Rapidity-odd directed-flow measurements at midrapidity are presented for $\mathrm{\Lambda }$, $\overline{\mathrm{\Lambda }}$, $K^{\pm }$, $K_s^0$, and $\varphi$ at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV in $\mathrm{Au}+\mathrm{Au}$ collisions recorded by the Solenoidal Tracker detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form via coalescence of constituent quarks. The pattern of departure from a coalescence-inspired sum rule can be a valuable new tool for probing the collision dynamics.

Recently, multiparticle-correlation measurements of relativistic $p/d/{}^3\mathrm{He}+\mathrm{Au}$, $p+\mathrm{Pb}$, and even $p+p$ collisions show surprising collective signatures. Here, we present beam-energy-scan measurements of two-, four-, and six-particle angular correlations in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200$, 62.4, 39, and 19.6 GeV. We also present measurements of two- and four-particle angular correlations in $p+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. We find the four-particle cumulant to be real valued for $d+\mathrm{Au}$ collisions at all four energies. We also find that the four-particle cumulant in $p+\mathrm{Au}$ has the opposite sign as that in $d+\mathrm{Au}$. Further, we find that the six-particle cumulant agrees with the four-particle cumulant in $d+\mathrm{Au}$ collisions at 200 GeV, indicating that nonflow effects are subdominant. These observations provide strong evidence that the correlations originate from the initial geometric configuration, which is then translated into the momentum distribution for all particles, commonly referred to as collectivity.

We propose a method of atom interferometry using a spinor Bose-Einstein condensate with a time-varying magnetic field acting as a coherent beam splitter. Our protocol creates long-lived superpositional counterflow states, which are of fundamental interest and can be made sensitive to both the Sagnac effect and magnetic fields on the sub-$\mu \mathrm{G}$ scale. We split a ring-trapped condensate, initially in the $m_f=0$ hyperfine state, into superpositions of internal $m_f=\pm 1$ states and condensate superflow, which are spin-orbit coupled. After interrogation, the relative phase accumulation can be inferred from a population transfer to the $m_f=\pm 1$ states. The counterflow generation protocol is adiabatically deterministic and does not rely on coupling to additional optical fields or mechanical stirring techniques. Our protocol can maximize the classical Fisher information for any rotation, magnetic field, or interrogation time and so has the maximum sensitivity available to uncorrelated particles. Precision can increase with the interrogation time and so is limited only by the lifetime of the condensate.

Dilute-gas Bose-Einstein condensates are an exceptionally versatile test bed for the investigation of novel solitonic structures. While matter-wave solitons in one- and two-component systems have been the focus of intense research efforts, an extension to three components has never been attempted in experiments. Here, we experimentally demonstrate the existence of robust dark-bright-bright (DBB) and dark-dark-bright solitons in a multicomponent $F=1$ condensate. We observe lifetimes on the order of hundreds of milliseconds for these structures. Our theoretical analysis, based on a multiscale expansion method, shows that small-amplitude solitons of these types obey universal long-short wave resonant interaction models, namely, Yajima-Oikawa systems. Our experimental and analytical findings are corroborated by direct numerical simulations highlighting the persistence of, e.g., the DBB soliton states, as well as their robust oscillations in the trap.

In this Letter we present a new technique for attaining efficient low-background coherent Raman scattering where the Raman coherence is mediated by a tunable infrared laser in two-photon resonance with a chosen vibrational transition. In addition to the traditional benefits of conventional coherent Raman schemes, this approach offers a number of advantages including potentially higher emission intensity, reduction of nonresonant four-wave mixing background, preferential excitation of the anti-Stokes field, and simplified phase matching conditions. In particular, this is demonstrated in gaseous methane along the ${\nu }_1$ ($A_1$) and ${\nu }_3$ ($T_2$) vibrational levels using an infrared field tuned between 1400 and $1600{\mathrm{cm}}^{-1}$ and a 532-nm pump field. This approach has broad applications, from coherent light generation to spectroscopic remote sensing and chemically specific imaging in microscopy.

Amplification of optical or microwave fields is often achieved by strongly driving a medium to induce population inversion such that a weak probe can be amplified through stimulated emission. Here we strongly couple a superconducting qubit, an artificial atom, to the field in a semi-infinite waveguide. When driving the qubit strongly on resonance such that a Mollow triplet appears, we observe a 7% amplitude gain for a weak probe at frequencies in between the triplet. This amplification is not due to population inversion, neither in the bare qubit basis nor in the dressed-state basis, but instead results from a four-photon process that converts energy from the strong drive to the weak probe. We find excellent agreement between the experimental results and numerical simulations without any free fitting parameters. Since our device consists of a single two-level artificial atom, the simplest possible quantum system, it can be viewed as the most fundamental version of a four-wave-mixing parametric amplifier.

Josephson current provides a phase-sensitive tool for probing the pairing symmetry. Here we present an experimental study of high-quality Josephson junctions between a conventional $s$-wave superconductor Nb and a multiband iron-pnictide ${\mathrm{Ba}}_{1-x}{\mathrm{Na}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$. Junctions exhibit a large enough critical current density to preclude the $d$-wave symmetry of the order parameter in the pnictide. However, the $I_c{R}_n$ product is very small $\simeq 3\mu \mathrm{V}$, which is not consistent with the sign-preserving $s_{++}$ symmetry either. We argue that the small $I_c{R}_n$ value, along with its unusual temperature dependence, provides evidence for the sign-reversal $s_{\pm }$ symmetry of the order parameter in ${\mathrm{Ba}}_{1-x}{\mathrm{Na}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$. We conclude that it is the phase sensitivity of our junctions that leads to an almost complete (below a subpercent) cancellation of supercurrents from sign-reversal bands in the pnictide.

Current understanding of the critical outbreak condition on temporal networks relies on approximations (time scale separation, discretization) that may bias the results. We propose a theoretical framework to compute the epidemic threshold in continuous time through the infection propagator approach. We introduce the weak commutation condition allowing the interpretation of annealed networks, activity-driven networks, and time scale separation into one formalism. Our work provides a coherent connection between discrete and continuous time representations applicable to realistic scenarios.

We show how experimentally available bilayer lattice systems can be used to prepare quantum many-body states with exceptionally low entropy in one layer, by dynamically disentangling the two layers. This disentangling operation moves one layer—subsystem $A$—into a regime where excitations in $A$ develop a single-particle gap. As a result, this operation maps directly to cooling for subsystem $A$, with entropy being shuttled to the other layer. For both bosonic and fermionic atoms, we study the corresponding dynamics showing that disentangling can be realized cleanly in ongoing experiments. The corresponding entanglement entropies are directly measurable with quantum gas microscopes, and, as a tool for producing lower-entropy states, this technique opens a range of applications beginning with simplifying production of magnetically ordered states of bosons and fermions.

In 2014, several groups reported hints for a yet unidentified line in astrophysical x-ray signals from galaxies and galaxy clusters at an energy of 3.5 keV. While it is not unlikely that this line is simply a reflection of imperfectly modeled atomic transitions, it has renewed the community’s interest in models of keV-scale dark matter, whose decay would lead to such a line. The alternative possibility of dark matter annihilation into monochromatic photons is far less explored, a lapse that we strive to amend in this Letter. More precisely, we introduce a novel model of fermionic dark matter $\chi$ with $\mathcal{O}(\mathrm{keV})$ mass, annihilating to a scalar state $\varphi$ which in turn decays to photons, for instance via loops of heavy vectorlike fermions. The resulting photon spectrum is box shaped, but if $\chi$ and $\varphi$ are nearly degenerate in mass, it can also resemble a narrow line. We discuss dark matter production via two different mechanisms—misalignment and freeze-in—which both turn out to be viable in vast regions of parameter space. We constrain the model using astrophysical x-ray data, and we demonstrate that, thanks to the velocity dependence of the annihilation cross section, it has the potential to reconcile the various observations of the 3.5 keV line. We finally argue that the model can easily avoid structure formation constraints on keV-scale dark matter.

We present a Ward identity for nonlinear sigma models using generalized nonlinear shift symmetries, without introducing current algebra or coset space. The Ward identity constrains correlation functions of the sigma model such that the Adler’s zero is guaranteed for $S$-matrix elements, and gives rise to a subleading single soft theorem that is valid at the quantum level and to all orders in the Goldstone decay constant. For tree amplitudes, the Ward identity leads to a novel Berends-Giele recursion relation as well as an explicit form of the subleading single soft factor. Furthermore, interactions of the cubic biadjoint scalar theory associated with the single soft limit, which was previously discovered using the Cachazo-He-Yuan representation of tree amplitudes, can be seen to emerge from matrix elements of conserved currents corresponding to the generalized shift symmetry.

How do isolated quantum systems approach an equilibrium state? We experimentally and theoretically address this question for a prototypical spin system formed by ultracold atoms prepared in two Rydberg states with different orbital angular momenta. By coupling these states with a resonant microwave driving, we realize a dipolar $XY$ spin-$1/2$ model in an external field. Starting from a spin-polarized state, we suddenly switch on the external field and monitor the subsequent many-body dynamics. Our key observation is density dependent relaxation of the total magnetization much faster than typical decoherence rates. To determine the processes governing this relaxation, we employ different theoretical approaches that treat quantum effects on initial conditions and dynamical laws separately. This allows us to identify an intrinsically quantum component to the relaxation attributed to primordial quantum fluctuations.

The present work reports on progress in the research of a microshock wave. Because of the lack of a good understanding of the propagation mechanism of the microshock flow system (shock wave, contact surface, and boundary layer), the current work concentrates on measuring microshock flows with special attention paid to the contact surface. A novel setup involving a glass capillary (with a 200 or $300\mu \mathrm{m}$ hydraulic diameter $D$) and a high-speed magnetic valve is applied to generate a shock wave with a maximum initial Mach number of 1.3. The current work applies a laser differential interferometer to perform noncontact measurements of the microshock flow’s trajectory, velocity, and density. The current work presents microscale measurements of the shock-contact distance $L$ that solves the problem of calculating the scaling factor $\mathrm{Sc}=\mathrm{Re}\times D/(4L)$ (introduced by Brouillette), which is a parameter characterizing the scaling effects of shock waves. The results show that in contrast to macroscopic shock waves, shock waves at the microscale have a different propagation or attenuation mechanism (key issue of this Letter) which cannot be described by the conventional “leaky piston” model. The main attenuation mechanism of microshock flow may be the ever slower moving contact surface, which drives the shock wave. Different from other measurements using pressure transducers, the current setup for density measurements resolves the whole microshock flow system.

We report the lifetime of intense-laser ($2\times {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$) generated relativistic electron pulses in solids by measuring the time evolution of their Cherenkov emission. Using a picosecond resolution optical Kerr gating technique, we demonstrate that the electrons remain relativistic as long as 50 picoseconds—more than 1000 times longer than the incident light pulse. Numerical simulations of the propagation of relativistic electrons and the emitted Cherenkov radiation with Monte Carlo geant4 package reproduce the striking experimental findings.

Anderson localization of light is traditionally described in analogy to electrons in a random potential. Within this description, the random potential depends on the wavelength of the incident light. For transverse Anderson localization, this leads to the prediction that the distribution of localization lengths—and, hence, its average—strongly depends on the wavelength. In an alternative description, in terms of a spatially fluctuating electric modulus, this is not the case. Here, we report on an experimentum crucis in order to investigate the validity of the two conflicting theories using optical samples exhibiting transverse Anderson localization. We do not find any dependence of the observed average localization radii on the light wavelength. We conclude that the modulus-type description is the correct one and not the potential-type one. We corroborate this by showing that in the derivation of the traditional potential-type theory, a term in the wave equation has been tacitly neglected. In our new modulus-type theory, the wave equation is exact. We check the consistency of the new theory with our data using the nonlinear sigma model. We comment on the consequences for the general case of three-dimensional disorder.

Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, one-dimensional charge carrier mobilities along the columnar axes, making them prominent model systems for functional, self-organized matter. We show by high-resolution optical birefringence and synchrotron-based x-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly propagates layer by layer towards the pore center in the supercooled domain of the bulk isotropic-columnar transition and thus allows one to switch on and off reversibly single, nanosized rings through small temperature variations. By establishing a Gibbs free energy phase diagram we trace the phase transition quantization to the discreteness of the layers’ excess bend deformation energies in comparison to the thermal energy, even for this near room-temperature system. Monte Carlo simulations yielding spatially resolved nematic order parameters, density maps, and bond-orientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.