Rheo-dielectric spectroscopy is employed to investigate the effect of external shear on Debye-like relaxation of a model monohydroxy alcohol, i.e., the 2-ethyl-1-hexanol (2E1H). Shear deformation leads to strong acceleration in the structural relaxation, the Debye relaxation, and the terminal relaxation of 2E1H. Moreover, the shear-induced reduction in structural relaxation time, ${\tau }_{\alpha }$, scales quadratically with that of Debye time, ${\tau }_D$, and the terminal flow time, ${\tau }_f$, suggesting a relationship of ${\tau }_D^2\sim {\tau }_{\alpha }$. Further analyses reveal ${\tau }_D^2/{\tau }_{\alpha }$ of 2E1H follows Arrhenius temperature dependence that applies remarkably well to many other monohydroxy alcohols with different molecular sizes, architectures, and alcohol types. These results cannot be understood by the prevailing transient chain model, and suggest a H-bonding breakage facilitated sub-supramolecular reorientation as the origin of Debye relaxation of monohydroxy alcohols, akin to the molecular mechanism for the terminal relaxation of unentangled “living” polymers.

We unveil the signature of many-body interference across dynamical regimes of the Bose-Hubbard model. Increasing the particles’ indistinguishability enhances the temporal fluctuations of few-body observables, with a dramatic amplification at the onset of quantum chaos. By resolving the exchange symmetries of partially distinguishable particles, we explain this amplification as the fingerprint of the initial state’s coherences in the eigenbasis.

Despite the conceptual importance of contextuality in quantum mechanics, there is a hitherto limited number of applications requiring contextuality but not entanglement. Here, we show that for any quantum state and observables of sufficiently small dimensions producing contextuality, there exists a communication task with quantum advantage. Conversely, any quantum advantage in this task admits a proof of contextuality whenever an additional condition holds. We further show that given any set of observables allowing for quantum state-independent contextuality, there exists a class of communication tasks wherein the difference between classical and quantum communication complexities increases as the number of inputs grows. Finally, we show how to convert each of these communication tasks into a semi-device-independent protocol for quantum key distribution.

We present the first direct and nonperturbative computation of the graviton spectral function in quantum gravity. This is achieved with the help of a novel Lorentzian renormalization group approach, combined with a spectral representation of correlation functions. We find a positive graviton spectral function, showing a massless one-graviton peak and a multigraviton continuum with an asymptotically safe scaling for large spectral values. We also study the impact of a cosmological constant. Further steps to investigate scattering processes and unitarity in asymptotically safe quantum gravity are indicated.

In this Letter, we present a recursive method for computing one-loop off-shell integrands in colored quantum field theories. First, we generalize the perturbiner method by recasting the multiparticle currents as generators of off-shell tree-level amplitudes. After, by taking advantage of the underlying color structure, we define a consistent sewing procedure to iteratively compute the one-loop integrands. When gauge symmetries are involved, the whole procedure is extended to multiparticle solutions involving ghosts, which can then be accounted for in the full loop computation. Since the required input here is equations of motion and gauge symmetry, our framework naturally extends to one-loop computations in certain non-Lagrangian field theories.

Using a sample of $4.3\times {10}^5$ ${\eta }^{\prime }\to \eta {\pi }^0{\pi }^0$ events selected from the ten billion $J/\psi$ event dataset collected with the BESIII detector, we study the decay ${\eta }^{\prime }\to \eta {\pi }^0{\pi }^0$ within the framework of nonrelativistic effective field theory. Evidence for a structure at ${\pi }^{+}{\pi }^{-}$ mass threshold is observed in the invariant mass spectrum of ${\pi }^0{\pi }^0$ with a statistical significance of around $3.5\sigma$, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the $\pi \pi$ scattering length combination $a_0-a_2$ is determined to be $0.226\pm 0.060_{\mathrm{stat}}\pm 0.013_{\mathrm{syst}}$, which is in good agreement with theoretical calculation of $0.2644\pm 0.0051$.

We report the beam energy and collision centrality dependence of fifth and sixth order cumulants ($C_5$, $C_6$) and factorial cumulants (${\kappa }_5$, ${\kappa }_6$) of net-proton and proton number distributions, from center-of-mass energy ($\sqrt{s_{NN}}$) 3 GeV to 200 GeV $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC. Cumulant ratios of net-proton (taken as proxy for net-baryon) distributions generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at 3 GeV. The measured values of $C_6/C_2$ for 0%–40% centrality collisions show progressively negative trend with decreasing energy, while it is positive for the lowest energy studied. These observed negative signs are consistent with QCD calculations (for baryon chemical potential, ${\mu }_B\le 110\mathrm{MeV}$) which contains the crossover transition range. In addition, for energies above 7.7 GeV, the measured proton ${\kappa }_n$, within uncertainties, does not support the two-component ($\mathrm{Poisson}+\mathrm{binomial}$) shape of proton number distributions that would be expected from a first-order phase transition. Taken in combination, the hyperorder proton number fluctuations suggest that the structure of QCD matter at high baryon density, ${\mu }_B\sim 750\mathrm{MeV}$ at $\sqrt{s_{NN}}=3\mathrm{GeV}$ is starkly different from those at vanishing ${\mu }_B\sim 24\mathrm{MeV}$ at $\sqrt{s_{NN}}=200\mathrm{GeV}$ and higher collision energies.

Little is known about how rotating molecular ions interact with multiple ${}^4\mathrm{He}$ atoms and how this relates to microscopic superfluidity. Here, we use infrared spectroscopy to investigate ${{}^4\mathrm{He}}_N\cdots {\mathrm{H}}_3{\mathrm{O}}^{+}$ complexes and find that ${\mathrm{H}}_3{\mathrm{O}}^{+}$ undergoes dramatic changes in rotational behavior as ${}^4\mathrm{He}$ atoms are added. We present evidence of clear rotational decoupling of the ion core from the surrounding helium for $N>3$, with sudden changes in rotational constants at $N=6$ and 12. In sharp contrast to studies on small neutral molecules microsolvated in helium, accompanying path integral simulations show that an incipient superfluid effect is not needed to account for these findings.

We report the first experimental demonstration of coherent combining of phase-steerable high power microwaves (HPMs) generated by X-band relativistic triaxial klystron amplifier modules under the guidance of pulsed magnetic fields. Electronically agile manipulation of the HPM phase is achieved with a mean discrepancy of 4° at the gain level of 110 dB, and the coherent combining efficiency has reached as high as 98.4%, leading to combined radiations with equivalent peak power of 4.3 GW and average pulse duration of 112 ns. The underlying phase-steering mechanism during the nonlinear beam-wave interaction process is furthermore explored by particle-in-cell simulation and theoretical analysis. This Letter paves the way for high power phase array in large scale and may stimulate new interest in research of phase-steerable high power masers.

Explosive desorption of guest molecules embedded in amorphous solid water upon its crystallization is known as the “molecular volcano.” Here, we describe an abrupt ejection of ${\mathrm{NH}}_3$ guest molecules from various molecular host films toward a Ru(0001) substrate upon heating, utilizing both temperature programmed contact potential difference and temperature programmed desorption measurements. ${\mathrm{NH}}_3$ molecules abruptly migrate toward the substrate due to either crystallization or desorption of the host molecules, following an “inverse volcano” process considered a highly probable phenomenon for dipolar guest molecules that strongly interact with the substrate.

We demonstrate that semiconductor quantum dots can be excited efficiently in a resonant three-photon process, while resonant two-photon excitation is highly suppressed. Time-dependent Floquet theory is used to quantify the strength of the multiphoton processes and model the experimental results. The efficiency of these transitions can be drawn directly from parity considerations in the electron and hole wave functions in semiconductor quantum dots. Finally, we exploit this technique to probe intrinsic properties of InGaN quantum dots. In contrast to nonresonant excitation, slow relaxation of charge carriers is avoided, which allows us to measure directly the radiative lifetime of the lowest energy exciton states. Since the emission energy is detuned far from the resonant driving laser field, polarization filtering is not required and emission with a greater degree of linear polarization is observed compared to nonresonant excitation.

We study two-dimensional materials where electrons are coupled to the vacuum electromagnetic field of a cavity. We show that, at the onset of the superradiant phase transition towards a macroscopic photon occupation of the cavity, the critical electromagnetic fluctuations, consisting of photons strongly overdamped by their interaction with electrons, can in turn lead to the absence of electronic quasiparticles. Since transverse photons couple to the electronic current, the appearance of non-Fermi-Liquid behavior strongly depends on the lattice. In particular, we find that in a square lattice the phase space for electron-photon scattering is reduced in such a way to preserve the quasiparticles, while in a honeycomb lattice the latter are removed due to a nonanalytical frequency dependence of the damping $\propto |\omega {|}^{2/3}$. Standard cavity probes could allow us to measure the characteristic frequency spectrum of the overdamped critical electromagnetic modes responsible for the non-Fermi-liquid behavior.

Photonic crystal cavities with bowtie defects that combine ultrahigh $Q$ and ultralow mode volume are theoretically studied for low-power nanoscale optical trapping. By harnessing the localized heating of the water layer near the bowtie region, combined with an applied alternating current electric field, this system provides long-range electrohydrodynamic transport of particles with average radial velocities of $30\mathrm{\mu }\mathrm{m}/\mathrm{s}$ towards the bowtie region on demand by switching the input wavelength. Once transported to a given bowtie region, synergistic interaction of optical gradient and attractive negative thermophoretic forces stably trap a 10 nm quantum dot in a potential well with a depth of $10k_{B}T$ using a mW input power.

The propagating density gradients of a plasma wakefield may frequency upshift a trailing witness laser pulse, a process known as “photon acceleration.” In uniform plasma, the witness laser will eventually dephase because of group delay. We find phase-matching conditions for the pulse using a tailored density profile. An analytic solution for a 1D nonlinear plasma wake with an electron beam driver indicates that, even though the plasma density decreases, the frequency shift reaches no asymptotic limit, i.e., is unlimited provided the wake can be sustained. In fully self-consistent 1D particle-in-cell (PIC) simulations, more than 40 times frequency shifts were demonstrated. In quasi-3D PIC simulations, frequency shifts up to 10 times were observed, limited only by simulation resolution and nonoptimized driver evolution. The pulse energy increases in this process, by a factor of 5, and the pulse is guided and temporally compressed by group velocity dispersion, resulting in the resulting extreme ultraviolet laser pulse having near-relativistic ($a_0\sim 0.4$) intensity.

The spatial extent of excitons in molecular systems underpins their photophysics and utility for optoelectronic applications. Phonons are reported to lead to both exciton localization and delocalization. However, a microscopic understanding of phonon-induced (de)localization is lacking, in particular, how localized states form, the role of specific vibrations, and the relative importance of quantum and thermal nuclear fluctuations. Here, we present a first-principles study of these phenomena in solid pentacene, a prototypical molecular crystal, capturing the formation of bound excitons, exciton-phonon coupling to all orders, and phonon anharmonicity, using density functional theory, the ab initio $GW$-Bethe-Salpeter equation approach, finite-difference, and path integral techniques. We find that for pentacene zero-point nuclear motion causes uniformly strong localization, with thermal motion providing additional localization only for Wannier-Mott-like excitons. Anharmonic effects drive temperature-dependent localization, and, while such effects prevent the emergence of highly delocalized excitons, we explore the conditions under which these might be realized.

We report the manifestation of field-induced Berezinskii-Kosterlitz-Thouless (BKT) correlations in the weakly coupled spin-$1/2$ Heisenberg layers of the molecular-based bulk material $[\mathrm{Cu}(\mathrm{pz}{)}_2(2\text{−}\mathrm{HOpy}{)}_2]({\mathrm{PF}}_6{)}_2$. At zero field, a transition to long-range order occurs at 1.38 K, caused by a weak intrinsic easy-plane anisotropy and an interlayer exchange of $J^{\prime }/k_B\approx 1\mathrm{mK}$. Because of the moderate intralayer exchange coupling of $J/k_B=6.8\mathrm{K}$, the application of laboratory magnetic fields induces a substantial $XY$ anisotropy of the spin correlations. Crucially, this provides a significant BKT regime, as the tiny interlayer exchange $J^{\prime }$ only induces 3D correlations upon close approach to the BKT transition with its exponential growth in the spin-correlation length. We employ nuclear magnetic resonance measurements to probe the spin correlations that determine the critical temperatures of the BKT transition as well as that of the onset of long-range order. Further, we perform stochastic series expansion quantum Monte Carlo simulations based on the experimentally determined model parameters. Finite-size scaling of the in-plane spin stiffness yields excellent agreement of critical temperatures between theory and experiment, providing clear evidence that the nonmonotonic magnetic phase diagram of $[\mathrm{Cu}(\mathrm{pz}{)}_2(2\text{−}\mathrm{HOpy}{)}_2]({\mathrm{PF}}_6{)}_2$ is determined by the field-tuned $XY$ anisotropy and the concomitant BKT physics.

We experimentally investigate the stochastic phase dynamics of planar Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) defined in epitaxial $\mathrm{InAs}/\mathrm{Al}$ heterostructures, and characterized by a large ratio of Josephson energy to charging energy. We observe a crossover from a regime of macroscopic quantum tunneling to one of phase diffusion as a function of temperature, where the transition temperature $T^{*}$ is gate-tunable. The switching probability distributions are shown to be consistent with a small shunt capacitance and moderate damping, resulting in a switching current which is a small fraction of the critical current. Phase locking between two JJs leads to a difference in switching current between that of a JJ measured in isolation and that of the same JJ measured in an asymmetric SQUID loop. In the case of the loop, $T^{*}$ is also tuned by a magnetic flux.