Many complex generative systems use languages to create structured objects. We consider a model of random languages, defined by weighted context-free grammars. As the distribution of grammar weights broadens, a transition is found from a random phase, in which sentences are indistinguishable from noise, to an organized phase in which nontrivial information is carried. This marks the emergence of deep structure in the language, and can be understood by a competition between energy and entropy.

Massive fields in the primordial Universe function as standard clocks and imprint clock signals in the density perturbations that directly record the scale factor of the primordial Universe as a function of time, $a(t)$. A measurement of such signals would identify the specific scenario of the primordial Universe in a model-independent fashion. In this Letter, we introduce a new mechanism through which quantum fluctuations of massive fields function as standard clocks. The clock signals appear as scale-dependent oscillatory signals in the power spectrum of alternative scenarios to inflation.

Colloids are rarely perfectly uniform but follow a distribution of sizes, shapes, and charges. This dispersity can be inherent (static) or develop and change over time (dynamic). Despite a long history of research, the conditions under which nonuniform particles crystallize and which crystal forms is still not well understood. Here, we demonstrate that hard spheres with Gaussian radius distribution and dispersity up to 19% always crystallize if compressed slowly enough, and they do so in surprisingly complex ways. This result is obtained by accelerating event-driven simulations with particle swap moves for static dispersity and particle resize moves for dynamic dispersity. Above 6% dispersity, $A{B}_2$ Laves, $A{B}_{13}$, and a region of Frank-Kasper phases are found. The Frank-Kasper region includes a quasicrystal approximant with Pearson symbol oS276. Our findings are relevant for ordering phenomena in soft matter and alloys.

High-energy nuclear collisions produce a nonequilibrium plasma of quarks and gluons which thermalizes and exhibits hydrodynamic flow. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution. We build such a framework using nonequilibrium Green’s functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. We demonstrate that this approach can be easily incorporated into existing hydrodynamic simulations, leading to stronger constraints on the energy density at early times and the transport properties of the QCD medium. Based on (conformal) scaling properties of the Green’s functions, we further obtain pragmatic bounds for the applicability of hydrodynamics in nuclear collisions.

We experimentally realize cavity cooling of all three translational degrees of motion of a levitated nanoparticle in vacuum. The particle is trapped by a cavity-independent optical tweezer and coherently scatters tweezer light into the blue detuned cavity mode. For vacuum pressures around ${10}^{-5}\mathrm{mbar}$, minimal temperatures along the cavity axis in the millikelvin regime are observed. Simultaneously, the center-of-mass (c.m.) motion along the other two spatial directions is cooled to minimal temperatures of a few hundred millikelvin. Measuring temperatures and damping rates as the pressure is varied, we find that the cooling efficiencies depend on the particle position within the intracavity standing wave. This data and the behavior of the c.m. temperatures as functions of cavity detuning and tweezer power are consistent with a theoretical analysis of the experiment. Experimental limits and opportunities of our approach are outlined.

We report three-dimensional (3D) cooling of a levitated nanoparticle inside an optical cavity. The cooling mechanism is provided by cavity-enhanced coherent scattering off an optical tweezer. The observed 3D dynamics and cooling rates are as theoretically expected from the presence of both linear and quadratic terms in the interaction between the particle motion and the cavity field. By achieving nanometer-level control over the particle location we optimize the position-dependent coupling and demonstrate axial cooling by two orders of magnitude at background pressures of $6\times {10}^{-2}\mathrm{mbar}$. We also estimate a significant ($>40\mathrm{dB}$) suppression of laser phase noise heating, which is a specific feature of the coherent scattering scheme. The observed performance implies that quantum ground state cavity cooling of levitated nanoparticles can be achieved for background pressures below $1\times {10}^{-7}\mathrm{mbar}$.

The friction between a liquid swollen soft elastomer and a solid surface depends on the state of a confined liquid. To measure the physical state of the confined liquid, an interface-sensitive sum frequency generation spectroscopy technique was used to probe the contact region. We find that during sliding (friction) and pull-off (adhesion) experiments of pentadecane-swollen poly(dimethyl siloxane) lenses submerged in linear alkane (pentadecane) on a sapphire substrate, crystallinelike ordering of the liquid occurs only at the contact line, where we anticipate the highest shear. This crystallinelike structure of pentadecane molecules is transient and shows Arrhenius temperature dependence with unusually long relaxation times (hundreds of seconds) and an activation energy ($50\mathrm{kJ}/\mathrm{mole}$), which is twice that of the bulk pentadecane liquid, at temperatures that are $14–70°\mathrm{C}$ higher than the bulk melting temperature ($T_m=9°\mathrm{C}$). This unusual long-lived crystallinelike ordering may explain why these systems show higher friction coefficients (boundary lubrication) compared to values predicted using bulk viscosity of pentadecane (hydrodynamic lubrication).

We report a new scheme of ghost imaging by using a spatially structured pump in the Fourier domain of spontaneous parametric down-conversion for quantum-correlation-based pattern recognition. We exploit the mathematical feature of Laguerre-Gaussian mode’s Fourier transform to describe the pump-modulated formation of a ghost image. Of particular interest is the experimental demonstration of a quantum equivalence of a Vander Lugt filter, based on which the nonlocal spiral phase contrast for vortex mapping and quantum-correlation-based human face recognition are implemented successfully. The photons used for probing a test object, scanning the database, and producing a correlation signal can belong to three different light beams, which suggests some security applications where low-light-level illumination and covert operation are desired.

The control of the valley degree of freedom lies at the core of interest in monolayer transition metal dichalcogenides, where specific valley-spin excitation can be created using circularly polarized light. Measurement and manipulation of the valley index has also been achieved, but mainly with purely optical methods. Here, in monolayer ${\mathrm{MoS}}_2$, we identify a response to the valley polarization of excitons in the longitudinal electrical transport when the valley degeneracy is broken by an out-of-plane magnetic field $B_z$. The spin information is also simultaneously determined with spin-sensitive contacts. In the presence of $B_z$, a significant modulation of the photocurrent is observed as a function of the circular polarization state of the excitation. We attribute this effect to unbalanced transport of valley-polarized trions induced by the opposite Zeeman shifts of two ($K$ and $K^{\prime }$) valleys. Our interpretation is supported by the contrasting behavior in bilayer ${\mathrm{MoS}}_2$, as well as the observed doping and spatial dependence of the valley photocurrent.

We report on a significant and broadband enhancement of the transmission through an opaque barrier, when placed between symmetric diffusive disordered slabs. The transmission enhancement is accompanied by a bimodal distribution of the transmission eigenvalues, and, for a given transmittance of the barrier, it finds an optimal value for a particular length of the disordered slabs. A simple model allows us to quantify the scalings between the parameters that show that the stronger the barrier, the stronger the maximum possible enhancement. The sensitivity to symmetry defects is also explored, displaying potential interest for wave based sensing.

Polarized inelastic neutron scattering experiments recently identified the amplitude (Higgs) mode in ${\mathrm{C}}_9{\mathrm{H}}_{18}{\mathrm{N}}_2{\mathrm{CuBr}}_4$, a two-dimensional near-quantum-critical spin-$1/2$ two-leg ladder compound, which exhibits a weak easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin structure factor of such planar coupled spin-ladder systems using large-scale quantum Monte Carlo simulations. This allows us to provide a quantitative account of the experimental neutron scattering data within a consistent quantum spin model. Moreover, we trace the details of the continuous evolution of the amplitude mode from a two-particle bound state of coupled ladders in the classical Ising limit all the way to the quantum spin-$1/2$ Heisenberg limit with fully restored SU(2) symmetry, where it gets overdamped by the two-magnon continuum in neutron scattering.

An outstanding goal in quantum optics and scalable photonic quantum technology is to develop a source that each time emits one and only one entangled photon pair with simultaneously high entanglement fidelity, extraction efficiency, and photon indistinguishability. By coherent two-photon excitation of a single InGaAs quantum dot coupled to a circular Bragg grating bull’s-eye cavity with a broadband high Purcell factor of up to 11.3, we generate entangled photon pairs with a state fidelity of 0.90(1), pair generation rate of 0.59(1), pair extraction efficiency of 0.62(6), and photon indistinguishability of 0.90(1) simultaneously. Our work will open up many applications in high-efficiency multiphoton experiments and solid-state quantum repeaters.

One of the most fundamental and yet elusive collective phases of an interacting electron system is the quantum Wigner crystal (WC), an ordered array of electrons expected to form when the electrons’ Coulomb repulsion energy eclipses their kinetic (Fermi) energy. In low-disorder, two-dimensional (2D) electron systems, the quantum WC is known to be favored at very low temperatures ($T$) and small Landau level filling factors ($\nu$), near the termination of the fractional quantum Hall states. This WC phase exhibits an insulating behavior, reflecting its pinning by the small but finite disorder potential. An experimental determination of a $T$ vs $\nu$ phase diagram for the melting of the WC, however, has proved to be challenging. Here we use capacitance measurements to probe the 2D WC through its effective screening as a function of $T$ and $\nu$. We find that, as expected, the screening efficiency of the pinned WC is very poor at very low $T$ and improves at higher $T$ once the WC melts. Surprisingly, however, rather than monotonically changing with increasing $T$, the screening efficiency shows a well-defined maximum at a $T$ that is close to the previously reported melting temperature of the WC. Our experimental results suggest a new method to map out a $T$ vs $\nu$ phase diagram of the magnetic-field-induced WC precisely.

Quasicrystals are long-range ordered and yet nonperiodic. This interplay results in a wealth of intriguing physical phenomena, such as the inheritance of topological properties from higher dimensions, and the presence of nontrivial structure on all scales. Here, we report on the first experimental demonstration of an eightfold rotationally symmetric optical lattice, realizing a two-dimensional quasicrystalline potential for ultracold atoms. Using matter-wave diffraction we observe the self-similarity of this quasicrystalline structure, in close analogy to the very first discovery of quasicrystals using electron diffraction. The diffraction dynamics on short timescales constitutes a continuous-time quantum walk on a homogeneous four-dimensional tight-binding lattice. These measurements pave the way for quantum simulations in fractal structures and higher dimensions.

We report the preparation and verification of a genuine 12-qubit entanglement in a superconducting processor. The processor that we designed and fabricated has qubits lying on a 1D chain with relaxation times ranging from 29.6 to $54.6\mu \mathrm{s}$. The fidelity of the 12-qubit entanglement was measured to be above $0.5544\pm 0.0025$, exceeding the genuine multipartite entanglement threshold by 21 statistical standard deviations. After thermal cycling, the 12-qubit state fidelity was further improved to be above $0.707\pm 0.008$. Our entangling circuit to generate linear cluster states is depth invariant in the number of qubits and uses single- and double-qubit gates instead of collective interactions. Our results are a substantial step towards large-scale random circuit sampling and scalable measurement-based quantum computing.

The ability of the internal states of a working fluid to be in a coherent superposition is one of the basic properties of a quantum heat engine. It was recently predicted that in the regime of small engine action, this ability can enable a quantum heat engine to produce more power than any equivalent classical heat engine. It was also predicted that in the same regime, the presence of such internal coherence causes different types of quantum heat engines to become thermodynamically equivalent. Here, we use an ensemble of nitrogen vacancy centers in diamond for implementing two types of quantum heat engines, and experimentally observe both effects.

The development of compact accelerator facilities providing high-brightness beams is one of the most challenging tasks in the field of next-generation compact and cost affordable particle accelerators, to be used in many fields for industrial, medical, and research applications. The ability to shape the beam longitudinal phase space, in particular, plays a key role in achieving high-peak brightness. Here we present a new approach that allows us to tune the longitudinal phase space of a high-brightness beam by means of plasma wakefields. The electron beam passing through the plasma drives large wakefields that are used to manipulate the time-energy correlation of particles along the beam itself. We experimentally demonstrate that such a solution is highly tunable by simply adjusting the density of the plasma and can be used to imprint or remove any correlation onto the beam. This is a fundamental requirement when dealing with largely time-energy correlated beams coming from future plasma accelerators.

Plasma discharges with a negative triangularity ($\delta =-0.4$) shape have been created in the DIII-D tokamak with a significant normalized beta (${\beta }_N=2.7$) and confinement characteristic of the high confinement mode ($H_{98y2}=1.2$) despite the absence of an edge pressure pedestal and no edge localized modes (ELMs). These inner-wall-limited plasmas have a similar global performance as a positive triangularity ($\delta =+0.4$) ELMing $H$-mode discharge with the same plasma current, elongation and cross sectional area. For cases both of dominant electron cyclotron heating with $T_e/T_i>1$ and dominant neutral beam injection heating with $T_e/T_i=1$, turbulent fluctuations over radii $0.5<\rho <0.9$ were reduced by 10–50% in the negative triangularity shape compared to the matching positive triangularity shape, depending on the radius and conditions.

We study the quantum dynamics of fractional excitations in quantum spin ice. We focus on the density of states in the two-monopole sector, $\rho (\omega )$, as this can be connected to the wave-vector-integrated dynamical structure factor accessible in neutron scattering experiments. We find that $\rho (\omega )$ exhibits a strikingly characteristic singular and asymmetric structure that provides a useful fingerprint for comparison to experiment. $\rho (\omega )$ obtained from the exact diagonalization of a finite cluster agrees well with that, from the analytical solution of a hopping problem on a Husimi cactus representing configuration space, but not with the corresponding result on a face-centered cubic lattice, on which the monopoles move in real space. The main difference between the latter two lies in the inclusion of the emergent gauge field degrees of freedom, under which the monopoles are charged. This underlines the importance of treating both sets of degrees of freedom together, and it presents a novel instance of dimensional transmutation.