Weekly Papers on Quantum Foundations (10)

Authors: David CrouseJoseph Skufca

In this work, the relativistic phenomena of Lorentz-Fitzgerald contraction and time dilation are derived using a modified distance formula that is appropriate for discrete space. This new distance formula is different than the Pythagorean theorem but converges to it for distances large relative to the Planck length. First, four candidate formulas developed by different people over the last 70 years will be discussed. Three of the formulas are shown to be identical for conditions that best describe discrete space. It is shown that this new distance formula is valid for all size-scales — from the Planck length upwards — and solves two major problems historically associated with the discrete space-time (DST) model. One problem it solves is the widely believed anisotropic nature of most discrete space models. Just as commonly believed is the second problem — the incompatibility of DST’s concept of an immutable atom of space and the length contraction of this atom required by special relativity. The new formula for distance in DST solves this problem. It is shown that length contraction of the atom of space does not occur for any relative velocity of two reference frames. It is also shown that time dilation of the atom of time does not occur. Also discussed is the possibility of any object being able to travel at the speed of light for specific temporal durations given by an equation derived in this work. Also discussed is a method to empirical verify the discreteness of space by studying any observed anomalies in the motion of astronomical bodies, such as differences in the bodies’ inertial masses and gravitational masses. The importance of the new distance formula for causal set theory and other theories of quantum gravity is also discussed.

Barwich, Ann-Sophie (2018) How to be rational about empirical success in ongoing science: The case of the quantum nose and its critics. Studies in History and Philosophy of Science.
Publication date: Available online 7 March 2018
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Bryan W. Roberts
How should we characterise the observable aspects of quantum theory? This paper argues that philosophers and physicists should jettison a standard dogma: that observables must be represented by self-adjoint or Hermitian operators. Four classes of non-standard observables are identified: normal operators, symmetric operators, real-spectrum operators, and none of these. The philosophical and physical implications of each are explored.
Publication date: 26 April 2018
Source:Physics Letters A, Volume 382, Issue 16
Author(s): Debarshi Das, Shiladitya Mal, Dipankar Home
Generalized quantum measurements with two outcomes are fully characterized by two real parameters, dubbed as sharpness parameter and biasedness parameter and they can be linked with different aspects of the experimental setup. It is known that sharpness parameter characterizes precision of the measurements and decreasing sharpness parameter of the measurements reduces the possibility of probing quantum features like quantum mechanical (QM) violation of local-realism (LR) or macro-realism (MR). Here we investigate the effect of biasedness together with that of sharpness of measurements and find a trade-off between those two parameters in the context of probing QM violations of LR and MR. Interestingly, we also find that the above mentioned trade-off is more robust in the latter case.

Author(s): J. Bengtsson, M. Nilsson Tengstrand, A. Wacker, P. Samuelsson, M. Ueda, H. Linke, and S. M. Reimann

We show that a quantum Szilard engine containing many bosons with attractive interactions enhances the conversion between information and work. Using an ab initio approach to the full quantum-mechanical many-body problem, we find that the average work output increases significantly for a larger numb…
[Phys. Rev. Lett. 120, 100601] Published Fri Mar 09, 2018

Authors: Don Weingarten

Beginning with the Everett-DeWitt many-worlds interpretation of quantum mechanics there have been a series of proposals for how the state vector of a quantum system might be split at any instant into orthogonal branches, each of which exhibits approximately classical behavior. Here we propose a decomposition of a state vector into branches by finding the minimum of a measure of the net quantum complexity of the branch decomposition. The net complexity depends on a parameter with units of length, the branching threshold b, which controls the cross over from quantum behavior into classical. The parameter b should in principle be measurable. We then propose a method for finding an ensemble of possible branch initial state vectors from which a randomly selected member, if evolved by ordinary Hamiltonian time evolution, will follow a single sequence of branches of many-worlds quantum mechanics. For any particular draw, the resulting deterministic system appears to exhibit random behavior as a result of the successive emergence over time of information present in the initial state but not previously observed.

Authors: Peng XuLi-E Qiang

Interplays between quantum physics and gravity has long inspired exciting studies, which also reveals subtle connections between quantum laws and the general notion of curved spacetime. One important example is the uniqueness of free-falling motions in both quantum and gravitational physics. In this work, we study, from a different perspective, the free motions of quantum test wave packets that distributed over weakly curved spacetime backgrounds. Except for the de Broglie relations, no assumption of priori given Hamiltonians or least actions satisfied by the quantum system is made. We find that the mean motions of quantum test wave packets can be deduced naturally from the de Broglie relations with a generalized treatment of gravitational time dilations in the quantum waves. Such mean motions of quantum test systems are independent of their masses and compositions, and restores exactly the free-falling or geodesic motions of classical test masses in curved spacetime. This suggests a novel perspective that weak equivalence principle, which states the universality of free-fall and serves as the foundations of gravitational theories, may be deeply rooted in quantum physics and be a phenomena emergent from the quantum world.

Authors: M. Trassinelli (INSP, INSP-E10)

We present a discussion on the three postulates of Relational Quantum Mechanics (RQM) and the definition of probability within this framework. The first two RQM postulates are based on the information that can be extracted from interaction of different systems, and the third postulate defines the properties of the probability function. Here we demonstrate that from a rigorous definition of the conditional probability for the possible outcomes of different measurements, the third postulate is unnecessary and the Born’s rule naturally emerges from the first two postulates by applying the Gleason’s theorem. We demonstrate in addition that the probability function is uniquely defined for classical and quantum phenomena. The presence or not of interference terms is demonstrated to be related to the precise formulation of the conditional probability where distributive property on its arguments cannot be taken for granted. In the particular case of Young’s slits experiment, the two possible argument formulations correspond to the possibility or not to determine the particle passage through a particular path.

Authors: Edward J. Gillis

Because quantum measurements have probabilistic outcomes they appear to violate conservation laws in individual experiments. In this note some simple examples are used to show that when pre-existing entanglement relations of the measured system are taken into account, quantities such as momentum, energy, and angular momentum can be strictly conserved, despite appearances to the contrary. The relationship between conservation laws and measurement processes is then framed in more general terms. I close with a discussion of the possible consequences for various views on the fundamental nature of quantum measurement processes.

Oriti, Daniele (2018) The Bronstein hypercube of quantum gravity. [Preprint]
A new paper uses the Schrödinger equation to describe debris disks around stars and black holes—and provides an object lesson about what “quantum” really means– Read more on ScientificAmerican.com


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In the history of quantum physics several no-go theorems have been proved, and many of them have played a central role in the development of the theory, such as Bell’s or the Kochen–Specker theorem. A recent paper by F. Laudisa has raised reasonable doubts concerning the strategy followed in proving some of these results, since they rely on the standard framework of quantum mechanics, a theory that presents several ontological problems. The aim of this paper is twofold: on the one hand, I intend to reinforce Laudisa’s methodological point by critically discussing Malament’s theorem in the context of the philosophical foundation of quantum field theory; secondly, I rehabilitate Gisin’s theorem showing that Laudisa’s concerns do not apply to it.

Lewis, Peter J. (2018) Quantum Mechanics and its (Dis)Contents. [Preprint]

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