Weekly Papers on Quantum Foundations (27)

Authors: Manabendra Nath BeraArnau RieraMaciej LewensteinAndreas Winter

In this work we formulate thermodynamics as an exclusive consequence of information conservation. The framework can be applied to most general situations, beyond the traditional assumptions in thermodynamics, where systems and thermal-baths could be quantum, of arbitrary sizes and even could posses inter-system correlations. Further, it does not require a priory predetermined temperature associated to a thermal-bath, which does not carry much sense for finite-size cases. Importantly, the thermal-baths and systems are not treated here differently, rather both are considered on equal footing. This leads us to introduce a "temperature"-independent formulation of thermodynamics. We rely on the fact that, for a given amount of information, measured by the von Neumann entropy, any system can be transformed to a state that possesses minimal energy. This state is known as a completely passive state that acquires a Boltzmann--Gibb's canonical form with an intrinsic temperature. We introduce the notions of bound and free energy and use them to quantify heat and work respectively. We explicitly use the information conservation as the fundamental principle of nature, and develop universal notions of equilibrium, heat and work, universal fundamental laws of thermodynamics, and Landauer's principle that connects thermodynamics and information. We demonstrate that the maximum efficiency of a quantum engine with a finite bath is in general different and smaller than that of an ideal Carnot's engine. We introduce a resource theoretic framework for our intrinsic-temperature based thermodynamics, within which we address the problem of work extraction and inter-state transformations. We also extend the framework to the cases of multiple conserved quantities.


Ben-Israel and Vaidman (Found Phys 47:467–470, 2017) have raised objections to my arguments that there are cases where a quantum mechanical weak value can be said not to represent the system to which it pertains. They are correct in pointing out that some of my conclusions were too general. However, for weak values of projection operators my conclusions still stand.

Authors: Catherine M Reason

This is a brief comment on the paper "Quantum mechanics needs no consciousness" by Shan Yu and Danko Nikolic [1]. Yu and Nikolic argue that the "consciousness causes collapse hypothesis" interpretation of quantum mechanics, or CCCH, can be falsified by a particular experimental setup. This claim is incorrect and the cause of the error appears to be a confusion over where and when a collapse can be assumed to occur.

Publication date: Available online 4 July 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Boris Kožnjak
In this paper, I analyze the historical context, scientific and philosophical content, and the implications of the thus far historically largely neglected Ninth Symposium of the Colston Research Society held in Bristol at the beginning of April 1957, the first major international event after World War II gathering eminent physicists and philosophers to discuss the foundational questions of quantum mechanics, in respect to the early reception of the causal quantum theory program mapped and defended by David Bohm during the five years preceding the Symposium. As will be demonstrated, contrary to the almost unanimously negative and even hostile reception of Bohm's ideas on hidden variables in the early 1950s, in the close aftermath of the 1957 Colston Research Symposium Bohm's ideas received a more open-minded and ideologically relaxed critical rehabilitation, in which the Symposium itself played a vital and essential part.

Authors: Tejinder P. Singh

We argue that space and space-time emerge as a consequence of dynamical collapse of the wave function of macroscopic objects. Locality and separability are properties of our approximate, emergent universe. At the fundamental level, space-time is non-commutative, and dynamics is non-local and non-separable.

Authors: Rajat Kumar Pradhan

Quantum effects arising from manifestly broken time-reversal symmetry are investigated using time-dependent perturbation theory in a simple model. The forward time and the backward time Hamiltonians are taken to be different and hence the forward and backward amplitudes become unsymmetrical and are not complex conjugates of each other. The effects vanish when the symmetry breaking term is absent and ordinary quantum mechanical results such as Fermi Golden rule are recovered.

Authors: Meng-Jun HuYong-Sheng Zhang

A universal amplification scheme of ultra-small phase based on weak measurements is given and a weak measurements amplification based laser interferometer gravitational-wave observatory (WMA-LIGO) is suggested. The WMA-LIGO has potential to amplify the ultra-small phase signal to at least $10^{3}$ order of magnitude such that the sensitivity and bandwidth of gravitational-wave detector can be further improved. Our results not only shed a new light on the quantum measurement but also open a new way to the gravitational-wave detection.

McCabe, Gordon (2017) Cosmology and entropy: in search of further clarity. [Preprint]

Authors: A. S. Sanz

Since its inception Bohmian mechanics has been generally regarded as a hidden-variable theory aimed at providing an objective description of quantum phenomena. To date, this rather narrow conception of Bohm's proposal has caused it more rejection than acceptance. Now, after 65 years of Bohmian mechanics, should still be such an interpretational aspect the prevailing appraisal? Why not favoring a more pragmatic view, as a legitimate picture of quantum mechanics, on equal footing in all respects with any other more conventional quantum picture? These questions are used here to introduce a pedagogical discussion at an elementary level, suitable for undergraduate students, on how to deal with Bohmian mechanics at present, enhancing its aspect as an efficient and useful picture or formulation to tackle, explore, describe and explain quantum phenomena where phase and correlation (entanglement) are key elements. This discussion is presented through two building blocks. The first block is aimed at briefly revisiting the historical context that gave rise to the appearance of Bohmian mechanics, and how this approach or analogous ones have been used in different physical contexts. This discussion will be used to put aside the traditional hidden-variable issue from a more pragmatic view, which is precisely the aspect of interest from a pedagogical viewpoint at the classroom. The second block focuses on elementary aspects of Bohmian mechanics, illustrating them with an application to a simple model of Young's two-slit experiment. The simplicity of this model allows to understand in an easy way how the information conveyed by the Bohmian formulation relates to other more conventional concepts in quantum mechanics, thus showing the potential interest to introduce this approach in undergraduate quantum mechanics courses as a working tool.

Authors: Gerd Christian Krizek

A physical theory consists of the mathematical formalism and an interpretation, which contains the definition of symbols, measurement assignments, concepts and principles, and an ontology. We present a scheme to classify these different levels of a physical theory and apply it to Newtonian Mechanics and the interpretations of Quantum Mechanics. We show that this classification scheme is embedded in the methodology of philosophy of science. With this scheme, different interpretations of Quantum Mechanics can be compared concerning the formalism and the used conceptions, and it serves as a guidance to identify ontological entities and reality conceptions in the different interpretations. Inspired by the commitments on the ontological level, we propose two heuristics concerning ontological statements.

Determining the Quantum Expectation Value by Measuring a Single Photon

Quantum mechanics, one of the keystones of modern physics, exhibits several peculiar properties, differentiating it from classical mechanics. One of the most intriguing is that variables might not have definite values. A complete quantum description provides only probabilities for obtaining various eigenvalues of a quantum variable. These and corresponding probabilities specify the expectation value of a physical observable, which is known to be a statistical property of an ensemble of quantum systems. In contrast to this paradigm, we demonstrate a unique method allowing to measure the expectation value of a physical variable on a single particle, namely, the polarisation of a single protected photon. This is the first realisation of quantum protective measurements.

Comments: Nature Physics, in press (this version corresponds to the one initially submitted to Nature Physics)
Subjects: Quantum Physics (quant-ph)
Cite as: arXiv:1706.08918 [quant-ph]

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