Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q29: Focus Session: Quantum Information for Quantum Foundations - Experiments and Tests |
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Sponsoring Units: GQI Chair: Christoph Schaeff, University of Vienna Room: C148 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q29.00001: Foundational aspects of energy-time entanglement Jan-{\AA}ke Larsson This presentation will discuss whether energy-time entanglement is a properly Quantum Information representation, by considering its relation to Einstein-Podolsky-Rosen (EPR) elements of reality. The interferometric experiment proposed by J.\ D. Franson in 1989 provides the background, and the main issue here is whether a Local Realist model can give the Quantum-Mechanical predictions for this setup. The Franson interferometer gives the same interference pattern as the usual Bell experiment (modulo postselection). Even so, depending on the precise requirements made on the Local Realist model, this can imply a) no violation, b) smaller violation than usual, or c) full violation of the appropriate statistical bound. The discussion will include the nature of the requirements, the motivation for making them, and their effect. The alternatives include using a) only the measurement outcomes as EPR elements of reality, b) the emission time as EPR element of reality, and c) path realism. These subtle requirements need to be taken into account when designing and setting up future experiments of this kind, intended to test Local Realism, or indeed to do Quantum Information Processing. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q29.00002: Large violation of Bell's inequalities using both counting and homodyne measurements Valerio Scarani, Daniel Cavalcanti, Nicolas Brunner, Paul Skrzypczyk, Alejo Salles So far, all the optical demonstrations of violations of Bell's inequalities have involved discrete degrees of freedom (e.g. polarization, time-bins) and are plagued by the detection-efficiency loophole. Continuous degrees of freedom would be a very interesting alternative because of the efficiency of the homodyne measurement; but the feasible schemes proposed so far reach very weak violations. We show that large violations for easily-prepared states can be achieved if both photon counting and homodyne detections are used. Our simple scheme may lead to the first violation of Bell's inequalities with continuous variables and pave the way for a loophole-free Bell test. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q29.00003: A non-local quantum eraser X. Ma, J. Kofler, A. Qarry, N. Tetik, T. Scheidl, R. Ursin, S. Ramelow, L. Ratschbacher, T. Herbst, A. Fedrizzi, T. Jennewein, A. Zeilinger The complementarity behavior of quantum systems is strikingly illustrated by the quantum eraser, where one can actively choose whether or not to erase which-path information of one particle by performing suitable measurements on another particle entangled with it [1-2]. Quantum mechanics predicts that this choice can be arbitrarily delayed and spatially separated from interference [1-3]. We report the first quantum eraser experiment performed under Einstein locality, i.e. under relativistic space-like separation. We employ the hybrid entanglement between path and polarization of photon pairs and distribute the photons over an optical fibre link of 55 m and, in another experiment, over a free-space link of 144 km. A complementarity inequality is measured and well fits the predictions of quantum mechanics. Our experiment represents a conclusive demonstration of the quantum eraser concept. \\[0pt] [1] M. O. Scully, K. Dr\"{u}hl, Phys. Rev. A 25, 2208 (1982). [2] J. A. Wheeler, in Quantum Theory and Measurement (1984). [3] V. Jacques, \textit{et al.}, Science 315, 966 (2007). [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q29.00004: On the Experimental Violation of Mermin's High-Spin Bell Inequalities in the Schwinger Representation Ruffin Evans, Olivier Pfister Since Bell's original paper in 1964, a wide variety of experimental tests have overwhelmingly supported the completeness of quantum mechanics over local hidden-variable theories. However, relatively little effort has focused on systems of spins larger than $\frac{1}{2}$; generalizing Bell's result to higher dimensions is difficult, and the experiments needed to test these high-spin Bell inequalities are exacting. New advances in high efficiency photon-number-resolving detectors suggest that experimental tests of these inequalities should be possible in the Schwinger representation, using the continuous-variable entangled (two-mode squeezed) fields produced by an optical parametric oscillator below threshold. In this paper, we explore the realistic experimental implementation of this proposal to violate Mermin's high-spin inequalities. We demonstrate that violation for spin values greater than 1 should be attainable under a range of feasible experimental conditions that include finite squeezing and nonideal detection efficiency. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q29.00005: Surface based detection schemes for molecular interferometry experiments - implications and possible applications Thomas Juffmann, Adriana Milic, Michael Muellneritsch, Markus Arndt Surface based detection schemes for molecular interferometry experiments [1] might be crucial in the search for the quantum properties of larger and larger objects [2] since they provide single particle sensitivity. Here we report on molecular interferograms of different biomolecules imaged using fluorescence microscopy. Being able to watch the build-up of an interferogram live and in situ reveals the matter-wave behavior of these complex molecules in an unprecedented way. We examine several problems encountered due to van-der-Waals forces between the molecules and the diffraction grating and discuss possible ways to circumvent these. Especially the advent of ultra-thin (1-100 atomic layers) diffraction masks might path the way towards molecular holography. We also discuss other possible applications such as coherent molecular microscopy.\\[4pt] [1] T. Juffmann, S. Truppe, P. Geyer, A.G. Major, S. Deachapunya, H. Ulbricht, M. Arndt, Phys. Rev. Lett. 103, 263601 (2009).\\[0pt] [2] T. Juffmann, S. Nimmrichter, M. Arndt, H. Gleiter, K.Hornberger, in print, Foundations of Physics. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q29.00006: Matter wave interferometry with large and complex molecules Stefan Gerlich, Sandra Eibenberger, Mathias Tomandl, Jens T\"{u}xen, Marcel Mayor, Markus Arndt Matter wave interferometry with molecules of increasing size, mass and complexity explores the frontiers of quantum mechanics and it is a promising tool for determining molecular properties with high precision. The quantum wave nature of organic molecules is used in a Kapitza-Dirac-Talbot-Lau interferometer to generate a set of high-contrast interference fringes that are highly sensitive to external forces. This is exploited to access thermally averaged internal molecular properties, such as optical and static polarizabilities, static and thermally activated electric dipole moments, information about conformational differences and state changes, optical absorption spectra and more. The information about the internal states can be extracted through conservative interactions, i.e. allowing the persistence of full quantum delocalization in position space. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q29.00007: Violation of local realism with freedom of choice Johannes Kofler, Thomas Scheidl, Rupert Ursin, Sven Ramelow, Xiao-Song Ma, Thomas Herbst, Lothar Ratschbacher, Alessandro Fedrizzi, Nathan Langford, Thomas Jennewein, Anton Zeilinger Bell's theorem shows that local realistic theories place strong restrictions on observable correlations between different systems, giving rise to Bell's inequality which can be violated in experiments using entangled quantum states. Bell's theorem is based on the assumptions of realism, locality, and the freedom to choose between measurement settings. In experimental tests, ``loopholes'' arise which allow observed violations to still be explained by local realistic theories. Violating Bell's inequality while simultaneously closing all such loopholes is one of the most significant still open challenges in fundamental physics today. We present an experiment that violates Bell's inequality while simultaneously closing the locality loophole and addressing the freedom-of-choice loophole, also closing the latter within a reasonable set of assumptions. Reference: T. Scheidl et al., Proc. Natl. Acad. Sci. USA 107, 19708 (2010) [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q29.00008: Experimental non-classicality of an indivisible system Radek Lapkiewicz, Peizhe Li, Christoph Schaeff, Nathan Langford, Sven Ramelow, Marcin Wiesniak, Anton Zeilinger In Quantum Mechanics (QM) not all properties can be simultaneously well defined. An important question is whether a joint probability distribution can describe the outcomes of all possible measurements, allowing a quantum system to be mimicked by classical means. Klyachko et al. [PRL 101, 020403 (2008)] derived an inequality which allowed us to answer this question experimentally. The inequality involves only five measurements and QM predicts its violation for single spin-1 particles. This is the simplest system where such a contradiction is possible. It is also indivisible and as such cannot contain entanglement. In our experiment with single photons distributed among three modes (isomorphic to stationary spin-1 particles) we obtained a value of -3.893(9), which lies more than 90 standard deviations below the ``classical'' bound of -3. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q29.00009: Testing spontaneous localization with ultra-massive cluster interferometry Stefan Nimmrichter, Klaus Hornberger, Markus Arndt Understanding the transition from the microscopic domain of quantum mechanics to our everyday classical world is still an open problem in modern physics. Collapse models are a possible way to resolve this issue by introducing mechanisms which break the quantum superposition principle above a certain mass and time scale. One of the best studied models is the theory of continuous spontaneous localization (CSL) by Ghirardi, Pearle and Rimini [1]. We show that it should be possible to test the predictions of the CSL model in the new matter-wave interferometer for heavy metal clusters that is currently built in Vienna. Extending the original Talbot-Lau setup for biomolecules, the new scheme will operate in the time-domain using three pulsed standing-wave gratings of UV laser light. We argue that this should enable us to see single-particle interference in an unprecedented mass range from $10^5$ up to even $10^8$ atomic mass units. Recent estimates of the strength of the CSL effect by Adler and Bassi [2,3] suggest that a breakdown of the quantum superposition principle would occur in precisely this mass regime.\\[4pt] [1] Phys. Rev. A 42, 78 (1990)\\[0pt] [2] J. Phys. A 40, 2935 (2007)\\[0pt] [3] arxiv eprint 1011.3767v1 (2010) [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q29.00010: Hardy's paradox and a violation of a state-independent Bell inequality in time Alessandro Fedrizzi, Marcelo P. Almeida, Matthew A. Broome, Andrew G. White, Marco Barbieri Tests such as Bell's inequality and Hardy's paradox highlight the differences between local realistic theories and quantum predictions for measurement probabilities and correlations between distant particles. Transposing these tests to the temporal domain, i.e. making two measurements on the one quantum particle at different times, yield Hardy and Bell tests mathematically identical to their spatial counterparts, but give very different physical results. Here, we use a photonic entangling gate to implement non-destructive temporal measurements on a quantum system. We measure a much stronger form of Hardy's paradox and demonstrate violation of a Bell inequality in time independent of the quantum state, including for fully-mixed states. Our work yields interesting fundamental insights and opens up a path to more efficient quantum information processing protocols based on temporal quantum correlations. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q29.00011: Experimental Violation of Two-Party Leggett-Garg Inequalities with Semi-weak Measurements Justin Dressel, Curtis Broadbent, John Howell, Andrew Jordan We generalize the derivation of Leggett-Garg inequalities to systematically treat a larger class of experimental situations by allowing multi-particle correlations, invasive detection, and ambiguous detector results. Furthermore, we show how many such inequalities may be tested simultaneously with a single setup. As a proof of principle, we violate several such two-particle inequalities with data obtained from a polarization-entangled biphoton state and a semi-weak polarization measurement based on Fresnel reflection. We also point out a non-trivial connection between specific two-party Leggett-Garg inequality violations and convex sums of strange weak values. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q29.00012: Causality, Bell's theorem, and Ontic Definiteness Joe Henson Bell's theorem shows that the reasonable relativistic causal principle known as ``local causality'' is not compatible with the predictions of quantum mechanics. It is not possible maintain a satisfying causal principle of this type while dropping any of the better-known assumptions of Bell's theorem. However, another assumption of Bell's theorem is the use of classical logic. One part of this assumption is the principle of \textit{ontic definiteness}, that is, that it must in principle be possible to assign definite truth values to all propositions treated in the theory. Once the logical setting is clarified somewhat, it can be seen that rejecting this principle does not in any way undermine the type of causal principle used by Bell. Without ontic definiteness, the deterministic causal condition known as Einstein Locality succeeds in banning superluminal influence (including signalling) whilst allowing correlations that violate Bell's inequalities. Objections to altering logic, and the consequences for operational and realistic viewpoints, are also addressed. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q29.00013: On dipole anisotropy in spatial distribution of Plank's constant values Simon Berkovich The work relates to the remarkable fact discovered by John Webb et al. of angular variations of the fine structure constant $\alpha $ = e$^{2}$/hc. We elaborate on this fact using our model of quantum mechanics (see [1] and references within). The peculiarity of quantum behavior stems from interactive holography appearing on top of the cellular automaton mechanism of the Universe. Nonlocality comes naturally from sliced holographic processing. As to the anisotropy of $\alpha $, its is due to variations of h caused by different undulation control patterns in different positions with respect to the source of the holographic reference beam. The angular divergences in $\alpha $ are determined by the eccentric placement of the Solar system with respect to this reference holographic beam. This eccentricity factor imposes dipole structuring on several types of astrophysical observations. So, following [1], small opposite changes in h with respect to the eccentricity displacement of the Solar system could be anticipated. Before we have shown that the same eccentricity factor leads to the appearance of the ``axis-of-evil'' in CMB. Further, the recently discovered anisotropy in high-energy cosmic rays should be also determined by the eccentricity factor, i.e. it should adhere to the same dipole. [1] S. Berkovich, ''A Comprehensive Explanation of Quantum Mechanics'', http://www.bestthinking.com/topics/science/physics/ quantum{\_}physics/a-comprehensive-explanation-of-quantum-mechanics [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q29.00014: Scaling of quantum Zeno dynamics in thermodynamic systems Wing Chi Yu, Li-Gang Wang, Shi-Jian Gu Quantum Zeno effect (QZE) refers to the inhabitation of the unitary time evolution of a quantum system by repeated frequent measurements. It has been studied intensively within the content of quantum optics in recent decades. Among those analyses, the systems under consideration are only of a few levels. Little attention of QZE in thermodynamic systems has been paid so far. In this presentation, we will investigate the QZE in thermodynamic systems from the viewpoint of condensed matter physics. We take the one-dimensional transverse-field Ising model and the Lipkin-Meshkov-Glick (LMG) model as examples to illustrate analytically the criteria, in terms of the size dependence of the leading term of the survival probability in the short-time limit, for observing the QZE. Our analysis shows that in order to observe the QZE in the Ising model, the frequency of the projective measurement should be of comparable order to that of the system sizes. The same criterion also holds in the symmetry broken phase of the LMG model. However, in the polarized phase of the LMG model, the leading term of the survival probability is independent of the system size and the QZE can be easily observed. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q29.00015: Decoherence Free Neutron Interferometry Dmitry A. Pushin, David G. Cory, Michael G. Huber, Mohamed Abutaleb, Muhammad Arif, Charles W. Clark A neutron interferometer (NI) is a unique example of the macroscopic quantum coherence and has been used to test fundamental principles of quantum mechanics. In practice, neutron interferometers are not widely used because of their extreme sensitivity to environmental noise which is in part due to the slow velocity (relative to light) of the neutron. We show that a neutron interferometer design can benefit from concepts of quantum information processing. We have machined a Decoherence Free (DF) neutron interferometer designed using a quantum error correction code,\footnote{D. A. Pushin, M. Arif, and D. G. Cory, Phys. Rev. A (http://pra.aps.org/abstract/PRA/v79/i5/e053635) 79, 053635 (2009)} and have shown it to be much less sensitive to mechanical vibrations than is the standard Mach-Zehnder (MZ) interferometer. Both the MZ and DF geometries are incorporated in one crystal, which allows direct comparisons to be made. We believe that our results and related quantum information approaches, such as ``the power of one qubit,''\footnote{E. Knill and R. Laflamme, Phys. Rev. Lett. (http://prl.aps.org/abstract/PRL/v81/i25/p5672\_1) 81, 5672 (1998)} will enable a new series of compact neutron interferometers that can be tailored to specific applications in soft condensed matter and spintronics. [Preview Abstract] |
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