Abstract: Massive mechanical oscillators have recently been measured and controlled in the quantum regime, providing a testbed for investigating the limits of quantum mechanics and its possible interplay with gravity. The stabilized entanglement of massive mechanical oscillators has been measured both indirectly and directly. Further, sensing of the motion of a mechanical oscillator beyond conventional quantum limits has been demonstrated. There exist further proposals for the realization of enhanced force sensing and many-body quantum state control in optomechanics, and problems in optomechanics have spurred the development of novel theoretical techniques.

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Quantum Nature of Gravity in the Lab: Assumptions, Implementation and Applications on the Way

Abstract: There is no empirical evidence yet as to “whether” gravity has a quantum mechanical origin. Motivated by this, Sougato Bose presents a feasible idea for testing the quantum origin of the Newtonian interaction based on the simple fact that two objects cannot be entangled without a quantum mediator. He shows that despite its weakness, gravity can detectably entangle two adjacent micron sized test masses held in quantum superpositions even when they are placed far apart enough to keep Casimir-Polder forces at bay. A prescription for witnessing this entanglement through spin correlations is also provided. Further, he clarifies the assumptions underpinning the above proposal such as our reasonable definition of “classicality”, as well as relativistic causality. He notes a few ways to address principal practical challenges: Decoherence, Screening EM forces and Inertial noise reduction. He also describes how unprecedented compact sensors for classical gravity (including meter scale sensors for low frequency gravitational waves) will arise on the way to the above grand goal.

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Abstract: By using complex-variable methods one can extend conventional Hermitian quantum theories into the complex domain. The result is a huge and exciting new class of non-Hermitian parity-time-symmetric (PT-symmetric) theories that still obey the fundamental laws of quantum mechanics. These new theories have remarkable physical properties, which are currently under intense study by theorists and experimentalists. Many theoretical predictions have been verified in recent beautiful laboratory experiments.

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Abstract: All clocks, periodic and non-periodic, are open dissipative systems driven from thermal equilibrium so that the Helmholtz free energy is increased. In this talk Gerard Milburn discusses the thermodynamic constraints for classical and quantum clocks. He also discusses clocks driven not by work but by information extraction and makes a connection to Rovelli's thermal time hypothesis as a proposed solution to the problem of time in quantum gravity.

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Abstract: Stochastic resonance, where noise synchronizes a system’s response to an external drive, is a phenomenon that occurs in a wide variety of noisy systems ranging from the dynamics of neurons to the periodicity of ice ages. In this webinar Susan Coppersmith will present theory and experiments on a quantum system that exhibits stochastic resonance — the quantum tunneling of the magnetization of a single Fe atom measured using spin-polarized scanning tunneling microscopy. Stochastic resonance is shown deep in the quantum regime, where fluctuations are driven by tunneling of the magnetization, as well as in a semi-classical crossover region where thermal excitations set in. Combining theory and experiment enables one to probe the dynamics on time scales shorter than can be resolved experimentally.

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Abstract: After reviewing the basics of our current understanding of fundamental particles and their interactions, as enshrined in the Standard Model, Raymond Volkas briefly surveys the well-established evidence that this is an incomplete theory. The main part of the talk is then about recent measurements of the muon anomalous magnetic moment, and the rates of some B-meson decays, which point to possible further inadequacies of the Standard Model. Interestingly, the strongest current hints for this all involve muons.

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Abstract: The nature and origin of dark matter is one of the key unresolved questions of fundamental physics. Astrophysical and cosmological data provide powerful probes of dark matter properties, although to date no signal has been confirmed. In this webinar Tracy Slatyer discusses a number of claimed possible signals of novel dark matter physics in astrophysical datasets, alternative explanations, and open questions, with a focus on the Galactic Center Excess in GeV-scale gamma rays.

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