Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A33: Focus Session: Quantum Foundations: Quantum Theory Meets Relativity |
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Sponsoring Units: GQI Chair: Jonathan Oppenheim, University College London Room: 706 |
Monday, March 3, 2014 8:00AM - 8:36AM |
A33.00001: Quantum computation versus firewalls Invited Speaker: Patrick Hayden |
Monday, March 3, 2014 8:36AM - 8:48AM |
A33.00002: Quantum capacity of quantum black holes Chris Adami, Kamil Bradler The fate of quantum entanglement interacting with a black hole has been an enduring mystery, not the least because standard curved space field theory does not address the interaction of black holes with matter. We discuss an effective Hamiltonian of matter interacting with a black hole that has a precise analogue in quantum optics and correctly reproduces both spontaneous and stimulated Hawking radiation with grey-body factors. We calculate the quantum capacity of this channel in the limit of perfect absorption, as well as in the limit of a perfectly reflecting black hole (a white hole). We find that the white hole is an optimal quantum cloner, and is isomorphic to the Unruh channel with positive quantum capacity. The complementary channel (across the horizon) is entanglement-breaking with zero capacity, avoiding a violation of the quantum no-cloning theorem. The black hole channel on the contrary has vanishing capacity, while its complement has positive capacity instead. Thus, quantum states can be reconstructed faithfully behind the black hole horizon, but not outside. This work sheds new light on black hole complementarity because it shows that black holes can both reflect and absorb quantum states without violating the no-cloning theorem, and makes quantum firewalls obsolete. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A33.00003: Direct detection of classically undetectable dark matter through quantum decoherence C. Jess Riedel Although various pieces of indirect evidence about the nature of dark matter have been collected, its direct detection has eluded experimental searches despite extensive effort. If the mass of dark matter is below 1 MeV, it is essentially imperceptible to conventional detection methods because negligible energy is transferred to nuclei during collisions. Here I propose directly detecting dark matter through the quantum decoherence it causes rather than its classical effects such as recoil or ionization. I show that quantum spatial superpositions are sensitive to low-mass dark matter which is inaccessible to classical techniques. This provides new independent motivation for matter interferometry with large masses, especially on spaceborne platforms. The apparent dark matter wind we experience as the Sun travels through the Milky Way ensures interferometers and related devices are directional detectors, and so are able to provide unmistakable evidence that decoherence has galactic origins. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A33.00004: Difficult Requirements for a Gravitational Wave Mission using Atom Interferometry Peter L. Bender A PRL paper by Graham, Hogan, Kasevich, and Rajendran in April, 2013 suggested gravitational wave observations in space using single photon transitions on highly forbidden optical lines for atom interferometry measurements. The main example given was based on use of the 698 nm optical clock transition in Sr-87, a 1000 km baseline, and large momentum transfer laser pulse sequences producing 2400 state transitions for a given atom over a 100 s observation period. A specific scenario for such a mission is needed in order to permit evaluation of the requirements. As a stop-gap, a laser power of 30 W, square laser pulses, 1 m diam. transmitting telescopes, and operation of 4 concurrent pairs of atom interferometers are being assumed. Based on these assumptions, the atom cloud temperature requirement would be below 0.1 pK, and the number of atoms required per cloud would be extremely high. Such a mission would be much more complex than a laser interferometry mission with better overall sensitivity, such as the extensively studied LISA mission or the recently proposed evolved-LISA (eLISA) mission. A LISA Pathfinder mission is scheduled for launch in 2015, funded mainly by ESA . A gravitational wave observation theme is being considered by ESA as part of their Cosmic Vision Programme. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A33.00005: Local two-level PT symmetric system violates no-signalling condition Yi-Chan Lee, Min-Hsiu Hsieh, Steven Flammia, Ray-Kuang Lee We examine $\mathcal{PT}$ symmetric quantum theory by considering a composite physical system. The parties of this composite system are spatially separated and each hold half of a part of a maximally entangled state. According to the transition rule between Hermitian quantum systems and $\mathcal{PT}$ symmetric quantum systems which is used in previous literature, the existence of a local $\mathcal{PT}$ symmetric quantum system will cause a violation of the non-signalling condition. Our results reveal that either the transition rules need to be modified or $\mathcal{PT}$ symmetric quantum theory is not a local theory. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A33.00006: Inferring causal structure: a quantum advantage Katja Ried, Robert Spekkens The problem of inferring causal relations from observed correlations is central to science, and extensive study has yielded both important conceptual insights and widely used practical applications. Yet some of the simplest questions are impossible to answer classically: for instance, if one observes correlations between two variables (such as taking a new medical treatment and the subject's recovery), does this show a direct causal influence, or is it due to some hidden common cause? We develop a framework for quantum causal inference, and show how quantum theory provides a unique advantage in this decision problem. The key insight is that certain quantum correlations can only arise from specific causal structures, whereas pairs of classical variables can exhibit any pattern of correlation regardless of whether they have a common cause or a direct-cause relation. For example, suppose one measures the same Pauli observable on two qubits. If they share a common cause, such as being prepared in an entangled state, then one never finds perfect (positive) correlations in every basis, whereas perfect anticorrelations are possible (if one prepares the singlet state). Conversely, if a channel connects the qubits, hence a direct causal influence, perfect anticorrelations are impossible. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A33.00007: Trapping light by mimicking gravitational lensing Hui Liu, Chong Sheng, Shining Zhu, Dentcho Genov One of the most fascinating predictions of the theory of general relativity is the effect of gravitational lensing, the bending of light in close proximity to massive stellar objects. Recently, artificial optical materials have been proposed to study the various aspects of curved spacetimes, including light trapping and Hawking's radiation. However, the development of experiments 'toy' models that simulate gravitational lensing in curved spacetimes remains a challenge, especially for visible light. Here, by utilizing a microstructured optical waveguide around a microsphere, we propose to mimic curved spacetimes caused by gravity, with high precision. We experimentally demonstrate both far-field gravitational lensing effects and the critical phenomenon in close proximity to the photon sphere of astrophysical objects under hydrostatic equilibrium. The proposed microstructured waveguide can be used as an omnidirectional absorber, with potential light harvesting and microcavity applications. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A33.00008: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 10:00AM - 10:12AM |
A33.00009: The Dirac Equation in Curved Space-Time and the Nonrelativistic Limit Jonathan Noble, Ulrich Jentschura The Foldy-Wouthuysen transformation is applied to a number of generalized Dirac particles in curved space-times. The Dirac-Schwarzschild Hamiltonian is covariantly coupled to a central gravitational field (black hole) within general relativity. We identify the averaged trajectory (after the elimination of the zitterbewegung which proceeds at the velocity of light). The transformed Hamiltonian is much easier to understand as it clearly displays the gravitational correction terms. These include terms describing the kinetic corrections to the gravitational coupling, a Darwin (zitterbewegung) term, and a spin orbit coupling term. Additionally, we apply the transformation to the transition current, and find a gravitational kinetic correction as well as gravitational corrections to the magnetic coupling. We also obtain results for a few other phenomenologically interesting generalized Dirac Hamiltonians, such as those describing a Dirac particle in a non-inertial frame. Finally, we discuss the possible pitfalls which one can encounter when preforming the transformation, including the ``chiral'' method which has some elegant analytic properties, but does break the fundamental symmetries of the original Hamiltonian, as well as change the physical interpretation. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A33.00010: Complex Teichm\"{u}ller Space below the Planck Length for the Interpretation of Quantum Mechanics Friedwardt Winterberg As Newton's mysterious action at a distance law of gravity was explained as a Riemannian geometry by Einstein, it is proposed that the likewise mysterious non-local quantum mechanics is explained by the analytic continuation below the Planck length into a complex Teichm\"{u}ller space. Newton's theory worked extremely well, as does quantum mechanics, but no satisfactory explanation has been given for quantum mechanics. In one space dimension, sufficient to explain the EPR paradox, the Teichm\"{u}ller space is reduced to a space of complex Riemann surfaces. Einstein's curved space-time theory of gravity was confirmed by a tiny departure from Newton's theory in the motion of the planet Mercury, and an experiment is proposed to demonstrate the possible existence of a Teichm\"{u}ller space below the Planck length. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A33.00011: Origin of Dynamical Quantum Non-locality Cesar E. Pachon, Leonardo A. Pachon Non-locality is one of the hallmarks of quantum mechanics and is responsible for paradigmatic features such as entanglement and the Aharonov-Bohm effect. Non-locality comes in two ``flavours'': a \emph{kinematic non-locality}-- arising from the structure of the Hilbert space-- and a \emph{dynamical non-locality}-- arising from the quantum equations of motion--. Kinematic non-locality is unable to induce any change in the probability distributions, so that the ``action-at-a-distance'' cannot manifest. Conversely, dynamical non-locality does create explicit changes in probability, though in a ``causality-preserving'' manner. The origin of non-locality of quantum measurements and its relations to the fundamental postulates of quantum mechanics, such as the uncertainty principle, have been only recently elucidated. Here we trace the origin of dynamical non-locality to the superposition principle. This relation allows us to establish and identify how the uncertainty and the superposition principles determine the non-local character of the outcome of a quantum measurement. Being based on group theoretical and path integral formulations, our formulation admits immediate generalizations and extensions to to, e.g., quantum field theory. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A33.00012: Experimental unconditionally secure bit commitment Yang Liu, Yuan Cao, Marcos Curty, Sheng-Kai Liao, Jian Wang, Ke Cui, Yu-Huai Li, Ze-Hong Lin, Qi-Chao Sun, Dong-Dong Li, Hong-Fei Zhang, Yong Zhao, Teng-Yun Chen, Cheng-Zhi Peng, Qiang Zhang, Adan Cabello, Jian-Wei Pan Quantum physics allows unconditionally secure communication between parties that trust each other. However, when they do not trust each other such as in the bit commitment, quantum physics is not enough to guarantee security. Only when relativistic causality constraints combined, the unconditional secure bit commitment becomes feasible. Here we experimentally implement a quantum bit commitment with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than $20$ km. Bits are successfully committed with less than $5.68\times10^{-2}$ cheating probability. This provides an experimental proof of unconditional secure bit commitment and demonstrates the feasibility of relativistic quantum communication. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A33.00013: No Drama Quantum Electrodynamics? Andrey Akhmeteli Is it possible to offer a ``no drama'' quantum electrodynamics, as simple (in principle) as classical electrodynamics -- a theory described by a system of partial differential equations (PDE) in 3+1 dimensions, but reproducing unitary evolution of a quantum field theory in the Fock space? The following results suggest an affirmative answer: 1. The scalar field can be algebraically eliminated from scalar electrodynamics. 2. After introduction of a complex 4-potential (producing the same electromagnetic field (EMF) as the standard real 4-potential), the spinor field can be algebraically eliminated from spinor electrodynamics. 3. The resulting theories describe independent evolution of EMF and can be embedded into quantum field theories. Another fundamental result: in a general case, the Dirac equation is equivalent to a 4th order PDE for just one component, which can be made real by a gauge transform. Issues related to the Bell theorem and the connection with Barut's self-field electrodynamics are discussed. A. Akhmeteli, Int'l Journal of Quantum Information, Vol. 9, Suppl., 17-26 (2011) A. Akhmeteli, Journal of Mathematical Physics, Vol. 52, 082303 (2011) A. Akhmeteli, quant-ph/1111.4630 A. Akhmeteli, European Physical Journal C, Vol. 73, 2371 (2013) (open access) [Preview Abstract] |
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