Events
Condensed Matter Seminar
Shedding single-photon light on many-body physics
Mr. Amir Burshtein
TAU
Mon, 07 Apr 2025, 11:10
Sacta-Rashi Building for Physics (54), room 207
Abstract: Photon decay is a notoriously inefficient process. The culprit is the fine structure constant \alpha – while photon splitting into other photons at lower frequencies may be mediated by interaction with matter, the small value of \alpha (~1/137) famously sets this interaction in the perturbative regime. A qualitatively different picture can emerge in superconducting circuits: carefully designed waveguides, implemented by arrays of Josephson junctions, provide an order unity \alpha environment for the photons. Coupling the waveguide to artificial atoms (qubits) then leads to the simulation of strong light-matter interaction, allowing for the decay of a single photon with order unity probability, demonstrated in recent experiments. I will show how this exotic effect can be leveraged to illuminate surprising aspects of fundamental quantum many-body phenomena, observed in experiments from the Manucharyan (EPFL) and Kuzmin (UW-Madison) groups. I will explain how the scattering rates of the photons, natural observables in such experiments, can capture dynamical signatures of quantum tunneling events, reveal the existence of inelastic collisions in integrable systems, and explore the onset and the breakdown of Fermi’s golden rule. I will further show that the scattering of a single photon off an artificial atom can serve as a highly sensitive probe of a fragile quantum phase transition. These works set the stage for utilizing the strong light-matter interaction to study nonequilibrium setups and harnessing the efficient photon splitting for quantum information processing applications.
This talk is mostly based on the following papers (theory and experiment, respectively):
- AB and M. Goldstein, "Inelastic decay from Integrability", PRX Quantum 5 020323 (2024)
- R. Kuzmin, N. Mehta, N. Grabon, R. A. Mencia, AB, M. Goldstein, and V. E. Manucharyan, "Observation of the Schmid-Bulgadaev dissipative quantum phase transition", Nature Physics s41567-024-02695-7 (2024)
Particles and Fields Seminar
Singular hypersurfaces in quadratic gravity
Dr. Inna Ivanova
BGU
Mon, 07 Apr 2025, 14:00
Sacta-Rashi Building for Physics (54), room 207
Abstract: It is shown that the equations of motion for singular hypersurfaces in quadratic gravity can be derived using the least action principle for any type of hypersurface, including lightlike ones. It turns out that for the Gauss-Bonnet model, neither double layers nor thin shells exist when the Lichnerowicz junction conditions are satisfied. For all types of hypersurfaces, criteria are established to determine whether a singular hypersurface represents a double layer or a thin shell. Our study reveals that Lichnerowicz conditions can be relaxed for lightlike hypersurfaces, and that "external pressure" vanishes for this type of hypersurfaces. Spherically symmetric singular hypersurfaces of all types are investigated that separate two spherically symmetric solutions of conformal gravity, such as various vacuums and Vaidya-type solutions. Using the matching of corresponding solutions, analogues of physical models like "vacuum burning", cosmological phase transition and thin shell collapse are analyzed in the context of conformal gravity. To clarify the physical meaning of "external pressure" and "external flow" (which are zero in general relativity), these components of the surface energy-momentum tensor are derived directly from the matter Lagrangian. Specifically, the surface energy-momentum tensor is obtained from the action of perfect fluid with a variable number of particles in the Eulerian picture.
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