Publications Clemens ULM

2025

Article

• E. Poli, A. Litvinov, E. Casotti, C. Ulm, L. Klaus, M. J. Mark, G. Lamporesi, T. Bland, F. Ferlaino Synchronization in rotating supersolids, Nature Phys. (2025-10-23), http://dx.doi.org/10.48550/arXiv.2412.11976 doi:10.48550/arXiv.2412.11976 (ID: 721565) Toggle Abstract
  Synchronization is a widespread phenomenon in natural and engineered systems, governing the emergence of collective dynamics in different domains including biology and classical and quantum physics. In quantum many-body systems, synchronization has emerged as a tool to probe out-of-equilibrium behaviour and internal correlations. Supersolids—quantum phases that combine crystalline order and superfluidity—offer a platform to explore synchronization in systems with coexisting broken symmetries. Here we investigate the dynamics of a dipolar supersolid subjected to external rotation. We show that, above a critical driving frequency, the crystal revolution undergoes a sudden synchronization with the rotating field seeded by the nucleation of quantized vortices, hallmark of superfluidity. This transition reflects the interplay between the solid-like and superfluid responses of the system. By comparing simulations of the extended Gross–Pitaevskii equation with experimental observations, we demonstrate that synchronization can serve as a dynamical indicator for vortex nucleation. This approach provides a complementary method to determine the critical rotation frequency for vortex formation in supersolids.

2024

Article

• E. Casotti, E. Poli, L. Klaus, A. Litvinov, C. Ulm, C. Politi, M. J. Mark, T. Bland, F. Ferlaino Observation of vortices in a dipolar supersolid, Nature 635 331 (2024-11-06), http://dx.doi.org/10.1038/s41586-024-08149-7 doi:10.1038/s41586-024-08149-7 (ID: 721336) Toggle Abstract
  Supersolids are states of matter that spontaneously break two continuous symmetries: translational invariance owing to the appearance of a crystal structure and phase invariance owing to phase locking of single-particle wavefunctions, responsible for superfluid phenomena. Although originally predicted to be present in solid helium1,2,3,4,5, ultracold quantum gases provided a first platform to observe supersolids6,7,8,9,10, with particular success coming from dipolar atoms8,9,10,11,12. Phase locking in dipolar supersolids has been investigated through, for example, measurements of the phase coherence8,9,10 and gapless Goldstone modes13, but quantized vortices, a hydrodynamic fingerprint of superfluidity, have not yet been observed. Here, with the prerequisite pieces at our disposal, namely a method to generate vortices in dipolar gases14,15 and supersolids with two-dimensional crystalline order11,16,17, we report on the theoretical investigation and experimental observation of vortices in the supersolid phase (SSP). Our work reveals a fundamental difference in vortex seeding dynamics between unmodulated and modulated quantum fluids. This opens the door to study the hydrodynamic properties of exotic quantum systems with numerous spontaneously broken symmetries, in disparate domains such as quantum crystals and neutron stars18.

Preprint

• E. Poli, A. Litvinov, E. Casotti, C. Ulm, L. Klaus, M. J. Mark, G. Lamporesi, T. Bland, F. Ferlaino Synchronization in rotating supersolids, (2024-12-16), http://dx.doi.org/10.48550/arXiv.2412.11976 doi:10.48550/arXiv.2412.11976 (ID: 721335) Toggle Abstract
  Synchronization is ubiquitous in nature at various scales and fields. This phenomenon not only offers a window into the intrinsic harmony of complex systems, but also serves as a robust probe for many-body quantum systems. One such system is a supersolid: an exotic state that is simultaneously superfluid and solid. Here, we show that putting a supersolid under rotation leads to a synchronization of the crystal's motion to an external driving frequency triggered by quantum vortex nucleation, revealing the system's dual solid-superfluid response. Benchmarking the theoretical framework against experimental observations, we exploit this model as a novel method to investigate the critical frequency required for vortex nucleation. Our results underscore the utility of synchronization as a powerful probe for quantum systems.