Weekly Papers on Quantum Foundations (36)

Larvor, Brendan (2017) From Euclidean Geometry to Knots and Nets. [Preprint]

Authors: Ulf LeonhardtItay GriniastySander WildemanEmmanuel FortMathias Fink

In the Unruh effect an observer with constant acceleration perceives the quantum vacuum as thermal radiation. The Unruh effect has been believed to be a pure quantum phenomenon, but here we show theoretically how the effect arises from the classical correlation of noise. We demonstrate this idea with a simple experiment on water waves where we see the first indications of a Planck spectrum in the correlation energy.

Authors: Robert HeckOana VuculescuJens Jakob SørensenJonathan ZollerMorten G. AndreasenMark G. BasonPoul EjlertsenOttó ElíassonPinja HaikkaJens S. LaustsenLærke L. NielsenAndrew MaoRomain MüllerMario NapolitanoMads K. PedersenAske R. ThorsenCarsten BergenholtzTommaso Calarco,Simone MontangeroJacob F. Sherson

Despite recent advances driven by machine learning algorithms, experts agree that such algorithms are still often unable to match the experience-based and intuitive problem solving skills of humans in highly complex settings. Recent studies have demonstrated how the intuition of lay people in citizen science games [1] and the experience of fusion-scientists [2] have assisted automated search algorithms by restricting the size of the active search space leading to optimized results. Humans, thus, have an uncanny ability to detect patterns and solution strategies based on observations, calculations, or physical insight. Here we explore the fundamental question: Are these strategies truly distinct or merely labels we attach to different points in a high dimensional continuum of solutions? In the latter case, our human desire to identify patterns may lead us to terminate search too early. We demonstrate that this is the case in a theoretical study of single atom transport in an optical tweezer, where more than 200,000 citizen scientists helped probe the Quantum Speed Limit [1]. With this insight, we develop a novel global entirely deterministic search methodology yielding dramatically improved results. We demonstrate that this "bridging" of solution strategies can also be applied to closed-loop optimization of the production of Bose-Einstein condensates. Here we find improved solutions using two implementations of a novel remote interface. First, a team of theoretical optimal control researchers employ a Remote version of their dCRAB optimization algorithm (RedCRAB), and secondly a gamified interface allowed 600 citizen scientists from around the world to participate in the optimization. Finally, the "real world" nature of such problems allow for an entirely novel approach to the study of human problem solving, enabling us to run a hypothesis-driven social science experiment "in the wild".

Authors: D. Sokolovski

In a recent paper \cite{Matz}, Duprey and Matzin investigeated the meaning of vanishing "weak values" (WV), and their role in the retrodiction of the past of a pre- and post-selected quantum system in the presence of interference. Here we argue that any proposition, regarding the WV values, should be understood as a statement about the probability amplitudes, and revisit some of the conclusions reached in \cite{Matz}.

Knox, Eleanor (2017) Novel Explanation in the Special Sciences: Lessons from physics. [Preprint]
Knox, Eleanor (2017) Physical Relativity from a Functionalist Perspective. [Preprint]

The field of particle physics is in a peculiar state. The standard model of particle theory successfully describes every fundamental particle and force observed in laboratories, yet fails to explain properties of the universe such as the existence of dark matter, the amount of dark energy, and the preponderance of matter over antimatter. Huge experiments, of increasing scale and cost, continue to search for new particles and forces that might explain these phenomena. However, these frontiers also are explored in certain smaller, laboratory-scale "tabletop" experiments. This approach uses precision measurement techniques and devices from atomic, quantum, and condensed-matter physics to detect tiny signals due to new particles or forces. Discoveries in fundamental physics may well come first from small-scale experiments of this type.


The traditional standard theory of quantum mechanics is unable to solve the spin–statistics problem, i.e. to justify the utterly important “Pauli Exclusion Principle” but by the adoption of the complex standard relativistic quantum field theory. In a recent paper (Santamato and De Martini in Found Phys 45(7):858–873,2015) we presented a proof of the spin–statistics problem in the nonrelativistic approximation on the basis of the “Conformal Quantum Geometrodynamics”. In the present paper, by the same theory the proof of the spin–statistics theorem is extended to the relativistic domain in the general scenario of curved spacetime. The relativistic approach allows to formulate a manifestly step-by-step Weyl gauge invariant theory and to emphasize some fundamental aspects of group theory in the demonstration. No relativistic quantum field operators are used and the particle exchange properties are drawn from the conservation of the intrinsic helicity of elementary particles. It is therefore this property, not considered in the standard quantum mechanics, which determines the correct spin–statistics connection observed in Nature (Santamato and De Martini in Found Phys 45(7):858–873, 2015). The present proof of the spin–statistics theorem is simpler than the one presented in Santamato and De Martini (Found Phys 45(7):858–873, 2015), because it is based on symmetry group considerations only, without having recourse to frames attached to the particles. Second quantization and anticommuting operators are not necessary.

Dewar, Neil and Eva, Benjamin (2017) A Categorical Perspective on Symmetry and Equivalence. [Preprint]
De Haro, Sebastian (2017) The Invisibility of Diffeomorphisms. [Preprint]

Authors: Steffen GielenDaniele Oriti

The early universe provides an opportunity for quantum gravity to connect to observation by explaining the large-scale structure of the Universe. In the group field theory (GFT) approach, a macroscopic universe is described as a GFT condensate; this idea has already been shown to reproduce a semiclassical large universe under generic conditions, and to replace the cosmological singularity by a quantum bounce. Here we extend the GFT formalism by introducing additional scalar degrees of freedom that can be used as a physical reference frame for space and time. This allows, for the first time, the extraction of correlation functions of inhomogeneities in GFT condensates: in a way conceptually similar to inflation, but within a quantum field theory of both geometry and matter, quantum fluctuations of a homogeneous background geometry become the seeds of cosmological inhomogeneities. We compute the power spectrum of scalar cosmological perturbations and find that it is naturally approximately scale invariant, with a naturally small amplitude. This confirms the potential of GFT condensate cosmology to provide a purely quantum gravitational foundation for the understanding of the early universe.

Authors: T. ShojiK. AiharaY. Yamamoto

The quantum theory of coherent Ising machines, based on degenerate optical parametric oscillators and measurement-feedback circuits, is developed using the positive $P(\alpha,\beta)$ representation of the density operator. The theory is composed of the c-number stochastic differential equations for describing open dissipative quantum dynamics and the replicator dynamics equations for describing measurement-induced collapse of the wave functions. We apply the present theory to simulate two simple Ising spin models and elucidate the unique features of this computing machine.

Authors: Fang Song

This is a note accompanying "CS 410/510: INTRO TO QUANTUM COMPUTING" I taught at Portland State University in Spring 2017. It is a review and summary of some early results related to Grover's quantum search algorithm in a consistent way. I had to go back and forth among several books, notes and original papers to sort out various details when preparing the lectures, which was a pain. This is the motivation behind this note. I would like to thank Peter H{\o}yer for valuable feedback on this note.

Quantum gravity: Quantum effects in the gravitational field

Nature 549, 7670 (2017). doi:10.1038/549031a

Authors: Sabine Hossenfelder, Chiara Marletto & Vlatko Vedral

I agree with Chiara Marletto and Vlatko Vedral that we need to test quantum gravity experimentally (Nature547, 156–158;10.1038/547156a2017). However, the idea of measuring quantum superpositions of the gravitational field, as Richard Feynman described, is hardly new.

Quantum communication offers many advantages over classical methods, but it has been limited to sending signals across a few hundred kilometres. Two studies overcome this limitation. See Article p.43 & Letter p.70

Nature 549 41 doi: 10.1038/549041a

Angeloni, Roberto (2017) Cassirer’s Functional-Based Approach in the Reconstruction of the First Quantum Theory. [Preprint]

Nature Physics 13, 826 (2017). doi:10.1038/nphys4255

Author: Andreas Trabesinger

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