Equilibrium Parametric Amplification in Raman-Cavity Hybrids.

Parametric resonances and amplification have led to extraordinary photoinduced phenomena in pump-probe experiments. While these phenomena manifest themselves in out-of-equilibrium settings, here, we present the striking result of parametric amplification in equilibrium. We demonstrate that quantum and thermal fluctuations of a Raman-active mode amplifies light inside a cavity, at equilibrium, when the Raman mode frequency is twice the cavity mode frequency.

Shapiro Steps in Driven Atomic Josephson Junctions.

We study driven atomic Josephson junctions realized by coupling two two-dimensional atomic clouds with a tunneling barrier. By moving the barrier at a constant velocity, dc and ac Josephson regimes are characterized by a zero and nonzero atomic density difference across the junction, respectively. Here, we monitor the dynamics resulting in the system when, in addition to the above constant velocity protocol, the position of the barrier is periodically driven.

Observation of a phase transition from a continuous to a discrete time crystal.

Discrete (DTCs) and continuous time crystals (CTCs) are novel dynamical many-body states, that are characterized by robust self-sustained oscillations, emerging via spontaneous breaking of discrete or continuous time translation symmetry. DTCs are periodically driven systems that oscillate with a subharmonic of the external drive, while CTCs are continuously driven and oscillate with a frequency intrinsic to the system. Here, we explore a phase transition from a continuous time crystal to a discrete time crystal.

Dissipationless Counterflow Currents above T_{c} in Bilayer Superconductors.

We report the existence of dissipationless currents in bilayer superconductors above the critical temperature T_{c}, assuming that the superconducting phase transition is dominated by phase fluctuations. Using a semiclassical U(1) lattice gauge theory, we show that thermal fluctuations cause a transition from the superconducting state at low temperature to a resistive state above T_{c}, accompanied by the proliferation of unbound vortices. Remarkably, while the proliferation of vortex excitations causes dissipation of homogeneous in-plane currents, we find that counterflow currents, flowing in the opposite direction within a bilayer, remain dissipationless.

Universal scaling of the dynamic BKT transition in quenched 2D Bose gases.

The understanding of nonequilibrium dynamics in many-body quantum systems is a fundamental issue in statistical physics. Experiments that probe universal properties of these systems can address such foundational questions. In this study, we report the measurement of universal dynamics triggered by a quench from the superfluid to normal phase across the Berezinskii-Kosterlitz-Thouless transition in a two-dimensional (2D) Bose gas.

ICU stays that are judged to be non-beneficial: A qualitative study of the perception of nursing staff.

Introduction: Non-beneficial stays in the intensive care unit (ICU) may have repercussions for patients and their families, but can also cause suffering among the nursing staff. We aimed explore the perceptions of nursing staff in the ICU about patient stays that are deemed to be "non-beneficial" for the patient, to identify areas amenable to intervention, with a view to improving how the nursing staff perceive the patient pathway before, during and after intensive care.

Methods: Multicentre, qualitative study using individual, semi-structured interviews.

Can Telehealth Provide Timely and Equitable Quality Medical Forensic Services? Perspectives of Illinois Hospital Administrators.

Introduction: Research has shown the viability of telehealth consultations to provide medical forensic services, particularly in areas with a dearth of medical examiners. This study examined Illinois hospital administrators' willingness to utilize telehealth to meet new requirements under Illinois Public Act 100-0775, which intends to increase timely access to quality forensic examiners. Consequently, as of March 2021, roughly half of Illinois hospitals unable to meet these requirements have opted not to treat some or all patients presenting for medical forensic services of sexual assault.

Condensate Formation in a Dark State of a Driven Atom-Cavity System.

We demonstrate the formation of a condensate in a dark state of momentum states, in a pumped and shaken cavity-BEC system. The system consists of an ultracold quantum gas in a high-finesse cavity, which is pumped transversely by a phase-modulated laser. This phase-modulated pumping couples the atomic ground state to a superposition of excited momentum states, which decouples from the cavity field.

Observation of the Berezinskii-Kosterlitz-Thouless Transition in a Two-Dimensional Bose Gas via Matter-Wave Interferometry.

We probe local phase fluctuations of trapped two-dimensional Bose gases using matter-wave interferometry. This enables us to measure the phase correlation function, which changes from an algebraic to an exponential decay when the system crosses the Berezinskii-Kosterlitz-Thouless (BKT) transition. We determine the temperature dependence of the BKT exponent η and find the critical value η_{c}=0.

Observation of a continuous time crystal.

Time crystals are classified as discrete or continuous depending on whether they spontaneously break discrete or continuous time translation symmetry. Although discrete time crystals have been extensively studied in periodically driven systems, the experimental realization of a continuous time crystal is still pending. We report the observation of a limit cycle phase in a continuously pumped dissipative atom-cavity system that is characterized by emergent oscillations in the intracavity photon number.

Realization of a Periodically Driven Open Three-Level Dicke Model.

A periodically driven open three-level Dicke model is realized by resonantly shaking the pump field in an atom-cavity system. As an unambiguous signature, we demonstrate the emergence of a dynamical phase, in which the atoms periodically localize between the antinodes of the pump lattice, associated with an oscillating net momentum along the pump axis. We observe this dynamical phase through the periodic switching of the relative phase between the pump and cavity fields at a small fraction of the driving frequency, suggesting that it exhibits a time crystalline character.

Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid.

Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid, extending previous work at unitarity.

Observation of a Dissipative Time Crystal.

We present the first experimental realization of a time crystal stabilized by dissipation. The central signature in our implementation in a driven open atom-cavity system is a period doubled switching between distinct checkerboard density wave patterns, induced by the interplay between controlled cavity dissipation, cavity-mediated interactions, and external driving. We demonstrate the robustness of this dynamical phase against system parameter changes and temporal perturbations of the driving.

Orbital Many-Body Dynamics of Bosons in the Second Bloch Band of an Optical Lattice.

We explore Josephson-like dynamics of a Bose-Einstein condensate of rubidium atoms in the second Bloch band of an optical square lattice providing a double well structure with two inequivalent, degenerate energy minima. This oscillation is a direct signature of the orbital changing collisions predicted to arise in this system in addition to the conventional on-site collisions. The observed oscillation frequency scales with the relative strength of these collisional interactions, which can be readily tuned via a distortion of the unit cell.

COVID-19 or not COVID-19? Compared characteristics of patients hospitalized for suspected COVID-19.

During an epidemic period, we compared patients hospitalized for initial suspicion of COVID-19 but for whom an alternative diagnosis was finally retained (n = 152) with those who had COVID-19 (n = 222). Most common diagnoses were another infectious disease and heart failure. COVID-19-negative patients were more often active smokers had less often cough, fever, and digestive symptoms, as compared to the 222 COVID-19-positive patients.

An ideal Josephson junction in an ultracold two-dimensional Fermi gas.

The role of reduced dimensionality in high-temperature superconductors is still under debate. Recently, ultracold atoms have emerged as an ideal model system to study such strongly correlated two-dimensional (2D) systems. Here, we report on the realization of a Josephson junction in an ultracold 2D Fermi gas.

Light-Induced Coherence in an Atom-Cavity System.

We demonstrate a light-induced formation of coherence in a cold atomic gas system that utilizes the suppression of a competing density wave (DW) order. The condensed atoms are placed in an optical cavity and pumped by an external optical standing wave, which induces a long-range interaction mediated by photon scattering and a resulting DW order above a critical pump strength. We show that the light-induced temporal modulation of the pump wave can suppress this DW order and restore coherence.

Dynamical Control of Order in a Cavity-BEC System.

We demonstrate dynamical control of the superradiant transition of cavity-BEC system via periodic driving of the pump laser. We show that the dominant density wave order of the superradiant state can be suppressed, and that the subdominant competing order of Bose-Einstein condensation emerges in the steady state. Furthermore, we show that additional, nonequilibrium density wave orders, which do not exist in equilibrium, can be stabilized dynamically.

Probing optically silent superfluid stripes in cuprates.

Unconventional superconductivity in the cuprates coexists with other types of electronic order. However, some of these orders are invisible to most experimental probes because of their symmetry. For example, the possible existence of superfluid stripes is not easily validated with linear optics, because the stripe alignment causes interlayer superconducting tunneling to vanish on average.

Observation of Topological Bloch-State Defects and Their Merging Transition.

Topological defects in Bloch bands, such as Dirac points in graphene, and their resulting Berry phases play an important role for the electronic dynamics in solid state crystals. Such defects can arise in systems with a two-atomic basis due to the momentum-dependent coupling of the two sublattice states, which gives rise to a pseudospin texture. The topological defects appear as vortices in the azimuthal phase of this pseudospin texture.

Designing exotic many-body states of atomic spin and motion in photonic crystals.

Cold atoms coupled to photonic crystals constitute an exciting platform for exploring quantum many-body physics. For example, such systems offer the potential to realize strong photon-mediated forces between atoms, which depend on the atomic internal (spin) states, and where both the motional and spin degrees of freedom can exhibit long coherence times. An intriguing question then is whether exotic phases could arise, wherein crystalline or other spatial patterns and spin correlations are fundamentally tied together, an effect that is atypical in condensed matter systems.

Cerium-Complex-Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side-On μ-Peroxo Dicerium(IV) Complex.

A new Ce(IV) complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)2] (1), bearing a dianionic pentadentate ligand with an N3O2 donor set, has been prepared by treating (NH4)2Ce(NO3)6 with the sodium salt of ligand L1. Complex 1 in the presence of TEMPO and 4 Å molecular sieves (MS4 A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)(THF)] (2), its side-on μ-O2 adduct [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)]2(μ-η(2):η(2)-O2) (3), and the hydroxo-bridged Ce(IV) complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)]2(μ-OH)2 (4) as key intermediates during the catalytic cycle.

Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles.

Reactions of cerium(III) nitrate, Ce(NO3 )3 ⋅6 H2 O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4-methoxybenzoic acid, in the presence of a tridentate N,N,N-donor ligand, diethylenetriamine (L(1) ), under aerobic conditions yielded the corresponding cerium hexamers Ce6 O8 (O2 CtBu)8 (L(1) )4 (1), Ce6 O8 (O2 CC6 H5 )8 (L(1) )4 (2), and Ce6 O8 (O2 CC6 H4 -4-OCH3 )8 (L(1) )4 (3). Hexamers 1, 2, and 3 contain the same octahedral Ce(IV) 6 O8 core, in which all interstitial oxygen atoms are connected by μ3 -oxo bridging ligands. In contrast, treatment of the Ce(IV) precursor (NH4 )2 Ce(NO3 )6 (CAN) with pivalic acid and the ligand L(1) under the same conditions afforded Ce6 O4 (OH)4 (O2 CtBu)12 (L(1) )2 (4), exhibiting a deformed octahedral Ce(IV) 6 O4 (OH)4 core containing μ3 -oxo and μ3 -hydroxo moieties in defined positions.

Observing chiral superfluid order by matter-wave interference.

The breaking of time-reversal symmetry via the spontaneous formation of chiral order is ubiquitous in nature. Here, we present an unambiguous demonstration of this phenomenon for atoms Bose-Einstein condensed in the second Bloch band of an optical lattice. As a key tool, we use a matter-wave interference technique, which lets us directly observe the phase properties of the superfluid order parameter and allows us to reconstruct the spatial geometry of certain low-energy excitations, associated with the formation of domains of different chirality.