Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session C5: Quantum Computation |
Hide Abstracts |
Chair: Marianna Safronova, University of Delaware Room: Knoxville Convention Center 301AB |
Wednesday, May 17, 2006 10:30AM - 10:42AM |
C5.00001: Rapid control and measurement of clock-state qubits in Yb and Sr Barry C. Sanders, Nathan S. Babcock, Artem M. Dudarev, Mark G. Raizen, Rene Stock 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 extremely long-lived $^1$S$_0$ and $^3$P$_0$ states are dipole and parity forbidden, respectively. Whereas this results in highly desirable low-decoherence rates, it also represents the main problem for fast coherent manipulation and measurement of qubits for quantum information processing. In this work, we determine the feasibility of using a coherent, recoil-free, three- photon transition [1] for fast coherent rotation of qubits followed by ultrafast readout of the $^3$P$_0$ state via photo ionization. Rapid control and measurement of atomic qubits are crucial for high-speed synchronization of quantum information processors. Furthermore, we explore the possibility of loophole free tests of Bell inequalities using spatially separated entangled qubits via fast measurements. [1] T. Hong, C. Cramer, W. Nagourney, E. N. Fortson, Phys. Rev. Lett. 94, 050801 (2005) [Preview Abstract] |
Wednesday, May 17, 2006 10:42AM - 10:54AM |
C5.00002: Preserving Coherence in Rydberg Quantum Bits. Russell S. Minns, Mary R. Kutteruf, Melissa A. Comisso, Hussain Zaidi, Lung Ko, Robert R. Jones Pulsed electric fields are used to create and manipulate qubits, made of the \textit{np} Rydberg states of Li. The coherence time of the qubits is extended by three separate decoherence suppression schemes. One is based on a decoherence free sub-space (DFS) where the qubit is stored in a basis which is unaffected by its surrounding environment, and two are based on dynamic decoupling (DD) schemes. The SO interaction creates an approximate DFS where the qubit remains unaffected by small stray magnetic and electric fields. Despite this predicted stability, appreciable decoherence is observed within $\sim $10 $\mu $s, more active control is therefore required to extend the coherence time beyond this limit. The first DD scheme utilizes fast rising and falling electric field pulses to rapidly toggle between states where the SO coupling is on or off. This toggling is used to repeatedly flip the state vector of the system canceling out environmental interactions. The second scheme utilizes resonant RF pulses to continuously flip the state via Rabi flopping. Both DD schemes maintained coherence for times comparable to the spontaneous lifetime of the system. [Preview Abstract] |
Wednesday, May 17, 2006 10:54AM - 11:06AM |
C5.00003: Dipolar switching for robust quantum computation with polar molecules Susanne Yelin, Kate Kirby, Robin Cote We propose to use a new platform -- ultracold polar molecules -- for quantum computing with switchable interactions. The on/off switch is accomplished by selective excitation of one of the ``0'' or ``1'' qubits -- long-lived molecular states -- to an ``excited'' molecular state with a considerably different dipole moment. We describe various schemes based on this switching of dipolar interactions where the selective excitation between ground and excited states is accomplished via optical, micro-wave, or electric fields. We also generalized the schemes to take advantage of the {\it dipole blockade} mechanism when dipolar interactions are very strong. These schemes can be realized in several recently proposed architectures. [Preview Abstract] |
Wednesday, May 17, 2006 11:06AM - 11:18AM |
C5.00004: Qubit Control and Entangling Collisions in an Optical Lattice Worawarong Rakreungdet, Brian E. Mischuck, Poul S. Jessen We describe recent progress in an experiment to observe and control coherent ground state collisions between Cs atoms in a 3D optical lattice, in a configuration that lends itself to the implementation of two-qubit quantum logic. The collisional phase shifts can be probed in ensemble experiments where individual atoms interfere in overlapping Mach-Zender interferometers. In our experiment the lattice is loaded with atoms from a Magneto-Optical Trap, and sideband-cooled close to the vibrational ground state of individual sites. The resulting sparsely filled lattice requires new techniques to detect and distinguish pairs of qubits that pick up collisional phase shifts from the background of atoms that don't have a collision partner. We will discuss some essential steps, such as our ability to perform high fidelity ($\sim $99{\%}) single qubit rotations, coherent transport by real-time control of the lattice polarization, and a novel real-time detection method used for both one- and two- qubit gate experiments. [Preview Abstract] |
Wednesday, May 17, 2006 11:18AM - 11:30AM |
C5.00005: Fast Ground State Manipulation of Neutral Atoms in Microscopic Dipole Traps Deniz Yavuz, Erich Urban, Todd Johnson, Pasad Kulatunga, Marie Delaney, Thomas Henage, Nick Proite, Thad Walker, Mark Saffman We demonstrate Rabi flopping at MHz rates between ground hyperfine states of neutral $^{87}$Rb atoms that are trapped in two micron sized optical traps. Using tightly focused laser beams we demonstrate high fidelity, site specific Rabi rotations with crosstalk on neighboring sites separated by $8~\mu\rm m$ at the level of $10^{-3}$. Ramsey spectroscopy is used to measure a dephasing time of $870~\mu\rm s$ which is $\approx$~5000 times longer than the time for a $\pi/2$ pulse. We also demonstate the suppression of Rydberg excitation in a dipole trap which is the first step towards demonstrating a two- qubit gate between neutral atoms. [Preview Abstract] |
Wednesday, May 17, 2006 11:30AM - 11:42AM |
C5.00006: Trapped ion quantum computation with transverse phonon modes Shi-Liang Zhu, Chris Monroe, L.-M. Duan We propose a scheme to implement quantum gates on any pair of trapped ions immersed in a large linear crystal, using interaction mediated by the transverse phonon modes. Compared with the conventional approaches based on the longitudinal phonon modes, this scheme is much more insensitive to the ion heating and thermal motion outside of the Lamb-Dicke limit thanks to the stronger confinement in the transverse direction. The cost for such a gain is only a moderate increase of the laser power to achieve the same gate speed. We also show how to realize arbitrary-speed quantum gates with transverse phonon modes based on control of the laser pulses. [Preview Abstract] |
Wednesday, May 17, 2006 11:42AM - 11:54AM |
C5.00007: Steps towards fault-tolerant quantum operations in trapped-ion Quantum information experiments R. Ozeri, C. Langer, J.D. Jost , R.B. Blakestad, J. Britton, J. Chiaverini, D. Hume, W.M. Itano, E. Knill, D. Leibfried, R. Reichle, S. Seidelin, J.H. Wesenberg, D.J. Wineland Fault-tolerant Quantum Information Processing (QIP) requires that the error in a quantum gate be smaller than a certain threshold, currently believed to be on the $\sim $10$^{-4}$ level. Here we discuss progress toward realizing such low error rates in trapped-ion QIP experiments at NIST. Memory coherence times are extended using a qubit transition which, to first order, is independent of the magnetic field. The fundamental limits to laser driven quantum gates are investigated by studying the effect of spontaneous scattering of photons on hyperfine coherence. It is shown that the error due to the scattering of photons can be, at least in principle, reduced to very low values. [Preview Abstract] |
Wednesday, May 17, 2006 11:54AM - 12:06PM |
C5.00008: Free-Space Quantum Cryptography in a Hydrogen Fraunhofer Window Daniel Rogers, Joshua Bienfang, Alan Mink, Barry Hershman, Anastase Nakassis, Xiao Tang, Lijun Ma, David Su, Carl Williams, Charles Clark Quantum key distribution (QKD) has shown the potential for the production of cryptographic key for ultra-secure communications. The performance of any QKD system is ultimately limited by the signal to noise ratio on the single-photon channel, and over most useful communications links the resulting in key rates are impractical for performing continuous one-time-pad encryption of today's broadband communications. We have adapted clock and data recovery techniques from modern telecommunications practice to increase the repetition rate of a free-space QKD system by roughly 2 orders of magnitude over previous demonstrations. We have also designed the system to operate in the H-$\alpha$ Fraunhofer window at 656.28 nm, where the solar background is reduced by roughly 7 dB. To achieve high repetition rates this system takes advantage of silicon single-photon avalanche photodiodes with $<$ 50 ps timing resolution and high detection efficiency in the visible region. This free-space QKD system is designed to operate at a repetition rate of 2.5 GHz. We have identified scalable solutions for delivering sustained one-time-pad encryption at 10 Mbps, thus making it possible to integrate quantum cryptography with first-generation Ethernet protocols. [Preview Abstract] |
Wednesday, May 17, 2006 12:06PM - 12:18PM |
C5.00009: Implementation of Grover's search algorithm using entangled `clock state' qubits Kathy-Anne Brickman, Mark Acton, Louis Deslauriers, Paul Haljan, Patricia Lee, Christopher Monroe We experimentally demonstrate Grover's search algorithm over a space of N=4 elements with n=2 trapped $^{111}$Cd$^{+ }$ion qubits. One of the four states is marked, and with a single query it is recovered on average with a 60{\%} probability. This exceeds the performance of any possible classical search, which can only succeed with 50{\%} probability following a single query. The algorithm consists of two Molmer-Sorensen entangling gates paired with several single-qubit rotations and near-perfect qubit measurements. The Molmer-Sorensen gate has the unique advantage that it can entangle magnetic field insensitive `clock-state' qubits and hence can be relatively insensitive to an important source of noise in trapped ion quantum gates. [Preview Abstract] |
Wednesday, May 17, 2006 12:18PM - 12:30PM |
C5.00010: A Quantum Simulator From Trapped Ions Kendra Vant, Dana Berkeland, Warren Lybarger, Rolando Somma, Bernie Jokiel, Christopher Tigges, Malcolm Boshier, John Chiaverini, David Lizon, Robert Scarlett, Matthew Blain Many quantum systems cannot be simulated efficiently on a classical computer due to the large Hilbert space they inhabit. They may instead be investigated using a quantum simulator - ~a device which uses a number of more-easily controllable quantum bits to mimic the quantum spins in the system to be studied. The states of the simulator follow the nearly same equations of motion as the real system, yet are directly accessible to the experimenter. Trapped ions may make this kind of simulation possible. We will describe the experimental status of the proposed LANL trapped-ion quantum simulator including our ideas for the generation of spin-dependent optical forces to produce ion-ion interactions that mimic interactions in Ising-like model Hamiltonians.~ Prospects for using this interaction as the basis of a few-ion simulator for this model and others will also be described.~ In addition, recent collaboration between LANL and SNL has led to the construction of microfabricated ion traps; development of their use for quantum simulations will also be a major focus in the near future. These multizoned traps should be more suitable for quantum simulation than single well traps. We will discuss the trap development and testing. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700