We study a diffusive superconductor-normal–metal-superconductor junction in an environment with intrinsic incoherent fluctuations which couple to the junction through an electromagnetic field. When the temperature of the junction differs from that of the environment, this coupling leads to an energy transfer between the two systems, taking the junction out of equilibrium. We describe this effect in the linear response regime and show that the change in the supercurrent induced by this coupling leads to qualitative changes in the current-phase relation and, for a certain range of parameters, an increase in the critical current of the junction. In addition to normal metals, similar effects can be expected also in other conducting weak links.

Following a short discussion of the granular model for an inhomogeneous superconductor, we review the Uemura and Homes correlations and show how both follow in two limits of a simple granular superconductor model. Definite expressions are given for the almost universal coefficients appearing in these relationships in terms of known constants.

We perform a density-matrix renormalization group (DMRG) study of the $S=\frac{1}{2}$ Heisenberg antiferromagnet on the kagome lattice to identify the conjectured spin liquid ground state. Exploiting SU(2) spin symmetry, which allows us to keep up to 16 000 DMRG states, we consider cylinders with circumferences up to 17 lattice spacings and find a spin liquid ground state with an estimated per site energy of $-0.4386(5)$, a spin gap of $0.13(1)$, very short—range decay in spin, dimer and chiral correlation functions, and finite topological entanglement $\gamma$ consistent with $\gamma ={log}_{2}2$, ruling out gapless, chiral, or nontopological spin liquids in favor of a topological spin liquid of quantum dimension 2, with strong evidence for a gapped topological ${\mathbb{Z}}_2$ spin liquid.

We report on measurements, by polarized neutron elastic scattering, of the magnetization distribution induced in a single crystal of ${\mathrm{URu}}_2{\mathrm{Si}}_2$ under a magnetic field applied along the tetragonal $\mathbf{c}$ axis. A subtle change in this distribution, revealed by maximum entropy analysis of the data, is found when the temperature is decreased to the range of the hidden order. An analysis in terms of ${\mathrm{U}}^{4+}$ ionic states reveals that this change is a fingerprint of a freezing of rank 5 multipoles, i.e., dotriacontapoles.

Using small-angle neutron scattering, we explored the conformational behavior of a polymer in a mixture of good solvents near their critical demixing temperature $T_C$. Experiments at full and zero average neutron contrast were used to study the correlation length of concentration fluctuations $\xi$ and the radius of gyration $R_g$ of individual polymer coils as a function of temperature $T$. The results confirm a theoretically predicted partial collapse followed by reswelling of polymer coils to the original dimensions as $T\to T_C$. Reswelling begins when $\xi$ becomes comparable to the $R_g$ of the polymer.

We present experimental and numerical results regarding the stability of arches against external vibrations. Two-dimensional strings of mutually stabilizing grains are geometrically analyzed and subsequently submitted to a periodic forcing at fixed frequency and increasing amplitude. The main factor that determines the granular arch resistance against vibrations is the maximum angle among those formed between any particle of the arch and its two neighbors: the higher the maximum angle is, the easier it is to break the arch. On the basis of an analysis of the forces, a simple explanation is given for this dependence. From this, interesting information can be extracted about the expected magnitudes of normal forces and friction coefficients of the particles composing the arches.

Most helix-coil transition theories can be characterized by three parameters: energetic, describing the (free) energy cost of forming a helical state in one repeating unit; entropic, accounting for the decrease of entropy due to formation of the helical state; and geometric, indicating how many repeating units are affected by the formation of one helical state. Depending on their effect on the helix-coil transition, solvents or cosolutes can be classified with respect to their action on these parameters. Solvent interactions that alter the entropic cost of helix formation by their osmotic action can affect both the stability (transition temperature) and the cooperativity (transition interval) of the helix-coil transition. Consistent inclusion of osmotic pressure effects in a description of helix-coil transition, for poly(L-glutamic acid) in solution with polyethylene glycol, can offer an explanation of the experimentally observed linear dependence of transition temperature on osmotic pressure as well as the concurrent changes in the cooperativity of the transition.

We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up to 180 eV. By varying the photon energy of the x rays that both create and probe the plasma, and observing the $K\mathrm{\text{−}}\alpha$ fluorescence, we can directly measure the position of the $K$ edge of the highly charged ions within the system. The results are found to disagree with the predictions of the extensively used Stewart-Pyatt model, but are consistent with the earlier model of Ecker and Kröll, which predicts significantly greater depression of the ionization potential.

The duration of structural transitions in biopolymers is only a fraction of the time spent searching diffusively over the configurational energy landscape. We found the transition time, ${\tau }_{\mathrm{TP}}$, and the diffusion constant, $D$, for DNA and RNA folding using energy landscapes obtained from single-molecule trajectories under tension in optical traps. DNA hairpins, RNA pseudoknots, and a riboswitch all had ${\tau }_{\mathrm{TP}}\sim 10\mu \mathrm{s}$ and $D\sim {10}^{-13–14}{\mathrm{m}}^2/\mathrm{s}$, despite widely differing unfolding rates. These results show how energy-landscape analysis can be harnessed to characterize brief but critical events during folding reactions.

We demonstrate high-fidelity, quantum nondemolition, single-shot readout of a superconducting flux qubit in which the pointer state distributions can be resolved to below one part in 1000. In the weak excitation regime, continuous measurement permits the use of heralding to ensure initialization to a fiducial state, such as the ground state. This procedure boosts readout fidelity to 93.9% by suppressing errors due to spurious thermal population. Furthermore, heralding potentially enables a simple, fast qubit reset protocol without changing the system parameters to induce Purcell relaxation.

We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations nondestructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization.

Systems of strongly interacting atoms and photons, which can be realized wiring up individual cavity QED systems into lattices, are perceived as a new platform for quantum simulation. While sharing important properties with other systems of interacting quantum particles, here we argue that the nature of light-matter interaction gives rise to unique features with no analogs in condensed matter or atomic physics setups. By discussing the physics of a lattice model of delocalized photons coupled locally with two-level systems through the elementary light-matter interaction described by the Rabi model, we argue that the inclusion of counterrotating terms, so far neglected, is crucial to stabilize finite-density quantum phases of correlated photons out of the vacuum, with no need for an artificially engineered chemical potential. We show that the competition between photon delocalization and Rabi nonlinearity drives the system across a novel $Z_2$ parity symmetry-breaking quantum criticality between two gapped phases that share similarities with the Dicke transition of quantum optics and the Ising critical point of quantum magnetism. We discuss the phase diagram as well as the low-energy excitation spectrum and present analytic estimates for critical quantities.

A quantum state of light is the excitation of a particular spatiotemporal mode of the electromagnetic field. A precise control of the mode structure is therefore essential for processing, detecting, and using photonic states in novel quantum technologies. Here we demonstrate an adaptive scheme, combining techniques from the fields of ultrafast coherent control and quantum optics, for probing the arbitrary complex spectrotemporal profile of an ultrashort quantum light pulse. The ability to access the modal structure of a quantum light state could boost the capacity of current quantum information protocols.

We have examined the direct effect of manipulating the number of free surfaces on the measured glass transition temperature $T_{\mathrm{g}}$ of thin polystyrene films. Thin films in the range $35\mathrm{nm}<h<114\mathrm{nm}$ with molecular weights of $592\mathrm{kg}/\mathrm{mol}$ and $1144\mathrm{kg}/\mathrm{mol}$ were studied. Ellipsometry was used to determine the temperature dependence of the thickness and refractive index of freestanding films. By noting the change in slope in each of these quantities, a $T_{\mathrm{g}}$ value can be assigned in quantitative agreement with previously reported results. For thin freestanding films this value is reduced from that of the bulk. The exact same films are then transferred to a Si substrate and the $T_{\mathrm{g}}$ of the resulting supported film was determined. The $T_{\mathrm{g}}$ values of the now supported films are the same as the bulk value and the same as previous reports of similar supported films. These experiments unambiguously show that free interfaces are the dominant cause of the $T_{\mathrm{g}}$ reductions for the film thicknesses studied.

Silicene, a sheet of silicon atoms in a honeycomb lattice, was proposed to be a new Dirac-type electron system similar to graphene. We performed scanning tunneling microscopy and spectroscopy studies on the atomic and electronic properties of silicene on Ag(111). An unexpected $\sqrt{3}\times \sqrt{3}$ reconstruction was found, which is explained by an extra-buckling model. Pronounced quasiparticle interferences (QPI) patterns, originating from both the intervalley and intravalley scatter, were observed. From the QPI patterns we derived a linear energy-momentum dispersion and a large Fermi velocity, which prove the existence of Dirac fermions in silicene.

We provide a new quantum algorithm that efficiently determines the quality of a least-squares fit over an exponentially large data set by building upon an algorithm for solving systems of linear equations efficiently [Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)]. In many cases, our algorithm can also efficiently find a concise function that approximates the data to be fitted and bound the approximation error. In cases where the input data are pure quantum states, the algorithm can be used to provide an efficient parametric estimation of the quantum state and therefore can be applied as an alternative to full quantum-state tomography given a fault tolerant quantum computer.

With a classical ensemble model that includes electron correlations during the whole ionization process, we investigate strong-field sequential double ionization of Ar by elliptically polarized pulses at the quantitative level. The experimentally observed intensity-dependent three-band or four-band structures in the ion momentum distributions are well reproduced with this classical model. More importantly, the experimentally measured ionization time of the second electrons by A. N. Pfeiffer et al. [Nature Phys. 7, 428 (2011)], which cannot be predicted by the standard independent-electron model, is quantitatively reproduced by this fully classical correlated model. The success of our work encourages classical descriptions and interpretations of the complex multielectron effects in strong-field ionization where nonperturbative quantum approaches are currently not feasible.

We present the first experimental demonstration of a dc electric cloak for steady current fields. Using the analogy between electrically conducting materials and resistor networks, a dc invisibility cloak is designed, fabricated, and tested using the circuit theory. We show that the dc cloak can guide electric currents around the cloaked region smoothly and keep perturbations only inside the cloak. Outside the cloak, the current lines return to their original directions as if nothing happens. The measurement data agree exceptionally well with the theoretical prediction and simulation result, with nearly perfect cloaking performance. The proposed method can be directly used to realize other dc electric devices with anisotropic conductivities designed by the transformation optics. Manipulation of steady currents with the control of anisotropic conductivities has a lot of potential applications, such as electric impedance tomography, graphene, natural resource exploration, and military camouflage.

An experimental study of the kinematic viscosity has been carried out for dust particles of size $0.95$ and $3.92\mu \mathrm{m}$, in weakly ionized plasma over a wide range of dust coupling parameters. Measurements of viscosity for weakly correlated dusty-plasma systems are presented for the first time. An approximation for the estimation of viscosity constants is proposed. The measured viscosity constants are compared with theoretical estimates and numerical data.

We describe x-ray photon correlation spectroscopy (XPCS) experiments tracking the motion of gold nanoparticles within solutions of high-molecular-weight polystyrene. Over displacements from nanometers to tens of nanometers, the particles undergo subdiffusive motion that is dictated by the temporal evolution of the entangled polymer mesh in the immediate vicinity of the particles. The results thus provide a novel microscopic dynamical characterization of this key structural property of polymers and more broadly demonstrate the capability of XPCS-based microrheology to interrogate heterogeneous mechanical environments in nanostructured soft materials.