# Weekly Papers on Quantum Foundations (2)

Quantum mechanics via quantum tomography. (arXiv:2110.05294v3 [quant-ph] UPDATED)

Starting from a new basic principle inspired by quantum tomography rather than from Born’s rule, this paper gives an elementary, and self-contained deductive approach to quantum mechanics and quantum measurement. A suggestive notion for what constitutes a quantum detector and for the behavior of its responses leads to a logically impeccable definition of measurement. Applications to measurement schemes for optical states, position measurements and particle tracks demonstrate that this definition is applicable to complex realistic experiments without any idealization.

The various forms of quantum tomography for quantum states, quantum detectors, quantum processes, and quantum instruments are discussed. The traditional dynamical and spectral properties of quantum mechanics are derived from a continuum limit of quantum processes. In particular, the Schr\”odinger equation for the state vector of a pure, nonmixing quantum system and the Lindblad equation for the density operator of a mixing quantum system are shown to be consequences of the new approach. Normalized density operators are shown to play the role of quantum phase space variables, in complete analogy to the classical phase space variables position and momentum. A slight idealization of the measurement process leads to the notion of quantum fields, whose smeared quantum expectations emerge as reproducible properties of regions of space accessible to measurements.

A variety of quotes from the literature illuminate the formal exposition with historical and philosophical aspects.

Theory-experiment comparison for the Casimir force between metallic test bodies: A spatially nonlocal dielectric response. (arXiv:2112.07283v2 [quant-ph] UPDATED)

It has been known that the Lifshitz theory of the Casimir force comes into conflict with the measurement data if the response of conduction electrons in metals to electromagnetic fluctuations is described by the well tested dissipative Drude model. The same theory is in a very good agreement with measurements of the Casimir force from graphene whose spatially nonlocal electromagnetic response is derived from the first principles of quantum electrodynamics. Here, we propose the spatially nonlocal phenomenological dielectric functions of metals which lead to nearly the same response, as the standard Drude model, to the propagating waves, but to a different response in the case of evanescent waves. Unlike some previous suggestions of this type, the response functions considered here depend on all components of the wave vector as is most natural in the formalism of specular reflection used. It is shown that these response functions satisfy the Kramers-Kronig relations. We derive respective expressions for the surface impedances and reflection coefficients. The obtained results are used to compute the effective Casimir pressure between two parallel plates, the Casimir force between a sphere and a plate, and its gradient in configurations of the most precise experiments performed with both nonmagnetic (Au) and magnetic (Ni) test bodies. It is shown that in all cases (Au-Au, Au-Ni, and Ni-Ni test bodies) the predictions of the Lifshitz theory found by using the dissipative nonlocal response functions are in as good agreement with the measurement data, as was reached previously with the dissipationless plasma model. Possible developments and applications of these results are discussed.

Single Phonon Detection for Dark Matter via Quantum Evaporation and Sensing of $^3$Helium. (arXiv:2201.00738v1 [hep-ex] CROSS LISTED)

Dark matter is five times more abundant than ordinary visible matter in our Universe. While laboratory searches hunting for dark matter have traditionally focused on the electroweak scale, theories of low mass hidden sectors motivate new detection techniques. Extending these searches to lower mass ranges, well below 1 GeV/c$^2$, poses new challenges as rare interactions with standard model matter transfer progressively less energy to electrons and nuclei in detectors. Here, we propose an approach based on phonon-assisted quantum evaporation combined with quantum sensors for detection of desorption events via tracking of spin coherence. The intent of our proposed dark matter sensors is to extend the parameter space to energy transfers in rare interactions to as low as a few meV for detection of dark matter particles in the keV/c$^2$ mass range.

Time as Change. (arXiv:2201.01944v1 [physics.hist-ph])

Authors: Marcello Poletti

According to Aristotle “time is the number of change with respect to the before and after”. That’s certainly a vague concept, but at the same time it’s both simple and satisfying from a philosophical point of view: things do not change along time, but they do change and the measurement of such changes is what we call time. This deprives time of any attribute of substantiality, meanwhile depriving it of all problems in defining the properties of time as a substance. With the rise of Classical Mechanics, Aristotle’s view is abandoned and Newton’s concept of “true” and absolute time imposes itself; time flows independently on changes of any kind. Relativity will then radically modify our concept of time, but won’t actually modify the fundamental idea: things keep changing along time — changes do not make time. This work will argue Aristotle’s thesis, showing how such an approach automatically leads to the principles of Special Relativity. An interesting consequence and, at least virtually, measurable will also be highlighted: the fact that synchronizing two clocks with a precision greater than a certain scale is impossible, estimating such scale around $10^{-22}$s.

Quantum physics in space

Publication date: 11 March 2022

Source: Physics Reports, Volume 951

Author(s): Alessio Belenchia, Matteo Carlesso, Ömer Bayraktar, Daniele Dequal, Ivan Derkach, Giulio Gasbarri, Waldemar Herr, Ying Lia Li, Markus Rademacher, Jasminder Sidhu, Daniel K.L. Oi, Stephan T. Seidel, Rainer Kaltenbaek, Christoph Marquardt, Hendrik Ulbricht, Vladyslav C. Usenko, Lisa Wörner, André Xuereb, Mauro Paternostro, Angelo Bassi

Thermodynamically consistent entropic-force cosmology. (arXiv:2201.01835v1 [gr-qc])

Authors: D. J. ZamoraC. Tsallis

We analyze the thermodynamical consistency of entropic-force cosmological models. Our analysis is based on a generalized entropy scaling with an arbitrary power of the Hubble radius. The Bekenstein-Hawking entropy, proportional to the area, and the nonadditive $S_{\delta=3/2}$-entropy, proportional to the volume, are particular cases. One of the points to be solved by entropic-force cosmology for being taken as a serious alternative to mainstream cosmology is to provide a physical principle that points out what entropy and temperature have to be used. We determine the temperature of the universe horizon by requiring that the Legendre structure of thermodynamics is preserved. We compare the performance of thermodynamically consistent entropic-force models with regard to the available supernovae data by providing appropriate constraints for optimizing alternative entropies and temperatures of the Hubble screen. Our results point out that the temperature differs from the Hawking one.

Cosmological constant problem on the horizon. (arXiv:2201.02016v1 [gr-qc])

Authors: Hassan Firouzjahi

We revisit the quantum cosmological constant problem and highlight the important roles played by the dS horizon of zero point energy. We argue that fields which are light enough to have dS horizon of zero point energy comparable to the FLRW Hubble radius are the main contributor to dark energy. On the other hand, the zero point energy of heavy fields develop nonlinearities on sub-Hubble scales and can not contribute to dark energy. Our proposal provides a simple resolution for both the old and new cosmological constant problems by noting that there exits a field, the (lightest) neutrino, which happens to have a mass comparable to the present background photon temperature. The natures of dark energy and dark matter are unified in this proposal in which the zero point energy of light fields are the source of dark energy while dark matter is sourced by the zero point energy of heavy fields. The proposal predicts multiple transient periods of dark energy in early and late expansion history of the universe yielding to a higher value of the current Hubble expansion rate which can resolve the $H_0$ tension problem.

Full Network Nonlocality

Author(s): Alejandro Pozas-Kerstjens, Nicolas Gisin, and Armin Tavakoli

Networks have advanced the study of nonlocality beyond Bell’s theorem. Here, we introduce the concept of full network nonlocality, which describes correlations that necessitate all links in a network to distribute nonlocal resources. Showcasing that this notion is stronger than standard network nonl…

[Phys. Rev. Lett. 128, 010403] Published Fri Jan 07, 2022

Thermodynamic Stability Implies Causality

Author(s): L. Gavassino, M. Antonelli, and B. Haskell

The stability conditions of a relativistic hydrodynamic theory can be derived directly from the requirement that the entropy should be maximized in equilibrium. Here, we use a simple geometrical argument to prove that, if the hydrodynamic theory is stable according to this entropic criterion, then l…

[Phys. Rev. Lett. 128, 010606] Published Thu Jan 06, 2022

The Literalist Fallacy & the Free Energy Principle: Model-building, Scientific Realism and Instrumentalism

Kirchhoff, Michael and Kiverstein, Julian and Robertson, Ian (2022) The Literalist Fallacy & the Free Energy Principle: Model-building, Scientific Realism and Instrumentalism. [Preprint]

The ~In~Determinacy of Computation

Curtis-Trudel, Andre E (2022) The ~In~Determinacy of Computation. [Preprint]