Unraveling the Quantum Nature of Atomic Self-Ordering in a Ring Cavity.

Atomic self-ordering to a crystalline phase in optical resonators is a consequence of the intriguing nonlinear dynamics of strongly coupled atom motion and photons. Generally the resulting phase diagrams and atomic states can be largely understood on a mean-field level. However, close to the phase transition point, quantum fluctuations and atom-field entanglement play a key role and initiate the symmetry breaking. Here we propose a modified ring cavity geometry, in which the asymmetry imposed by a tilted pump beam reveals clear signatures of quantum dynamics even in a larger regime around the phase transition point. Quantum fluctuations become visible both in the dynamic and steady-state properties. Most strikingly we can identify a regime where a mean-field approximation predicts a runaway instability, while in the full quantum model the quantum fluctuations of the light field modes stabilize uniform atomic motion. The proposed geometry thus allows to unveil the "quantumness" of atomic self-ordering via experimentally directly accessible quantities.

Multiple magnetic resonance imaging in patients with implanted sacral nerve stimulator.

AIM: The aim of this study was to assess possible impacts of multiple magnetic resonance imaging (MRI) scans on the function of InterStim™ sacral neurostimulator systems (SNS; Medtronic Inc.) devices and on patient's safety. METHODS: Over the course of 17 years, a total of 16 patients required 72 MRI examinations in various parts of the body. Each time an MRI was performed, the implanting urologist evaluated the SNS device function and deactivated the implant before the scan. Patients were monitored continuously during and after the procedure. After the MRI session, the site of the implanted device was examined, and the SNS device was reactivated. RESULTS: None of the patients experienced pain or discomfort during or after the MRI scan. Impedances and stimulation amplitudes were recorded before and after MRI and showed no statistically significant changes regarding implant function. Micturition-time charts after MRI procedures were compared with previous records and showed no deviations either. No negative consequences of multiple MRIs have been observed. CONCLUSION: This is the first report of patients successfully undergoing multiple MRI scans despite a previously implanted SNS. Sixteen patients underwent more than one MRI scan, with no negative effect on the functional outcome of SNS or negative side effects for the patients.

Driven-Dissipative Supersolid in a Ring Cavity.

Supersolids are characterized by the counterintuitive coexistence of superfluid and crystalline order. Here we study a supersolid phase emerging in the steady state of a driven-dissipative system. We consider a transversely pumped Bose-Einstein condensate trapped along the axis of a ring cavity and coherently coupled to a pair of degenerate counterpropagating cavity modes. Above a threshold pump strength the interference of photons scattered into the two cavity modes results in an emergent superradiant lattice, which spontaneously breaks the continuous translational symmetry towards a periodic atomic pattern. The crystalline steady state inherits the superfluidity of the Bose-Einstein condensate, thus exhibiting genuine properties of a supersolid. A gapless collective Goldstone mode correspondingly appears in the superradiant phase, which can be nondestructively monitored via the relative phase of the two cavity modes on the cavity output. Despite cavity-photon losses the Goldstone mode remains undamped, indicating the robustness of the supersolid phase.