09:00 - 09:40
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Florian Marquardt
(Max Planck Institute for the Science of Light Erlangen)
Synchronizing systems as a neuromorphic platform
We study a transversely laser-driven atomic BEC coupled to an optical cavity, where atom interactions are mediated by laser-pump and cavity photons. This has been realized experimentally using different setups and parameters [1][2]. In these setups the atoms can form a superradiant crystal which supports constructive interference of scattered laser photons above a threshold determined by the driving frequency and intensity. While a minimal model describing this transition is the two-state Dicke model, here, we perform a full mean-field analysis of the system, including all relevant 2D momentum states and the cavity field. With this description we uncover phases and dynamics of the atom-cavity system that are neither captured by the simplified two-level Dicke model nor by a 1D description. We map out the complete phase diagram depending on pump strength and cavity detuning, and provide an in depth understanding of the instabilities that are linked to the emergence of spatio-temporal patterns. We find parameter regimes of mean-field bistability, and regimes where the atom-cavity dynamics forms chaotic trajectories and limit cycles triggered by density-wave resonances.
[1] Baumann, K., Guerlin, C., Brennecke, F. \& Esslinger, T. Dicke quantum phase transition with a superfluid gas in an optical cavity. Nature 464, 1301–1306 (2010).
[2] Klinder, J., Keßler, H., Wolke, M., Mathey, L. \& Hemmerich, A. Dynamical phase transition in the open Dicke model. Proc. Natl. Acad. Sci. (U.S.A.) 112, 3290–3295 (2015).
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09:40 - 10:20
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Michel Fruchart
(CNRS, ESPCI Paris)
Nonreciprocal Ising model
The quantum $O(n)$ model is a paradigmatic example of a many-body quantum systems which exibith interesting equilibrium and out-of-equilibrium features. We show that the model is completely integrable in the large $n$ limit regarless of the dimension $d$, already at the lattice model. As a consequence qe are able to characterize the dynamics and the spectrum of the model in the thermodynamic limit: in partivular we find that the system theramalizes toward a Generalized Gibbs Enseble ensemble in the Quantum Field Theory limit in which the lattice space is sent to zero, while persistent, self-susatained oscillations arises at the lattice level, when the momentum cutoff is kept finite.
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10:20 - 10:50
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COFFEE BREAK
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10:50 - 11:30
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Matteo Brunelli
(JEIP, UAR 3573 CNRS, Collège de France, Paris)
Nonreciprocal phase transition in active quantum spins
Here I will give a general algebraic theory of synchronization in both open and closed time independent many-body systems based on the recently introduced theory of dynamical symmetries. Closed locally interacting many-body systems can act as their own baths thus inducing synchronization that spreads inside a light cone given by a Lieb-Robinson bound. I will use Krylov Liouvillian approaches to demonstrate the existence of a phase transition between a regime where synchronization is present and absent controlled by onsite disorder. More specifically, this new kind of transition can be associated with a level crossing in the complex eigenfrequencies of the Krylov Liouvillian and the associated transient dynamical symmetries. An example of a disordered spin chain will be studied.
References:
N. Loizeau, B. Buca, D. Sels. arXiv preprint arXiv:2503.07403
B. Buca. Phys. Rev. X 13, 031013 (2023).
B Buca, C Booker, D Jaksch. SciPost Physics 12 (3), 097 (2022)
D. E. Parker, X. Cao, A. Avdoshkin, T. Scaffidi, E. Altman. Phys. Rev. X 9, 041017 (2019).
B Buca, J Tindall, D Jaksch. Nat. Comm. 10 (1), 1730 (2019)
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11:30 - 11:50
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Benjamin Stickler
(University of Ulm)
Non-reciprocal interactions and entanglement between optically levitated nanoparticles
Optically levitating dielectric nanoparticles in ultra-high vacuum, where their motion can be cooled into the deep quantum regime, provides a promising platform for force and torque sensing and for high-mass tests of quantum physics. In this talk I will discuss recent results on the coupled dynamics of co-levitated nanoparticles interacting via optical binding and via electrostatic forces. I will show how non-reciprocal interactions [1,2] and mechanical entanglement [3,4] between two particles can be generated and observed by controlling the light fields suspending them.
[1] Rieser, Ciampini, Rudolph, Kiesel, Hornberger, Stickler, Aspelmeyer, and Delić, Science 377, 987 (2022)
[2] Reisenbauer, Rudolph, Egyed, Hornberger, Zasedatelev, Abuzarli, Stickler, and Delić, Nat. Phys. (2024)
[3] Rudolph, Delić, Aspelmeyer, Hornberger, and Stickler, Phys. Rev. Lett. 129, 193602 (2022)
[4] Rudolph, Delić, Hornberger, and Stickler, 133, 233603 (2024)
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11:50 - 12:10
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Tobias Nadolny
(University of Basel)
Synchronziation and nonreciprocal interactions in superradiant lasers
Superradiant lasers, which consist of incoherently driven atoms coupled to a lossy cavity, are a promising source of coherent light with an extremely narrow linewidth. In this talk, I will discuss how the narrow linewidth arises through a Kuramoto-like synchronization transition from an incoherent to a phase-locked state. When a fraction of the atoms is not driven, nonreciprocal interactions emerge, i.e., a competition between alignment and antialignment of the atomic dipoles. These nonreciprocal interactions, which are usually studied in the context of active matter, result in a frequency shift of the superradiant laser. Our work shows that concepts of synchronization and active matter offer insights into the quantum-optical model of a superradiant laser.
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12:10 - 13:40
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LUNCH
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13:40 - 14:20
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Berislav Buċa
(Université Paris-Saclay, CNRS, LPTMS, Orsay)
A general theory of autonomous quantum synchronization
I will consider two very different open quantum systems that can synchronize to an external periodic signal. Specifically, I will analyze a squeezed quantum van der Pol oscillator [1,2] and a central spin model subject to periodic resetting [3]. The former has an intuitive classical limit from which the synchronization dynamics can be well understood. In contrast, the considered spin model has no well defined thermodynamic or classical limit. I will show that both systems can display subharmonic synchronization to an external periodic signal. Despite their different nature, I will show that this phenomenon displays the same spectral features in both cases, namely the opening of a spectral gap between several low lying excitations and the rest [1,2,3]. Hence, the regime of subharmonic synchronization manifests as a metastable dynamical regime in which, after a short transient, the systems display a very long plateau of oscillations locked to a fraction of the signal frequency. Eventually, these oscillations decay out due to the effects of quantum fluctuations. By applying the theory of quantum metastability, I will show that this eventual relaxation corresponds to a classical stochastic (activation) process between the different phases at which these systems can lock. Finally, I will comment on connections of these phenomena with discrete time crystals in dissipative quantum systems.
[1] A. Cabot, G. L. Giorgi, R. Zambrini, New J. Phys. 23, 103017 (2021).
[2] A. Cabot, G. L. Giorgi, R. Zambrini, PRX Quantum 5, 030325 (2024).
[3] A. Cabot, F. Carollo, I. Lesanovsky, Phys. Rev. B 106, 134311 (2022).
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14:20 - 14:40
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Shu Zhang
(Okinawa Institute of Science and Technology)
Spectral Fingerprints of Limit Cycles and Critical Slowing Down in Open Quantum Systems
Among the most iconic features of classical dissipative dynamics are persistent limit-cycle oscillations
and critical slowing down at the onset of such oscillations, where the system relaxes purely algebraically in
time. On the other hand, quantum systems subject to generic Markovian dissipation decohere exponentially
in time, approaching a unique steady state. Here we show how coherent limit-cycle oscillations and
algebraic decay can emerge in a quantum system governed by a Markovian master equation as one
approaches the classical limit, illustrating general mechanisms using a single-spin model and a two-site
lossy Bose-Hubbard model. In particular, we demonstrate that the fingerprint of a limit cycle is a slowdecaying branch with vanishing decoherence rates in the Liouville spectrum, while a power-law decay is
realized by a spectral collapse at the bifurcation point. We also show how these are distinct from the case of
a classical fixed point, for which the quantum spectrum is gapped and can be generated from the linearized
classical dynamics.
S Dutta, S Zhang, M Haque, Physical Review Letters 134, 050407 (2025)
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14:40 - 15:00
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Albert Cabot
(University of Tübingen)
Metastable subharmonic synchronization in open quantum systems
I will consider two very different open quantum systems that can synchronize to an external periodic signal. Specifically, I will analyze a squeezed quantum van der Pol oscillator [1,2] and a central spin model subject to periodic resetting [3]. The former has an intuitive classical limit from which the synchronization dynamics can be well understood. In contrast, the considered spin model has no well defined thermodynamic or classical limit. I will show that both systems can display subharmonic synchronization to an external periodic signal. Despite their different nature, I will show that this phenomenon displays the same spectral features in both cases, namely the opening of a spectral gap between several low lying excitations and the rest [1,2,3]. Hence, the regime of subharmonic synchronization manifests as a metastable dynamical regime in which, after a short transient, the systems display a very long plateau of oscillations locked to a fraction of the signal frequency. Eventually, these oscillations decay out due to the effects of quantum fluctuations. By applying the theory of quantum metastability, I will show that this eventual relaxation corresponds to a classical stochastic (activation) process between the different phases at which these systems can lock. Finally, I will comment on connections of these phenomena with discrete time crystals in dissipative quantum systems.
[1] A. Cabot, G. L. Giorgi, R. Zambrini, New J. Phys. 23, 103017 (2021).
[2] A. Cabot, G. L. Giorgi, R. Zambrini, PRX Quantum 5, 030325 (2024).
[3] A. Cabot, F. Carollo, I. Lesanovsky, Phys. Rev. B 106, 134311 (2022).
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15:00 - 15:30
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COFFEE BREAK
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15:30 - 16:10
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Oded Zilberberg
(University of Konstanz)
Sideband instabilities via an internal resonance
Synchronization is one of the most intriguing collective phenomena in nature. It is intimately related to diverse fields ranging from engineering, biology, mathematics and physics [1]. Intriguingly, synchronization is related to pattern formation, and it is one example of self-organization in manybody systems under non-equilibrium conditions [2]. Most of the developments in the theory of synchronization are based on nonlinear dynamical systems. It is therefore an open question if quantum signatures or fingerprints of synchronization appear in quantum systems, whose dynamics is inherently linear. Recently, there has been an onset of interest in the investigation of quantum synchronization, with impressive developments providing measures of synchronization in diverse systems such as quantum Van der Pol and Stuart Landau oscillators [3-8].
In this talk I will discuss quantum fingerprints of synchronization induced by a classical drive that undergoes a synchronization transition. Specifically, I consider a one-dimensional spin chain locally driven by a classical Kuramoto model. I initialize the phases of the Kuramoto model randomly. As a result, the spin chain does not have any spatial symmetries. When the Kuramoto undergoes a synchronization transition, there are emergent spatial and temporal symmetries that are quantum fingerprints of classical synchronization [9]. At the end of my talk I will discuss how the Kuramoto model can induce emergent topological behavior in the spin chain. I envision our results to open a new direction of research on self-organization of quantum manybody systems driven by classical synchronization.
[1] A. Pikovsky, M. Rosenblum, and J. Kurths, Synchronization: A Universal Concept in Nonlinear Sciences, Cambridge Nonlinear Science Series (Cambridge University Press, 2001).
[2] M. C. Cross and P. C. Hohenberg, Pattern formation outside of equilibrium, Rev. Mod. Phys. 65, 851 (1993).
[3] T. E. Lee and H. R. Sadeghpour, Quantum synchronization of quantum van der pol oscillators with trapped ions, Phys. Rev. Lett. 111, 234101 (2013).
[4] S. Walter, A. Nunnenkamp, and C. Bruder, Quantum synchronization of a driven self-sustained oscillator, Phys. Rev. Lett. 112, 094102 (2014).
[5] V. M. Bastidas, I. Omelchenko, A. Zakharova, E. Scholl, and T. Brandes, Quantum signatures of chimera states, Phys. Rev. E 96, 052210 (2017).
[6] S. Sonar, M. Hajdusek, M. Mukherjee, R. Fazio, V. Vedral, S. Vinjanampathy, and L.-C. Kwek, Squeezing enhances quantum synchronization, Phys. Rev. Lett. 120, 163601 (2018).
[7] C. W. Wachtler and G. Platero, Topological synchronization ¨ of quantum van der pol oscillators, Phys. Rev. Res. 5, 023021 (2023).
[8] C. W. Wachtler and J. E. Moore, Topological quantum synchronization of fractionalized spins, Phys. Rev. Lett. 132, 196601 (2024).
[9] V. M Bastidas, arXiv:2406.17062 (2024).
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16:30
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DEPARTURE
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