Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T35: Quantum FoundationsFocus Recordings Available
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Sponsoring Units: DQI Chair: Jens Koch, Northwestern University Room: McCormick Place W-193B |
Thursday, March 17, 2022 11:30AM - 12:06PM |
T35.00001: Relational Quantum Mechanics Invited Speaker: Carlo Rovelli The relational interpretation of quantum mechanics (RQM) solves the measurement problem avoiding both hidden variables and many worlds, and yet remaining realistic, by considering an ontology of sparse relative events, instead than a quantum state ontology. Events are realized in interactions between any two physical systems and are relative to these systems. The relativity of the events can be neglected in the approximation where decoherence hides interference, thus making them (approximately) absolute. RQM is a refinement of the traditional "Copenhagen" views, that replaces the Copenhagen's classical observer with any arbitrary physical system. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T35.00002: Experimental Violation of the Leggett-Garg Inequality Using the Polarization of Classical Light Wenlei Zhang In contrast to Bell's inequalities which test the correlations between multiple spatially separated systems, the Leggett-Garg inequalities test the temporal correlations between measurements of a single system. We experimentally demonstrate the violation of the Leggett-Garg inequality in a classical and macroscopic optical system using only the polarization degree-of-freedom of a laser beam. Our system is macroscopic due to the large number of particles involved and a laser beam is the closest experimental approximation to a coherent state, which is considered to be a classical state in the quantum optical sense. For a Gaussian beam under the paraxial approximation, the time evolution is equivalent to its propagation through space. The polarization of such a beam is measured with polarizing beamsplitters. The correlation functions can be obtained by placing the measurement devices at appropriate locations along the path. Our results show maximal violations of the Leggett-Garg inequality, which is evidence that classical wave mechanics is not a macrorealistic theory. The possibility of violating the Leggett-Garg inequality with the polarization of classical light comes from the superposition of temporally coherent fields. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T35.00003: The Relativity Principle at the Foundation of Quantum Mechanics William M Stuckey Quantum information theorists have created axiomatic reconstructions of quantum mechanics (QM) that are very successful at identifying precisely what distinguishes quantum probability theory from classical and more general probability theories in terms of information-theoretic principles. In this talk, I will show how the principle of "Information Invariance & Continuity" maps to the relativity principle as it pertains to the invariant measurement of Planck's constant h for Stern-Gerlach spin measurements in exact analogy to the relativity principle as it pertains to the invariant measurement of the speed of light c for special relativity (SR). Essentially, quantum information theorists have extended Einstein's use of the relativity principle from the boost invariance of measurements of c to include the SO(3) invariance of measurements of h between different reference frames of mutually complementary spin measurements. Consequently, the "average-only" conservation represented by the Bell states that is responsible for the Tsirelson bound is understood to result from conservation per Information Invariance & Continuity between different reference frames of mutually complementary measurements, and this maps to conservation per the relativity principle in spacetime. Thus, the axiomatic reconstructions of QM have succeeded in producing a principle account of QM that is every bit as robust as the postulates of SR, revealing a still broader role for the relativity principle in the foundations of physics. |
Thursday, March 17, 2022 12:30PM - 12:42PM |
T35.00004: Classical Model Refuting Certain Loophole-Free Tests of Local Realism Gabriel D Ko, Brian R La Cour We consider two recent experimental tests of local realism purporting to be loophole free and demonstrate that they can, in fact, be explained by a local, deterministic classical model. In particular, we show that apparent violations of the Clauser-Horne-Eberhard inequality can arise from the local dependence of coherence times on the settings of each polarizer due to the presence of additional vacuum modes. Consequently, different settings produce differing numbers of effective independent trials within a fixed coincidence window, suppressing singles counts and enhancing coincidence counts. The resulting contextual dependence permits a violation of the inequality. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T35.00005: Hierarchy of Theories with Indefinite Causal Structures Nitica Sakharwade, Lucien Hardy The Causaloid framework introduced by Hardy suggests a research program aimed at finding a theory of Quantum Gravity. On one side General Relativity while deterministic (once the metric is provided) features dynamic causal structures, on the other side Quantum Theory while having fixed causal structures is probabilistic in nature. It is natural to then expect Quantum Gravity to house both of the radical aspects of GR and QT, and therefore incorporate indefinite causal structure. The Causaloid framework is operational, it is based on the assertion that any physical theory, whatever it does, must correlate recorded data. Imagine a person inside a closed space, having access to a stack of cards with recorded data (procedures, outcomes, locations); and the person is tasked with inferring(aspects of) the underlying physical theory that governs the data. The correlation of recorded data due to the physical theory means the stack of cards is riddled with redundancy. The person in the box distills away the redundancy by compressing the data. We call this physical compression. In this framework there are three levels of compression: 1) Tomographic Compression, 2) CompositionalCompression and 3) Meta Compression. In this work, we present a diagrammatic form for physical compression to facilitate exposition of the Causaloid framework. Further, building upon the work from we study Meta compression and find a hierarchy of theories characterised by Meta Compression for which we provide a general form. We will proceed to populate this hierarchy. The theory of circuits forms the simplest case, which we express diagrammatically through Duotensors, following which we construct Triotensors using hyper3wires (hyperedges connecting three operations)for the next rung in the hierarchy. Finally, we discuss the broad implications of this work. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T35.00006: The Unactualized Certainty-Actuality (UC-A) Correspondence Armin Nikkhah Shirazi This talk investigates the correspondence between a set of ontic possibilities of unit measure ("unactualized certainties") and actualities, a correspondence which appears whenever possibilities and actualities are explicitly distinguished within a mathematical formalism. It does this first through the lens of a recently proposed enrichment of axiomatic probability, and then through the lens of a recently proposed modification of the standard quantum formalism, entitled the the Heisenberg Interpretation, both of which implement the formal distinction (unlike the resepctive standard formalisms). |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T35.00007: Eavesdropping on the Decohering Environment: Quantum Darwinism, Amplification, and the Origin of Objective Classical Reality Akram Touil, Bin Yan, Davide Girolami, Sebastian Deffner, Wojciech H Zurek "How much information about a system S can one extract from a fragment F of the environment E that decohered it?" is the central question of Quantum Darwinism. To date, most answers relied on the quantum mutual information of SF, or on the data extracted by measuring S directly. These are reasonable upper bounds on what is really needed but much harder to calculate -- the channel capacity of the fragment F for the information about S. We consider a model based on imperfect c-not gates where all the above can be computed, and discuss its implications for the emergence of objective classical reality. We find that all relevant quantities, such as the quantum mutual information as well as the channel capacity exhibit similar behavior. In the regime relevant for the emergence of objective classical reality this includes scaling independent from the quality of the imperfect c-not gates or the size of E, and even nearly independent of the initial state of S. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T35.00008: Quantitative limits to quantum correlations in many-body systems: a signature of classical objectivity Davide Girolami, Akram Touil, Bin Yan, Sebastian Deffner, Wojciech H Zurek We quantify how much information about a quantum system can be recorded in its environment, by establishing quantitative limits to bipartite quantum correlations in many-body systems. In particular, bounds on quantum discord imply that independent observers that monitor environment fragments inevitably eavesdrop only classical information about the system, i.e. information about a pointer observable. The result validates the core idea of Quantum Darwinism: classical objectivity is not accidental, but rather a compelling feature of quantum theory. We also recast the information-theoretic signature of classical objectivity in analytical form by means of the conditional mutual information. This result enables one to monitor without hard numerical optimizations when objective reality emerges from the quantum substrate. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T35.00009: Testing quantum causal influences with photons Emanuele Polino, Iris Agresti, Davide Poderini, Beatrice Polacchi, Nikolai Miklin, Miriami Gachechiladze, Alessia Suprano, Giorgio Milani, Gonzalo Carvacho, Rafael Chaves, Fabio Sciarrino Bell’s theorem and violation of Bell’s inequalities represent the first evidence of the incompatibility between quantum theory and the classical notion of local causality. Bell’s tests rely only on input/output correlations, and allow to infer the non-classical nature of physical systems with minimal assumptions on the adopted apparatus in the so-called device-independent approach. The certification of quantum non-classicality is of crucial importance for several applications in quantum information tasks, but sometimes this task can be very demanding or even impossible in some experimental causal structures. |
Thursday, March 17, 2022 1:42PM - 1:54PM |
T35.00010: Causal Process Tomography of a Fiber-Based Quantum SWITCH Michael Antesberger, Lee A Rozema, Philip Walther The field of indefinite causal order in quantum mechanics has seen more and more interest in the past years, both theoretically and experimentally. In such processes, different parties act in a superposition of different orders. Since the first experimental realization of a process with an indefinite causal order, the quantum SWITCH, several protocols taking advantage of this new resource have emerged. In previous experiments, the causal non-separability of two parties has been verified by measuring a so-called 'causal witness'. Nevertheless, the corresponding process matrix has only been evaluated theoretically. Here, we experimentally reconstruct the process matrix of a new passively-stable fiber-based architecture for the quantum SWITCH based on time-bin encoded qubits, which can readily be scaled to more parties. We perform a full characterization of this new type of quantum SWITCH by implementing causal process tomography for the first time. We then compare the tomography results to those obtained by directly measuring several different causal witnesses. Finally, we present the first measurement of the fidelity of our experimental quantum SWITCH to the ideal quantum SWITCH. |
Thursday, March 17, 2022 1:54PM - 2:06PM |
T35.00011: Observation of vacuum electric field correlations outside the light cone Jerome Faist, Fabiana Settembrini, Frieder Lindel, Stefan Buhmann, Alexa Herter According to quantum field theory, empty space is permeated by quantum-vacuum fluctuations. Their presence lead to a series of measurable phenomena such as the Casimir force. A counter-intuitive feature of these fluctuating fields, shown theoretically, is the fact that they exhibit correlations between space-time points which are causally disconnected according to special relativity[1]. Using electro-optic sampling correlation measurements on vacuum[2], we have proved experimentally the existence of correlations of the vacuum fields for non-causally connected space-time points. This result is obtained by using two 195 fs laser pulses separated by a time of flight of 490 fs which propagate through a nonlinear crystal. Our theory enables to attribute the vast majority of the correlations as stemming from space-time points outside the light cone. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T35.00012: Emergence of the Born rule in strongly driven dissipative systems Rangeet Bhattacharyya, Nilanjana Chanda To understand the dynamical origin of the measurement in quantum mechanics, several models have been put forward which have a quantum system coupled to an apparatus. The system and the apparatus evolve in time, and the Born rule for the system to be in various eigenstates of the observable is naturally obtained. In this paper, we show that the effect of the drive-induced dissipation in an open quantum system can lead to the Born rule, even if there is no separate apparatus. The applied drive needs to be much stronger than the system-environment coupling. In this condition, we show that the dynamics of the driven-dissipative system could be reduced to a Milburn-like form, using a recently proposed fluctuation-regulated quantum master equation [A. Chakrabarti and R. Bhattacharyya, Phys. Rev. A 97, 063837 (2018).]. The irreversible part of the dynamics is caused by drive-induced dissipation. The resulting mixed state is identical to that obtained by using the Born rule. |
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