This is a list of this week’s papers on quantum foundations published in the various journals or uploaded to the preprint servers such as arxiv.org and PhilSci Archive.
Nonclassical Paths in Quantum Interference Experiments
PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
on 2014-9-19 2:00pm GMT
Author(s): Rahul Sawant, Joseph Samuel, Aninda Sinha, Supurna Sinha, and Urbasi Sinha
Quantum mechanics permits particles to follow bizarre, looping and curving trajectories, usually with very low probability. But a calculation shows that in some cases, these paths can have significant and possibly measurable effects.
[Phys. Rev. Lett. 113, 120406] Published Fri Sep 19, 2014
on 2014-9-19 2:07am GMT
The classical limits of quantum mechanics on a non-commutative configuration space has been recently studied through the possible ways of removing the non-commutativity based on the classical limit context known as anti-Wick quantization. The conclusion is that the removal of non-commutativity from the configuration space and from the canonical operators are not commuting operations. In order to give an interpretation to the non-exchangeability of the limits, we calculate the Wigner functions of the gaussian-like states of the non-commutative quantum harmonic oscillators and their limits when $\hbar \rightarrow 0$ and $\theta\neq 0$. The reason of the non-exchangeability of the limits is not dynamical.
on 2014-9-19 2:06am GMT
We show that the phenomenon of anomalous weak values is not limited to quantum theory. In particular, we show that the same features occur in a simple model of a coin subject to a form of classical backaction with pre- and post-selection. This provides evidence that weak values are not inherently quantum, but rather a purely statistical feature of pre- and post-selection with disturbance.
on 2014-9-19 2:06am GMT
Experimental free-will or measurement independence is one of the crucial assumptions in derivation of any nonlocal theorem. Any nonlocal correlation obtained in quantum world can have a local deterministic explanation if there is no experimental free-will in choosing the measurement settings. Recently, in [Phys. Rev. Lett. {\bf105}, 250404 (2010)] it has been shown that to obtain a local deterministic description for singlet state correlation one does not need to give up measurement independence completely, but a partial measurement dependence suffices. In three party scenario considering GHZ correlation one can exhibit absolute contradiction between quantum theory and local realism. In this paper we show that such correlation also has local deterministic description if measurement independence is given up, even if not completely. We provide a local deterministic model for equatorial Von Neumann measurements on tripartite GHZ state by sacrificing measurement independence partially.
on 2014-9-19 2:06am GMT
In a recent Letter [PRL 113, 120404 (2014)] Ferrie and Combes claimed to show “that weak values are not inherently quantum, but rather a purely statistical feature of pre- and post-selection with disturbance.” In this Comment I will show that this claim is not valid. It follows from Ferrie and Combes misunderstanding of the concept of weak value.
Effects of dynamical collapse theory on trapped ultra-cold atoms. (arXiv:1409.5388v1 [quant-ph])
on 2014-9-19 2:06am GMT
The Continuous Spontaneous Localization (CSL) theory alters the Schr\”odinger equation. It describes wave function collapse as a dynamical process instead of an ill-defined postulate, thereby providing macroscopic uniqueness and solving the so-called measurement problem of standard quantum theory. CSL contains a parameter $\lambda$ giving the collapse rate of an isolated nucleon in a superposition of two spatially separated states and, more generally, characterizing the collapse time for any physical situation. CSL is experimentally testable, since it predicts some behavior different from that predicted by standard quantum theory. One example is the narrowing of wave functions, which results in energy imparted to particles. Here we consider energy given to trapped ultra-cold atoms. Since these are the coldest samples under experimental investigation, it is worth inquiring how they are affected by the CSL heating mechanism. We examine the CSL heating of a BEC in contact with its thermal cloud. Of course, other mechanisms also provide heat and also particle loss. From varied data on optically trapped cesium BEC’s, we present an energy audit for known heating and loss mechanisms. The result provides an upper limit on CSL heating and thereby an upper limit on the parameter $\lambda$. We obtain $\lambda\lesssim 1(\pm1)\times 10^{-7}$sec$^{-1}$.
Measurements according to Consistent Histories
on 2014-9-18 8:19pm GMT
Publication date: November 2014
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, Volume 48, Part A
Author(s): Elias Okon , Daniel Sudarsky
We critically evaluate the treatment of the notion of measurement in the Consistent Histories approach to quantum mechanics. We find such a treatment unsatisfactory because it relies, often implicitly, on elements external to those provided by the formalism. In particular, we note that, in order for the formalism to be informative when dealing with measurement scenarios, one needs to assume that the appropriate choice of framework is such that apparatuses are always in states of well defined pointer positions after measurements. The problem is that there is nothing in the formalism to justify this assumption. We conclude that the Consistent Histories approach, contrary to what is claimed by its proponents, fails to provide a truly satisfactory resolution for the measurement problem in quantum theory.
How the Result of a Single Coin Toss Can Turn Out to be 100 Heads
on 2014-9-18 2:00pm GMT
Author(s): Christopher Ferrie and Joshua Combes
A classical model is proposed that exhibits the same anomalous weak values as a quantum system, suggesting that weak values are not inherently quantum.
[Phys. Rev. Lett. 113, 120404] Published Thu Sep 18, 2014
Quantum Mechanics in symmetry language. (arXiv:1305.4349v5 [quant-ph] UPDATED)
on 2014-9-18 11:39am GMT
We consider symmetry as a foundational concept in quantum mechanics and rewrite quantum mechanics and measurement axioms in this description. We argue that issues related to measurements and physical reality of states can be better understood in this view. In particular, the abstract concept of symmetry provides a basis-independent definition for observables. Moreover, we show that the apparent projection/collapse of the state as the final step of measurement or decoherence is the result of breaking of symmetries. This phenomenon is comparable with a phase transition by spontaneous symmetry breaking, and makes the process of decoherence and classicality a natural fate of complex systems consisting of many interacting subsystems. Additionally, we demonstrate that the property of state space as a vector space representing symmetries is more fundamental than being an abstract Hilbert space, and its $L2$ integrability can be obtained from the imposed condition of being a representation of a symmetry group and general properties of probability distributions.
An Inquiry into the Possibility of Nonlocal Quantum Communication. (arXiv:1409.5098v1 [quant-ph])
on 2014-9-18 11:39am GMT
The possibility of nonlocal quantum communication is considered in the context of several gedankenexperiments. A new quantum paradox is suggested in which the presence or absence of an interference pattern in a path-entangled two photon system, controlled by measurement choice, provides a nonlocal signal. We show that for all of the cases considered, the intrinsic complementarity between one-particle and two-particle interference blocks the potential nonlocal signal.
A local-time-induced unique pointer basis
J. Jeknić-Dugić , M. Arsenijević , M. Dugić
Published 17 September 2014
There is a solution to the problem of asymptotic completeness in many-body scattering theory that offers a specific view of the quantum unitary dynamics which allows for the straightforward introduction of local time for every, at least approximately closed, many-particle system. In this approach, time appears as a hidden classical parameter of the unitary dynamics of a many-particle system. We show that a closed many-particle system can exhibit behaviour that is characteristic for open quantum systems and there is no need for the ‘state collapse’ or environmental influence. On the other hand, closed few-particle systems bear high quantum coherence. This local-time scheme encompasses concepts including ‘emergent time’, ‘relational time’ as well as the ‘hybrid system’ models with possibly induced gravitational uncertainty of time.
on 2014-9-17 2:33am GMT
We study the mechanism by which the particle-antiparticle entangled state collapses instantaneously at a distance. By making two key assumptions, we are able to show not only that instantaneous collapse of a wave function at a distance is possible but also that it is an invariant quantity under Lorentz transformation and compatible with relativity. In addition, we will be able to detect in which situation a many-body entangled system exhibits the maximum collapse speed among its entangled particles. Finally we suggest that every force in nature acts via entanglement.
Entanglement and disentanglement in relativistic quantum mechanics
on 2014-9-16 8:15pm GMT
Publication date: Available online 16 September 2014
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Jeffrey A. Barrett
A satisfactory formulation of relativistic quantum mechanics requires that one be able to represent the entangled states of spacelike separated systems and describe how such states evolve. This paper presents two stories that one must be able to tell coherently in order to understand relativistic entangled systems. These stories help to illustrate why one׳s understanding of entanglement in relativistic quantum mechanics must ultimately depend on the details of one׳s strategy for addressing the quantum measurement problem.
Bell-inequality violation with entangled photons, free of the coincidence-time loophole
on 2014-9-16 2:00pm GMT
Author(s): Jan-Åke Larsson, Marissa Giustina, Johannes Kofler, Bernhard Wittmann, Rupert Ursin, and Sven Ramelow
In a local realist model, physical properties are defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. Proper experimental violation of a Bell inequality would show that the world cannot be described with such a model. Experiments in…
[Phys. Rev. A 90, 032107] Published Tue Sep 16, 2014
Limits on Observation in Quantum Gravity and Black Holes. (arXiv:1409.4365v1 [gr-qc])
on 2014-9-16 11:50am GMT
We discuss how the bounds on observation associated with the Planck units would affect an observers perception of a black hole. By simply imposing Planck scale quantities as the lower bounds for length, time, and mass of black hole formation, interesting insights into the nature of black holes can be gained.
physics.hist-ph updates on arXiv.org
on 2014-9-16 11:50am GMT
After stating the author’s ontic position, a collage of relevant thoughts of some distinguished foundationally-minded physicists are quoted and polemically commented upon. Thus, a kind of historical background of the recent ontic breakthrough is given. The brealthrough itself is presented in Part II.
Motion and gravity effects in the precision of quantum clocks. (arXiv:1409.4235v1 [quant-ph])
on 2014-9-16 11:49am GMT
We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.
Leggett-Garg Inequalities, Pilot Waves and Contextuality. (arXiv:1409.4104v1 [quant-ph])
on 2014-9-16 11:49am GMT
In this paper we first analyse Leggett and Garg’s argument to the effect that macroscopic realism contradicts quantum mechanics. After making explicit all the assumptions in Leggett and Garg’s reasoning, we argue against the plausibility of their auxiliary assumption of non-invasive measurability, using Bell’s construction of stochastic pilot-wave theories as a counterexample. Violations of the Leggett-Garg inequality thus do not provide a good argument against macrorealism. We then apply Dzhafarov and Kujala’s analysis of contextuality in the presence of signalling to the case of the Leggett-Garg inequalities, with rather surprising results. An analogy with pilot-wave theory again helps to clarify the situation.
General relativity as the equation of state of spin foam
Classical and Quantum Gravity – latest papers
on 2014-9-16 12:00am GMT
Building on recent significant results of Frodden, Ghosh and Perez (FGP) and Bianchi, I present a quantum version of Jacobsonʼs argument that the Einstein equations emerge as the equation of state of a quantum gravitational system. I give three criteria a quantum theory of gravity must satisfy if it is to allow Jacobsonʼs argument to be run. I then show that the results of FGP and Bianchi provide evidence that loop quantum gravity satisfies two of these criteria, and argue that the third should also be satisfied in loop quantum gravity. I also show that the energy defined by FGP is the canonical energy associated with the boundary term of the Holst action.
The Status of Determinism in Proofs of the Impossibility of a Noncontextual Model of Quantum Theory
Latest Results for Foundations of Physics
on 2014-9-16 12:00am GMT
Abstract
In order to claim that one has experimentally tested whether a noncontextual ontological model could underlie certain measurement statistics in quantum theory, it is necessary to have a notion of noncontextuality that applies to unsharp measurements, i.e., those that can only be represented by positive operator-valued measures rather than projection-valued measures. This is because any realistic measurement necessarily has some nonvanishing amount of noise and therefore never achieves the ideal of sharpness. Assuming a generalized notion of noncontextuality that applies to arbitrary experimental procedures, it is shown that the outcome of a measurement depends deterministically on the ontic state of the system being measured if and only if the measurement is sharp. Hence for every unsharp measurement, its outcome necessarily has an indeterministic dependence on the ontic state. We defend this proposal against alternatives. In particular, we demonstrate why considerations parallel to Fine’s theorem do not challenge this conclusion.
A Minimal Framework for Non-Commutative Quantum Mechanics
Latest Results for Foundations of Physics
on 2014-9-14 12:00am GMT
Abstract
Deformation quantisation is applied to ordinary Quantum Mechanics by introducing the star product in a configuration space combining a Riemannian structure with a Poisson one. A Hilbert space compatible with such a configuration space is designed. The dynamics is expressed by a Hermitian Hamiltonian containing a scalar potential and a one-form potential. As a simple illustration, it is shown how a particular type of non-commutativity of the star product is interpretable as generating the Zeeman effect of ordinary Quantum Mechanics.
