Local diffusion coefficients in disordered materials such as living cells are highly heterogeneous. We consider finite systems with quenched disorder in order to investigate the effects of sample disorder fluctuations and confinement on single-particle diffusivity. While the system is ergodic in a single disorder realization, the time-averaged mean square displacement depends crucially on the disorder; i.e., the system is ergodic but non-self-averaging. Moreover, we show that the disorder average of the time-averaged mean square displacement decreases with the system size. We find a universal distribution for diffusivity in the sense that the shape of the distribution does not depend on the dimension. Quantifying the degree of the non-self-averaging effect, we show that fluctuations of single-particle diffusivity far exceed the corresponding annealed theory and also find confinement effects. The relevance for experimental situations is also discussed.

The piston system (particles in a box) is the simplest paradigmatic model in traditional thermodynamics. However, the recently established framework of stochastic thermodynamics (ST) fails to apply to this model system due to the embedded singularity in the potential. In this Letter, we study the ST of a particle in a box by adopting a novel coordinate transformation technique. Through comparing with the exact solution of a breathing harmonic oscillator, we obtain analytical results of work distribution for an arbitrary protocol in the linear response regime and verify various predictions of the fluctuation-dissipation relation. When applying to the Brownian Szilard engine model, we obtain the optimal protocol ${\lambda }_t={\lambda }_0{2}^{t/\tau }$ for a given sufficiently long total time $\tau$. Our study not only establishes a paradigm for studying ST of a particle in a box but also bridges the long-standing gap in the development of ST.

Quantum-dense metrology constitutes a special case of quantum metrology in which two orthogonal phase space projections of a signal are simultaneously sensed beyond the shot-noise limit. Previously, it was shown that the additional sensing channel that is provided by quantum-dense metrology contains information that can be used to identify and to discard corrupted segments from the measurement data. Here, we propose and demonstrate a new method in which this information is used for improving the sensitivity without discarding any measurement segments. Our measurement reached sub-shot-noise performance, although initially strong classical noise polluted the data. The new method has high potential for improving the noise spectral density of gravitational-wave detectors at signal frequencies of high astrophysical relevance.

The ${}^{19}\mathrm{Ne}(p,\gamma ){}^{20}\mathrm{Na}$ reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$ reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in ${}^{20}\mathrm{Na}$ in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction ${}^{19}\mathrm{Ne}(d,n){}^{20}\mathrm{Na}$ is measured with a beam of the radioactive isotope ${}^{19}\mathrm{Ne}$ at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the ${}^{19}\mathrm{Ne}$ ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned $3^{+}$, $1^{+}$, and ($0^{+}$), respectively. In addition, we identify two resonances with the first excited state in ${}^{19}\mathrm{Ne}$, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in ${}^{19}\mathrm{Ne}(p,\gamma ){}^{20}\mathrm{Na}$, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.

Bright squeezed vacuum, a promising tool for quantum information, can be generated by high-gain parametric down-conversion. However, its frequency and angular spectra are typically quite broad, which is undesirable for applications requiring single-mode radiation. We tailor the frequency spectrum of high-gain parametric down-conversion using an SU(1,1) interferometer consisting of two nonlinear crystals with a dispersive medium separating them. The dispersive medium allows us to select a narrow band of the frequency spectrum to be exponentially amplified by high-gain parametric amplification. The frequency spectrum is thereby narrowed from $(56.5\pm 0.1)$ to $(1.22\pm 0.02)\mathrm{THz}$ and, in doing so, the number of frequency modes is reduced from approximately 50 to $1.82\pm 0.02$. Moreover, this method provides control and flexibility over the spectrum of the generated light through the timing of the pump.

Vertically bounded fingering double diffusive convection is numerically investigated, focusing on the influences of different velocity boundary conditions, i.e., the no-slip condition, which is inevitable in the lab-scale experimental researches, and the free-slip condition, which is an approximation for the interfaces in many natural environments, such as the oceans. For both boundary conditions the flow is dominated by fingers and the global responses follow the same scaling laws, with enhanced prefactors for the free-slip cases. Therefore, the laboratory experiments with the no-slip boundaries serve as a good model for the finger layers in the ocean. Moreover, in the free-slip case, although the tangential shear stress is eliminated at the boundaries, the local dissipation rate in the near-wall region may exceed the value found in the no-slip cases, which is caused by the stronger vertical motions of horizontally focused fingers and sheet structures near the free-slip boundaries. This counterintuitive result might be relevant for properly estimating and modeling the mixing and entrainment phenomena at free surfaces and interfaces widespread in oceans and geophysical flows.

We study the impact of spin-exchange collisions on the dynamics of Bose-Einstein condensation by rapidly cooling a chromium multicomponent Bose gas. Despite relatively strong spin-dependent interactions, the critical temperature for Bose-Einstein condensation is reached before the spin degrees of freedom fully thermalize. The increase in density due to Bose-Einstein condensation then triggers spin dynamics, hampering the formation of condensates in spin-excited states. Small metastable spinor condensates are, nevertheless, produced, and they manifest in strong spin fluctuations.

The no-enclave percolation (NEP) model introduced recently by Sheinman et al. can be mapped to a problem of holes within a standard percolation backbone, and numerical measurements of such holes give the same size-distribution exponent $\tau =1.82(1)$ as found for the NEP model. An argument is given that $\tau =1+d_B/2\approx 1.822$ for backbone holes, where $d_B$ is the backbone dimension. On the other hand, a model of simple holes within a percolation cluster yields $\tau =1+d_f/2=187/96\approx 1.948$, where $d_f$ is the fractal dimension of the cluster, and this value is consistent with the experimental results of gel collapse of Sheinman et al., which give $\tau =1.91(6)$. This suggests that the gel clusters are of the universality class of percolation cluster holes. Both models give a discontinuous maximum hole size at $p_c$, signifying explosive percolation behavior.

We report simultaneous transport and scanning microwave impedance microscopy to examine the correlation between transport quantization and filling of the bulk Landau levels in the quantum Hall regime in gated graphene devices. Surprisingly, a comparison of these measurements reveals that quantized transport typically occurs below the complete filling of bulk Landau levels, when the bulk is still conductive. This result points to a revised understanding of transport quantization when carriers are accumulated by gating. We discuss the implications on transport study of the quantum Hall effect in graphene and related topological states in other two-dimensional electron systems.

Forbidden transitions between energy levels typically involve violation of selection rules imposed by symmetry and/or conservation laws. A nanomagnet tunneling between up and down states violates angular momentum conservation because of broken rotational symmetry. Here we report observations of highly forbidden transitions between spin states in a ${\mathrm{Ni}}_4$ single-molecule magnet in which a single photon can induce the spin to change by several times $\hslash$, nearly reversing the direction of the spin. These observations are understood as tunneling-assisted transitions that lift the standard $\mathrm{\Delta }m=\pm 1$ selection rule for single-photon transitions. These transitions are observed at low applied fields, where tunneling is dominated by the molecule’s intrinsic anisotropy and the field acts as a perturbation. Such transitions can be exploited to create macroscopic superposition states that are not typically accessible through single-photon $\mathrm{\Delta }m=\pm 1$ transitions.

We demonstrate that interactions can substantially undermine the free-particle description of magnons in ferromagnets on geometrically frustrated lattices. The anharmonic coupling, facilitated by the Dzyaloshinskii-Moriya interaction, and a highly degenerate two-magnon continuum yield a strong, nonperturbative damping of the high-energy magnon modes. We provide a detailed account of the effect for the $S=1/2$ ferromagnet on the kagome lattice and propose further experiments.

Near equilibrium, where all currents of a system vanish on average, the fluctuation-dissipation relation (FDR) connects a current’s spontaneous fluctuations with its response to perturbations of the conjugate thermodynamic force. Out of equilibrium, fluctuation-response relations generally involve additional nondissipative contributions. Here, in the framework of stochastic thermodynamics, we show that an equilibriumlike FDR holds for internally equilibrated currents, if the perturbing conjugate force only affects the microscopic transitions that contribute to the current. We discuss the physical requirements for the validity of our result and apply it to nanosized electronic devices.

This Letter presents a measurement of the inelastic proton-proton cross section using $60{\mu \mathrm{b}}^{-1}$ of $pp$ collisions at a center-of-mass energy $\sqrt{s}$ of 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region ($2.07<|\eta |<3.86$) of the detector. A cross section of $68.1\pm 1.4\mathrm{mb}$ is measured in the fiducial region $\xi =M_X^2/s>{10}^{-6}$, where $M_X$ is the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this $\xi$ range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with $M_X>13\mathrm{GeV}$. The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of $78.1\pm 2.9\mathrm{mb}$ is measured, consistent with the inelastic cross section increasing with center-of-mass energy.

We study shear banding in soft glassy materials subject to a large amplitude oscillatory shear flow (LAOS). By numerical simulations of the widely used soft glassy rheology model, supplemented by more general physical arguments, we demonstrate strong banding over an extensive range of amplitudes and frequencies of the imposed shear rate $\dot{\gamma }(t)={\dot{\gamma }}_0\cos (\omega t)$, even in materials that do not permit banding as their steady state response to a steadily imposed shear flow $\dot{\gamma }={\dot{\gamma }}_0=\text{const}$. Highly counterintuitively, banding persists in LAOS even in the limit of zero frequency $\omega \to 0$, where one might a priori have expected a homogeneous flow response in a material that does not display banding under conditions of steadily imposed shear. We explain this finding in terms of an alternating competition within each cycle between glassy aging and flow rejuvenation. Our predictions have far-reaching implications for the flow behavior of aging yield stress fluids, suggesting a generic expectation of shear banding in flows of even arbitrarily slow time variation.