Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P09: Quantum Foundations IIFocus

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Sponsoring Units: DQI Chair: Mark Wilde, Louisiana State University, Baton Rouge Room: 106 
Wednesday, March 4, 2020 2:30PM  2:42PM 
P09.00001: Objectivity In Different Quantum Reference Frames Thao Le, Piotr Mironowicz, Pawel Horodecki Quantum Darwinism and its frameworks describe objectivity of quantum systems via their information in the environment. However, the observation of these environments must be done with respect to a frame of reference. Given so, is objectivity consistent across different reference frames? Here, we take the quantum reference frame structure of [1] and consider the scenario where system and environment are static particles distributed across space. In this prescription, entanglement and coherence are interchangeable framedependent properties, and statistical mixedness and classical correlations are equivalently interchangeable. We find that the consistency of objectivity depends on the distinguishability of states in all relevant quantum reference frames, which in turn depends on nondegenerate relative separations, sharp localisation, and sufficiently large macrofractions. 
Wednesday, March 4, 2020 2:42PM  2:54PM 
P09.00002: The NakanoNishijimaGellMann Formula From Galois Fields Satoshi Tanda, Tomoo Ohaga, Keiji Nakatsugawa, Toshiyuki Fujii, Toyoki Matsuyama If world has a finite compact space (I_{120}: Poincare Dodecahedron) [1] and discrete coordinates [2,3], what happens? In this case, the problem of infinities in gravity and in the standard model might be avoided. To avoid this problem, quantum gravity theories such as the superstring theory or the loop quantum gravity are developing, but neither of those theories have been completed. We reconstruct the NakanoNishijimaGellMann (NNG) formula by using a discrete Galois field without using continuous coordinate. When we reconstruct new theories with a Galois field, these new theories must satisfy fundamental conservation law related to unitary, Lorentz, and gauge invariance. 
Wednesday, March 4, 2020 2:54PM  3:06PM 
P09.00003: Quantum Fields from Quantum Cellular Automata? A NoGo Theorem and a Path Forward Todd Brun, Leonard Mlodinow A quantum walk (QW) is a unitary analogue of a classical random walk, and a quantum cellular automaton (QCA) is a unitary analogue of a classical cellular automaton. QWs can be treated as the oneparticle sector of a QCA. Since quantum walks on the bodycentered cubic lattice give rise to relativistic wave equations in the long wavelength limit, it is natural to seek for QCAs that give rise to quantum field theories in a similar limit. We show that this can be done in one spatial dimension, with the QCA being naturally described in terms of creation and annihilation operators that create or destroy particle locally, evolve straightforwardly under the QCA unitary, and obey the usual anticommutation relations (ACR). However, generalizing this construction to two or more spatial dimensions fails: the requirements on the creation and annihilation operators are inconsistent with a local QCA. For a QCA to give rise to a quantum field theory in the longwavelength limit, one must give up at least one of the desired properties. A likely choice is to give up the requirement that the creation and annihilation operators create and destroy localized states. 
Wednesday, March 4, 2020 3:06PM  3:42PM 
P09.00004: Quantum mechanics and the covariance of physical laws in quantum reference frames Invited Speaker: Flaminia Giacomini In physics, every observation is made with respect to a frame of reference. Although reference frames are usually not considered as degrees of freedom, in all practical situations it is a physical system which constitutes a reference frame. Can a quantum system be considered as a reference frame and, if so, which description would it give of the world? In my talk, I will introduce a general method to quantise reference frame transformations, which generalises the usual reference frame transformation to a “superposition of coordinate transformations”. With this method, it is possible to describe states, measurement, and dynamical evolution in different quantum reference frames, without appealing to an external, absolute reference frame, and find that entanglement and superposition are framedependent features. The transformation also leads to a generalisation of the notion of covariance of dynamical physical laws, and to the possibility of defining the rest frame of a quantum system. This last feature allows us to find an operational definition of the relativistic spin of a Dirac particle, and to devise a "relativistic SternGerlach experiment". 
Wednesday, March 4, 2020 3:42PM  3:54PM 
P09.00005: Quantum Mechanics of a Single Photon and the question of its Localizability in Space Hassan Babaei, Ali Mostafazadeh We use the dynamical Maxwell equations to determine the space of state vectors of a single photon. We endow this space with a relativistically invariant positivedefinite inner product to make it into a Hilbert space. We identify the Hamiltonian operator with the generator of time translations, construct momentum and helicity operators, and introduce a chirality (directionoftime) operator. Next, we construct a position operator that has commuting components. These also commute with the helicity and chirality operators. We obtain the eigenstates of the position operator, which we identify with the localized states of the photon, and use them to determine photon’s position wave function. The position wave function for the localized states has a deltafunction singularity at a single point in space, but their electromagnetic fields diverge on a particular plane containing this point. This behavior turns out to be related to an implicit freedom in the choice of the position operator. Each choice for the position operator determines the plane at which the electromagnetic fields of a given localized state diverge. 
Wednesday, March 4, 2020 3:54PM  4:06PM 
P09.00006: Quantized ElectromagneticField Propagation in a General NonLocal and NonStationary Dispersive and Absorbing Medium Verne Jacobs We develop dynamical descriptions for the propagation of quantized electromagnetic fields, in the presence of environmental interactions. These descriptions are systematically and selfconsistently developed in the complimentary Schrödinger and Heisenberg pictures. An opensystems (nonequilibrium) quantumelectrodynamics and quantumstatistical description is thereby provided for electromagneticfield propagation in a general nonlocal and nonstationary dispersive and absorbing optical medium, including a fundamental microscopic treatment of decoherence and relaxation processes due to environmental collisional and electromagnetic interactions. Particular interest is centered on entangled states and other nonclassical states of electromagnetic fields, which may be created by nonlinear electromagnetic interactions and detected by the measurement of various electromagneticfield correlation functions. Accordingly, we develop dynamical descriptions based on general forms of electromagneticfield correlation functions involving both the electricfield and the magneticfield components of the electromagnetic field, which are treated on an equal footing. 
Wednesday, March 4, 2020 4:06PM  4:42PM 
P09.00007: Probability arises from entropy in axiomatic information thermodynamics Invited Speaker: Michael Westmoreland Axiomatic information thermodynamics (Entropy 2018, 20(4), 237) is a formal mathematical system that describes thermodynamic processes including those in which information is acquired, transformed or discarded. A central concept in the theory is the "eidostate", which is a simple array of possible states, including both thermodynamic macrostates and information records. Wellmotivated axioms lead to an entropy function that describes the irreversibility of eidostate processes, and this function in turn leads to a unique probability measure for the states and records in a uniform eidostate. Does this development shed light on the kinds of reasoning available to physical agents that observe and intervene in the quantum world? 
Wednesday, March 4, 2020 4:42PM  4:54PM 
P09.00008: Emergence of the Born rule in quantum optics Morgan Williamson, Brian La Cour The Born rule provides a fundamental connection between theory and observation in quantum mechanics, yet its origin remains a mystery. We consider this problem within the context of quantum optics using only classical physics and the assumption of a quantum electrodynamic vacuum that is real rather than virtual. The connection to observation is made via classical intensity threshold detectors that are used as a simple, deterministic model of singlephoton detection. By following standard experimental conventions of data analysis on discrete detection events, it can be shown that this model is capable of reproducing several observed phenomena thought to be uniquely quantum in nature. 
Wednesday, March 4, 2020 4:54PM  5:06PM 
P09.00009: InteractionFree Energy Transfer Mordecai Waegell, Cyril Elouard, Benjamin Huard, Andrew N Jordan The interactionfree measurement scheme of Elitzur and Vaidman enables a probe particle to detect the presence of an object blocking one arm of a MachZender (MZ) interferometer without the probe ever locally interacting with that object. THE MZ is tuned so that without the block, the dark port detector never fires. The presence of the block changes the interference pattern in the MZ, allowing the dark port to fire, in which case the block is detected while the probe traveled the unblocked arm. We consider a quantum block in the ground state of a confining potential, a superposition of inside and outside one arm of the MZ. When the dark port detector fires, the quantum block is localized inside the arm, which increases its energy. This energy is delivered by the probe even though it traveled the unblocked arm to reach the dark port, and we thus obtain interactionfree energy transfer. This effect obtains even though the coupling Hamiltonian is local. 
Wednesday, March 4, 2020 5:06PM  5:18PM 
P09.00010: Diffractionbased InteractionFree Measurements Spencer Rogers, Yakir Aharonov, Cyril Elouard, Andrew N Jordan We consider the problem of determining if a singleslit contains a bomb in its middle region using a single photon test. We notice that the quantum case allows the bomb to significantly increase the probability for the photon to reach certain detection positions, in particular the dark bands of the singleslit pattern. The bomb's presence can be inferred without exploding it when the photon lands at one of these positions. We thus find a diffractive extension to the interactionfree measurement protocol of Elitzur and Vaidman. In addition, we consider the role of time in interactionfree measurements. We find that, if the bomb is thought of as a measuring device which checks periodically if the photon is in its space, then it can only find the particle (and "explode") if its measurement rate is finite. The alternative is the Zeno limit, where the bomb acts like an infinite potential barrier. Critics of interactionfree measurement may find it interesting that the normal, nonZeno bomb can be passed through without setting it off. 
Wednesday, March 4, 2020 5:18PM  5:30PM 
P09.00011: Quantum mysteries for anybody: Solved William Stuckey In 1981, Mermin published a now famous paper titled, "Bringing home the atomic world: Quantum mysteries for anybody." Therein, he presented the 'Mermin device' that illustrates the conundrum of entanglement per the spin singlet state for the "general reader." He then challenged the "physicist reader" to explain the way the device works "in terms meaningful to a general reader struggling with the dilemma raised by the device." I will show how conservation per no preferred reference frame (NPRF) answers that challenge, but still leaves a mystery for those who seek dynamical explanation via hidden variables or 'causal influences'. Since NPRF also underwrites the postulates of special relativity, we see a common theme between relativistic and nonrelativistic modern physics. 
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