We report phase-programmable Gaussian boson sampling (GBS) which produces up to 113 photon detection events out of a 144-mode photonic circuit. A new high-brightness and scalable quantum light source is developed, exploring the idea of stimulated emission of squeezed photons, which has simultaneously near-unity purity and efficiency. This GBS is programmable by tuning the phase of the input squeezed states. The obtained samples are efficiently validated by inferring from computationally friendly subsystems, which rules out hypotheses including distinguishable photons and thermal states. We show that our GBS experiment passes a nonclassicality test based on inequality constraints, and we reveal nontrivial genuine high-order correlations in the GBS samples, which are evidence of robustness against possible classical simulation schemes. This photonic quantum computer, Jiuzhang 2.0, yields a Hilbert space dimension up to $\sim {10}^{43}$, and a sampling rate $\sim {10}^{24}$ faster than using brute-force simulation on classical supercomputers.

Motivated by the observation of two distinct superconducting phases in the moiréless $ABC$-stacked rhombohedral trilayer graphene, we investigate the electron-acoustic-phonon coupling as a possible pairing mechanism. We predict the existence of superconductivity with the highest $T_c\sim 3\mathrm{K}$ near the Van Hove singularity. Away from the Van Hove singularity, $T_c$ remains finite in a wide range of doping. In our model, the $s$-wave spin-singlet and $f$-wave spin-triplet pairings yield the same $T_c$, while other pairing states have negligible $T_c$. Our theory provides a simple explanation for the two distinct superconducting phases in the experiment and suggests that superconductivity and other interaction-driven phases (e.g., ferromagnetism) can have different origins.

Plasma wakefield acceleration in the blowout regime is particularly promising for high-energy acceleration of electron beams because of its potential to simultaneously provide large acceleration gradients and high energy transfer efficiency while maintaining excellent beam quality. However, no equivalent regime for positron acceleration in plasma wakes has been discovered to date. We show that after a short propagation distance, an asymmetric electron beam drives a stable wakefield in a hollow plasma channel that can be both accelerating and focusing for a positron beam. A high charge positron bunch placed at a suitable distance behind the drive bunch can beam-load or flatten the longitudinal wakefield and enhance the transverse focusing force, leading to high efficiency and narrow energy spread acceleration of the positrons. Three-dimensional quasistatic particle-in-cell simulations show that an over 30% energy extraction efficiency from the wake to the positrons and a 1% level energy spread can be simultaneously obtained. Further optimization is feasible.

Diffusive transport is characterized by a diffusivity tensor which may, in general, contain both a symmetric and an antisymmetric component. Although the latter is often neglected, we derive Green-Kubo relations showing it to be a general characteristic of random motion breaking time-reversal and parity symmetries, as encountered in chiral active matter. In analogy with the odd viscosity appearing in chiral active fluids, we term this component the odd diffusivity. We show how odd diffusivity emerges in a chiral random walk model, and demonstrate the applicability of the Green-Kubo relations through molecular dynamics simulations of a passive tracer particle diffusing in a chiral active bath.

The movement of single kinesin molecules was observed while applying noisy external forces that mimic intracellular active fluctuations. We found kinesin accelerates under noise, especially when a large hindering load is added. The behavior quantitatively conformed to a theoretical model that describes the kinesin movement with simple two-state reactions. The universality of the kinetic theory suggests that intracellular enzymes share a similar noise-induced acceleration mechanism, i.e., active fluctuations in cells are not just noise but are utilized to promote various physiological processes.

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5-m-long traveling-wave Stark decelerator. The SrF molecules in $X^2{\mathrm{\Sigma }}^{+}(v=0,N=1)$ state are brought to rest as the velocity of the moving traps is gradually reduced from $190\mathrm{m}/\mathrm{s}$ to zero. The molecules are held for up to 50 ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of $1{\mathrm{mm}}^3$ and a velocity spread of $5(1)\mathrm{m}/\mathrm{s}$, which corresponds to a temperature of 60(20) mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark decelerated and trapped. Heavy molecules ($\mathrm{mass}>100\mathrm{amu}$) offer a highly increased sensitivity to probe physics beyond the standard model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement, and trapping experiments.

It is shown that electrostatic plasma wakefields can efficiently radiate at harmonics of the plasma frequency when the plasma has a positive density gradient along the propagation direction of a driver. The driver propagating at a subluminal group velocity excites the plasma wakefield with the same phase velocity. However, due to the positive density gradient, the wake phase velocity steadily increases behind the driver. As soon as the phase velocity becomes superluminal, the electrostatic wakefield couples efficiently to radiative electromagnetic modes. The period of time when the phase velocity stays above the speed of light depends on the density gradient scale length. The wake radiates at well-defined harmonics of the plasma frequency in the terahertz band. The angle of emission depends on the gradient scale and the time passed behind the driver. For appropriate plasma and driver parameters, the wake can radiate away nearly all its energy, which potentially results in an efficient, narrow-band, and tunable source of terahertz radiation.

We report the observation of long-lived Floquet prethermal states in a bulk solid composed of dipolar-coupled ${}^{13}\mathrm{C}$ nuclei in diamond at room temperature. For precessing nuclear spins prepared in an initial transverse state, we demonstrate pulsed spin-lock Floquet control that prevents their decay over multiple-minute-long periods. We observe Floquet prethermal lifetimes $T_2^{\prime }\approx 90.9\mathrm{s}$, extended $>60000$-fold over the nuclear free induction decay times. The spins themselves are continuously interrogated for $\sim 10\min$, corresponding to the application of $\approx 5.8\times {10}^6$ control pulses. The ${}^{13}\mathrm{C}$ nuclei are optically hyperpolarized by lattice nitrogen vacancy centers; the combination of hyperpolarization and continuous spin readout yields significant signal-to-noise ratio in the measurements. This allows probing the Floquet thermalization dynamics with unprecedented clarity. We identify four characteristic regimes of the thermalization process, discerning short-time transient processes leading to the prethermal plateau and long-time system heating toward infinite temperature. This Letter points to new opportunities possible via Floquet control in networks of dilute, randomly distributed, low-sensitivity nuclei. In particular, the combination of minutes-long prethermal lifetimes and continuous spin interrogation opens avenues for quantum sensors constructed from hyperpolarized Floquet prethermal nuclei.

This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a $\varphi$ meson. The result is obtained from two-particle correlations of combined $p\text{−}\varphi \oplus \overline{p}\text{−}\varphi$ pairs measured in high-multiplicity $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ by the ALICE Collaboration. The spin-averaged scattering length and effective range of the $p\text{−}\varphi$ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the $p\text{−}\varphi$ interaction. These data demonstrate that the interaction is dominated by elastic $p\text{−}\varphi$ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the $N\text{−}\varphi$ coupling constant is found to be $g_{N\text{−}\varphi }=0.14\pm 0.03(\mathrm{stat})\pm 0.02(\mathrm{syst})$. This work provides valuable experimental input to accomplish a self-consistent description of the $N\text{−}\varphi$ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium.

At nanometer separation, the dominant interaction between an atom and a material surface is the fluctuation-induced Casimir–Polder potential. We demonstrate that slow atoms crossing a silicon nitride transmission nanograting are a remarkably sensitive probe for that potential. A 15% difference between nonretarded (van der Waals) and retarded Casimir–Polder potentials is discernible at distances smaller than 51 nm. We discuss the relative influence of various theoretical and experimental parameters on the potential in detail. Our work paves the way to high-precision measurement of the Casimir–Polder potential as a prerequisite for understanding fundamental physics and its relevance to applications in quantum-enhanced sensing.

We study the representational power of Boltzmann machines (a type of neural network) in quantum many-body systems. We prove that any (local) tensor network state has a (local) neural network representation. The construction is almost optimal in the sense that the number of parameters in the neural network representation is almost linear in the number of nonzero parameters in the tensor network representation. Despite the difficulty of representing (gapped) chiral topological states with local tensor networks, we construct a quasilocal neural network representation for a chiral $p$-wave superconductor. These results demonstrate the power of Boltzmann machines.

We propose a relativistic gravitational theory leading to modified Newtonian dynamics, a paradigm that explains the observed universal galactic acceleration scale and related phenomenology. We discuss phenomenological requirements leading to its construction and demonstrate its agreement with the observed cosmic microwave background and matter power spectra on linear cosmological scales. We show that its action expanded to second order is free of ghost instabilities and discuss its possible embedding in a more fundamental theory.

Compressing electron pulses is important in many applications of electron beam systems. In this study, we propose to use optical beat notes to compress electron pulses. The beat frequency is chosen to match the initial electron pulse duration, which enables the compression of electron pulses with a wide range of durations. This functionality extends the optical control of electron beams, which is important in compact electron beam systems such as dielectric laser accelerators. We also find that the dominant frequency of the electron charge density changes continuously along its drift trajectory, which may open up new opportunities in coherent interaction between free electrons and quantum or classical systems.

We introduce a computational method for global optimization of structure and ordering in atomic systems. The method relies on interpolation between chemical elements, which is incorporated in a machine-learning structural fingerprint. The method is based on Bayesian optimization with Gaussian processes and is applied to the global optimization of Au-Cu bulk systems, Cu-Ni surfaces with CO adsorption, and Cu-Ni clusters. The method consistently identifies low-energy structures, which are likely to be the global minima of the energy. For the investigated systems with 23–66 atoms, the number of required energy and force calculations is in the range 3–75.

We show that ribbed elastic strips under tension present large spontaneous curvature and may close into tubes. In this single material architectured system, transverse bending results from a bilayer effect induced by Poisson contraction as the textured ribbon is stretched. Surprisingly, the induced curvature may reverse if ribs of different orientations are considered. Slender ribbed structures may also undergo a nontrivial buckling transition. We use analytical calculations to describe the evolution of the morphology of the ribbon and the transitions between the different experimental regimes as a function of material properties, geometrical parameters, and stretching strain. This scale-independent phenomenon may help the manufacturing of tubular textured structures or easily controllable grippers at small scale.

We report an improved measurement of the free neutron lifetime ${\tau }_n$ using the $\mathrm{UCN}\tau$ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately $38\times {10}^6$ surviving ultracold neutrons (UCNs) after storing in $\mathrm{UCN}\tau$’s magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract ${\tau }_n$ from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate ${\tau }_n$ measurements and by performing a global likelihood fit to all data while self-consistently incorporating the $\beta$-decay lifetime. Both techniques achieve consistent results and find a value ${\tau }_n=877.75\pm 0.28_{\mathrm{stat}}+0.22/-0.16_{\mathrm{syst}}\mathrm{s}$. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.

Controlling and sensing spin polarization of electrons forms the basis of spintronics. Here, we report a study of the effect of helium on the spin polarization of the tunneling current and magnetic contrast in spin-polarized scanning tunneling microscopy (SP STM). We show that the magnetic contrast in SP STM images recorded in the presence of helium depends sensitively on the tunneling conditions. From tunneling spectra and their variation across the atomic lattice we establish that the helium can be reversibly ejected from the tunneling junction by the tunneling electrons. The energy of the tunneling electrons required to eject the helium depends on the relative spin polarization of the tip and sample, making the microscope sensitive to the magnetic exchange interactions. We show that the time-averaged spin polarization of the tunneling current is suppressed in the presence of helium and thereby demonstrate voltage control of the spin polarization of the tunneling current across the tip-sample junction.

Ferroelectric materials, upon electric field biasing, display polarization discontinuities known as Barkhausen jumps, a subclass of a more general phenomenon known as crackling noise. Herein, we follow and visualize in real time the motion of single 90° needle domains induced by an electric field applied in the polarization direction of the prototypical ferroelectric ${\mathrm{BaTiO}}_3$, inside a transmission electron microscope. The nature of motion and periodicity of the Barkhausen pulses leads to distinctive interactions between domains forming a herringbone pattern. Remarkably, the tips of the domains do not come into contact with the body of the perpendicular domain, suggesting the presence of strong electromechanical fields around the tips of the needle domains. Additionally, interactions of the domains with the lattice result in relatively free movement of the domain walls through the dielectric medium, indicating that their motion-related activation energy depends only on weak Peierls-like potentials. Control over the kinetics of ferroelastic domain wall motion can lead to novel nanoelectronic devices pertinent to computing and data storage applications.

We generalize the thermodynamic uncertainty relation (TUR) and thermodynamic speed limit (TSL) for deterministic chemical reaction networks (CRNs). The scaled diffusion coefficient derived by considering the connection between macro- and mesoscopic CRNs plays an essential role in our results. The TUR shows that the product of the entropy production rate and the ratio of the scaled diffusion coefficient to the square of the rate of concentration change is bounded below by two. The TSL states a trade-off relation between speed and thermodynamic quantities, the entropy production, and the time-averaged scaled diffusion coefficient. The results are proved under the general setting of open and nonideal CRNs.

Hydrodynamic phenomena can be observed with light thanks to the analogy between quantum gases and nonlinear optics. In this Letter, we report an experimental study of the superfluid-like properties of light in a ($1+1$)-dimensional nonlinear optical mesh lattice, where the arrival time of optical pulses plays the role of a synthetic spatial dimension. A spatially narrow defect at rest is used to excite sound waves in the fluid of light and measure the sound speed. The critical velocity for superfluidity is probed by looking at the threshold in the deposited energy by a moving defect, above which the apparent superfluid behavior breaks down. Our observations establish optical mesh lattices as a promising platform to study fluids of light in novel regimes of interdisciplinary interest, including non-Hermitian and/or topological physics.