Weekly Papers on Quantum Foundations (14)

Authors: Carlos Sabín

We show how to use quantum metrology to detect a wormhole. A coherent state of the electromagnetic field experiences a phase shift with a slight dependence on the throat radius of a possible distant wormhole. We show that this tiny correction is, in principle, detectable by homodyne measurements after long propagation lengths for a wide range of throat radii and distances to the wormhole, even if the detection takes place very far away from the throat, where the spacetime is very close to a flat geometry. We use realistic parameters from state-of-the-art long-baseline laser interferometry, both Earth-based and space-borne. The scheme is, in principle, robust to optical losses and initial mixedness.

Authors: Francesco VedovatoCostantino AgnesiMatteo SchiavonDaniele DequalLuca CalderaroMarco TomasinDavide Giacomo MarangonAndrea StancoVincenza LuceriGiuseppe BiancoGiuseppe Vallone,Paolo Villoresi

Gedankenexperiments have consistently played a major role in the development of quantum theory. A paradigmatic example is Wheeler's delayed-choice experiment, a wave-particle duality test that cannot be fully understood using only classical concepts. Here, we implement Wheeler's idea along a satellite-ground interferometer which extends for thousands of kilometers in Space. We exploit temporal and polarization degrees of freedom of photons reflected by a fast moving satellite equipped with retro-reflecting mirrors. We observed the complementary wave-like or particle-like behaviors at the ground station by choosing the measurement apparatus while the photons are propagating from the satellite to the ground. Our results confirm quantum mechanical predictions, demonstrating the need of the dual wave-particle interpretation, at this unprecedented scale. Our work paves the way for novel applications of quantum mechanics in Space links involving multiple photon degrees of freedom.

Dawid, Richard and Hartmann, Stephan (2017) The No Miracles Argument without the Base Rate Fallacy. [Preprint]

Author(s): Philipp Strasberg, Gernot Schaller, Tobias Brandes, and Massimiliano Esposito

Nanomachines are subject to random thermal and quantum fluctuations that are not captured by traditional thermodynamic theory. A new theoretical investigation offers a step toward a unified nanoscale theory by showing how externally prepared systems (e.g., atoms in an optical cavity or DNA bases in an enzyme reaction) that interact with a nanoscopic device can be a source of nonequilbrium free energy.


[Phys. Rev. X 7, 021003] Published Fri Apr 07, 2017

Author(s): Yuan-Yuan Zhao, Paweł Kurzyński, Guo-Yong Xiang, Chuan-Feng Li, and Guang-Can Guo

The original Heisenberg error-disturbance relation was recently shown to be not universally valid and two different approaches to reformulate it were proposed. The first one focuses on how the error and disturbance of two observables A and B depend on a particular quantum state. The second one asks …
[Phys. Rev. A 95, 040101(R)] Published Fri Apr 07, 2017

Publication date: Available online 6 April 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Katie Robertson
Over many years, Aharonov and co-authors have proposed a new interpretation of quantum mechanics: the two-time interpretation. This interpretation assigns two wavefunctions to a system, one of which propagates forwards in time and the other backwards. In this paper, I argue that this interpretation does not solve the measurement problem. In addition, I argue that it is neither necessary nor sufficient to attribute causal power to the backwards-evolving wavefunction 〈 Φ | and thus its existence should be denied, contra the two-time interpretation. Finally, I follow Vaidman in giving an epistemological reading of 〈 Φ | .

Authors: Gabor Etesi

In this letter we make a proposal that the second law of thermodynamics holds true for a closed physical system consisting of pure antimatter in the thermodynamical limit, but in a reversed form. We give two plausible arguments in favour to this proposal: one is based on the $CPT$ theorem of relativistic quantum field theories while the other one is based on Noether's theorem of theoretical physics. However in our understanding the ultimate validity or invalidity of this idea can be decided only by future physical experiments.

As a consequence of the proposal we argue that the dynamical evolution of pure macroscopic antimatter systems can be very different from that of ordinary matter systems in the sense that sufficiently massive antimatter systems could have stronger tendency to form black holes during time evolution than their ordinary counterparts. Taking into account the various "no-hair" theorems in black hole physics as well, as a result, antimatter could tracelessly disappear behind black hole event horizons faster in time than ordinary matter. The observed asymmetry of matter and antimatter could then be explained even if their presence in the Universe was symmetric in the beginning.

Authors: Stan Gudder

This paper begins with a theoretical explanation of why spacetime is discrete. The derivation shows that there exists an elementary length which is essentially Planck's length. We then show how the existence of this length affects time dilation in special relativity. We next consider the symmetry group for discrete spacetime. This symmetry group gives a discrete version of the usual Lorentz group. However, it is much simpler and is actually a discrete version of the rotation group. From the form of the symmetry group we deduce a possible explanation for the structure of elementary particle classes. Energy-momentum space is introduced and mass operators are defined. Discrete versions of the Klein-Gordon and Dirac equations are derived. The final section concerns discrete quantum field theory. Interaction Hamiltonians and scattering operators are considered. In particular, we study the scalar spin~0 and spin~1 bosons as well as the spin~$1/2$ fermion cases

Abstract

Frauchiger and Renner have recently claimed to prove that “Single-world interpretations of quantum theory cannot be self-consistent”. This is contradicted by a construction due to Bell, inspired by Bohmian mechanics, which shows that any quantum system can be modelled in such a way that there is only one “world” at any time, but the predictions of quantum theory are reproduced. This Bell–Bohmian theory is applied to the experiment proposed by Frauchiger and Renner, and their argument is critically examined. It is concluded that it is their version of “standard quantum theory”, incorporating state vector collapse upon measurement, that is not self-consistent.

Maroney, O J E and Timpson, C G (2017) How is there a Physics of Information? On characterising physical evolution as information processing. [Preprint]
Gao, Shan (2017) Can particle configurations represent measurement results in Bohm's theory? [Preprint]
Arnold, Eckhart and Kästner, Johannes (2013) When can a Computer Simulation act as Substitute for an Experiment? A Case-Study from Chemisty. [Preprint]
Roberts, Bryan W. (2017) Rovelli on disharmony between the quantum arrows of time. [Preprint]
Roberts, Bryan W. (2017) Unreal Observables. Philosophy of Science.
Roberts, Bryan W. (2017) Observables, Disassembled. [Preprint]

Author(s): Dongfeng Gao, Jin Wang, and Mingsheng Zhan

Various models of quantum gravity imply the Planck-scale modifications of Heisenberg's uncertainty principle into a so-called generalized uncertainty principle (GUP). The GUP effects on high-energy physics, cosmology, and astrophysics have been extensively studied. Here, we focus on the weak-equival…
[Phys. Rev. A 95, 042106] Published Thu Apr 06, 2017

Authors: Yoav LevineDavid YakiraNadav CohenAmnon Shashua

Deep convolutional networks have witnessed unprecedented success in various machine learning applications. Formal understanding on what makes these networks so successful is gradually unfolding, but for the most part there are still significant mysteries to unravel. The inductive bias, which reflects prior knowledge embedded in the network architecture, is one of them. In this work, we establish a fundamental connection between the fields of quantum physics and deep learning. We use this connection for asserting novel theoretical observations regarding the role that the number of channels in each layer of the convolutional network fulfills in the overall inductive bias. Specifically, we show an equivalence between the function realized by a deep convolutional arithmetic circuit (ConvAC) and a quantum many-body wave function, which relies on their common underlying tensorial structure. This facilitates the use of quantum entanglement measures as well-defined quantifiers of a deep network's expressive ability to model intricate correlation structures of its inputs. Most importantly, the construction of a deep ConvAC in terms of a Tensor Network is made available. This description enables us to carry a graph-theoretic analysis of a convolutional network, with which we demonstrate a direct control over the inductive bias of the deep network via its channel numbers, that are related min-cut in the underlying graph. This result is relevant to any practitioner designing a convolutional network for a specific task. We theoretically analyze ConvACs, and empirically validate our findings on more common ConvNets which involve ReLU activations and max pooling. Beyond the results described above, the description of a deep convolutional network in well-defined graph-theoretic tools and the formal connection to quantum entanglement, are two interdisciplinary bridges that are brought forth by this work.

Authors: Bharath Ron

Physics is studying a system based on the information available about it. There are two approaches to physics deterministic and the nondeterministic. The deterministic approaches assume complete availability of information. Since full information about the system is never available nondeterministic approaches such as statistical physics and quantum physics are of high importance. This article is concerned with informational foundations of Physics and a description of time in terms of information. This article addresses the problem of time and a cluster of problems around measurement in quantum mechanics. It gives an interpretation for time in terms of information. The thermal time is shown to be emergent from the noncommutativity of quantum theory.

Author(s): D. J. Bedingham and O. J. E. Maroney

The notion of a physical collapse of the wave function is embodied in dynamical collapse models. These involve a modification of the unitary evolution of the wave function so as to give a dynamical account of collapse. The resulting dynamics is at first sight time asymmetric for the simple reason th…
[Phys. Rev. A 95, 042103] Published Wed Apr 05, 2017

Huggett, Nick (2014) Reading the Past in the Present. [Preprint]
Gao, Shan (2017) Failure of psychophysical supervenience in Everett's theory. [Preprint]
Publication date: Available online 31 March 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Alexei Grinbaum
Dirac sought an interpretation of mathematical formalism in terms of physical entities and Einstein insisted that physics should describe “the real states of the real systems”. While Bell inequalities put into question the reality of states, modern device-independent approaches do away with the idea of entities: physical theory may contain no physical systems. Focusing on the correlations between operationally defined inputs and outputs, device-independent methods promote a view more distant from the conventional one than Einstein׳s ‘principle theories’ were from ‘constructive theories’. On the examples of indefinite causal orders and almost quantum correlations, we ask a puzzling question: if physical theory is not about systems, then what is it about? Device-independent models suggest that physical theory can be ‘about’ languages.

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