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1. Ultrastrong magnon–magnon coupling dominated by antiresonant interactions

   https://doi.org/10.1038/s41467-021-23159-z  

   Makihara, Takuma; Hayashida, Kenji; Noe II, G. Timothy; Li, Xinwei; Marquez Peraca, Nicolas; Ma, Xiaoxuan; Jin, Zuanming; Ren, Wei; Ma, Guohong; Katayama, Ikufumi; et al (December 2021, Nature Communications)

   Abstract Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics systems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations owing to antiresonant terms in the Hamiltonian. However, such predictions have not been realized because antiresonant interactions are typically negligible compared to resonant interactions in light-matter systems. Here we report an unusual, ultrastrongly coupled matter-matter system of magnons that is analytically described by a unique Hamiltonian in which the relative importance of resonant and antiresonant interactions can be easily tuned and the latter can be made vastly dominant. We found a regime where vacuum Bloch-Siegert shifts, the hallmark of antiresonant interactions, greatly exceed analogous frequency shifts from resonant interactions. Further, we theoretically explored the system’s ground state and calculated up to 5.9 dB of quantum fluctuation suppression. These observations demonstrate that magnonic systems provide an ideal platform for exploring exotic quantum vacuum phenomena predicted in ultrastrongly coupled light-matter systems. 

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2. Quantum simulation of an extended Dicke model with a magnetic solid

   https://doi.org/10.1038/s43246-024-00479-3  

   Marquez Peraca, Nicolas; Li, Xinwei; Moya, Jaime M.; Hayashida, Kenji; Kim, Dasom; Ma, Xiaoxuan; Neubauer, Kelly J.; Fallas Padilla, Diego; Huang, Chien-Lung; Dai, Pengcheng; et al (March 2024, Communications Materials)

   Abstract The Dicke model describes the cooperative interaction of an ensemble of two-level atoms with a single-mode photonic field and exhibits a quantum phase transition as a function of light–matter coupling strength. Extending this model by incorporating short-range atom–atom interactions makes the problem intractable but is expected to produce new physical phenomena and phases. Here, we simulate such an extended Dicke model using a crystal of ErFeO₃, where the role of atoms (photons) is played by Er³⁺spins (Fe³⁺magnons). Through terahertz spectroscopy and magnetocaloric effect measurements as a function of temperature and magnetic field, we demonstrated the existence of a novel atomically ordered phase in addition to the superradiant and normal phases that are expected from the standard Dicke model. Further, we elucidated the nature of the phase boundaries in the temperature–magnetic-field phase diagram, identifying both first-order and second-order phase transitions. These results lay the foundation for studying multiatomic quantum optics models using well-characterized many-body solid-state systems. 

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3. Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica

   https://doi.org/10.1126/science.1256697  

   Rebesco, M; Domack, E; Zgur, F; Lavoie, C; Leventer, A; Brachfeld, S; Willmott, V; Halverson, G; Truffer, M; Scambos, T; et al (September 2014, Science)

   Top-down rather than bottom-up change The Larsen-B Ice Shelf in Antarctica collapsed in 2002 because of a regional increase in surface temperature. This finding, reported by Rebescoet al., will surprise many who supposed that the shelf's disintegration probably occurred because of thinning of the ice shelf and the resulting loss of support by the sea floor beneath it. The authors mapped the sea floor beneath the ice shelf before it fell apart, which revealed that the modern ice sheet grounding line was established around 12,000 years ago and has since remained unchanged. If the ice shelf did not collapse because of thinning from below, then it must have been caused by warming from above. Science, this issue p.1354 

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4. Exact solution for the collective non-Markovian decay of two fully excited quantum emitters

   https://doi.org/10.1103/PhysRevResearch.6.033196  

   Lanuza, Alfonso; Schneble, Dominik (August 2024, Physical Review Research)

   Waveguide quantum electrodynamics constitutes a modern paradigm for the interaction of light and matter, in which strong coupling, bath structure, and propagation delays can break the radiative conditions that quantum emitters typically encounter in free space. These characteristics intertwine the excitations of quantum emitters and guided radiation modes to form complex multiphoton dynamics. So far, combining the collective decay of the emitters with the non-Markovian effects induced by the modes has escaped a full solution and the detailed physics behind these systems remains unknown. Here we analyze such a collective non-Markovian decay in a minimal system of two excited emitters coupled to a one-dimensional single-band waveguide. We develop an exact solution for this system in terms of elementary functions that unveils hidden symmetries and predicts new forms of spontaneous decay. The collective non-Markovian dynamics, which are strongly dependent on the vacuum coupling and the detuning from the center of the band, show exotic features that can be characterized with a simple and readily available criterion. Our analytic methods shed light on the complexity of collective light-matter interactions and open up a pathway for understanding multiparticle open quantum systems. Published by the American Physical Society2024 

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5. Super- and subradiant dynamics of quantum emitters mediated by atomic matter waves

   https://doi.org/10.1038/s41567-024-02676-w  

   Kim, Y; Lanuza, A; Schneble, D (November 2024, Nature Physics)

   The cooperative modification of spontaneous radiative decay exemplifies a many-emitter effect in quantum optics. So far, its experimental realizations have relied on interactions mediated by rapidly escaping photons, which do not play an active role in the emitter dynamics. Here we use a platform of ultracold atoms in a one-dimensional optical lattice geometry to explore cooperative non-Markovian dynamics of synthetic quantum emitters that decay by radiating slow atomic matter waves. By preparing and manipulating arrays of emitters hosting weakly and strongly interacting many-body phases of excitations, we demonstrate directional collective emission and study the interplay between retardation and super- and subradiant dynamics. Moreover, we directly observe the spontaneous buildup of coherence among emitters. Our results on collective radiative dynamics establish ultracold matter waves as a versatile tool for studying many-body quantum optics in spatially extended and ordered systems. 

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