Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X44: Measurement, Characterization, and Emulation |
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Sponsoring Units: GQI Chair: Ken Brown, Georgia Institute of Techology Room: 347 |
Friday, March 18, 2016 8:00AM - 8:12AM |
X44.00001: Consecutive Measurements in Quantum Mechanics Jennifer R. Glick, Christoph Adami The physics of quantum measurement still continues to puzzle with no resolution in sight between competing interpretations, in particular because no interpretation has so far produced predictions that would be falsifiable via experiment. Here we present an analysis of consecutive projective measurements performed on a quantum state using quantum information theory, where the entanglement between the quantum system and a measuring device is explicitly taken into account, and where the consecutive measurements increase the joint Hilbert space while the wavefunction of the joint system never collapses. Using this relative-state formalism we rederive well-known results for the pairwise correlation between any two measurement devices, but show that considering the joint as well as conditional entropy of three devices reveals a difference between the collapse and no-collapse pictures of quantum measurement that is experimentally testable. [Preview Abstract] |
Friday, March 18, 2016 8:12AM - 8:24AM |
X44.00002: Hidden Variables Theorems with Fewer Measurements Jay Lawrence A Greenberger-Horne-Zeilinger (GHZ) contradiction may be thought of as a sequence of measurements on a system of $N$ particles, for which each may be duplicated by local hidden variables up to, but not including the last of an irreducible set. Each measurement consists of $N$ spatially separated local measurements on individual particles. Existing contradictions require more such measurements than there are particles, the minimum number being $N+1$. By allowing successive measurements to impose incremental local constraints on the hidden variables (as opposed to global constraints associated with products of hidden variables), we derive contradictions that require fewer measurements. We have found protocols for which the number of measurements, $N_m$, grows more slowly than linearly with the number of particles: Asymptotically, $N_m \sim \sqrt{2N}$ for large $N$ if the particles are qubits, and a similar relation holds for particles of higher spins. [Preview Abstract] |
Friday, March 18, 2016 8:24AM - 8:36AM |
X44.00003: Statistical and optimal behaviours of weak continuous quantum measurement using stochastic path integral formalism Areeya Chantasri, Andrew Jordan We study stochastic behaviour and optimal dynamics of quantum systems under weak continuous measurement. Using the stochastic path integral formalism and action principle introduced in [Phys. Rev. A 88, 042110 (2013) and Phys. Rev. A 92, 032125 (2015)], the optimal evolution, such as the most likely paths, can be obtained by extremizing the action of the stochastic path integral. We also show that any statistical information, such as multi-time correlation functions for quantum state variables, can be derived by applying functional methods and a perturbative approach to the stochastic path integral. Examples are given in one-qubit and two-qubit case. Moreover, we consider an example of qubit measurement with feedback control, using the action principle to investigate the global dynamics of its most likely paths, and finding that qubit state stabilization at any desired pure state is possible with linear feedback. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X44.00004: Localizing and observing Kochen-Specker quantum contextuality using weak measurements. Mordecai Waegell, Jeff Tollaksen, Yuji Hasegawa, Stephan Sponar, Tobias Denkmayr, Hermann Geppert Experimental tests of the Kochen-Specker (KS) theorem conventionally require a set of different measurement settings, and the test can furthermore be applied to an arbitrary prepared state. These experiments show that nature is contextual, but they do not indicate which specific observables must behave nonclassically. We show that, using pre- and post-selected states from within a set of projectors that prove the KS theorem, it is possible to identify another specific projector in the set that behaves nonclassically, in this case because it has an anomalous weak value. We explore specific KS sets that gives rise to the Quantum Pigeonhole Effect (QPE), and use weak measurements on a large ensemble of identically pre- and post-selected neutrons to verify the QPE, and also to measure the anomalous weak value of the nonclassical projector. We construct a new contextuality inequality based on the recent result of Pusey showing that any projector with a negative weak value is a proof of contextuality, and show that our measured weak value is many standard deviations below zero. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X44.00005: Direct Characterization of Quantum Dynamics with Noisy Ancilla Eugene Dumitrescu, Travis Humble We present methods for the direct characterization of quantum dynamics (DCQD) in which both the principal and ancilla systems undergo noisy processes. Using a concatenated error detection code, we discriminate between located and unlocated errors on the principal system in what amounts to filtering of ancilla noise. The example of composite noise involving amplitude damping and depolarizing channels is used to demonstrate the method, while we find the rate of noise filtering is more generally dependent on code distance. Our results indicate the accuracy of quantum process characterization can be greatly improved while remaining within reach of current experimental capabilities. [Preview Abstract] |
Friday, March 18, 2016 9:00AM - 9:12AM |
X44.00006: Realizing quantum advantage without entanglement in single-photon states Alejandra Maldonado-Trapp, Pablo Solano, Anzi Hu, Charles W. Clark Correlations allow us to measure, and quantitatively study, the properties of physical systems, their evolution and their interactions. Quantum discord expresses quantum correlations beyond those associated with entanglement.\footnote{K Modi, {\em et al., Rev. Mod. Phys. } {\bf 84}, 1655 (2012)}. However, discord has not yet been adopted as a standard subject of study by the experimental community. Here we propose a feasible optical setup to generate symmetric two-qubit $X$-states with controllable coherences, where the two qubits correspond to the spin and path of a photon. With these states we show how a classical random variable $K$ can be encoded by Alice and decoded by Bob. Using our previous results \footnote{A. Maldonado-Trapp, {\em et al., Quantum Inf. Process} {\bf 14} 1947 (2015)} we study the correlations between the spin and path qubits and its relation with the information about $K$ that can be decoded by Bob using local measurements with or without two-qubit gate operations.\footnote{M. Gu, {\em et al., Nature Phys. }{\bf 8}, 671 (2012)} Discord is the mutual information contained in the coherences of the system, and it is possible to exploit it for quantum advantage even in the absence of entanglement. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X44.00007: A novel computational approach towards the certification of large-scale boson sampling Joonsuk Huh Recent proposals of boson sampling and the corresponding experiments exhibit the possible disproof of extended Church-Turning Thesis. Furthermore, the application of boson sampling to molecular computation has been suggested theoretically [1]. Till now, however, only small-scale experiments with a few photons have been successfully performed. The boson sampling experiments of 20-30 photons are expected to reveal the computational superiority of the quantum device. A novel theoretical proposal for the large-scale boson sampling using microwave photons is highly promising due to the deterministic photon sources and the scalability [2]. Therefore, the certification protocol of large-scale boson sampling experiments should be presented to complete the exciting story. We propose, in this presentation, a computational protocol towards the certification of large-scale boson sampling. The correlations of paired photon modes and the time-dependent characteristic functional with its Fourier component can show the fingerprint of large-scale boson sampling. [1] J. Huh, G. G. Guerreschi, B. Peropadre, J. R. McClean, and A. Aspuru-Guzik. \textit{Nature Photon}. 9 (2015): pp 615-620. [2] B, Peropadre, G. G. Guerreschi, J. Huh, and A. Aspuru-Guzik. Preprint: arXiv:1510.08064.\\ \\ This work was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(NRF-2015R1A6A3A04059773), the ICT R&D program of MSIP/IITP [2015-019, Fundamental Research Toward Secure Quantum Communication] and Mueunjae Institute for Chemistry (MIC) postdoctoral fellowship. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X44.00008: Occupation number entanglement in mesoscopic conductors David Dasenbrook, Christian Flindt The controlled entanglement of electrons in mesoscopic conductors has been theoretically investigated before using the spin- and orbital degrees of freedom. By contrast, entanglement of two spatially separated electronic channels using the fermionic occupation number has mostly been considered inaccessible due to the charge superselection rule. However, using non-local measurements or combining several copies of occupation number entangled states, the superselection rules can be lifted and the entanglement can be detected using current and noise measurements. We present the theory for an interferometric setup to detect entanglement in the electron-hole degree of freedom of electronic excitations [1] as well as a mesoscopic setup that demonstrates entanglement and non-locality of a single electron. [1] D. Dasenbrook and C. Flindt, Phys. Rev. B 92, 161412(R) (2015) [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X44.00009: Neutron interferometry for precise characterization of quantum systems Dusan Sarenac, Chandra Shahi, Taisiya Mineeva, Christopher J. Wood, Michael G. Huber, Muhammad Arif, Charles W. Clark, David G. Cory, Dmitry A. Pushin Neutron interferometry (NI) is among the most precise techniques used to test the postulates of quantum mechanics. It has demonstrated coherent spinor rotation and superposition, gravitationally induced quantum interference, the Aharonov-Casher effect, violation of a Bell-like inequality, and generation of a single-neutron entangled state. As massive, penetrating and neutral particles neutrons now provide unique capabilities in classical imaging applications that we seek to extend to the quantum domain. We present recent results on NI measurements of quantum discord in a bipartite quantum system\footnote{``Quantum correlations in a noisy neutron interferometer,'' C. J. Wood {\em et al., Phys. Rev. A} {\bf 90}, 032315 (2014)} and neutron orbital angular momentum multiplexing,\footnote{``Controlling neutron orbital angular momentum,'' C. W. Clark {\em et al., Nature} {\bf 525}, 504 (2015)} and review progress on our commissioning of a decoherence-free-subspace NI user facility at the NIST Center for Neutron Research.\footnote{``Experimental realization of decoherence-free subspace in neutron interferometry,'' D. A. Pushin {\em et al., Phys. Rev. Lett.} {\bf 107}, 150401 (2011)} [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X44.00010: Recovering the ideal results of a perturbed quantum emulator Michael Marthaler, Lin Tian, Iris Schwenk We consider a quantum emulator which is a model of an ideal Hamiltonian of interest $H_S$. However, inevitably the system is perturbed by coupling to additional degrees of freedom. We study the case where we are interested in extracted a correlator from the emulated system in equilibrium. We show that it is possible to extract the ideal correlator from a perturbed system under certain conditions. The ideal correlator can be reconstructed if any n-time correlator of the ideal system can be written as a product of two-time correlators. [Preview Abstract] |
Friday, March 18, 2016 10:00AM - 10:12AM |
X44.00011: Experimental observation of melting of the effective Minkowski spacetime Igor Smolyaninov, Vera Smolyaninova Cobalt nanoparticle-based ferrofluid in the presence of an external magnetic field forms a self-assembled hyperbolic metamaterial, which may be described as an effective 3D Minkowski spacetime for extraordinary photons. Moreover, such extraordinary photons perceive thermal gradients in the ferrofluid as an effective gravitational field, which obeys the Newton law. If the magnetic field is not strong enough, the effective Minkowski spacetime gradually melts under the influence of thermal fluctuations. On the other hand, it may restore itself if the magnetic field is increased back to its original value. Here we present direct microscopic visualization of such a Minkowski spacetime melting/crystallization, which is somewhat similar to hypothesized formation of the Minkowski spacetime in loop quantum cosmology [1]. [1] M. Bojowald, J. Mielczarek, ``Some implications of signature-change in cosmological models of loop quantum gravity'', arXiv:1503.09154 [gr-qc] [Preview Abstract] |
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