Next CQD Colloquium (funded by Structures) will be given by Dr. Simon Balthasar Jäger
Please note the place and time:
Wednesday, 21th of May at 4:30 p.m., PI, INF 226, K 1-3, Goldbox
The main talk will be given by Dr. Simon Balthasar Jäger about:
Quantum technologies using cavity-mediated interactions and dissipation
Abstract:
Coupling atoms to optical cavities allows one to explore collective effects that emerge from strong light-matter interactions. In such setups the cavity mediates long-range atom-atom interactions that can be used to explore many-body effects such as spin squeezing, sub- and superradiance. This is not only of fundamental interest but has also direct applications in quantum technologies. In this talk I will discuss a quantum technology which harnesses such effects: the superradiant laser. This laser operates in a regime where the atomic lifetime exceeds by several orders of magnitude the cavity photon lifetime. As a consequence this laser is extremely robust against cavity length fluctuations which makes it a good candidate for atomic clock applications. I will discuss the theory and the general working principles of this laser and show how it can overcome different forms of broadening and disorder in the atomic ensemble and reach narrow laser linewidths. This is due to a synchronization mechanism of the individual atomic emission amplitudes that is mediated by the cavity. Taking the superradiant laser as a first example I will more generally discuss how cavity modes can be used to engineer tailored interactions and dissipation. Here, I will describe a theory which allows one to integrate out the cavity modes and to obtain effective atom-only Lindblad master equations that describe the atomic dynamics. I will demonstrate the validity of this approach and outline how it can be used to describe networks of interacting and dissipative spins.
The pretalk will be given by Hannes Koeper, KIP, University of Heidelberg.
For information about the CQD Colloquium, please see: https://cqd.uni-heidelberg.de/events/cqdcolloquium
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Next CQD special seminar will be given by Victor Gondret, Université Paris-Saclay
Please note the special place and time:
When: Monday, the 19th of May, 16:00 p.m.,
Where: KIP, INF 227, SR 2403
He will talk about:
Quasi-particle entanglement in a Bose-Einstein condensate : an acoustic analog of the Dynamical Casimir Effect
Parametric resonance is a recurrent phenomenon in physics, observable at all scales. For example, the vibration of a mirror in a cavity leads to the production of photons, a phenomenon known as the dynamical Casimir effect. In 1831, Faraday observed that a container of water excited vertically in a sinusoidal manner generates patterns with a frequency that is half of the excitation frequency. In the primordial universe, after inflation, parametric oscillations of a field (the inflaton) led to the creation of particles from vacuum, whose thermalization subsequently gave rise to the hot, dense state often associated with the Big Bang.
The growth in the number of quasi-particles (or particles) in the excited mode(s) is triggered by the system’s fluctuations and, due to momentum conservation, quasi-particles are created in pairs in two modes of opposite momentum. At zero temperature, quantum fluctuations initiate this growth, but when the temperature is non-zero, both thermal and quantum fluctuations trigger the growth. In this case, the characteristic signature of quantum vacuum fluctuations is then carried by the entanglement between these modes.
In this seminar, I will report on the experimental observation of the growth and decay of quasi-particle in a parametrically excited Bose-Einstein condensate. I will also discuss the evolution of two-mode entanglement between the quasi-particles and its subsequent disappearance due to thermalization but also effect beyond Bogolyubov theory.
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