Gamma-ray beams with a large angular momentum may affect astrophysical phenomena, which calls for appropriate earth-based experimental investigations. For this purpose, we investigate the generation of well-collimated $\gamma$-ray beams with a very large orbital angular momentum using nonlinear Compton scattering of a strong laser pulse of twisted photons at ultrarelativistic electrons. Angular momentum conservation among absorbed laser photons, quantum radiation, and electrons is numerically demonstrated in the quantum radiation-dominated regime. We point out that the angular momentum of the absorbed laser photons is not solely transferred to the emitted $\gamma$ photons, but due to radiation reaction shared between the $\gamma$ photons and interacting electrons. The efficiency of the angular momentum transfer is optimized with respect to the laser and electron beam parameters. The accompanying process of electron-positron pair production is furthermore shown to enhance the orbital angular momentum gained by the $\gamma$-ray beam.

Water exhibits numerous anomalous properties, many of which remain poorly understood. One of its intriguing behaviors is that it exhibits a temperature of maximum density (TMD) at $4°\mathrm{C}$. We provide here new experimental evidence for hitherto unknown abrupt changes in proton transfer kinetics at the TMD. In particular, we show that the lifetime of ${\mathrm{OH}}^{-}$ ions has a maximum at this temperature, in contrast to hydronium ions. Furthermore, base-catalyzed proton transfer shows a sharp local minimum at this temperature, and activation energies change abruptly as well. The measured lifetimes agree with earlier theoretical predictions as the temperature approaches the TMD. Similar results are also found for heavy water at its own TMD. These findings point to a high propensity of forming fourfold coordinated ${\mathrm{OH}}^{-}$ solvation complexes at the TMD, underlining the asymmetry between hydroxide and hydronium transport. These results could help to further elucidate the unusual properties of water and related liquids.

A novel shape evolution in the Sn isotopes by the state-of-the-art application of the Monte Carlo shell model calculations is presented in a unified way for the ${}^{100–138}\mathrm{Sn}$ isotopes. A large model space consisting of eight single-particle orbits for protons and neutrons is taken with the fixed Hamiltonian and effective charges, where protons in the $1g_{9/2}$ orbital are fully activated. While the significant increase of the $B(E2;0_1^{+}\to 2_1^{+})$ value, seen around ${}^{110}\mathrm{Sn}$ as a function of neutron number ($N$), has remained a major puzzle over decades, it is explained as a consequence of the shape evolution driven by proton excitations from the $1g_{9/2}$ orbital. A second-order quantum phase transition is found around $N=66$, connecting the phase of such deformed shapes to the spherical pairing phase. The shape and shell evolutions are thus described, covering topics from the Gamow-Teller decay of ${}^{100}\mathrm{Sn}$ to the enhanced double magicity of ${}^{132}\mathrm{Sn}$.

We present a flexible scheme to realize non-Markovian dynamics of an electronic spin qubit, using a nitrogen-vacancy center in diamond where the inherent nitrogen spin serves as a regulator of the dynamics. By changing the population of the nitrogen spin, we show that we can smoothly tune the non-Markovianity of the electron spin’s dynamics. Furthermore, we examine the decoherence dynamics induced by the spin bath to exclude other sources of non-Markovianity. The amount of collected measurement data is kept at a minimum by employing Bayesian data analysis. This allows for a precise quantification of the parameters involved in the description of the dynamics and a prediction of so far unobserved data points.

The present study demonstrates that large electric fields progressively enhance the conductivity of ionic systems up to timescales corresponding to those on which their structural rearrangements take place. Yet, in many ionic materials, some regarded as candidates for electrical energy storage applications, the structural relaxation process can be tremendously slower than (or highly decoupled from) the charge fluctuations. Consequently, nonlinear dielectric spectroscopy may be employed to access rheological information in dynamically decoupled ionic conductors, whereas the combination of large electric power density and good mechanical stability, both technologically highly desired, imposes specific experimental constraints to reliably determine the steady-state conductivity of such materials.

We establish a large deviation principle for the Kardar-Parisi-Zhang (KPZ) equation, providing precise control over the left tail of the height distribution for narrow wedge initial condition. Our analysis exploits an exact connection between the KPZ one-point distribution and the Airy point process—an infinite particle Coulomb gas that arises at the spectral edge in random matrix theory. We develop the large deviation principle for the Airy point process and use it to compute, in a straightforward and assumption-free manner, the KPZ large deviation rate function in terms of an electrostatic problem (whose solution we evaluate). This method also applies to the half-space KPZ equation, showing that its rate function is half of the full-space rate function. In addition to these long-time estimates, we provide rigorous proof of finite-time tail bounds on the KPZ distribution, which demonstrate a crossover between exponential decay with exponent 3 (in the shallow left tail) to exponent $5/2$ (in the deep left tail). The full-space KPZ rate function agrees with the one computed in Sasorov et al. [J. Stat. Mech. (2017) 063203] via a WKB approximation analysis of a nonlocal, nonlinear integrodifferential equation generalizing Painlevé II which Amir et al. [Commun. Pure Appl. Math. 64, 466 (2011)] related to the KPZ one-point distribution.

Permutational quantum computing (PQC) [Quantum Inf. Comput., 10, 470–497 (2010)] is a natural quantum computational model conjectured to capture nonclassical aspects of quantum computation. An argument backing this conjecture was the observation that there was no efficient classical algorithm for estimation of matrix elements of the $S_n$ irreducible representation matrices in the Young’s orthogonal form, which correspond to transition amplitudes of a broad class of PQC circuits. This problem can be solved with a PQC machine in polynomial time, but no efficient classical algorithm for the problem was previously known. Here we give a classical algorithm that efficiently approximates the transition amplitudes up to polynomial additive precision and hence solves this problem. We further extend our discussion to show that transition amplitudes of a broader class of quantum circuits—the quantum Schur sampling circuits—can also be efficiently classically approximated.

It has been suggested that both quantum superpositions and nonlinear interactions are important resources for quantum metrology. However, to date the different roles that these two resources play in the precision enhancement are not well understood. Here, we experimentally demonstrate a Heisenberg-scaling metrology to measure the parameter governing the nonlinear coupling between two different optical modes. The intense mode with $n$ (more than $10^6$ in our work) photons manifests its effect through the nonlinear interaction strength which is proportional to its average photon number. The superposition state of the weak mode, which contains only a single photon, is responsible for both the linear Hamiltonian and the scaling of the measurement precision. By properly preparing the initial state of single photon and making projective photon-counting measurements, the extracted classical Fisher information (FI) can saturate the quantum FI embedded in the combined state after coupling, which is $\sim n^2$ and leads to a practical precision $\simeq 1.2/n$. Free from the utilization of entanglement, our work paves a way to realize Heisenberg-scaling precision when only a linear Hamiltonian is involved.

If dark matter stems from the background of a very light gauge boson, this gauge boson could exert forces on test masses in gravitational wave detectors, resulting in displacements with a characteristic frequency set by the gauge boson mass. We outline a novel search strategy for such dark matter, assuming the dark photon is the gauge boson of $U(1{)}_B$ or $U(1{)}_{B-L}$. We show that both ground-based and future space-based gravitational wave detectors have the capability to make a $5\sigma$ discovery in unexplored parameter regimes.

The Sub-Electron-Noise Skipper CCD Experimental Instrument (SENSEI) uses the recently developed Skipper-CCD technology to search for electron recoils from the interaction of sub-GeV dark matter particles with electrons in silicon. We report first results from a prototype SENSEI detector, which collected 0.019 g day of commissioning data above ground at Fermi National Accelerator Laboratory. These commissioning data are sufficient to set new direct-detection constraints for dark matter particles with masses between $\sim 500\mathrm{keV}$ and 4 MeV. Moreover, since these data were taken on the surface, they disfavor previously allowed strongly interacting dark matter particles with masses between $\sim 500\mathrm{keV}$ and a few hundred MeV. We discuss the implications of these data for several dark matter candidates, including one model proposed to explain the anomalously large 21-cm signal observed by the EDGES Collaboration. SENSEI is the first experiment dedicated to the search for electron recoils from dark matter, and these results demonstrate the power of the Skipper-CCD technology for dark matter searches.

We propose a new method to produce an electric and magnetic dipolar gas of ultracold dysprosium atoms. The pair of nearly degenerate energy levels of opposite parity, at $17513.33{\mathrm{cm}}^{-1}$ with electronic angular momentum $J=10$, and at $17514.50{\mathrm{cm}}^{-1}$ with $J=9$, can be mixed with an external electric field, thus inducing an electric dipole moment in the laboratory frame. For field amplitudes relevant to current-day experiments, i.e., an electric field of $5\mathrm{kV}/\mathrm{cm}$, we predict a large magnetic dipole moment up to 13 Bohr magnetons, and sizeable electric dipole moment up to 0.22 D. When a magnetic field is present, we show that the induced electric dipole moment is strongly dependent on the angle between the fields. The lifetime of the field-mixed levels is found in the millisecond range, thus allowing for suitable experimental detection and manipulation.

Clusters and nanoparticles have been widely investigated to determine how plasmonic near fields influence the strong-field induced energetic electron emission from finite systems. We focus on the contrary, i.e., the slow electrons, and discuss a hitherto unidentified low-energy structure (LES) in the photoemission spectra of rare gas clusters in intense near-infrared laser pulses. For Ar and Kr clusters we find, besides field-driven fast electrons, a robust and nearly isotropic emission of electrons with $<4\mathrm{eV}$ kinetic energies that dominates the total yield. Molecular dynamics simulations reveal a correlated few-body decay process involving quasifree electrons and multiply excited ions in the nonequilibrium nanoplasma that results in a dominant LES feature. Our results indicate that the LES emission occurs after significant nanoplasma expansion, and that it is a generic phenomenon in intense laser nanoparticle interactions, which is likely to influence the formation of highly charged ions.

We explore the dynamical response of dissipative Kerr solitons to changes in pump power and detuning and show how thermal and nonlinear processes couple these parameters to the frequency-comb degrees of freedom. Our experiments are enabled by a Pound-Drever-Hall (PDH) stabilization approach that provides on-demand, radio-frequency control of the frequency comb. PDH locking not only guides Kerr-soliton formation from a cold microresonator but opens a path to decouple the repetition and carrier-envelope-offset frequencies. In particular, we demonstrate phase stabilization of both Kerr-comb degrees of freedom to a fractional frequency precision below ${10}^{-16}$, compatible with optical-time-keeping technology. Moreover, we investigate the fundamental role that residual laser-resonator detuning noise plays in the spectral purity of microwave generation with Kerr combs.

The radiation pressure force on a nearly single-order diffraction grating was measured for a transmission grating near the Littrow angles at wavelengths of 808 and 447 nm. The component of force parallel to the grating agreed well with our prediction, being proportional to the product of the grating order and the ratio of the wavelength and grating period. The normal component of force varied with the incident angle, vanishing near the Littrow angle as expected. The measurements verify a correspondence between the Fourier grating momentum and the mechanical momentum. This Letter provides opportunities for in-space fly-by-light sailcraft as well as terrestrial applications.

We demonstrated selective slice-dependent lasing by controlling the matching to the undulator of different slices within an electron bunch. The slice-dependent mismatch was realized through quadrupole wakefield generated in a corrugated structure. A deterministic procedure based on empirical beam transport and phase space information is used to match selected slices by turns to lase in the undulator while keeping all other slices from lasing, thus staying fresh. Measurements of time-resolved electron bunch energy loss by a transverse deflecting cavity confirmed the predicted behavior.

The hose instability of the drive beam constitutes a major challenge for the stable operation of plasma-wakefield accelerators. In this Letter, we show that drive beams with a transverse size comparable to the plasma blowout radius generate a wake with a varying focusing along the beam, which leads to a rapid detuning of the slice-betatron oscillations and suppresses the instability. This intrinsic stabilization principle provides an applicable and effective method for the suppression of the hosing of the drive beam and allows for a stable acceleration process.

The phase diagram of isotropically expanded graphene cannot be correctly predicted by ignoring either electron correlations, or mobile carbons, or the effect of applied stress, as was done so far. We calculate the ground state enthalpy (not just energy) of strained graphene by an accurate off-lattice quantum Monte Carlo correlated ansatz of great variational flexibility. Following undistorted semimetallic graphene at low strain, multideterminant Heitler-London correlations stabilize between $\simeq 8.5\%$ and $\simeq 15\%$ strain an insulating Kekulé-like dimerized (DIM) state. Closer to a crystallized resonating-valence bond than to a Peierls state, the DIM state prevails over the competing antiferromagnetic insulating state favored by density-functional calculations which we conduct in parallel. The DIM stressed graphene insulator, whose gap is predicted to grow in excess of 1 eV before failure near 15% strain, is topological in nature, implying under certain conditions 1D metallic interface states lying in the bulk energy gap.