Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session C3: Quantum Information with Trapped Ions |
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Chair: Boris Blinov, University of Washington Room: Gilmer Hall 190 |
Wednesday, May 20, 2009 2:00PM - 2:12PM |
C3.00001: Transport and heating in an X-junction ion trap array R.B. Blakestad, A.P. VanDevender, C. Ospelkaus, J.M. Amini, J. Britton, D. Leibfried, D.J. Wineland Key requirements for efficient large-scale quantum information processing (QIP) include reliable transport of information throughout the processor and the ability to perform gates between arbitrarily selected qubits. Trapped ions are a useful system for studying the elements of QIP and can potentially satisfy these requirements. For example, ions could be distributed over separate zones in an array, where information would be shared between zones by moving the ions [1]. Multidimensional arrays incorporating junctions would enable ions selected from arbitrary locations to be grouped together for multi-qubit gates. However, kinetic energy gained during transport would reduce computational fidelity and increase the duration required for ion re-cooling. Here, we report reliable transport of Be+ ions through a 2-D trap array that incorporates an ``X-junction", with low energy gain ($<$ 10 quanta). We also examine two sources of energy gain during transport: a particular radio-frequency noise heating mechanism and digital sampling noise. [1] D. Kielpinski, C. Monroe and D.J. Wineland. Nature \textbf{417}, 709 (2002) [Preview Abstract] |
Wednesday, May 20, 2009 2:12PM - 2:24PM |
C3.00002: Trapped Ion Imaging with Integrated Spherical Mirror Gang Shu, Matthew Dietrich, Nathan Kurz, Boris Blinov Efficient fluorescence collection is essential for trapped ion quantum computation and information. High photon counting rate implies fast, high-fidelity qubit state readout, more efficient single-photon generation by trapped ions or neutral atoms, and reliable ion-photon and distant ion entanglement generation. In an effort to increase solid angle of ion fluorescence collection we built a linear ion trap with an integrated concave spherical mirror. Our integrated mirror has an estimated numerical aperture of 0.9, representing more than an order of magnitude increase in covered solid angle as compared to a typical lens system. We demonstrate robust ion trapping in the presence of the mirror, and obtain sharp images of single ions and resolve multiple ions with no additional optics but the spherical mirror. The preliminary result show a substantial boost in photon counting rate. To exploit the full potential of this spherical mirror, we developed an aspheric corrector plate to be placed outside the vacuum chamber which will eliminate the mirror's inherent spherical aberration. Our simulations show that with such corrector a near diffraction-limited imaging of ions is possible. [Preview Abstract] |
Wednesday, May 20, 2009 2:24PM - 2:36PM |
C3.00003: Enhanced light collection from trapped ions J.D. Sterk, T.A. Manning, L. Luo, P. Maunz, S. Olmschenk, D. Hayes, D. Matsukevich, C. Monroe We present progress towards an ion trapping system capable of enhanced light collection based on nearby reflective optics~[1--3]. This may not only boost the fidelity and speed of trapped ion qubit measurement, but may also greatly improve probabilistic entangling schemes relying on the collection and interference of single photons~[4]. Two proposed schemes will be realized by placing a trapped Yb$^{+}$ ion either at the focus of a 5 mm spherical mirror or inside a one-sided optical cavity ($\mathcal{F}\approx$ 4500). Both experiments will utilize a double-endcap ion trap whereby the ion--electrode spacing can be varied \emph{in situ}~[5]. Additionally, we discuss several methods of generating entanglement within the context of the collection schemes. \\ \\ This work is supported by IARPA under ARO contract, the NSF PIF Program, and the NSF Physics Frontier Center at JQI. \\ \\ $[1]$ N. Lindlen, et al. {\it Laser Physics} {\bf 17},927 (2007) $[2]$ G. Guthorlein, et al., {\it Nature} {\bf 414}, 49 (2001) $[3]$ A. B. Mundt, et al. {\it Phys. Rev. Lett.}, {\bf 89}, 103001, (2002) $[4]$ D. L. Moehring, et al. {\it Nature} {\bf 449}, 68 (2007) $[5]$ L. Deslauriers, et al. {\it Phys. Rev. Lett.} {\bf 97}, 103007 (2006) [Preview Abstract] |
Wednesday, May 20, 2009 2:36PM - 2:48PM |
C3.00004: Ion-photon coupling with phase Fresnel lenses for large-scale quantum computing Erik Streed, Benjamin Norton, Justin Chapman, David Kielpinski Efficient ion-photon coupling is an important component for large-scale ion-trap quantum computing. We propose that arrays of phase Fresnel lenses (PFLs) are a favorable optical coupling technology to match with multi-zone ion traps. Both are scalable technologies based on conventional micro-fabrication techniques. The large numerical apertures (NAs) possible with PFLs can reduce the readout time for ion qubits. PFLs also provide good coherent ion-photon coupling by matching a large fraction of an ion's emission pattern to a single optical propagation mode (TEM$_{00})$. To this end we have optically characterized a large numerical aperture phase Fresnel lens (NA=0.64) designed for use at 369.5 nm, the principal fluorescence detection transition for Yb$^{+}$ ions. A diffraction-limited spot w$_{0}$=350+/-15 nm (1/e$^{2}$ waist) with mode quality M$^{2}$= 1.08+/-0.05 was measured with this PFL. From this we estimate the minimum expected free space coherent ion-photon coupling to be 0.64{\%}, which is twice the best previous experimental measurement using a conventional multi-element lens. We also evaluate two techniques for improving the entanglement fidelity between the ion state and photon polarization with large numerical aperture lenses. [Preview Abstract] |
Wednesday, May 20, 2009 2:48PM - 3:00PM |
C3.00005: Trapped-ion quantum logic gates based on oscillating magnetic fields Christian Ospelkaus, Christopher E. Langer, Jason M. Amini, Kenton R. Brown, Dietrich Leibfried, David J. Wineland Oscillating magnetic fields and field gradients can be used to implement single-qubit rotations and entangling multiqubit quantum gates for trapped-ion quantum information processing. With fields generated by currents in microfabricated surface-electrode traps, it should be possible to achieve gate speeds that are comparable to those of optically induced gates for realistic distances between the ions and the electrode surface. Magnetic-field-mediated gates have the potential to significantly reduce the overhead in laser-beam control and motional-state initialization compared to current QIP experiments with trapped ions and will eliminate spontaneous scattering decoherence, a fundamental source of decoherence in laser-mediated gates. A potentially beneficial environment for the implementation of such schemes is a cryogenic ion trap, because small length scale traps with low motional heating rates can be realized. A cryogenic ion trap experiment is currently under construction at NIST. [Preview Abstract] |
Wednesday, May 20, 2009 3:00PM - 3:12PM |
C3.00006: Individual addressing of ions using a magnetic field gradient in a surface-electrode ion trap Shannon X. Wang, Jaroslaw Labaziewicz, Yufei Ge, Isaac L. Chuang The ability to address individual ions is an important issue in using multiple trapped ions to perform quantum operations. Previous efforts have included using precisely focused laser beams aimed at only one ion at a time1, which poses a significant technical challenge. An alternative is to use field-dependent transitions and a magnetic field gradient to shift the transition frequencies of ions as a function of position. This requires good stability of the local field in order to achieve desired fidelity of quantum operations. In a cryogenic Sr$^+$ ion trap we use the $^5S_{1/2} \rightarrow ^4D_{5/2}$ transition as an optical qubit, which can be Zeeman shifted using a bias field. We demonstrate individual addressing of trapped ions in a microfabricated surface-electrode trap using a magnetic field gradient generated on-chip. A frequency splitting of 310(2) kHz for two ions separated by 5 um is achieved. Selective single qubit operations are performed on one of two trapped ions with an average of 2.2 $\pm$ 1.0\% crosstalk. Coherence time as measured by the spin-echo technique is unaffected by the field gradient. With appropriate phase correction, we present a scheme to realize two-ion gates. [Preview Abstract] |
Wednesday, May 20, 2009 3:12PM - 3:24PM |
C3.00007: Large Scale Quantum Computation in an Anharmonic Linear Ion Trap Guin-Dar Lin, Shi-Liang Zhu, Rajibul Islam, Kihwan Kim, Ming-Shien Chang, Simcha Korenblit, Christopher Monroe, Luming Duan We propose a large-scale quantum computer architecture by stabilizing a single large linear ion chain in a very simple trap geometry. By confining ions in an anharmonic linear trap with nearly uniform spacing between ions, we show that high-fidelity quantum gates can be realized in large linear ion crystals under the Doppler temperature based on coupling to a near-continuum of transverse motional modes with simple shaped laser pulses. [Preview Abstract] |
Wednesday, May 20, 2009 3:24PM - 3:36PM |
C3.00008: Sympathetic cooling and trapped-ion quantum logic gates David Hanneke, J.D. Jost, J.P. Home, J.M. Amini, R. Ozeri*, C. Langer**, J.J. Bollinger, D. Leibfried, D.J. Wineland Motional excitation in a trapped-ion quantum information processor degrades the performance of quantum logic gates. Excitations arise from noise emanating from the electrodes and from shuttling ions. Additional ions of a different species can be used to sympathetically cool qubit ions' motion, re-initializing the ground state while leaving intact quantum information stored in the internal state of a qubit ion. Here, we describe an experimental demonstration of a two-qubit entangling operation implemented after sympathetic cooling. We avoid decoherence during ion transport by using a field-independent hyperfine transition of $^9\rm{Be}^+$ as our qubit. \newline *Weizmann Institute of Science, Israel \newline **Lockheed Martin, CO [Preview Abstract] |
Wednesday, May 20, 2009 3:36PM - 3:48PM |
C3.00009: Sympathetic heating spectroscopy with laser cooled ions Kenneth Brown, Craig Clark, C. Ricardo Viteri, Yatis Dodia, James Goeders, Grahame Vittorini Sympathetic heating spectroscopy uses the coupled motion of two trapped ions to measure the spectra of one ion by observing changes in the fluorescence of the other ion. Sympathetic heating spectroscopy is a generalization of quantum logic spectroscopy, but does not require ions in the motional ground state or coherent control of the ion internal states. We present an experimental demonstration of the technique using two isotopes of Ca. Limits of the method and potential applications for cold molecular ion spectroscopy are also discussed. [Preview Abstract] |
Wednesday, May 20, 2009 3:48PM - 4:00PM |
C3.00010: Dynamical Decoupling Using Trapped Ions Michael Biercuk, Hermann Uys, Aaron VanDevender, Nobuyasu Shiga, Wayne Itano, John Bollinger We present a detailed experimental study of the Uhrig Dynamical Decoupling (UDD) sequence in a variety of noise environments. Our qubit system consists of a crystalline array of $^{9}$Be$^{+}$ ions confined in a Penning trap. We use an electron-spin-flip transition as our qubit manifold and drive qubit rotations using a quasi-optical 124 GHz microwave system. We study the effect of the UDD sequence in mitigating phase errors and compare against the well-known CPMG-style spin echo as a function of pulse number, rotation axis, noise spectrum, and noise strength. Our results show good agreement with theoretical predictions for qubit decoherence in the presence of classical phase noise, accounting for the effect of finite-duration $\pi$ pulses. Finally, we demonstrate that the Uhrig sequence is more robust against systematic over/underrotation and detuning errors than is multipulse spin echo, despite the precise prescription for pulse-timing in UDD. [Preview Abstract] |
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