Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session P7: Focus Session: Quantum Information with Atoms and Ions |
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Chair: Steven Olmshenk, Denison University Room: Delaware CD |
Thursday, June 11, 2015 2:00PM - 2:30PM |
P7.00001: TBD Invited Speaker: David Lucas |
Thursday, June 11, 2015 2:30PM - 2:42PM |
P7.00002: Quantum Computation under Micromotion in a Planar Ion Crystal Sheng-Tao Wang, Chao Shen, Luming Duan We propose a scheme to realize scalable quantum computation in a planar ion crystal confined by a Paul trap. We show that the inevitable in-plane micromotion affects the gate design via three separate effects: renormalization of the equilibrium positions, coupling to the transverse motional modes, and amplitude modulation in the addressing beam. We demonstrate that all of these effects can be taken into account and high-fidelity gates are possible in the presence of micromotion. This proposal opens the prospect to realize large-scale fault-tolerant quantum computation within a single Paul trap. [Preview Abstract] |
Thursday, June 11, 2015 2:42PM - 2:54PM |
P7.00003: Suppression of off-resonant carrier excitations via a standing wave gate beam Thomas deLaubenfels, Karl Burkhardt, Grahame Vittorini, Kenneth Brown, Kenton Brown, J. True Merrill, Jason Amini, Curtis Volin, Alexa Harter The motional dynamics of ions in rf traps lead to secular sidebands in their excitation spectra. The relative coupling strengths of the carrier and the sidebands are usually fixed by the Lamb-Dicke factor and ion temperature. We show that the strengths of the carrier resonance and the first order sidebands may be selectively emphasized or suppressed relative to one another. Using $^{40}$Ca$^+$ ions trapped in a surface electrode trap, we excite the $|S_{1/2}> \rightarrow |D_{5/2}>$ electric quadrupole (E2) transition with laser light that is normally incident to the trap's surface. Retroreflection off the trap surface produces a standing wave. For an E2 transition, the carrier couples to the gradient of the electric field and the sidebands to the magnitude. By moving the ion through the standing wave we alternatively suppress and excite the carrier and sideband transitions with the two sets of fringes 180 degrees out of phase. This technique could be used to suppress off-resonant carrier excitations in two qubit gates, and the fringes themselves provide a measure of the ion displacement that can be used to map out the trapping potentials. [Preview Abstract] |
Thursday, June 11, 2015 2:54PM - 3:24PM |
P7.00004: Quantum computing with cold atoms and Rydberg blockade Invited Speaker: Mark Saffman Optically trapped neutral atoms are one of several leading approaches to scalable quantum information processing. When prepared in electronic ground states in deep optical lattices atomic qubits are weakly interacting with long coherence times. Excitation to Rydberg states turns on strong interactions which enable fast gates and entanglement generation through either coherent evolution or dissipative dynamics. Rydberg interactions can be applied in a variety of ways enabling control of single atom qubits, multi-atom ensemble qubits, and hybrid entanglement between different types of atoms, between atoms and photons, or between atoms and solid state qubits. I will present advances that leverage strong Rydberg interactions for implementation of a small scale quantum computing device. We trap 30 or more atomic qubits in a 2D array of 49 sites. Single qubit gates are performed with fidelities better than 0.999 as characterized by random benchmarking. Two-qubit gates and entanglement are demonstrated between qubit pairs. Experimental gate fidelities are not yet sufficient for reliable error correction and scalable quantum computation. I will describe prospects for reaching the fault tolerance threshold based on new gate protocols with the potential for fast generation of entanglement at fidelities better than 0.9999. [Preview Abstract] |
Thursday, June 11, 2015 3:24PM - 3:36PM |
P7.00005: Entanglement of Qubits Encoded in Cesium Atoms via Rydberg Dressing Yuan-Yu Jau, Aaron Hankin, Tyler Keating, Ivan Deutsch, Grant Biedermann Neutral-atom qubits are normally encoded in the ground-state sublevels for long coherent operations, but strong, tunable long-range interactions between ground-state neutral atoms are difficult to achieve. By applying off-resonant Rydberg excitation lasers to the atoms, we can in principle generate Rydberg-dressed, AC-Stark shifted qubit or spin states. Owing to the electric dipole-dipole interactions (EDDI) between atoms in the Rydberg states, different collective qubit states can acquire different AC Stark shifts, which cause effective interactions between qubits. On the other hand, transition blockades between collective qubit states also occur. We have experimentally demonstrated a strong ground-state interaction strength ($\sim$ MHz) between the two singly trapped, Rydberg-dressed Cs atoms. With a transition blockade between the two-qubit states due to Rydberg dressing, we are able to produce Bell-state entanglements of with \textgreater 80{\%} fidelity excluding the atom loss event. The two-atom survival (no loss) probability is 74{\%} with about 10 Hz data rate. This gives us about 6 entangled qubit pair per second. [Preview Abstract] |
Thursday, June 11, 2015 3:36PM - 3:48PM |
P7.00006: Robust and High Fidelity Quantum Logic with the Rydberg-Dressed Blockade Tyler Keating, Robert Cook, Ivan Deutsch, Aaron Hankin, Yuan-Yu Jau, Grant Biedermann We study a scheme for implementing a controlled-Z (CZ) gate between two neutral-atom qubits based on the Rydberg blockade mechanism in a manner that is robust to errors caused by atomic motion. By adiabatically dressing the ground electronic state, we can protect the gate from decoherence due to random phase errors that typically arise from atomic thermal motion. The adiabatic protocol also allows for a Doppler-free configuration with counterpropagating lasers in a $\sigma_+/\sigma_-$ orthogonal polarization geometry that further reduces motional errors due to Doppler shifts. The residual error is dominated by dipole-dipole forces acting on doubly-excited Rydberg atoms when the blockade is imperfect. For reasonable parameters, with qubits encoded into the clock states of 133Cs, we predict that our protocol could produce a CZ gate in $<$10 $\mu$s with error probability of order $10^{-3}$[1]. We generalize this protocol to exploit the multi-body nature of the Rydberg blockade and go beyond two qubits. We show how one can implement a three-qubit Toffoli gate in a single-step. Finally, we consider encoding in collective states of small ensembles of atoms, and show how such a scheme can allow for scalable, robust, quantum logic.\\[4pt] [1] T. Keating et al., Phys. Rev. A 91, 012337 (2015). [Preview Abstract] |
Thursday, June 11, 2015 3:48PM - 4:00PM |
P7.00007: Neutralization of Rb Surface Adsorbate Electric Fields by Slow Electron Attachment Jonathon Sedlacek, Yuanxi Chao, James Shaffer We present progress on our studies of rubidium adsorbates on a z-cut single crystal quartz surface. Many systems that consist of cold atoms interacting with a surface or surface devices require knowledge and control of adsorbate fields. Rydberg EIT is used to measure the electric fields caused by the adsorbates. A macroscopic sheet of uniform dipoles is used to model the electric field produced by the adsorbates. Large adsorbate fields can be reduced in this system by binding free electrons with low kinetic energy to the dipole field produced by the adsorbates. The low energy electrons are produced by blackbody ionization of Rydberg atoms. Prospects for using the bound electrons for other experiments will be presented. [Preview Abstract] |
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