Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C06: Bose-Einstein Condensates, Photon Condensates, Atom Lasers, and DynamicsLive
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Chair: Martin Weitz, Bonn |
Tuesday, June 1, 2021 10:30AM - 10:42AM Live |
C06.00001: Thermally condensing photons into a coherently split state of light Christian Kurtscheid, Andreas Redmann, David Dung, Erik Busley, Frank Vewinger, Achim Rosch, Julian Schmitt, Martin Weitz Techniques to control the quantum state of light play a crucial role in a wide range of fields, from quantum information science to precision measurements. While for electrons in solid state materials complex quantum states can be created by mere cooling, in the field of optics manipulation and control currently builds on non-thermodynamic methods. Using an optical dye-filled microcavity, we have demonstrated that photon wavepackets can be split through thermalization within a potential with two minima subject to tunnel coupling. Even at room temperature, photons condense into a quantum-coherent bifurcated ground state. Fringe signals upon recombination show the relative coherence between the two wells, demonstrating a working interferometer with the non-unitary thermodynamic beamsplitter. |
Tuesday, June 1, 2021 10:42AM - 10:54AM Live |
C06.00002: Fluctuation-Dissipation relation of a grand-canonical photon Bose-Einstein condensate Fahri Emre E Öztürk, Frank Vewinger, Julian Schmitt, Martin Weitz In thermal equilibrium, fluctuations of the particle number are related to the isothermal compressibility and the thermal energy kBT. This relation has been observed in a variety of systems ranging from Brownian particles to quantum gases, but not yet in Bose-Einstein condensates despite these systems are intrinsically in thermal equilibrium. Here, we experimentally investigate the fluctuation-dissipation relation in a Bose-Einstein condensate of photons realized in a dye-microcavity. The photon gas is coupled to a reservoir of dye molecular excitations, which serve both as a heat bath and a particle reservoir. Our measurements demonstrate a good agreement with the expected ratio of statistical number fluctuations and compressibility for a thermalized photon gas system following the flucutation-dissipation theorem. |
Tuesday, June 1, 2021 10:54AM - 11:06AM Live |
C06.00003: Non-equilibrium evolution of Bose-Einstein condensate deformation in temporally controlled weak disorder Milan Radonjic, Axel Pelster We consider a time-dependent extension of a perturbative mean-field approach to the homogeneous dirty boson problem by considering how switching on and off a weak disorder potential affects the stationary state of an initially equilibrated Bose-Einstein condensate by the emergence of a disorder-induced condensate deformation. We find that in the switch on scenario the stationary condensate deformation turns out to be a sum of an equilibrium part, that actually corresponds to adiabatic switching on the disorder, and a dynamically-induced part, where the latter depends on the particular driving protocol. If the disorder is switched off afterwards, the resulting condensate deformation acquires an additional dynamically-induced part in the long-time limit, while the equilibrium part vanishes. We also present an appropriate generalization to inhomogeneous trapped condensates. Our results demonstrate that the condensate deformation represents an indicator of the generically non-equilibrium nature of steady states of a Bose gas in a temporally controlled weak disorder. |
Tuesday, June 1, 2021 11:06AM - 11:18AM Live |
C06.00004: Observation of a Non-Hermitian Phase Transition in an Optical Quantum Gas Julian Schmitt, Fahri Öztürk, Tim Lappe, Göran Hellmann, Jan Klaers, Frank Vewinger, Johann Kroha, Martin Weitz Quantum gases of light, such as photon or polariton condensates in optical microcavities, are collective quantum systems enabling a tailoring of dissipation from, for example, cavity loss. This makes them valuable tools to create and understand phases of systems, which are dissipatively coupled to the environment. Bose-Einstein condensates of photons, realized in dye-filled microcavities, provide a platform to study the dynamics emerging in an open, grand canonical situation where the condensate particles are coupled to reservoirs. The steady-state particle flux from the pump beam through the condensate and out to the environment induces a novel behavior of the particle number fluctuations. |
Tuesday, June 1, 2021 11:18AM - 11:30AM Live |
C06.00005: Hyperspherical approach to dipolar Bose-Einstein condensates Eli J Halperin, John L Bohn Recently a number of interesting phenomena have been observed in ultracold dipolar Bose gasses, such as droplets and supersolids. Typical theoretical descriptions of dipolar Bose-Einstein condensates (BECs) require use of the nonlinear Gross-Pitaevskii equation. Here we apply a hyperspherical approach to dipolar BECs, giving an entirely linear 2D Schrodinger equation. We use this to generate excited states of dipolar droplets and pancakes, and explore dynamics in this linear regime. We additionally show a general correspondence between hyperspherical methods and the Gaussian ansatz to the Gross-Pitaevskii equation in the limit of a large number of particles. |
Tuesday, June 1, 2021 11:30AM - 11:42AM Live |
C06.00006: Weak Measurement Induced Phonon Fluctuations in a Bose-Einstein Condensate Emine Altuntas, Ian Spielman Non-destructive imaging methods are weak measurement techniques that offer new opportunities for understanding the system-reservoir dynamics of many-body systems. Weak measurements yield a controlled reservoir and consequently allow time-resolved study of the system evolution. We consider the quantum backaction induced by weak measurements in quasi-one dimensional 87Rb Bose-Einstein condensates (BECs) using a common non-destructive imaging technique: phase contrast imaging. In this talk, I first discuss the theoretical model for weak measurement via phase contrast imaging (PCI) [1]. I then describe our experimental work and novel methodology of eliminating artifacts present in imperfect imaging systems. Weak measurements provide noisy information about the ultracold atoms system, and thus aberration-compensation is crucial for extracting the underlying quantum phenomena. Next, I present our preliminary results on the phonon fluctuations that result from the quantum backaction induced by repeated PCI of the condensate. Finally, I will discuss possible feedback control protocols for future applications of Hamiltonian engineering using weak measurements and feedback. |
Tuesday, June 1, 2021 11:42AM - 11:54AM Live |
C06.00007: Observation of dense soliton trains in a dilute-gas Bose-Einstein condensate Thomas M Bersano, Sean Mossman, Maren E Mossman, Peter W Engels From water waves to pulse propagation through optical fibers, the rich phenomenology of solitons is one of the prominent features of nonlinear dynamics. In dilute-gas BECs, various kinds of solitons have been demonstrated by balancing interaction and kinetic energy effects. While almost all studies so far have focused on single or just very few solitons, here we break new ground by investigating tightly packed soliton trains. We demonstrate a new method for the generation of dense dark-bright soliton trains which takes advantage of a Ramsey pulse sequence. We investigate the formation and evolution of solitons at various length scales and explore the properties of these features, such as their stability. |
Tuesday, June 1, 2021 11:54AM - 12:06PM Live |
C06.00008: Thermo-Optic Photon-Photon Interaction in Photon BECs at Dimensional Crossover from 2D to 1D Enrico Stein, Axel Pelster Since the discovery of photon Bose-Einstein condensates in 2010 [1] this phenomenon has been studied extensively. At its core this system consists of a dye solution filling the microcavity in which the photons are trapped. Due to cyclic absorption and reemission processes of photons the dye leads to a thermalisation of the photon gas at room temperature and finally to its Bose-Einstein condensation. Because of a non-ideal quantum efficiency, those cycles yield in addition a heating of the dye solution, which results in an effective photon-photon interaction [2]. |
Tuesday, June 1, 2021 12:06PM - 12:18PM Live |
C06.00009: Demonstration of fold and cusp caustics with a quasi-continuous atom laser Maren E Mossman, Thomas M Bersano, Michael Forbes, Peter W Engels The invention of the laser revolutionized modern scientific methods, creating a versatile tool used for a variety of applications. The demonstration of the "atom laser" two decades ago further established tabletop ultracold atomic systems as exceptional playgrounds for building quantum analog systems. In our experiment, we investigate the intriguing dynamics of a quasi-continuous atom laser when a repulsive or attractive potential is positioned into the coherent atom stream. From this, we observe sharply delineated features, as well as clear indications of fold and cusp caustics, that are strongly dependent on the shape, strength, and sign of the potential. This direct observation of caustics in terms of atomic matter waves opens up the field of "catastrophe atom-optics" where multiple potentials can be introduced to generate intricate patterns and potentially higher-order caustic effects. |
Tuesday, June 1, 2021 12:18PM - 12:30PM Live |
C06.00010: Studying caustics with a pulsed atom laser Peter W Engels, Maren E Mossman, Thomas M Bersano, Michael Forbes In a recent series of experiments, our group has demonstrated the emergence of caustics in a quasi-continuous atom laser. A rich phenomenology, including fold and cusp singularities and larger caustic networks, has been observed. Here, we first provide theoretical background for these studies and then extend them by presenting results obtained with a pulsed, rather than quasi-continuous, atom laser. Our experiments with pulsed atom lasers reveal additional insight: for example, some caustics are actual particle trajectories, while others only appear as envelops of trajectories. These studies advance our understanding of catastrophe atom optics and provide new tools for future atom optical experiments. |
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