendrik Weimer, Norman Yao, Chris Laumann, Mikhail Lukin We propose to use the process of symmetry breaking across a quantum phase transition to perform logical quantum operations between distant qubits. By adiabatically following the ground state from a disordered to an ordered phase we can create an effective interaction between the qubits. We derive general scaling relations and focus on a spin model with long-range interactions which exhibits a quantum phase transition from a paramagnet to a crystalline phase. We discuss possible experimental implementations with Rydberg atoms or nitrogen-vacancy centers in diamond. [Preview Abstract] |
Thursday, June 16, 2011 8:48AM - 9:00AM |
M5.00005: Quantum error correction of photon-scattering errors Nitzan Akerman, Yinnon Glickman, Shlomi Kotler, Roee Ozeri Photon scattering by an atomic ground-state superposition is often considered as a source of decoherence. The same process also results in atom-photon entanglement which had been directly observed in various experiments using single atom, ion or a diamond nitrogen-vacancy center. Here we combine these two aspects to implement a quantum error correction protocol. We encode a qubit in the two Zeeman-splitted ground states of a single trapped $^{88}Sr^+$ ion. Photons are resonantly scattered on the $S_{1/2}\rightarrow P_{1/2}$ transition. We study the process of single photon scattering i.e. the excitation of the ion to the excited manifold followed by a spontaneous emission and decay. In the absence of any knowledge on the emitted photon, the ion-qubit coherence is lost. However the joined ion-photon system still maintains coherence. We show that while scattering events where spin population is preserved (Rayleigh scattering) do not affect coherence, spin-changing (Raman) scattering events result in coherent amplitude exchange between the two qubit states. By applying a unitary spin rotation that is dependent on the detected photon polarization we retrieve the ion-qubit initial state. We characterize this quantum error correction protocol by process tomography and demonstrate an ability to preserve ion-qubit coherence with high fidelity. [Preview Abstract] |
Thursday, June 16, 2011 9:00AM - 9:12AM |
M5.00006: Photon Collection from a Trapped Ion in a Cavity T. Andrew Manning, Jonathan Sterk, Le Luo, Chris Monroe, Peter Maunz A micron-scale ion trap is integrated with a 2~mm Fabry-P\'erot cavity to enhance the spontaneous emission from a single trapped ytterbium ion. Exciting the atom from the side of the cavity with a near resonant laser beam, we measure the scattered emission rate from the fundamental, undriven cavity mode. We collect roughly 500 times more fluorescence compared to the expected free-space emission into the same solid angle subtended by the cavity mode. Progress towards a protocol for generating entanglement between the ion spin state and the output cavity photon polarization is presented, as well as a discussion of applying this method to improve the success probability of entangling remote ions [1,2]. \\[4pt] [1] L.-M. Duan and C. Monroe, \emph{Rev. Mod. Phys.} \textbf{82}, 1209 (2010) \\[0pt] [2]. J. D. Sterk, Ph.D. thesis, University of Michigan, Ann Arbor, Michigan (2011) [Preview Abstract] |
Thursday, June 16, 2011 9:12AM - 9:24AM |
M5.00007: Cluster state generation using long-range interactions Elena Kuznetsova, Tank Bragdon, Robin Cote, Susanne Yelin We propose and analyze generation of the cluster state with neutral atoms and polar molecules in optical lattices using long-range dipole-dipole and van der Waals interactions. The cluster state can be realized by performing a phase gate between pairs of neighboring atoms. A finite number of operations is required, making it easily scalable to a large number of qubits. We discuss the viability of the scheme with Rb and alkali dimers as examples. [Preview Abstract] |
Thursday, June 16, 2011 9:24AM - 9:36AM |
M5.00008: Efficient Sympathetic Cooling of Trapped Atomic Ions Grahame Vittorini, Craig Clark, Kenneth Brown A challenge of performing ion trap quantum computation with chains of ions is the heating of the trap vibrational modes. Trap heating can result in unwanted occupation of vibrational modes and a reduced fidelity for two ion gates. To combat this, specific ions within the chain can be tasked with cooling the entire chain via sympathetic cooling. The strength of the interaction between the cooling laser and cooling ions may have a significant effect on how efficiently the chain is sympathetically cooled. This interaction can be controlled via the intensity and detuning of the cooling beam as well as the time the cooling ions spend interacting with the cooling laser versus thermalizing with the ion chain. By using separate isotopes of Ca+, we can construct a chain of cooling and information ions with each isotope interacting with its resonant cooling laser independently. By adjusting the aforementioned interaction parameters and measuring the sideband spectrum of the information ions, we will be able to find the most efficient sympathetic cooling parameters. We will describe the experimental results so far as well as future related investigations. [Preview Abstract] |
Thursday, June 16, 2011 9:36AM - 9:48AM |
M5.00009: Single Motional Quantum Exchange between Independently Trapped Ions K.R. Brown, C. Ospelkaus, Y. Colombe, A.C. Wilson, D. Leibfried, D.J. Wineland The Coulomb coupling of ions in separate potential wells is a key feature of proposals to implement quantum simulation and could enable logic operations to be performed in a multi-zone quantum information processor without the requirement of bringing the ion qubits into the same trapping potential. It might also extend the capabilities of quantum logic spectroscopy to ions that cannot be trapped in the same potential well as the measurement ion, such as oppositely charged ions or even antimatter particles. We report recent results demonstrating tunable coupling of two $^{9}$Be$^{+}$ ions held in trapping potentials separated by 40 $\mu $m [1]. The ions are trapped 40 $\mu $m above the surface of a microfabricated planar trap with independently tunable axial frequencies of $\sim $4 MHz. The trap is cooled to 4.2 K with a helium bath cryostat to suppress anomalous heating and to extend the lifetime of ions from minutes to days. By preparing approximate motional number states with n=0 and n=1 in the respective wells, and tuning the confining wells into resonance, a single quantum of motion is exchanged between the ions in $\sim $200 $\mu $s. \\[4pt] [1] arXiv:1011.0473, accepted to \textit{Nature}. [Preview Abstract] |
Thursday, June 16, 2011 9:48AM - 10:00AM |
M5.00010: Adiabatic quantum computation with neutral atoms via the Rydberg blockade Krittika Goyal, Ivan Deutsch We study a trapped-neutral-atom implementation of the adiabatic model of quantum computation whereby the Hamiltonian of a set of interacting qubits is changed adiabatically so that its ground state evolves to the desired output of the algorithm. We employ the ``Rydberg blockade interaction,'' which previously has been used to implement two-qubit entangling gates in the quantum circuit model. Here it is employed via off-resonant virtual dressing of the excited levels, so that atoms always remain in the ground state. The resulting dressed-Rydberg interaction is insensitive to the distance between the atoms within a certain blockade radius, making this process robust to temperature and vibrational fluctuations. Single qubit interactions are implemented with global microwaves and atoms are locally addressed with light shifts. With these ingredients, we study a protocol to implement the two-qubit Quadratic Unconstrained Binary Optimization (QUBO) problem. We model atom trapping, addressing, coherent evolution, and decoherence. We also explore collective control of the many-atom system and generalize the QUBO problem to multiple qubits. [Preview Abstract] |
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