Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session Q5: Quantum Measurement and Entanglement |
Hide Abstracts |
Chair: Emily Edwards, University of Maryland Room: Arboretum I-III |
Friday, May 28, 2010 8:00AM - 8:12AM |
Q5.00001: Quantum State Mapping in the 133 Cs Hyperfine Ground Manifold Brian Anderson, Aaron Smith, Poul Jessen Quantum systems with Hilbert space dimension greater than two (qudits) are often thought of as carriers of quantum information. Quantum control of the entire qudit system could prove to be very useful for information processing task allowing for the implementation of novel protocols for robust quit manipulation and error correction. We will describe a method to achieve quantum control of the 16 dimensional hyperfine ground manifold of Cesium using a nearly decoherence free protocol involving the application of static, RF and microwave magnetic fields. Numerical optimization can be used to design time dependent control fields that map any initial state to any target state. We have implemented this control protocol and have mapped an initial state to all 16 magnetic eigenstates. Stern-Gerlach analysis shows apparent mapping fidelities around 95 percent, limited by error in the control fields and measurement accuracy. [Preview Abstract] |
Friday, May 28, 2010 8:12AM - 8:24AM |
Q5.00002: Environment Assisted Precision Magnetometry P. Cappellaro, G. Goldstein, J.R. Maze, L. Jiang, J.S. Hodges, A.S. Sorensen, M.D. Lukin We describe a method to enhance the sensitivity of magnetometry and achieve nearly Heisenberg-limited precision measurement using a novel class of entangled states. An individual qubit is used to sense the dynamics of surrounding ancillary qubits, which are in turn affected by the external field to be measured. The resulting sensitivity enhancement is determined by the number of ancillas strongly coupled to the sensor qubit, it does not depend on the exact values of the couplings (allowing to use disordered systems), and is resilient to decoherence. As a specific example we consider electronic spins in the solid-state, where the ancillary system is associated with the surrounding spin bath. The conventional approach has been to consider these spins only as a source of decoherence and to adopt decoupling scheme to mitigate their effects. Here we describe novel control techniques that transform the environment spins into a resource used to amplify the sensor spin response to weak external perturbations, while maintaining the beneficial effects of dynamical decoupling sequences. We discuss specific applications to improve magnetic sensing with diamond nano-crystals, using one Nitrogen-Vacancy center spin coupled to Nitrogen electronic spins. [Preview Abstract] |
Friday, May 28, 2010 8:24AM - 8:36AM |
Q5.00003: Integrated Single Atom Detector W. Rohringer, D. Fischer, M. Trupke, J. Schmiedmayer Detecting ingle atoms is a key ingredient in developing cold atom based quantum technologies. Here we present a detector for trapped atoms, fully integrated on an atom chip (M. Wilzbach, et al. Optics Letters \textbf{34}, 259 (2009) ). The detector consists of a tapered lensed single-mode fiber for precise delivery of excitation light and a multimode fiber to collect the fluorescence. Both are mounted in lithographically defined SU-8 holding structures on an atom chip. Single Rb atoms propagating freely in a magnetic guide are detected with an efficiency of 66{\%} with a signal to noise ratio in excess of 100. In the talk we will give examples of how this detector can be used to probe atom-atom correlations in ultra cold degenerate quantum many body systems. [Preview Abstract] |
Friday, May 28, 2010 8:36AM - 8:48AM |
Q5.00004: Optical Quantum State Synthesis Paul Kwiat, Kevin McCusker, Radhika Rangarajan Sources of well specified photon number are a critical resource for optical quantum information processing (QIP), e.g., quantum cryptography, computing, and metrology. Spontaneous downconversion has been the main method to produce such states, but there is an immediate limitation because the pairs are produced at random. Here we describe a time-multiplexing technique by which one can essentially remove much of the randomness from the process, effectively creating a pseudo-deterministic source of single photons. An extension of the technique allows one to create Fock states with higher photon numbers; due to the semi-deterministic nature of the process, this method is exponentially more efficient than experiments to date. By modifying the scheme, one can also produce more exotic multi-photon states, such as ``N00N'' states, which until now have only been created probabilistically. For all of these multi-photon state creation techniques, the photons from a given downconversion pair actually need to be unentangled in their spectral and spatial modes. We will describe our progress at producing such states, as well as the results of the time-multiplexed scheme for producing single photons on demand. [Preview Abstract] |
Friday, May 28, 2010 8:48AM - 9:00AM |
Q5.00005: Quantum state reconstruction of the 16 dimensional hyperfine manifold in cesium via continuous measurement and control Carlos Riofrio, Aaron Smith, Brian Anderson, Poul Jessen, Ivan Deutsch Quantum state reconstruction techniques based on weak continuous measurement have the advantage of being fast, robust, and almost non-perturbative. Moreover, they have been successfully implemented in experiments on large spin systems, e.g., the F=3 7 dimensional hyperfine manifold in cesium (PRL 97, 180403 (2006)). In this talk, we extend the tomographic algorithm developed by Silberfarb et al. (PRL 95, 030402 (2005)) to the reconstruction of quantum states stored in the complete 16 dimensional ground-electronic hyperfine manifolds (F=3, F=4) of an ensemble of Cs atoms controlled by microwave and radio-frequency magnetic fields. Simulations show that randomly generated control fields produce informationally complete measurement records and thus give high fidelity reconstructed states. Furthermore, appropriate operation regimes are found for possible experimental implementation. [Preview Abstract] |
Friday, May 28, 2010 9:00AM - 9:12AM |
Q5.00006: Multipartite entanglement for one photon shared among four optical modes K.S. Choi, S.B. Papp, A. Goban, H. Deng, P. Lougovski, S.J. van Enk, H.J. Kimble Access to multipartite entanglement enables advances in quantum information science and also contributes to the understanding of strongly correlated systems. A critical requirement for these scientific advances, however, is an efficient and unambiguous method to characterize the purported entangled states. We report the detection and characterization of heralded entanglement in a multipartite quantum state composed of four optical modes that coherently share one photon, a so-called W state [1]. By controlling the phase coherence between bipartite components of the W state, we observe smooth transitions from quadripartite to bipartite entanglement. These observations are possible for our system because our entanglement verification protocol makes use of quantum uncertainty relations to simultaneously detect entangled states that span the Hilbert space of interest [2]. We further describe an experiment that generates entanglement for collective excitations stored in four spatially distinct atomic ensembles. [1] Science 324, 764 (2009); [2] New J. Phys. 11, 063029 (2009) [Preview Abstract] |
Friday, May 28, 2010 9:12AM - 9:24AM |
Q5.00007: Quantifying Quantumness Daniel Braun, Olivier Giraud, Peter A. Braun We introduce and study a measure of ``quantumness'' of a quantum state based on its Hilbert-Schmidt distance from the set of classical states. ``Classical states'' were defined earlier as states for which a positive P-function exists, i.e.~they are mixtures of coherent states [1]. We study invariance properties of the measure, upper bounds, and its relation to entanglement measures. We evaluate the quantumness of a number of physically interesting states and show that for any physical system in thermal equilibrium there is a finite critical temperature above which quantumness vanishes. We then use the measure for identifying the ``most quantum'' states. Such states are expected to be potentially most useful for quantum information theoretical applications. We find these states explicitly for low-dimensional spin-systems, and show that they possess beautiful, highly symmetric Majorana representations. \\[4pt] [1] Classicality of spin states, Olivier Giraud, Petr Braun, and Daniel Braun, Phys. Rev. A 78, 042112 (2008) [Preview Abstract] |
Friday, May 28, 2010 9:24AM - 9:36AM |
Q5.00008: Spin Squeezing and Entanglement in an Ensemble of Spins Greater than 1/2 Leigh Norris, Collin Trail, Ivan Deutsch Spin squeezed states have generated great interest for their possible applications in metrology and quantum information processing. Substantial research has been directed both at producing spin squeezed states and understanding the properties of the states themselves. This has uncovered a complex relationship between collective spin squeezing and the entanglement between the individual spins. Whereas spin squeezing scales monotonically with the two-body concurrence in an ensemble of spin j=1/2 particles, an analogous relationship for j$>$1/2 less clear. We explore this problem for an ensemble of alkali atomic spins interacting with a single spatial mode of the electromagnetic field through the Faraday effect, a system that has previously been used for spin squeezing protocols. We investigate how the amplified projection noise of the large spin atoms leads to enhanced entangling interactions due to increased measurement backaction on the atoms and whether this entanglement can be converted into meaningful spin squeezing through local unitary control. [Preview Abstract] |
Friday, May 28, 2010 9:36AM - 9:48AM |
Q5.00009: The Invisible Quantum Tripwire: Analysis in the Presence of Photon Loss Daniel Lum, Petr Anisimov, Blane McCracken, Jonathan Dowling A quantum tripwire is a quantum interrogation technique based on single photon interference in a Mach-Zehnder interferometer (MZI). This interference is destroyed if one arm of the IFM is blocked, tripping an alarm. The original approach proposed by Elitzur and Vaidman gave an interaction free detection at 50{\%} maximal efficiency [1]. Kwiat and collaborators improved scheme incorporated a quantum Zeno effect (ZE) [2]. Symmetric hypothesis testing, the Chernoff bound, and the Chernoff information provided error estimation to optimize the system with a limited number of photons. We introduce a controlled loss in the detection arm so that a partial ZE occurs and results in high photon loss. If the path is blocked then full ZE is achieved leading to low photon loss. System optimization has shown that detection can be exponentially small without the single photon being lost to the object. References: [1] M. A. Kasevich, P. Kwait, G. Weinfurter, T. Herzog, and A. Zeilinger. Interaction-free measurement, June 1995. [2] A. J. DeWeerd. Interaction-free measurement. American Journal of Physics, 70(3):272--275, March 2002. [Preview Abstract] |
Friday, May 28, 2010 9:48AM - 10:00AM |
Q5.00010: The statistical strength of experiments to reject local realism with photon pairs and inefficient detectors Yanbao Zhang, Emanuel Knill, Scott Glancy Because of the fundamental importance of Bell's theorem, a loophole-free demonstration of a violation of local realism (LR) is highly desirable. Here, we study violations of LR involving photon pairs. We quantify the experimental evidence against LR by using measures of statistical strength related to the Kullback-Leibler (KL) divergence, as suggested by W. van Dam, P. Grunwald and R. Gill [IEEE Trans. Inf. Theory. 51, 2812 (2005)]. Specifically, we analyze a test of LR with entangled states created from two independent polarized photons passing through a polarizing beam splitter. We numerically study the detection efficiency required to achieve a specified statistical strength for the rejection of LR depending on whether photon counters or detectors are used. Based on our results, we find that a test of LR free of the detection loophole requires photon counters with efficiency at least 89.71{\%}, or photon detectors with efficiency at least 91.11{\%}. For comparison, we also perform this analysis with ideal unbalanced Bell states, which are known to allow rejection of LR with detector efficiencies above 2/3. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2019 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700