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 K4: Trapped Ion Quantum Information |
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Sponsoring Units: GQI Chair: Wes Campbell, University of Maryland Room: Regency Ballroom |
Thursday, May 27, 2010 10:30AM - 10:42AM |
K4.00001: Multiqubit Decoherence in Ion-trap Quantum Computation Thomas Monz, Philipp Schindler, Julio T. Barreiro, Michael Chwalla, Bill Coish, Markus T. Hennrich, Rainer Blatt We will report on the realisation of high-fidelity Schroedinger- Cat states with more than six qubits in a string of $^{40}$Ca$^ {+}$ ions stored in a linear ion trap. We achieved fidelities with the target states exceeding 95\% for up to four ions and 88\% for six ions. These high fidelities allow to investigate decoherence of highly entangled quantum states in the presence of collective dephasing, the predominant source of decoherence in ion-trap based and other physical realizations of quantum computation. Assuming the noise to be Gaussian and stationary, we derive and experimentally confirm a model that predicts an exponential decay of the state fidelity that scales as $N^2$ where $N$ is the number of qubits. Such a scaling behaviour has severe effects on quantum computation and related fields, such as metrology. [Preview Abstract] |
Thursday, May 27, 2010 10:42AM - 10:54AM |
K4.00002: Near field quantum control of trapped ions Christian Ospelkaus, Kenton R. Brown, Jason M. Amini, Dietrich Leibfried, David J. Wineland We report the near-field manipulation of trapped-ion qubits using oscillating magnetic fields produced by currents in a microfabricated surface-electrode trap. We trap $^{25}$Mg$^+$ ions at a distance of 30 $\mu$m from a planar gold surface. On a first-order magnetic-field insensitive hyperfine transition at 21.3 mT, we observe $\pi$ times for single-qubit rotations of less than 20 ns, nine orders of magnitude faster than the coherence time observed on similar transitions. The small distance of the ion from the surface leads to the presence of a sizeable gradient of the oscillating magnetic field, which is used to drive motional sideband transitions. For this purpose, it is desirable to produce an oscillating magnetic field gradient and a zero magnetic field at the mean ion position. We describe a technique to achieve this configuration and report the observation of motional sideband transitions on one-ion and two-ion normal modes driven by microwave fields. We also discuss steps towards the realization of a two-qubit entangling logic gate. [Preview Abstract] |
Thursday, May 27, 2010 10:54AM - 11:06AM |
K4.00003: Private random numbers produced by entangled ions and certified by Bell's theorem David Hayes, Dzmitry Matsukevich, Peter Maunz, Chris Monroe, Steven Olmschenk It has been shown that entangled particles can be used to generate numbers whose privacy and randomness are guaranteed by the violation of a Bell inequality [1,2]. The authenticity of the bit stream produced is guaranteed when the system used can close the detection loophole and when the entangled particles are non-interacting. We report the use of remotely located trapped ions with near perfect state detection efficiency as a private random number generator. By entangling the ions through photon interference and choosing the measurement settings using a pseudo-random number generator, we measure a CHSH correlation function that is more than seven standard deviations above the classical limit. With a total of 3016 events, we are able to certify the generation of 42 new random numbers with 99{\%} confidence. [1] S. Pironio et al.(submitted to Nature, arXiv:0911.3427) [2] Colbeck, R. PhD Dissertation (2007) [Preview Abstract] |
Thursday, May 27, 2010 11:06AM - 11:18AM |
K4.00004: Integrating Fiber Cavities and Ion Traps Tracy Northup, Birgit Brandst\"atter, Andreas Stute, Maximilian Harlander, Piet O. Schmidt, Rainer Blatt Trapping ions within fiber-based cavities offers several advantages for quantum computing. First, the fiber-coupled output mode of the cavities suggests the possibility of integrating multiple systems within a quantum network. Additionally, the small mode volume of such a system would allow us to reach the strong coupling regime of cavity QED, not yet achieved with single ions. We outline our efforts to access this regime with a new experiment using fiber-based mirrors, developed in collaboration with J. Reichel at ENS. We present results from measurements in which we approach trapped ions with an optical fiber in order to explore the effects of surface charges, and we discuss our characterization of high-finesse fiber cavities and plans for integration within a miniature Paul trap. [Preview Abstract] |
Thursday, May 27, 2010 11:18AM - 11:30AM |
K4.00005: Novel Ion Trap for Efficient Fluorescence Collection from Ion Qubits Gang Shu, Nathan Kurz, Matthew Dietrich, Shaw-Pin Chen, Boris Blinov Critical aspects of Trapped Ion Quantum Computation and Information such as qubit state readout and entanglement generation can directly benefit from improving the collection efficiency of ion fluorescence. By integrating a simple reflective optics to a linear Paul trap, we achieved a 10\% photon collection efficiency. To eliminate photon blocking due to the trap structure and to further increase the collection efficiency, we built a novel trap combining the reflective optical surface and RF electrode. While at least doubling the collection efficiency, the new trap enjoys the nice future of self-aligning with full electric/optical controlling. We expect to be able to efficiently couple the ion fluorescence photons into a single mode optical fiber for remote manipulation and entanglement of ions. [Preview Abstract] |
Thursday, May 27, 2010 11:30AM - 11:42AM |
K4.00006: Enhanced Light Collection from a Trapped Ion Using a Micromirror Integrated with Surface Trap Rachel Noek, Caleb Knoernschild, Taehyun Kim, Peter Maunz, True Merrill, Harley Hayden, C.S. Pai, Jungsang Kim Efficient collection of fluorescence from trapped atoms or ions is imperative for high speed, high fidelity quantum information processing. Using low f-number conventional collection optics, less than 7{\%} of light can be collected from a small field of view (FoV, $<$0.2mm). We add high numerical aperture micromirrors behind each point source, and image the reflected light from the micromirrors with a conventional f/2.55 imaging system and obtain a factor of 18 improvement in collection over the same system without the micromirrors. The FoV expands to 17.8 mm and the numerical aperture is limited by the micromirror behind the ion rather than the conventional optics. We used a fluorescent microbead mounted on a glass pipette and a custom fabricated 100 um diameter Al coated Si micromirror to demonstrate this principle. Micromirrors integrated with surface ion traps are currently under development for improved ion detection and FoV. [Preview Abstract] |
Thursday, May 27, 2010 11:42AM - 11:54AM |
K4.00007: Decoherence due to elastic Rayleigh scattering H. Uys, M.J. Biercuk, A.P. VanDevender, C. Ospelkaus, J.J. Bollinger, D. Meiser Off-resonant light scattering (spontaneous emission) is an important source of decoherence in many coherent control experiments. Typically one focuses on the effects of Raman scattering, in which an atomic state is changed by a single scattering event. We present theoretical and experimental studies of the decoherence of hyperfine ground-state superpositions due to \textit{elastic} Rayleigh scattering of off-resonant light. By a master equation technique we show that for a two-level superposition the elastic decoherence rate is the square of the difference between the two elastic scattering amplitudes. Thus, if the light detunings for the two states have opposite sign, the amplitudes interfere constructively and can result in a large decoherence rate. We calculate and measure the total decoherence rate for a superposition state of the valence electron spin in the ground state of $^{9}$Be$^{+}$ in a 4.5 T magnetic field. We find that for large ($\sim$20 GHz) detunings, decoherence due to elastic Rayleigh scattering can be 5 times larger than decoherence due to Raman scattering. This is in contrast with work\footnote{R. Ozeri, et al., PRL {\bf 95}, 030403 (2005)} at low magnetic field where decoherence was dominated by Raman scattering. [Preview Abstract] |
Thursday, May 27, 2010 11:54AM - 12:06PM |
K4.00008: Detection of Single Ion Spectra by Coulomb Crystal Heating Craig Clark, James Goeders, Yatis Dodia, C. Ricardo Viteri, Kenneth Brown Sympathetic Heating Spectroscopy (SHS) takes advantage of the Coulombic interaction between two trapped ions. SHS maps the information of the back action of the interrogating laser on the spectroscopy ion onto the control ion for measurement. SHS only requires Doppler cooling of the ions and measurement of the fluorescence. In this work, we use two individual isotopes of calcium: $^{40}$Ca$^{+}$ to cool the Coulomb crystal (control ion) and $^{44}$Ca$^{+}$ as the target spectroscopy ion. We demonstrate that it is possible to get spectroscopic information by heating the crystal through the spectroscopy ion and observing the changes in the fluorescence of the control ion as we re-cool the system .The resolution of the spectrum is limited by the accumulative stochastic heating mechanism. The main advantage of the SHS technique is that the read out is done on the control ion and not on the spectroscopy (heating) ion. Very low laser intensities are required to have a significant stochastic optical force that builds up very fast with the laser interaction time and affects dramatically the ions' trajectory. This results in a large Doppler shift of the control ion which can be observed in the re-cooling process. Potentially, SHS can become an effective tool to study dipole transitions that are weak or fall in regions of the electromagnetic spectrum where the sensitivity of detectors is marginal or non-existent. [Preview Abstract] |
Thursday, May 27, 2010 12:06PM - 12:18PM |
K4.00009: Thermalization and temperature distribution in a driven ion chain Guin-Dar Lin, Luming Duan We study thermalization and non-equilibrium dynamics in a dissipative quantum many-body system --- a chain of ions with two points of the chain driven by thermal bath under different temperature. Instead of a simple linear temperature gradient as one expects from the classical heat diffusion process, the temperature distribution in the ion chain shows surprisingly rich patterns, which depend on the ion coupling rate to the bath, the location of the driven ions, and the dissipation rates of the other ions in the chain. We discuss implementation issues and show these unusual temperature distribution patterns in the ion chain can be quantitatively tested through experimental observation. A direct application is continuous sympathetic cooling in a scalable trapped ion quantum computer. We demonstrate the architecture how the ion chain can be maintained cooled efficiently to guarantee high-fidelity computation. [Preview Abstract] |
Thursday, May 27, 2010 12:18PM - 12:30PM |
K4.00010: Micro-fabricated Surface Ion Traps for Quantum Computation Clark Highstrete, Matthew Blain, Kevin Fortier, Walter Gordy, Raymond Haltli, Shanalyn Kemme, Thomas Lindgren, David Moehring, Mark E. Smith, Daniel Stick, Chris Tigges We will present results of the design, operation, and performance of surface ion micro-traps fabricated at Sandia. Recent progress in the testing of the micro-traps will be highlighted, including successful motional control of ions and the validation of simulations with experiments. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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