We investigate the photoassociation dynamics of exactly two laser-cooled ${}^{85}\mathrm{Rb}$ atoms in an optical tweezer and reveal fundamentally different behavior to photoassociation in many-atom ensembles. We observe nonexponential decay in our two-atom experiment that cannot be described by a single rate coefficient and find its origin in our system’s pair correlation. This is in stark contrast to many-atom photoassociation dynamics, which are governed by decay with a single rate coefficient. We also investigate photoassociation in a three-atom system, thereby probing the transition from two-atom dynamics to many-atom dynamics. Our experiments reveal additional reaction dynamics that are only accessible through the control of single atoms and suggest photoassociation could measure pair correlations in few-atom systems. It further showcases our complete control over the quantum state of individual atoms and molecules, which provides information unobtainable from many-atom experiments.

We study a realistic Floquet topological superconductor, a periodically driven nanowire proximitized to an equilibrium s-wave superconductor. Because of the strong energy and density fluctuations caused by the superconducting proximity effect, the Floquet Majorana wire becomes dissipative. We show that the Floquet band structure is still preserved in this dissipative system. In particular, we find that the Floquet Majorana zero and $\pi$ modes can no longer be simply described by the Floquet topological band theory. We also propose an effective model to simplify the calculation of the lifetime of these Floquet Majoranas and find that the lifetime can be engineered by the external driving field.

Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this Letter, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than $e^2/h$. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phase-coherent conductors.

Glasses, unlike their crystalline counterparts, exhibit low-frequency nonphononic excitations whose frequencies $\omega$ follow a universal $\mathcal{D}(\omega )\sim {\omega }^4$ density of states. The process of glass formation generates positional disorder intertwined with mechanical frustration, posing fundamental challenges in understanding the origins of glassy nonphononic excitations. Here we suggest that minimal complexes—mechanically frustrated and positionally disordered local structures—embody the minimal physical ingredients needed to generate glasslike excitations. We investigate the individual effects of mechanical frustration and positional disorder on the vibrational spectrum of isolated minimal complexes, and demonstrate that ensembles of marginally stable minimal complexes yield $\mathcal{D}(\omega )\sim {\omega }^4$. Furthermore, glasslike excitations emerge by embedding a single minimal complex within a perfect lattice. Consequently, minimal complexes offer a conceptual framework to understand glasslike excitations from first principles, as well as a practical computational method for introducing them into solids.

The interaction between proteins and hydration water stabilizes protein structure and promotes functional dynamics, with water translational motions enabling protein flexibility. Engineered solvent-free protein-polymer hybrids have been shown to preserve protein structure, function, and dynamics. Here, we used neutron scattering, protein and polymer perdeuteration, and molecular dynamics simulations to explore how a polymer dynamically replaces water. Even though relaxation rates and vibrational properties are strongly modified in polymer coated compared to hydrated proteins, liquidlike polymer dynamics appear to plasticize the conjugated protein in a qualitatively similar way as do hydration-water translational motions.

Advanced LIGO-Virgo have reported a short gravitational-wave signal (GW190521) interpreted as a quasicircular merger of black holes, one at least populating the pair-instability supernova gap, that formed a remnant black hole of $M_f\sim 142M_{\odot }$ at a luminosity distance of $d_L\sim 5.3\mathrm{Gpc}$. With barely visible pre-merger emission, however, GW190521 merits further investigation of the pre-merger dynamics and even of the very nature of the colliding objects. We show that GW190521 is consistent with numerically simulated signals from head-on collisions of two (equal mass and spin) horizonless vector boson stars (aka Proca stars), forming a final black hole with $M_f=231_{-17}^{+13}{M}_{\odot }$, located at a distance of $d_L=571_{-181}^{+348}\mathrm{Mpc}$. This provides the first demonstration of close degeneracy between these two theoretical models, for a real gravitational-wave event. The favored mass for the ultralight vector boson constituent of the Proca stars is ${\mu }_{\mathrm{V}}=8.72_{-0.82}^{+0.73}\times {10}^{-13}\mathrm{eV}$. Confirmation of the Proca star interpretation, which we find statistically slightly preferred, would provide the first evidence for a long sought dark matter particle.

The energy dissipation rate in a nonequilibrium reaction system can be determined by the reaction rates in the underlying reaction network. By developing a coarse-graining process in state space and a corresponding renormalization procedure for reaction rates, we find that energy dissipation rate has an inverse power-law dependence on the number of microscopic states in a coarse-grained state. The dissipation scaling law requires self-similarity of the underlying network, and the scaling exponent depends on the network structure and the probability flux correlation. Existence of the inverse dissipation scaling law is shown in realistic biochemical systems such as biochemical oscillators and microtubule-kinesin active flow systems.

The transition between ergodic and many-body localization (MBL) phases lies at the heart of understanding quantum thermalization of many-body systems. Here, we predict a many-body critical (MBC) phase with finite-size scaling analysis in the one-dimensional extended Aubry-André-Harper-Hubbard model, which is different from both the ergodic phase and MBL phase, implying that the quantum system hosts three different fundamental phases in the thermodynamic limit. The level statistics in the MBC phase are well characterized by the so-called critical statistics, and the wave functions exhibit deep multifractal behavior only in the critical region. We further study the half-chain entanglement entropy and thermalization properties and show that the former, in the MBC phase, manifest a volume law scaling, while the many-body states violate the eigenstate thermalization hypothesis. The results are confirmed by the state-of-the-art numerical calculations with system size up to $L=22$. This work unveils a novel many-body phase which is extended but nonthermal.

First experimental results from a room-temperature tabletop phase-sensitive axion haloscope experiment are presented. The technique exploits the axion-photon coupling between two photonic resonator oscillators excited in a single cavity, allowing low-mass axions to be upconverted to microwave frequencies, acting as a source of frequency modulation on the microwave carriers. This new pathway to axion detection has certain advantages over the traditional haloscope method, particularly in targeting axions below $1\mu \mathrm{eV}$ (240 MHz) in energy. At the heart of the dual-mode oscillator, a tunable cylindrical microwave cavity supports a pair of orthogonally polarized modes (${\mathrm{TM}}_{0,2,0}$ and ${\mathrm{TE}}_{0,1,1}$), which, in general, enables simultaneous sensitivity to axions with masses corresponding to the sum and difference of the microwave frequencies. However, in the reported experiment, the configuration was such that the sum frequency sensitivity was suppressed, while the difference frequency sensitivity was enhanced. The results place axion exclusion limits between 7.44–19.38 neV, excluding a minimal coupling strength above $5\times {10}^{-7}1/\mathrm{GeV}$, after a measurement period of two and a half hours. We show that a state-of-the-art frequency-stabilized cryogenic implementation of this technique, ambitious but realizable, may achieve the best limits in a vast range of axion space.

Quasielastic ${}^{12}\mathrm{C}(e,e^{\prime }p)$ scattering was measured at spacelike 4-momentum transfer squared $Q^2=8$, 9.4, 11.4, and $14.2(\mathrm{GeV}/c{)}^2$, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no $Q^2$ dependence, up to proton momenta of $8.5\mathrm{GeV}/c$, ruling out the quantum chromodynamics effect of color transparency at the measured $Q^2$ scales in exclusive $(e,e^{\prime }p)$ reactions. These results impose strict constraints on models of color transparency for protons.

A kinematically complete quasifree $(p,pn)$ experiment in inverse kinematics was performed to study the structure of the Borromean nucleus ${}^{17}\mathrm{B}$, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for $1s_{1/2}$ and $0d_{5/2}$ orbitals, and a surprisingly small percentage of 9(2)% was determined for $1s_{1/2}$. Our finding of such a small $1s_{1/2}$ component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in ${}^{17}\mathrm{B}$. The present work gives the smallest $s$- or $p$-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of $s$ or $p$ orbitals is not a prerequisite for the occurrence of a neutron halo.

Exceptional points (EPs) of a non-Hermitian Hamiltonian with parity-time-reversal $(\mathcal{P}\mathcal{T})$ symmetry have the potential to drastically enhance the capabilities of metrology and sensing through their power-law growing sensitivity to external perturbation. With the ability of generating and tuning dissipation in a single trapped ion system, we observe rich dynamics and detailed quantum phase transitions from the $\mathcal{P}\mathcal{T}$-symmetric phase to the symmetry-breaking phase. In this single qubit full quantum system, we develop a method to precisely determine the location of EP without any fitting parameter, and extract the eigenvalues in a unified way through all parameter regions. We can also obtain the full density matrix by quantum state tomography. Finally, we suggest from theoretical analysis that the periodically driving $\mathcal{P}\mathcal{T}$-symmetric non-Hermitian system can be used to measure the magnitude, frequency, and phase of time-dependent perturbation with EP enhancement.

The spectroscopic techniques for time-resolved fine analysis of matter require coherent x-ray radiation with femtosecond duration and high average brightness. Seeded free-electron lasers (FELs), which use the frequency up-conversion of an external seed laser to improve temporal coherence, are ideal for providing fully coherent soft x-ray pulses. However, it is difficult to operate seeded FELs at a high repetition rate due to the limitations of present state-of-the-art laser systems. Here, we report a novel self-modulation method for enhancing laser-induced energy modulation, thereby significantly reducing the requirement of an external laser system. Driven by this scheme, we experimentally realize high harmonic generation in a seeded FEL using an unprecedentedly small external laser-induced energy modulation. An electron beam with a laser-induced energy modulation as small as 1.8 times the slice energy spread is used for lasing at the seventh harmonic of a 266-nm seed laser in a single-stage high-gain harmonic generation (HGHG) setup and the 30th harmonic of the seed laser in a two-stage HGHG setup. The results mark a major step toward a high-repetition-rate, fully coherent x-ray FEL.

In a plasma of sufficient size and density, photons emitted within the system have a probability of being reabsorbed and reemitted multiple times—a phenomenon known in astrophysics as resonant scattering. This effect alters the ratio of optically thick to optically thin lines, depending on the plasma geometry and viewing angle, and has significant implications for the spectra observed in a number of astrophysical scenarios, but has not previously been studied in a controlled laboratory plasma. We demonstrate the effect in the x-ray spectra emitted by cylindrical plasmas generated by high power laser irradiation, and the results confirm the geometrical interpretation of resonant scattering.

We introduce a simple physical picture to explain the process of molecular sorting, whereby specific proteins are concentrated and distilled into submicrometric lipid vesicles in eukaryotic cells. To this purpose, we formulate a model based on the coupling of spontaneous molecular aggregation with vesicle nucleation. Its implications are studied by means of a phenomenological theory describing the diffusion of molecules toward multiple sorting centers that grow due to molecule absorption and are extracted when they reach a sufficiently large size. The predictions of the theory are compared with numerical simulations of a lattice-gas realization of the model and with experimental observations. The efficiency of the distillation process is found to be optimal for intermediate aggregation rates, where the density of sorted molecules is minimal and the process obeys simple scaling laws. Quantitative measures of endocytic sorting performed in primary endothelial cells are compatible with the hypothesis that these optimal conditions are realized in living cells.