Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J32: Quantum Computing in AMO Systems |
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Sponsoring Units: DAMOP GQI Chair: Dana Berkeland, Los Alamos National Laboratory Room: Colorado Convention Center 402 |
Tuesday, March 6, 2007 11:15AM - 11:27AM |
J32.00001: Super-fluid assisted quantum computation with group II atoms David Hayes, Satyan Bhongale, Ivan Deutsch We investigate the possibility of using super-fluid immersion in order to suppress diabatic transitions in a system governed by a time-dependent Hamiltonian. A simple model has been used to study the question where quantum information is stored in the nuclear spin of a group II atom which is trapped in a harmonic oscillator that is traveling at a constant velocity inside of a stationary BEC. While the motion of the trap acts to heat the atom in the trap to higher vibrational levels, the motion of the trapped atom creates excitations in the BEC and carries the energy away in the form of phonons and decreases the effective heating. [Preview Abstract] |
Tuesday, March 6, 2007 11:27AM - 11:39AM |
J32.00002: Interfacing Collective Atomic Excitations and Single Photons Jonathan Simon, Haruka Tanji, James Thompson, Vladan Vuletic A variety of quantum communication and computing schemes rely on the storage and transfer of single photonic excitations. We demonstrate generation, storage, and adiabatic transfer of such excitations, using ensembles of Cs atoms within a low finesse optical resonator as a storage medium. We explore theoretical and practical limitations on read-out, experimentally realizing a peak atomic-photonic conversion efficiency of .84(11). The storage in the system exhibits two doppler times, which can be understood in terms of long- and short- wavelength spin gratings simultaneously written into the atomic ensemble. We demonstrate cavity mediated transfer of a quantized atomic excitation between atomic ensembles within the same optical resonator. These results pave the way towards a practical single photon generation and storage apparatus, useful in quantum communication, computation, and beyond. This work was supported in parts by the NSF, DARPA, and ARO. [Preview Abstract] |
Tuesday, March 6, 2007 11:39AM - 11:51AM |
J32.00003: Anyonic Braiding in Optical Lattices Chuanwei Zhang, Vito Scarola, Sumanta Tewari, Sankar Das Sarma Topological quantum computation proposes to use braiding of collective excitations implanted in topologically protected coherent quantum states of many particles, as opposed to a single particle, to aid in or even perform quantum computation. Here we explicitly work out a realistic experimental scheme to create, braid and detect topological excitations in the Kitaev model built on a tunable robust system, a cold atom optical lattice. A key feature of topological excitations is their braiding statistics, how they behave when one excitation is taken around another. An observation of the non-trivial braiding statistics described in this Report would directly establish the existence of anyons, quantum particles which are neither fermions nor bosons. Demonstrating anyonic braiding statistics is tantamount to observing a new form of matter, topological matter. Once created, excitations in quantum topological matter, as opposed to delicate single particle quantum states, can provide a robust way to encode and manipulate quantum information. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:03PM |
J32.00004: Turning back time in the optical lattice: How to measure the fidelity of a quantum simulation. Fernando Cucchietti I show how to perform a Loschmidt echo (time reversal) in the Bose-Hubbard model implemented with cold bosonic atoms in an optical lattice. The echo is obtained by applying a linear phase imprint on the lattice and a change in magnetic field to tune the boson-boson scattering length through a Feshbach resonance. I discuss how the echo can measure the fidelity of the quantum simulation, and also the intensity of an external potential (e.g. gravity), or the critical point of the superfluid-insulator quantum phase transition. [Preview Abstract] |
Tuesday, March 6, 2007 12:03PM - 12:15PM |
J32.00005: Characterization of scalable ion traps for quantum computation R.J. Epstein, J.J. Bollinger, D. Leibfried, S. Seidelin, J. Britton, J.H. Wesenberg, N. Shiga, J.M. Amini, R.B. Blakestad, K.R. Brown, J.P. Home, W.M. Itano, J.D. Jost, C. Langer, R. Ozeri, D.J. Wineland We discuss the experimental characterization of several scalable ion trap architectures for quantum information processing. We have developed an apparatus for testing planar ion trap chips \footnote{S. Seidelin \emph{et al.}, Phys. Rev. Lett. \textbf{96}, 253003 (2006).}$^,$\footnote{ J. Kim, \emph{et al.}, Quantum Inf. Comput. \textbf{5}, 515 (2005).}, which features: a standardized chip carrier for ease of interchanging traps, a single-laser Raman cooling scheme, and photo-ionization loading of Mg$^+$ ions. The primary benchmark for a given trap is the heating rate of the ion motional degrees of freedom, which can reduce multi-ion quantum gate fidelities. As the heating rate depends on the ion trap geometry and materials, our testing apparatus allows for efficient iteration and optimization of trap parameters. With the recent ability to fabricate planar traps with sufficiently low heating rates for quantum computation $^2$, we describe current results on the simulation and fabrication of planar traps with multiple intersecting trapping zones for versatile ion choreography. [Preview Abstract] |
Tuesday, March 6, 2007 12:15PM - 12:27PM |
J32.00006: Entangling operations and rapid measurement of clock-state qubits in Yb or Sr for quantum information processing Rene Stock, Nathan S. Babcock, Barry C. Sanders The optical clock-transitions in Yb and Sr are prime candidates for encoding qubits for quantum information processing applications. Electric dipole one- and two-photon transitions between the long-lived $^1$S$_0$ and $^3$P$_0$ states are angular momentum and parity forbidden, respectively. This results in a highly desirable low decoherence rate. In this work, we investigate the challenges involved in using these prime candidates. We devise entangling operations for Yb and Sr atoms trapped in optical microtraps, as well as determine the feasibility of rapid qubit rotation and measurement of qubits encoded in this desirable low-decoherence clock transition. We propose ultracold collisions for entangling operations and a recoil-free three-photon transition [1] for fast rotation of qubits, followed by ultrafast readout via resonant multiphoton ionization. The rapid control of atomic qubits is crucial for high-speed synchronization of quantum information processors, but is also of interest for tests of Bell inequalities. We investigate rapid measurement of clock-state qubits in the context of a Bell inequality test that avoids the detection loophole in spacelike separated entangled qubits. [1] T. Hong, C. Cramer, W. Nagourney, E. N. Fortson, Phys. Rev. Lett. 94, 050801 (2005) [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J32.00007: Quantum spin relaxation in mixtures of spinor cold atoms Yi-Ya Tian, Po-Chung Chen, Daw-Wei Wang Recently spin relaxation becomes an extensively studied subject in the field of spintronics. One of the most important mechanism of electron spin relaxation in a semiconductor quantum qubit results from the hyperfine interaction with nuclei spins. Due to limitations in solid state experiments, the effects of nuclei spins to the electron spin relaxation is still not fully understood yet. Here we propose that such electron-nuclei system can be modeled by a mixture of two species of spinor cold atoms (say $^{7}$Li and $^{87}$Rb), loaded in a bi-frequency optical lattices of large wavelength difference. We use exactly diagonalization method to study how an initially spin polarized ``electron" atom relaxs in a spin bath of ``nuclei" atoms. Our calculation shows that the spin relaxation are strongly sensitive to the polarization of ``nuclei'' atoms, while for the fully unpolarized case the relaxation is mainly determined by the density of states. Our theoretical results can be also applied in studying the electron spin relaxation dynamics in the solid state quantum qubit. [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J32.00008: Microfabricated surface-electrode ion traps for scalable quantum information processing Signe Seidelin, Joe Britton, John Chiaverini, Rainer Reichle, John Bollinger, Didi Leibfried, Janus Wesenberg, Brad Blakestad, Ryan Epstein, Jason Amini, Kenton Brown, Jonathan Home, David Hume, Nobu Shiga, Wayne Itano, John Jost, Emmanuel Knill, Chris Langer, Roee Ozeri, David Wineland We confine individual atomic ions in an rf Paul trap with a novel geometry where the electrodes are located in a single plane and the ions confined above this plane [1,2,3]. This device is realized with simple fabrication procedures, making it a potential candidate for a scalable ion trap for quantum information processing using large numbers of ions. We confine laser-cooled ions 40 micrometers above planar electrodes. These electrodes are fabricated from gold on a fused quartz substrate. The heating rate of the ions is low enough to make the trap useful for quantum information processing. [1] J. Chiaverini et al., Quantum Inf. Comput. \textbf{5}, 419 (2005). [2] S. Seidelin et al., Phys. Rev. Lett. \textbf{96}, 253003 (2006). [3] J. Britton et al., quant-ph/0605170. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J32.00009: A Point Paul Trap for Quantum Information Experiments Robert Clark, Li Yang, Isaac Chuang The point Paul trap is a surface electrode ion trap that provides three-dimensional confinement using a single radiofrequency ring electrode, with ground inside and outside. Such a trap may have applications in the development of ion trap lattices for quantum simulation and quantum computation, and has previously been demonstrated using charged microspheres. Here we present a point trap for strontium ions with a ring radius of 1.6 mm and a ring width of .3 mm, consisting of gold electrodes on a laminate susbstrate and loaded by laser ablation. Typical operating parameters are a trap depth of .8 eV and secular frequencies of 250 kHz, for a trap drive of 800 V at 2.5 MHz. Numerical models of the trap are compared to experimentally measured motional secular frequencies of the ions, and the efficiency of laser ablation loading as a function of trap depth is studied. An experiment to measure the heating rate of a single ion as a function of height in the trap is also discussed. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J32.00010: Optical MEMS Based Beam Steering for 2D lattice Caleb Knoernschild, Changsoon Kim, Felix Lu, Bin Liu, Jungsang Kim Most scalable quantum computation approaches using arrays of trapped ions or individual neutral atoms in optical lattices require the experimental capability to address individual qubits in the large array. It is difficult to achieve such flexibility with traditional optical systems utilizing bulky components aligned on optical tables. Optical micro-electromechanical systems (MEMS) technology can provide a flexible and scalable solution for this functionality. We have developed simple beam steering optics using controllable MEMS mirrors that enable one laser beam to address multiple qubit locations in a linear trap or 2D trap lattice. The system can individually address 25 different positions on a 5 x 5 square array. MEMS mirror settling times of $<$ 5$\mu $s were demonstrated which allow for fast access time between qubits. Characterization of beam quality and optical power throughput is also presented. This system has the advantage of providing multiple individually addressed spots of different colors simultaneously without any frequency shifts. [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J32.00011: surface-electrode ion trap loaded by laser ablation Paul Antohi, Waseem Bakr, Isaac Chuang, Jaroslaw Labaziewicz, Ken Brown traps operated at liquid helium temperatures offer many advantages \newline for exploring new physics, such as quantum interactions between ions \newline and superconductors; cooling may also reduce anomalously high ion \newline heating rates currently observed and attributed to surface charge \newline fluctuations. However, cryogenic traps are traditionally \newline experimentally challenging to realize, due to the careful attention \newline required to thermally anchor the trap, and due to the incompatibility \newline of standard high-temperature ion sources with a cryogenic environment. \newline We demonstrate a new approach to these challenges using a millimeter \newline scale printed-circuit board trap with surface electrode geometry, \newline operated in a liquid helium bath cryostat, to trap and cool strontium \newline 88 ions. The planar aspect of this trap simplifies anchoring to the \newline helium baseplate, and provides clear access for loading ions from an \newline ablation plume produced by $<$7 mJ pulses of a Q-switched Nd:YAG laser \newline incident on a Sr/Al alloy target. We are able to load traps with \newline depths as low as 0.7 eV, and with laser cooling we observe small ion \newline crystals with between one and twenty six optically resolved ions, with \newline individual ion lifetimes averaging 2 hours. Initial estimates based on \newline the observed residual gas collision rates are consistent with a vacuum \newline pressure below 10\^{}{\{}-9{\}} torr, and the true pressure is likely much lower. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J32.00012: Sideband cooling and anomalous heating of trapped $Sr^+$ ion. Jaroslaw Labaziewicz, Yufei Ge, Paul Antohi, Isaac Chuang Many schemes for entangling and quantum processing with trapped ions require cooling the ions close to motional ground state, and the anomalous heating of the ion can be the limiting factor in gate fidelity. We developed a simple laser system, based on external cavity diode lasers with optical feedback to a running-wave cavity to investigate this heating. Without the use of a high finesse cavity, or fast active feedback, we have achieved $<30$ kHz linewidths and $\approx 1$ MHz long term stability. This system was used to sideband cool a single $Sr^+$ ion to a motional ground state with $> 90\%$ probablity and observe Rabi oscillations on the $5S_{1/2} \rightarrow 4D_{5/2}$ transition. We present our results on heating and cooling rates of the ion in room temperature and cryogenic ion traps. [Preview Abstract] |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J32.00013: One-way quantum computing in optical lattices with many atom measurements. Timothy P. Friesen, David L. Feder In one-way quantum computation single qubit measurements on a highly entangled state, known as a cluster state, are sufficient to perform universal quantum computation. One of the most promising approaches for generating the cluster state is to manipulate ultracold atoms in optical lattices. Unfortunately, the small lattice spacing places severe constraints on the ability to sequentially measure the states of individual atoms by external lasers, a crucial requirement for one-way computing. With current technology, we are generally limited to many atom measurements. We have developed a deterministic protocol for one-way quantum computing based on many atom measurements on an optical lattice cluster state, requiring only polynomial classical overhead. Our scheme opens the way toward concrete experimental quantum computing in neutral atom systems. [Preview Abstract] |
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