Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session C6: Quantum Computation |
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Chair: Junsang Kim, Duke University Room: Nittany Lion Inn Boardroom II |
Wednesday, May 28, 2008 2:00PM - 2:12PM |
C6.00001: ABSTRACT WITHDRAWN |
Wednesday, May 28, 2008 2:12PM - 2:24PM |
C6.00002: Design of a many qubit quantum computer by ensemble encoding in Ho atoms Mark Saffman, Klaus Molmer We present a design for a many qubit, fully interconnected quantum computer using collective encoding in the hyperfine ground states of Ho. Using established optical techniques we describe a complete approach to preparation and manipulation of 60 qubit quantum registers encoded in symmetric multi-atom superpositions of Ho ground states. Single qubit operations rely on stimulated Raman transitions, two-qubit gates use Rydberg blockade, and measurements of individual register bits are performed by shelving to metastable states. Combining several 60 qubit registers in a small 2D array of optical traps leads to a fully connected design for a 1000 qubit scale quantum processor. [Preview Abstract] |
Wednesday, May 28, 2008 2:24PM - 2:36PM |
C6.00003: Robust manipulation of atomic qubits using composite pulses Thomas Henage, Erich Urban, Todd Johnson, Larry Isenhower, Thad Walker, Mark Saffman Scalable quantum computing relies on the development of techniques for robust and accurate qubit manipulation. We report on experimental progress in using composite pulses to provide accurate single qubit rotations that are insensitive to experimental errors in pulse area. The experiments use optically trapped cold Rb atoms that are manipulated by stimulated Raman transitions between hyperfine qubit states. The Raman laser system has fast amplitude and phase control electronics that allow arbitrary composite pulse sequences to be implemented at a rate of several MHz. Using this system we demonstrate the use of composite pulses for manipulation of trapped atomic qubits. [Preview Abstract] |
Wednesday, May 28, 2008 2:36PM - 2:48PM |
C6.00004: Fast Quantum Gates Using Chirped Pulses Vladimir Malinovsky A common method to implement quantum gates is based on the Rabi solution regime of a two-level system excited by external field. To construct a quantum gate one uses the exact form of evolution operator of the qubit under the external excitation. In the case of Rabi solution the qubit evolution has very simple and easily interpreted form. In essence, the whole dynamics of the qubit wave function is governed by the pulse area and it exhibits Rabi oscillations for the time less than the decoherence time. Various implementations of the quantum gates employ relatively weak pulses that results in slow gate operations of order microseconds. To make quantum gates faster one may use strong femtosecond pulses. However, direct implementation schemes are not so obvious because of strong field effects and large bandwidth of the pulses might give rise to unwanted excitations. Here we propose a scheme which provides a possibility to utilize strong pulses while keeps all advantages of 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 terms and to satisfy the adiabaticity conditions. Proposed Hadamard and phase-shift gate allow us to construct universal set of single qubit gates by controlling the effective pulse area and two-photon detuning. The proposed excitation scheme can be also used to implement CNOT gate. [Preview Abstract] |
Wednesday, May 28, 2008 2:48PM - 3:00PM |
C6.00005: Rapid measurement of ions for one-way quantum-computing architectures Rene Stock, Daniel F.V. James The tremendous progress achieved in the control of trapped ions has recently led to the creation of an entangled state of eight ions and the entanglement of many more ions for large-scale quantum computer seems very feasible. However, the slow entangling operation and slow readout of ions hinder fast operations and will limit the practical use of a future ion-trap quantum computer. One-way (i.e. measurement-based) quantum computing architectures offer a way out by parallelizing the slow entangling operations to create a many-body entangled state and by processing quantum information via fast readout and measurement of qubits. In this work, we investigate the challenges involved in developing a one-way quantum-computing scheme for ions. We devise an architecture for the creation of many-body entangled states and study the viability of fast rotation and readout of ions via multi-photon photoionization on a nanosecond timescale. After photoionization, the freed electron is expulsed from the ion trap by the quadrupole trap field and can be detected on a nanosecond timescale using multichannel plate detectors. We analyze the expulsion of the electron and the effect of the remaining double-ionized atom on the entangled atoms using detailed numerical calculations. [Preview Abstract] |
Wednesday, May 28, 2008 3:00PM - 3:12PM |
C6.00006: Quantum computation schemes based on polar molecules Elena Kuznetsova, Robin Cote, Kate Kirby, Susanne Yelin Polar molecules have recently attracted significant interest as a viable platform for quantum computing. They combine the advantages of neutral atoms and trapped ions, making them compatible with various architectures, e.g. optical lattices and solid-state systems. Molecules with large permanent dipole moments can display strong dipole-dipole interactions, allowing for the realization of fast conditional two-qubit gates. In recent work we proposed a model of controllable dipole-dipole interactions in which laser excitation from a ground electronic state with negligible dipole moment to an excited metastable electronic state with a large dipole moment allows one to ``switch on'' the interaction. In principle, two molecules in the excited state interact and acquire a phase shift. We study the robustness of such a phase gate and analyze the experimental feasibility of the approach, using the CO molecule as a specific example. We are continuing to investigate several other schemes involving polar molecules and novel architectures such as a solid-state approach with polar molecules doped into rare-gas matrices. [Preview Abstract] |
Wednesday, May 28, 2008 3:12PM - 3:24PM |
C6.00007: Scalable Quantum Information Processing Based on Two Ultracold Atomic Species in Optical Lattices with Single Site Addressability Kathy-Anne Brickman, Arjun Sharma, Scott Waitukaitis, Daniel Rivas, Nathan Gemelke, Cheng Chin We propose a new scheme for quantum information processing that utilizes two different atomic species held in two independently controlled optical lattices. One uniformly filled lattice holds fermionic Li atoms that act as quantum bits (qubits) in the system. The second less densely populated lattice (1atom/1000sites) holds bosonic Cs-133 atoms that will mediate entanglement among the qubit atoms. By controlling the relative phase between the lattices, the Cs atoms can be transported to interact with any Li atom in the lattice. In this way, the Cs atoms become messengers among the Li atoms. By using these auxiliary ``messenger'' atoms, each Li qubit can be individually addressed and any of the Li atoms in the lattice can be entangled through controlled collisions with the Cs atoms. This system is inherently scalable since the qubit lattice can contain 1000 atoms in a small volume ($\sim $5$\mu $m$^{3})$. [Preview Abstract] |
Wednesday, May 28, 2008 3:24PM - 3:36PM |
C6.00008: Experiments with single site addressable 3D optical lattice. Xiao Li, Karl D. Nelson, David S. Weiss We will describe an experiment directed toward making a neutral atom quantum computer. We have loaded and imaged hundreds of single Cs atoms in a random half of the sites in a 3D optical lattice with 5 micron spacing. We will briefly discuss 3D Raman sideband cooling in this lattice, our state detection method, and our approach to addressing individual lattice sites without affecting atoms at other sites. [Preview Abstract] |
Wednesday, May 28, 2008 3:36PM - 3:48PM |
C6.00009: Ytterbium Ion Qubits for Quantum Information Processing Steven Olmschenk, Dzmitry Matsukevich, Peter Maunz, David Moehring, Kelly Younge, Chris Monroe We present trapped ytterbium ions as quantum bits for quantum information processing. The viability of this atomic ion as a qubit is demonstrated through high-fidelity state initialization and detection of the first-order magnetic field-insensitive hyperfine ``clock'' states, with a measured coherence time of at least 2.5 seconds. The simple atomic structure, large fine and hyperfine splittings, and transition wavelengths that facilitate the use of optical fibers, may allow for the implementation of a variety of quantum information processing schemes. In addition, we present improved measurements of the ${}^2P_{1/2}$ excited state lifetime and branching ratio into ${}^2D_{3/2}$. [Preview Abstract] |
Wednesday, May 28, 2008 3:48PM - 4:00PM |
C6.00010: Preparation and detection of a $^{137}$Ba$^{+}$ hyperfine qubit M.R. Dietrich, R. Bowler, N. Kurz, V. Mirgon, J. Pirtle, J.S. Salacka, G. Shu, B.B. Blinov We report the initialization and state detection of $^{137}$Ba$^{+}$ hyperfine qubits. We load $^{137}$Ba$^{+}$ into a linear Paul trap by direct photoionization with a Xe discharge lamp. The qubit is initialized by optically pumping into the magnetic field insensitive hyperfine ground state (F=2 m$_{f}$=0). State selective shelving to the metastable D$_{5/2}$ state is accomplished by adiabatic rapid passage using a 1762 nm fiber laser stabilized to a high-finesse cavity, a process which is used for high efficiency state detection. Single qubit rotations are accomplished by RF pulses at the hyperfine splitting (8.037 GHz). [Preview Abstract] |
Wednesday, May 28, 2008 4:00PM - 4:12PM |
C6.00011: Four-electron quantum dot molecule in a magnetic field Shalva Tsiklauri, Roman Kezerashvili We have studied a two dimensional four-electron quantum dot molecule in a magnetic field using hyperspherical functions method. We calculate two lowest energy levels of the four-electron quantum dot molecule in a magnetic field. Our results show that the electron interactions are significant, as they can change the total spin of the four-electron ground state of the system by adjusting the magnetic field between $S$ = 0 and $S$ = 2. The energy difference between the lowest $S$ = 0 and $S$ = 2 states is shown as a function of the axial magnetic field. We found that the energy difference between the lowest $S$ = 0 and $S$ = 2 states in the strong-$B$ varies linearly. Our results should be important for constructing quantum gates and for studying strongly correlated quantum dot electronic states. [Preview Abstract] |
Wednesday, May 28, 2008 4:12PM - 4:24PM |
C6.00012: Geometric phases and Bloch sphere constructions for SU(N), with a complete description of SU(4) Dmitry Uskov, Ravi Rau A two-sphere (``Bloch'' or ``Poincare'') is familiar for describing the dynamics of a spin-1/2 particle or light polarization. Analogous objects are derived for unitary groups larger than SU(2). We focus, in particular, on the SU(4) of two qubits which describes all possible logic gates in quantum computation. For a general Hamiltonian of SU(4) with 15 parameters we derive Bloch-like rotation of unit vectors analogous to the one familiar for a single spin in a magnetic field. [Preview Abstract] |
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