Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session D14: Quantum Information Science in AMO |
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Sponsoring Units: DAMOP GQI Chair: J. Y. Vaishnav, National Institute of Standards and Technology Room: Morial Convention Center 205 |
Monday, March 10, 2008 2:30PM - 2:42PM |
D14.00001: Quantum Information Aspects of Cold Fermi Systems Razvan Teodorescu In the limit of fast switching of Feshbach resonance in cold fermionic systems, the dynamics is dominated by non-linear, coherent, multi-frequency quantum oscillations of the order parameter. This theoretical model is very rich and has known connections to several quantum field theories. In this talk, I will analyze the problem from the point of view of quantum information theory and indicate possible practical applications of the fast-switching regime. [Preview Abstract] |
Monday, March 10, 2008 2:42PM - 2:54PM |
D14.00002: Coherent Control of Trapped Bosons Analabha Roy, Linda Reichl We investigate the quantum behavior of a mesoscopic two-boson system produced by number-squeezing ultracold gases of alkali metal atoms. The quantum Poincare maps of the wavefunctions are affected by chaos in those regions of the phase space where the classical dynamics produces features that are comparable to $\hbar$. We also investigate the possibility for quantum control in the dynamics of excitations in these systems. Controlled excitations are mediated by pulsed signals that cause Stimulated Raman Adiabatic passage (STIRAP) from the ground state to a state of higher energy. The dynamics of this transition is affected by chaos caused by the pulses in certain regions of the phase space. A transition to chaos can thus provide a method of controlling STIRAP. [Preview Abstract] |
Monday, March 10, 2008 2:54PM - 3:06PM |
D14.00003: Phase transitions, entanglement and quantum noise interferometry in cold atoms Florian Mintert, Indubala Satija, Ana Maria Rey, Charles Clark Quantum entanglement represents one of the most fascinating features of quantum theory and has emerged as an important resource in quantum information science. Recent studies have suggested that the long range correlations that are established close to a quantum phase transition manifest themselves in a pronounced increase of entanglement. However, to show that is not an easy task given the fact that currently there is not consensus about the best method to define an entanglement measure for multi-particle systems. Using an entanglement measure that includes up to four point correlation functions we study the scaling properties of multi-particle entanglement in a one dimensional Ising chain around and at the critical point. Our study reveals that multiparticle entanglement indeed peaks at the phase transition, whereas pure biparticle entanglement measures often fail to reveal this feature. We discuss the connection between multiparticle entanglement measurements with noise correlations and the possibility of using these experimentally accessible quantities as a probe of entanglement in cold atomic systems. [Preview Abstract] |
Monday, March 10, 2008 3:06PM - 3:18PM |
D14.00004: ABSTRACT HAS BEEN MOVED TO SESSION W15 |
Monday, March 10, 2008 3:18PM - 3:30PM |
D14.00005: Topological Entropy of Quantum Hall states in rotating Bose gases Alexis Morris, David Feder Using exact numerical simulations of a small number of harmonically trapped ultracold alkali atoms at high rotation, we calculate the von Neumann entropy of the bosonic variant of the Laughlin and Pfaffian quantum Hall states. It has recently been shown that this entropy has a linear scaling with the boundary size. The y-intercept of this scaling relation corresponds to a universal quantity known as the topological entropy that is related to the quantum Hall filling factor. Through finite size scaling, we have extracted this quantity and compare the outcome to expected results. [Preview Abstract] |
Monday, March 10, 2008 3:30PM - 3:42PM |
D14.00006: Mapping photonic entanglement into and out of a quantum memory Hui Deng, Kyung S. Choi, Julien Laurat, H. Jeff Kimble Recent developments of quantum information science critically rely on entanglement. In particular, scalable quantum networks require capabilities to create, store, and distribute entanglement among distant nodes via photon channels. Atomic ensembles can serve as such nodes. In the photon counting regime, heralded entanglement between atomic ensembles has been demonstrated via probabilistic protocols. However, an inherent drawback of such protocols is the compromise between the fidelity of entanglement and its preparation probability, which hinders the schemes' scalability. Here we present a protocol where entanglement between atomic ensembles is created by coherent mapping of photonic entanglement. By splitting a single-photon and subsequent state transfer, we separate the generation of entanglement and its storage, enabling efficient scaling for high-fidelity quantum communication. After a programmable delay, chosen at 1us, the stored entanglement is mapped back into photon modes with an overall efficiency of 17{\%}. With improved retrieval efficiency and memory time, along with the development of on-demand single photon sources, our protocol enables the deterministic generation, storage, and distribution of entanglement among remote quantum memories for scalable quantum networks. [Preview Abstract] |
Monday, March 10, 2008 3:42PM - 3:54PM |
D14.00007: Broadband Multi-Spot Optical Beam Steering with Independent 2D Addressability for Quantum Information Processing Caleb Knoernschild, Changsoon Kim, Felix Lu, Jungsang Kim While quantum computation utilizing trapped ions or neutral atoms has seen significant advances in recent years, the necessary scalability of such implementations is limited in part by the distribution of laser resources. The capability to address multiple qubit locations with a single laser is an essential element in moving these experiments beyond individual quantum gate demonstrations. An optical system utilizing micro-electromechanical system (MEMS) technology can provide a scalable solution to address a qubit array with multiple independent beams concurrently. Broadband coatings can accommodate a large range of wavelengths, while fabrication techniques allow expansion to multiple parallel laser beams over a large number of trap locations. We demonstrate a two-spot beam steering system using MEMS mirrors that can simultaneously and independently illuminate any of 25 different locations within a 5x5 array with 2 laser beams of different wavelengths. Mirrors with settling times of $<$ 5$\mu $s have been fabricated allowing fast access times between qubits. Such systems can be used to implement two-qubit gates in a 1D or 2D array of qubits. [Preview Abstract] |
Monday, March 10, 2008 3:54PM - 4:06PM |
D14.00008: Phonon-Mediated Detection of Trapped Atomic Ions David Hume, Till Rosenband, David Wineland Both quantum information processing and quantum-limited metrology require sensitive detection of quantum states. Using trapped atomic ions, we investigate quantum non-demolition measurements in a two-species ion chain composed of Al$^{+}$ and Be$^{+}$. By mapping information from Al$^{+}$ to a shared phonon-mode then to Be$^{+}$ and detecting repetitively we have experimentally demonstrated a fidelity for state initialization and detection of 0.9994. We have also shown an increase in measurement efficiency through an adaptive procedure. Here we apply these ideas to the detection of states of multiple Al$^{+}$ using a single Be$^{+}$ ion, and describe the preparation of entangled states through measurement. [Preview Abstract] |
Monday, March 10, 2008 4:06PM - 4:18PM |
D14.00009: Towards a wire-mediated coupling of trapped ions Robert Clark, Tony Lee, Nikos Daniilidis, Sankaranarayanan S., Hartmut H\"{a}ffner Most schemes for ion trap quantum computation rely upon the exchange of information between ion-qubits in the same trap region, mediated by their shared vibrational mode. An alternative way to achieve this coupling is via the image charges induced in a conducting wire that connects different traps. This was shown to be theoretically possible by Heinzen and Wineland in 1990, but some important practical questions have remained unaddressed. Among these are how the presence of such a wire modifies the motional frequencies and heating rates of trapped ions. We thus have realized this system as a 1 mm-scale planar segmented rf ion trap combined with an electrically floating gold wire of 25 microns diameter and length 1 cm. This wire is placed close to trapped ions using a set of piezoelectric nanopositioners. We present here experimental measurements of the motional frequencies and heating rates of a single trapped calcium ion as the wire is moved from 3.0 mm to 0.2 mm away from the ion. We discuss the implications of these results for achieving wire-mediated coupling in the present apparatus, as well as in future improved setups. [Preview Abstract] |
Monday, March 10, 2008 4:18PM - 4:30PM |
D14.00010: Trapping and Detecting Polar Molecular Ions in a Closed-Cycle 4 K Ion Trap Gleb Akselrod, David Schuster, Paul Antohi, Ziliang Lin, Rob Schoelkopf, Isaac Chuang The rich internal structure of polar molecular ions make them attractive for interfacing with solid state systems in quantum information processing, yet it is this structure that makes trapping and detecting molecules difficult. We present an approach to this challenge which allows a superconducting cavity to be used as an integral part of a surface electrode ion trap, based on a closed-cycle cryostat operated at 4 K, and addressing the problem of loading molecules and detecting their presence. A mixture of Sr and SrCl ions is loaded into the trap by laser ablation. Subsequent laser cooling of the Sr ions sympathetically cools the molecular ions, producing a two-component Wigner crystal. ~This allows detection of the molecules using mass spectroscopy, observed indirectly through imaging of the Sr ions, or through coupling to microwave lines in the trap. Using a closed-cycle cryostat enables rapid testing and evaluation of ablation targets and trap geometries, at the cost of some trap vibration, measured to be below 160 nm in amplitude. [Preview Abstract] |
Monday, March 10, 2008 4:30PM - 4:42PM |
D14.00011: Microwave Cavity Quantum Electrodynamics in a Molecular Ion Trap David Schuster, Paul Antohi, Gleb Akselrod, Ziliang Lin, Isaac Chuang, David Demille, Robert Schoelkopf It has been proposed to use the rotational states of trapped neutral molecules inside of an on-chip superconducting microwave resonator for cavity quantum electrodynamics and quantum information processing. We investigate the potential of molecular ions, which have several properties that might be advantageous over neutral molecules. Ions can be loaded into deep RF traps which do not require ultra-stable lasers and trap independent of their rotational state. They can be cooled by both cryogenic buffer gas and sympathetic laser cooling with atomic ions. Further, the ion charge screens electric fields felt by the rotational dipole reducing dephasing due to trapping or spurious fields. In addition, this property should allow one to create stable ensembles of ions which could be used as a quantum memory. As with neutral proposals such a system could be both interrogated and manipulated with microwave fields. Finally, the system represents a high precision spectroscopy tool for studying microwave transitions of single molecules. [Preview Abstract] |
Monday, March 10, 2008 4:42PM - 4:54PM |
D14.00012: Cavity cooling of $^{88}Sr^+$ David Leibrandt, Yat Shan Au, Isaac Chuang Cavity cooling is a method of laser cooling which uses coherent scattering to cool atoms [V. Vuleti\'{c} and S. Chu, PRL \textbf{84}, 3787 (2000)]. The closed atomic transition used in Doppler cooling is replaced by a cavity resonance, so cavity cooling can be used to cool to sub-Doppler temperatures and is in principle applicable to complicated atoms or molecules without closed transitions. We describe an experiment to study three-dimensional cavity cooling of a single $^{88}Sr^+$ ion confined in a linear RF Paul trap. Large cooling rates can be attained by operating near the 422 nm $S_{1/2} \leftrightarrow P_{1/2}$ optical dipole transition and using a 5 cm long near-confocal Fabry-P\'{e}rot cavity with commercially available mirrors of finesse $10^4$. Given a cavity alignment error $\le 10$ $\mu$m and a trap frequency of 1 MHz, the resolved sideband cavity cooling limit is $\le$ 5 motional quanta. We present details of the experimental proposal and its implementation. [Preview Abstract] |
Monday, March 10, 2008 4:54PM - 5:06PM |
D14.00013: Microfabrication of Surface Electrode Ion Traps for Quantum Information Experiments Yufei Ge, Jaroslaw Labaziewicz, Paul Antohi, Isaac Chuang Surface electrode ion traps, while promising for large-scale quantum computation, have long been challenged by ion heating rates which increase rapidly as trap length scales are reduced. Through a series of measurements on over fifteen traps, we show that ion heating rates are surprisingly sensitive to electrode material and morphology, and in particular, to details of the fabrication procedure. For example, one $75$ $\mu$m size trap, made of chemically etched silver on a single crystal quartz substrate, showed a minimum heating rate of $\sim 40$ quanta/second, when prepared by annealing at $760^\circ$C in vacuum for one hour. This annealing smooths sharp edges, and significantly reduces breakdown voltage. However, if the annealing temperature is lowered to $720^\circ$C, leaving the breakdown voltage still robustly high, the heating rate jumps to $\sim1000$ quanta/second. With electroplated gold, on a silver seed layer, a record low heating rate of $\sim 2$ quanta/second is obtained. We present details of the fabrication procedures, evaluate alternative electrode materials such as niobium nitride, and explain how these measurements were obtained with an ion trap operated at $6$ Kelvin, containing a single strontium ion, sideband cooled to its quantum ground state of motion. [Preview Abstract] |
Monday, March 10, 2008 5:06PM - 5:18PM |
D14.00014: Temperature dependence of decoherence in ion traps Jaroslaw Labaziewicz, Yufei Ge, Shannon X. Wang, Ruth Shewmon, Isaac L. Chuang Dense arrays of trapped ions provide one way of scaling up ion trap quantum information processing. However, miniaturization of ion traps is currently limited by sharply increasing motional state decoherence at sub-100~$\mu$m ion-electrode distances. This decoherence has been demonstrated to be thermally driven, providing a plausible route to reduce it. In our experiment, we measure the heating rate out of the motional ground state of a single $Sr^+$ ion in a cryogenic surface electrode ion trap. We present our results on the temperature dependence of the heating rates as a function of electrode temperature in 10-100~K range. Heating rates at 6~K are observed to be as low as two quanta per second, but increase rapidly with temperature. [Preview Abstract] |
Monday, March 10, 2008 5:18PM - 5:30PM |
D14.00015: Individual ion addressing using a magnetic field gradient in a surface-electrode ion trap Shannon Wang, Jaroslaw Labaziewicz, Yufei Ge, Isaac 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 time, 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 generated by external coils. We present a scheme to create a local field gradient by integrating current sources onto a microfabricated surface-electrode trap. Taking advantage of the cryogenic environment, we stabilize the field at the trap site using superconducting rings as flux shields. The rings can be integrated with the trap, simplifying implementation and improving alignment to the ions. [Preview Abstract] |
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