Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session G7: Quantum Information Measurements & Techniques |
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Chair: Brian Neyenhuis, University of Maryland Room: 303 |
Wednesday, June 5, 2013 8:00AM - 8:12AM |
G7.00001: Coherent control of population transfer in multilevel atomic systems using pulse train Vladimir Malinovsky, Qudsia Quraishi, Patricia Lee Quantum control of the internal states of the atoms typically involves a combination of microwave, radio and optical fields. An all optical approach has distinct advantages for coherent control experiments which requires discrete momentum changes of the atomic cloud. Optical frequency comb, emitted by ultrafast modelocked pulsed laser, is an excellent tool to perform quantum information processing and quantum control in atomic media. Here we discuss several adiabatic passage techniques which are shown to be efficient for coherent population transfer in multilevel atomic systems using pulse trains. We present a general treatment and show some applications of the technique to manipulate population of the hyperfine levels of $^{87}$Rb atom. Also, we propose a pulse train arrangement to substantially reduce the detrimental effect of spontaneous emission. [Preview Abstract] |
Wednesday, June 5, 2013 8:12AM - 8:24AM |
G7.00002: Realization of Geometric Landau-Zener-St\"uckelberg Interferometry Junhua Zhang, Jingning Zhang, Xiang Zhang, Kihwan Kim We report the first experimental realization of a geometric Landau-Zener-St\"uckelberg (LZS) interferometry inspired by the proposal of Ref. [1] in a trapped ion system. We observe a pure geometric phase through successive Landau-Zener (LZ) transitions and its robustness against introduced intensity fluctuation in the driving field. The trapped ion system is an ideal two-level (qubit) system to realize the geometric LZS interferometer and to simulate effects of imperfections in other qubit technologies for the interferometry. In particular, we use two hyperfine ground states in an 171Yb+ ion for a qubit system and apply microwaves with various detunings and intensities for the driving field. This work was supported by the National Basic Research Program of China Grant 2011CBA00300, 2011CBA00301, 2011CBA00302, the National Natural Science Foundation of China Grant 61073174, 61033001, 61061130540. KK acknowledges the support from the Thousand Young Talents program.\\[4pt] REFERENCE:\\[0pt] [1] S. Gasparinetti, P. Solinas, and J. P. Pekola, Phys. Rev. Lett. 107, 207002 (2011).\\[0pt] [2] Zhang Xiang, et al., accepted in Phys. Rev. Lett. [Preview Abstract] |
Wednesday, June 5, 2013 8:24AM - 8:36AM |
G7.00003: Optimized pulse shaping for trapped ion quantum computing T. Andrew Manning, Shantanu Debnath, Taeyoung Choi, Caroline Figgatt, Chris Monroe We perform entangling phase gates between pairs of qubits in a chain of trapped atomic ytterbium ions. Beat notes between frequency comb lines of a pulsed laser coherently drive Raman transitions that couple the hyperfine qubits to multiple collective transverse modes of motion [1]. By optimizing the phase and amplitude of segmented laser pulses, we demonstrate a five-segment scheme [2] to entangle two qubits with high fidelity over a range of detunings. We compare this special case of full control of spin-motion entanglement to a traditional single-segment gate. We extend this scheme to selectively entangle pairs of qubits in larger chains using individual optical addressing, where we couple to all the motional modes. We show how these robust gates can achieve high fidelities for practical gate times in an approach that scales realistically to much larger numbers of qubits.\\[4pt] [1] D. Hayes et al., Phys. Rev. Lett 104, 140501 (2010).\\[0pt] [2] S.-L. Zhu et al., Europhys. Lett., 73 (4), pp. 485-491 (2006) [Preview Abstract] |
Wednesday, June 5, 2013 8:36AM - 8:48AM |
G7.00004: A single ion coupled to an optical fiber cavity Matthias Steiner, Hendrik-M. Meyer, Christian Deutsch, Jakob Reichel, Michael K\"ohl The development of an efficient ion-photon interface is a major challenge which needs to be overcome to realize large scale ion-based quantum networks. Such an interface could consist of a single ion coupled to high finesse optical cavity. Existing ion-cavity systems operate in a regime, where the coupling of light and ion is smaller than the excited state decay rate. In order to enhance the coupling, smaller cavity mode volumes must be used. We report on the realization of a combined trapped-ion and optical cavity system, in which a single Yb ion is confined by a micron-scale ion trap inside a 230 $\mu$m-long optical fibre cavity. We characterize the spatial ion-cavity coupling and measure the ion-cavity coupling strength using a cavity-stimulated $\Lambda$-transition. By using micro-machined optical fibre cavities, we achieve mode volumes more than two orders of magnitude smaller than previously reported. Owing to the small mode volume of the fibre resonator, the coherent coupling strength between the ion and a single photon exceeds the natural decay rate of the dipole moment. Our results indicate implicitly that stable trapping of single ions in close vicinity of dielectric surfaces does not impose fundamental problems, even at room temperature. [Preview Abstract] |
Wednesday, June 5, 2013 8:48AM - 9:00AM |
G7.00005: Ultrafast Spin-Motion Entanglement and Interferometry with a Single Atom Jonathan Mizrahi, Brian Neyenhuis, Kale Johnson, Chris Monroe We report entanglement of a single atom's hyperfine spin state with its motional state in a timescale of less than 3 ns. We engineer a short train of intense laser pulses to impart a spin-dependent momentum transfer of $2\hbar k$. We further create an atomic interferometer using pairs of momentum kicks and demonstrate collapse and revival of spin coherence as the motional wavepacket is split and recombined. The revival after a pair of kicks occurs only when the second kick is delayed by an integer multiple of the period of the harmonic trap, a signature of entanglement and disentanglement of the spin with the motion. Such quantum control may allow a new regime of ultrafast entanglement between atomic qubits. [Preview Abstract] |
Wednesday, June 5, 2013 9:00AM - 9:12AM |
G7.00006: Micromotion based single-qubit addressing with trapped-ions Nitzan Akerman, Nir Navon, Shlomi Kotler, Yinnon Glickman, Ido Almog, Roee Ozeri Individual-particle addressing is a necessary capability in many quantum information experiments. For example, characterization of multi-qubit operations with quantum process tomography (QPT). We propose and demonstrate a scheme that exploits the inhomogeneous excess micromotion in ion trap to address single-qubits in a chain of several ion-qubits, separated by only few microns. The scheme uses a laser field which is resonant with the micromotion sideband of a narrow optical quadrupole transition and acts as a dressing field with a spatially-dependent coupling along the chain. As a consequence, the level spacing of each ion, in the dressed state picture, becomes position dependent and individual ions can be spectrally separated. We have demonstrated Individual Rabi flops with 85\% fidelity in a three-ion chain. For the case of only two ions, the coupling can be tailored to vanish on one of the two. This allows preparing any two-qubit product state as well as completing state tomography without direct spatially-selective imaging. We demonstrate full QPT for two-qubit S{\o}rensen-M{\o}lmer entangling interaction (Bell-state preparation fidelity of 98\%) which has not been process-analyzed yet. Our tomography resulted process fidelity of 92\%. N. Navon et. al. arXiv:1210.7336(1012). [Preview Abstract] |
Wednesday, June 5, 2013 9:12AM - 9:24AM |
G7.00007: Efficient quantum state-estimation and feedback on trapped ions using unsharp measurement Hermann Uys, Shaun Burd, Sujit Choudhary, Sandeep Goyal, Thomas Konrad Parameter estimation and closed-loop feedback control is ubiquitous in every branch of classical science and engineering. Similar control of quantum systems is usually impossible due to two difficulties. Firstly, quantum phenomena are often short lived due to decoherence, and secondly, attempts to estimate the state of a quantum system through projective measurement, strongly disrupt the dynamics. One alternative is to use unsharp measurements, which are less invasive, but lead to less information gain about the system. A sequence of unsharp measurements, however, carried out in the presence of stronger dynamics, promise real-time state monitoring and control via feedback. Such measurements can be realised by periodically entangling an auxiliary quantum system with the target quantum system, and then carrying out projective measurements on the auxiliary system only. In this talk we discuss an efficient method of estimating both the state of a two-level system and the strength of its coupling to a drive field using unsharp measurement. We then model closed loop feedback control of the two-level dynamics, and explore the level of control over the parameter regime of the model. Finally, we summarize the prospects for implementing the scheme using trapped ions. [Preview Abstract] |
Wednesday, June 5, 2013 9:24AM - 9:36AM |
G7.00008: Sequential quantum measurements: What can be gained by measuring the same system twice Mark Hillery, Janos Bergou, Edgar Feldman It is usually assumed that when a quantum system is measured, the system's state is reset to an eigenstate of the measured observable, and no further information about the initial state of the system can be gained by subsequent measurements. We give two examples to show that this picture is too simple. The first due to Rapcan, et al.\footnote{P. Rapcan, et al., Phys. Rev. A, 84, 032326 (2012).} shows that if Bob is given a qubit, which Alice has previously measured, and Bob has no information about Alice's measurement, he can nonetheless gain information about the initial state of the system by making a further measurement. The second shows that if Alice sends a qubit in one of two nonorthogonal states to Bob, Bob can perform an unambiguous state discrimination measurement on the qubit and then send the same qubit on to Charlie, who can also perform an unambiguous discrimination measurement on it, even though the state of the qubit was disturbed by Bob's measurement. This allows both Bob and Charlie to determine, with a certain probability, in which state Alice prepared the qubit. This procedure could be useful in quantum communication schemes. [Preview Abstract] |
Wednesday, June 5, 2013 9:36AM - 9:48AM |
G7.00009: State readout by coherent motion with few-photon seeding Yen-Wei Lin, Scott Williams, Brian Odom The motion of a single trapped ion resonantly driven by pulsed radiation pressure is studied. We demonstrated that the driven ion quickly builds up coherent oscillations above the thermal motion, after scattering of order only one hundred photons. The motion is analyzed by Doppler velocimetry with subsequent motional amplification. Since the radiation pressure is state-dependent, this motional seeding technique provides a simple method to read out spectroscopy results from a single non-fluorescing ion with a partially closed cycling transition. [Preview Abstract] |
Wednesday, June 5, 2013 9:48AM - 10:00AM |
G7.00010: A single qubit gate with single neutral atoms in a 3D optical lattice Yang Wang, Theodore A. Corcovilos, David S. Weiss We present a quantum computing experiment using individual Cs atoms in a 5 $\mu$m-spaced 3D optical lattice as qubits. We can select a single atom in a 5$\times$5$\times$5 array by crossing two perpendicular far-off-resonance addressing beams at the target atom. The addressing beams minimally affect the mF=0 qubit states, but they AC Stark shift the mF=1 sublevels of the target atoms by at least twice as much as adjacent atoms. Microwave pulses can then be applied that are only resonant with the target atom. The addressing beams can be steered to any site in the array using MEMS mirrors within 10 $\mu$s, allowing for arbitrary single qubit gates in $\leq$ 100 $\mu$s. Future work will involve selectively moving atoms around to fill vacancies by translating a state-dependent optical lattice and entangling adjacent atoms via the Rydberg blockade mechanism. [Preview Abstract] |
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