SAMOP 2023 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 26: Quantum Gases: Bosons III

Q 26.4: Talk

Wednesday, March 8, 2023, 11:45–12:00, E214

Quantum phase transitions of excited states in spinor BECs — •Bernd Meyer-Hoppe¹, Fabian Anders¹, Polina Feldmann^2,3, Luis Santos², and Carsten Klempt¹ — ¹Leibniz Universität Hannover, Institut für Quantenoptik, Welfengarten 1, 30167 Hannover, Germany — ²Leibniz Universität Hannover, Institut für Theoretische Physik, Appelstraße 2, 30167 Hannover, Germany — ³Stewart Blusson Quantum Matter Institute, The University of British Columbia, 2355 East Mall, Vancouver BC V6T 1Z4, Canada

Depending on external control parameters, the physically realized states of a given system can be grouped into phases that are defined by a measurable order parameter. For ultracold systems, where quantum fluctuations dominate thermal ones, quantum phases arise, which are separated by quantum phase transitions (QPTs) with a vanishing energy gap between the ground state and the first excited state. Today, ultracold quantum many-body systems can also be prepared at non-zero energy without thermalization. For such systems, it is possible to define excited-state quantum phase transitions (ESQPTs) by an analogous divergence of the density of states.

Here we present the experimental determination of a quantum phase diagram in a spinor BEC, where the energy of the system is one of the control parameters. The quantum phases are detected by the measurement of an interferometric order parameter that abruptly changes at the ESQPTs. We identify three quantum phases and their transitions by varying two control parameters: the effective magnetic field and the excitation energy.