Tobias Ulrik Donner

Last Name

Donner

First Name

Tobias Ulrik

ORCID

0000-0001-7016-587X

Organisational unit

03599 - Esslinger, Tilman / Esslinger, Tilman

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Publications 1 - 10 of 42

First order phase transition between two centro-symmetric superradiant crystals
Li, Xiangliang; Dreon, Davide; Zupancic, Philip; et al. (2021)
Physical Review Research
We observe a structural phase transition between two configurations of a superradiant crystal by coupling a Bose-Einstein condensate to an optical cavity and applying imbalanced transverse pump fields. The transition can be interpreted as a transition between two nonpolar, centro-symmetric structures involving a change in polarization. We find that this first order phase transition is accompanied by transient dynamics of the order parameter which we measure in real time. The phase transition and the excitation spectrum can be derived from a microscopic Hamiltonian, in quantitative agreement with our experimental data.
Optical transport and manipulation of an ultracold atomic cloud using focus-tunable lenses
Léonard, Julian; Lee, Moonjoo; Morales, Andrea; et al. (2014)
New Journal of Physics
We present an optical setup with focus-tunable lenses to dynamically control the waist and focus position of a laser beam, in which we transport a trapped ultracold cloud of 87Rb over a distance of $28\;{\rm cm}$. The scheme allows us to shift the focus position at constant waist, providing uniform trapping conditions over the full transport length. The fraction of atoms that are transported over the entire distance comes near to unity, while the heating of the cloud is in the range of a few microkelvin. We characterize the position stability of the focus and show that residual drift rates in focus position can be compensated for by counteracting with the tunable lenses. Beyond being a compact and robust scheme to transport ultracold atoms, the reported control of laser beams makes dynamic tailoring of trapping potentials possible. As an example, we steer the size of the atomic cloud by changing the waist size of the dipole beam.
Long-range interacting quantum systems
Defenu, Nicolò; Donner, Tobias Ulrik; Macrì, Tommaso; et al. (2023)
Reviews of Modern Physics
In this review recent investigations are summarized of many-body quantum systems with long-range interactions, which are currently realized in Rydberg atom arrays, dipolar systems, trapped-ion setups, and cold atoms in cavities. In these experimental platforms parameters can be easily changed, and control of the range of the interaction has been achieved. The main aim of the review is to present and identify the common and mostly universal features induced by long-range interactions in the behavior of quantum many-body systems. Discussed are the case of strong nonlocal couplings, i.e., the nonadditive regime, and the one in which energy is extensive, but low-energy, long-wavelength properties are altered with respect to the short-range case. When possible, comparisons with the corresponding results for classical systems are presented. Finally, cases of competition with local effects are also reviewed.
Dissipation-induced non-equilibrium phases with temporal and spatial order
Zhang, Zhao; Dreon, Davide; Esslinger, Tilman; et al. (2025)
Communications Physics
Understanding spatial and temporal order in many-body systems is a key challenge, particularly in out-of-equilibrium settings. A major hurdle is developing controlled model systems to study these phases. We propose an experiment with a driven quantum gas coupled to a dissipative optical cavity, realizing a non-equilibrium phase diagram featuring both spatial and temporal order. The system’s control parameter is the detuning between the drive frequency and cavity resonance. Negative detunings yield a spatially ordered phase, while positive detunings produce phases with both spatial order and persistent oscillations, forming dissipative spatio-temporal lattices. We also identify a phase where the dynamics dephase, leading to chaotic behavior. Numerical and analytical evidence supports these superradiant phases, showing that the spatio-temporal lattice originates from cavity dissipation. The atoms experience accelerated transport, either via uniform acceleration or abrupt momentum transitions. Our work provides insights into temporal phases of matter not possible at equilibrium.
Measuring the dynamic structure factor of a quantum gas undergoing a structural phase transition
Landig, Renate; Brennecke, Ferdinand; Mottl, Rafael; et al. (2015)
Nature Communications
The dynamic structure factor is a central quantity describing the physics of quantum many-body systems, capturing structure and collective excitations of a material. In condensed matter, it can be measured via inelastic neutron scattering, which is an energy-resolving probe for the density fluctuations. In ultracold atoms, a similar approach could so far not be applied because of the diluteness of the system. Here we report on a direct, real-time and nondestructive measurement of the dynamic structure factor of a quantum gas exhibiting cavity-mediated long-range interactions. The technique relies on inelastic scattering of photons, stimulated by the enhanced vacuum field inside a high finesse optical cavity. We extract the density fluctuations, their energy and lifetime while the system undergoes a structural phase transition. We observe an occupation of the relevant quasi-particle mode on the level of a few excitations, and provide a theoretical description of this dissipative quantum many-body system.
Metastability and avalanche dynamics in strongly correlated gases with long-range interactions
Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; et al. (2018)
Proceedings of the National Academy of Sciences of the United States of America
Quantum Fluctuation Dynamics of Dispersive Superradiant Pulses in a Hybrid Light-Matter System
Stitely, Kevin C.; Finger, Fabian; Rosa-Medina Pimentel, Rodrigo Felipe; et al. (2023)
Physical Review Letters
We consider theoretically a driven-dissipative quantum many-body system consisting of an atomic ensemble in a single-mode optical cavity as described by the open Tavis-Cummings model. In this hybrid light-matter system, the interplay between coherent and dissipative processes leads to superradiant pulses with a buildup of strong correlations, even for systems comprising hundreds to thousands of particles. A central feature of the mean-field dynamics is a self-reversal of two spin degrees of freedom due to an underlying time-reversal symmetry, which is broken by quantum fluctuations. We demonstrate a quench protocol that can maintain highly non-Gaussian states over long timescales. This general mechanism offers interesting possibilities for the generation and control of complex fluctuation patterns, as suggested for the improvement of quantum sensing protocols for dissipative spin amplification.
Two-mode Dicke model from nondegenerate polarization modes
Morales, Andrea; Dreon, Davide; Li, Xiangliang; et al. (2019)
Physical Review A
We realize a nondegenerate two-mode Dicke model with competing interactions in a Bose-Einstein condensate (BEC) coupled to two orthogonal polarization modes of a single optical cavity. The BEC is coupled to the cavity modes via the scalar and vectorial part of the atomic polarizability. We can independently change these couplings and determine their effect on a self-organization phase transition. Measuring the phases of the system, we characterize a crossover from a single-mode to a two-mode Dicke model. This work provides perspectives for the realization of coupled phases of spin and density.
Roton-Type Mode Softening in a Quantum Gas with Cavity-Mediated Long-Range Interactions
Mottl, Rafael; Brennecke, Ferdinand; Baumann, Kristian; et al. (2012)
Science
Quantum simulation with atoms and photons
Brantut, Jean-Philippe; Donner, Tobias Ulrik (2022)
SPG Mitteilungen
Quantum simulation, i.e. the use of a fully controlled quantum device to understand the properties of complex many-body systems, is among the most important applications of emergent quantum technologies. Among the platforms available for this task, ultra-cold atoms are the most widespread, thanks to their native ability to represent both Bosons and Fermions, to explore a wide range of geometries using laser-induced potentials, and the possibility to reach the strongly interacting regime. Here, we present the use of cavity quantum electrodynamics together with cold atomic gases to realize novel types of quantum simulations. We review the different ways by which cold atoms can couple with light, and describe their applications to quantum simulations of models involving long range interactions.

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Tobias Ulrik Donner

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