We report on laboratory experiments of wave-driven rotating turbulence. A set of wave makers produces inertial-wave beams that interact nonlinearly in the central region of a water tank mounted on a rotating platform. The forcing thus injects energy into inertial waves only. For moderate forcing amplitude, part of the energy of the forced inertial waves is transferred to subharmonic waves, through a standard triadic resonance instability. This first step is broadly in line with the theory of weak turbulence. Surprisingly however, stronger forcing does not lead to an inertial-wave turbulence regime. Instead, most of the kinetic energy condenses into a vertically invariant geostrophic flow, even though the latter is unforced. We show that resonant quartets of inertial waves can trigger an instability—the “quartetic instability”—that leads to such spontaneous emergence of geostrophy. In the present experiment, this instability sets in as a secondary instability of the classical triadic instability.

In multivalley semiconductors, the valley degree of freedom can be potentially used to store, manipulate, and read quantum information, but its control remains challenging. The valleys in bilayer graphene can be addressed by a perpendicular magnetic field which couples by the valley $g$ factor $g_v$. However, control over $g_v$ has not been demonstrated yet. We experimentally determine the energy spectrum of a quantum point contact realized by a suitable gate geometry in bilayer graphene. Using finite bias spectroscopy, we measure the energy scales arising from the lateral confinement as well as the Zeeman splitting and find a spin $g$ factor $g_s\sim 2$. $g_v$ can be tuned by a factor of 3 using vertical electric fields, $g_v\sim 40–120$. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field.

Rydberg atoms are remarkable tools for quantum simulation and computation. They are the focus of an intense experimental activity, mainly based on low-angular-momentum Rydberg states. Unfortunately, atomic motion and levels lifetime limit the experimental timescale to about $100\mu \mathrm{s}$. Here, we demonstrate two-dimensional laser trapping of long-lived circular Rydberg states for up to 10 ms. Our method is very general and opens many opportunities for quantum technologies with Rydberg atoms. The 10 ms trapping time corresponds to thousands of interaction cycles in a circular-state-based quantum simulator. It is also promising for quantum metrology and quantum information with Rydberg atoms, by bringing atom-field interaction times into unprecedented regimes.

Spin-reorientation phase transitions that involve the rotation of a crystal’s magnetization have been well characterized in distorted-perovskite oxides such as orthoferrites. In these systems spin reorientation occurs due to competing rare-earth and transition metal anisotropies coupled via $f\text{−}d$ exchange. Here, we demonstrate an alternative paradigm for spin reorientation in distorted perovskites. We show that the $R_2{\mathrm{CuMnMn}}_4{\mathrm{O}}_{12}$ ($R=\mathrm{Y}$ or Dy) triple $A$-site columnar-ordered quadruple perovskites have three ordered magnetic phases and up to two spin-reorientation phase transitions. Unlike the spin-reorientation phenomena in other distorted perovskites, these transitions are independent of rare-earth magnetism, but are instead driven by an instability towards antiferromagnetic spin canting likely originating in frustrated Heisenberg exchange interactions, and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.

Much of our knowledge about dynamics and functionality of molecular systems has been achieved with femtosecond time-resolved spectroscopy. Despite extensive technical developments over the past decades, some classes of systems have eluded dynamical studies so far. Here, we demonstrate that superfluid helium nanodroplets, acting as a thermal bath of 0.4 K temperature to stabilize weakly bound or reactive systems, are well suited for time-resolved studies of single molecules solvated in the droplet interior. By observing vibrational wave packet motion of indium dimers (${\mathrm{In}}_2$) for tens of picoseconds, we demonstrate that the perturbation imposed by this quantum liquid can be lower by a factor of 10–100 compared to any other solvent, which uniquely allows us to study processes depending on long nuclear coherence in a dissipative environment. Furthermore, tailor-made microsolvation environments inside droplets will enable us to investigate the solvent influence on intramolecular dynamics in a wide tuning range from molecular isolation to strong molecule-solvent coupling.

We propose a mechanism called axiogenesis where the cosmological excess of baryons over antibaryons is generated from the rotation of the QCD axion. The Peccei-Quinn (PQ) symmetry may be explicitly broken in the early Universe, inducing the rotation of a PQ charged scalar field. The rotation corresponds to the asymmetry of the PQ charge, which is converted into the baryon asymmetry via QCD and electroweak sphaleron transitions. In the concrete model we explore, interesting phenomenology arises due to the prediction of a small decay constant and the connections with new physics at the LHC and future colliders and with axion dark matter.

Generation of quasiparticle-hole pairs in gapped graphene monolayers in the combined field of two counterpropagating light waves is studied. The process represents an analog of electron-positron pair production from the vacuum of quantum electrodynamics (QED) by the Breit-Wheeler effect. We show, however, that the two-dimensional structure of graphene causes some striking differences between both scenarios. In particular, contrary to the QED case, it allows for nonzero pair production rates at the energy threshold when the Breit-Wheeler reaction proceeds nonlinearly with absorption of three photons.

We investigate phonon spin transport in an insulating ferromagnet–nonmagnet–ferromagnet heterostructure. We show that the magnetoelastic interaction between the spins and the phonons leads to nonlocal spin transfer between the magnets. This transfer is mediated by a local phonon spin current and accompanied by a phonon spin accumulation. The spin conductance depends nontrivially on the system size, and decays over millimeter length scales for realistic material parameters, far exceeding the decay lengths of magnonic spin currents.

We demonstrate remote entanglement of trapped-ion qubits via a quantum-optical fiber link with fidelity and rate approaching those of local operations. Two ${}^{88}{\mathrm{Sr}}^{+}$ qubits are entangled via the polarization degree of freedom of two spontaneously emitted 422 nm photons which are coupled by high-numerical-aperture lenses into single-mode optical fibers and interfere on a beam splitter. A novel geometry allows high-efficiency photon collection while maintaining unit fidelity for ion-photon entanglement. We generate heralded Bell pairs with fidelity 94% at an average rate $182{\mathrm{s}}^{-1}$ (success probability $2.18\times {10}^{-4}$).

First ever measurements of the ratios of free cyclotron frequencies of heavy, highly charged ions with $Z>50$ with relative uncertainties close to ${10}^{-11}$ are presented. Such accurate measurements have become realistic due to the construction of the novel cryogenic multi-Penning-trap mass spectrometer PENTATRAP. Based on the measured frequency ratios, the mass differences of five pairs of stable xenon isotopes, ranging from ${}^{126}\mathrm{Xe}$ to ${}^{134}\mathrm{Xe}$, have been determined. Moreover, the first direct measurement of an electron binding energy in a heavy highly charged ion, namely of the 37th atomic electron in xenon, with an uncertainty of a few eV is demonstrated. The obtained value agrees with the calculated one using two independent, different implementations of the multiconfiguration Dirac-Hartree-Fock method. PENTATRAP opens the door to future measurements of electron binding energies in highly charged heavy ions for more stringent tests of bound-state quantum electrodynamics in strong electromagnetic fields and for an investigation of the manifestation of light dark matter in isotopic chains of certain chemical elements.

The exotic topological surface states of Dirac or Weyl semimetals, namely Fermi arcs, are predicted to be spin polarized, while their spin polarization nature is still not revealed by transport measurements. Here, we report the spin-polarized transport in a Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ nanowire employing the ferromagnetic electrodes for spin detection. The spin-up and spin-down states can be changed by reversing the current polarity, showing the spin-momentum locking property. Moreover, the nonlocal measurements show a high fidelity of the spin signals, indicating the topological protection nature of the spin transport. As tuning the Fermi level away from the Dirac point by gate voltages, the spin signals gradually decrease and finally are turned off, which is consistent with the fact that the Fermi arc surface state has the maximum ratio near the Dirac point and disappears above the Lifshitz transition point. Our results should be valuable for revealing the transport properties of the spin-polarized Fermi arc surface states in topological semimetals.

To characterize the generic behavior of open quantum systems, we consider random, purely dissipative Liouvillians with a notion of locality. We find that the positivity of the map implies a sharp separation of the relaxation timescales according to the locality of observables. Specifically, we analyze a spin-$1/2$ system of size $\ell$ with up to $n$-body Lindblad operators, which are $n$ local in the complexity-theory sense. Without locality ($n=\ell$), the complex Liouvillian spectrum densely covers a “lemon”-shaped support, in agreement with recent findings [S. Denisov et al., Phys. Rev. Lett. 123, 140403 (2019)]. However, for local Liouvillians ($n<\ell$), we find that the spectrum is composed of several dense clusters with random matrix spacing statistics, each featuring a lemon-shaped support wherein all eigenvectors correspond to $n$-body decay modes. This implies a hierarchy of relaxation timescales of $n$-body observables, which we verify to be robust in the thermodynamic limit. Our findings for $n$ locality generalize immediately to the case of spatial locality, introducing further splitting of timescales due to the additional structure.

This Letter reports on a cavity haloscope search for dark matter axions in the Galactic halo in the mass range $2.81–3.31\mu \mathrm{eV}$. This search utilizes the combination of a low-noise Josephson parametric amplifier and a large-cavity haloscope to achieve unprecedented sensitivity across this mass range. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong $CP$ problem of quantum chromodynamics.

Wakefield based accelerators capable of accelerating gradients 2 orders of magnitude higher than present accelerators offer a path to compact high energy physics instruments and light sources. However, for high gradient accelerators, beam instabilities driven by commensurately high transverse wakefields limit beam quality. Previously, it has been theoretically shown that transverse wakefields can be reduced by elliptically shaping the transverse sizes of beams in dielectric structures with planar symmetry. Here, we report experimental measurements that demonstrate reduced transverse wakefields for elliptical beams in planar symmetric structures which are consistent with theoretical models. These results may enable the design of gigavolt-per-meter gradient wakefield based accelerators that produce and stably accelerate high quality beams.

Moiré flatbands, occurring, e.g., in twisted bilayer graphene at magic angles, have attracted ample interest due to their high degree of experimental tunability and the intriguing possibility of generating novel strongly interacting phases. Here we consider the core problem of Coulomb interactions within fractionally filled spin and valley polarized Moiré flatbands and demonstrate that the dual description in terms of holes, which acquire a nontrivial hole dispersion, provides key physical intuition and enables the use of standard perturbative techniques for this strongly correlated problem. In experimentally relevant examples such as ABC stacked trilayer and twisted bilayer graphene aligned with boron nitride, it leads to emergent interaction-driven Fermi liquid states at electronic filling fractions down to around $1/3$ and $2/3$, respectively. At even lower filling fractions, the electron density still faithfully tracks the single-hole dispersion while exhibiting distinct non-Fermi liquid behavior. Most saliently, we provide microscopic evidence that high temperature fractional Chern insulators can form in twisted bilayer graphene aligned with hexagonal boron nitride.

Recent developments in twisted and lattice-mismatched bilayers have revealed a rich phase space of van der Waals systems and generated excitement. Among these systems are heterobilayers, which can offer new opportunities to control van der Waals systems with strong in plane correlations such as spin-orbit-assisted Mott insulator $\alpha \text{−}{\mathrm{RuCl}}_3$. Nevertheless, a theoretical ab initio framework for mismatched heterobilayers without even approximate periodicity is sorely lacking. We propose a general strategy for calculating electronic properties of such systems, mismatched interface theory (MINT), and apply it to the $\mathrm{graphene}/\alpha \text{−}{\mathrm{RuCl}}_3$ ($\mathrm{GR}/\alpha \text{−}{\mathrm{RuCl}}_3$) heterostructure. Using MINT, we predict uniform doping of 4.77% from graphene to $\alpha \text{−}{\mathrm{RuCl}}_3$ and magnetic interactions in $\alpha \text{−}{\mathrm{RuCl}}_3$ to shift the system toward the Kitaev point. Hence, we demonstrate that MINT can guide targeted materialization of desired model systems and discuss recent experiments on $\mathrm{GR}/\alpha \text{−}{\mathrm{RuCl}}_3$ heterostructures.

The lowest order amplitudes for [$\text{graviton+graviton → photon +photon}]$ lead to cross sections of order $G^2$, where $G$ is the gravitational constant. These are too small to be of any interest. However, in dense clouds of pure gravitons there are collective effects utilizing these same amplitudes that under the right circumstances can lead to copious production of photons.

Dirac materials, unlike the Weyl materials, have not been found in experiments to support intrinsic topological surface states, as the surface arcs in existing systems are unstable against symmetry-preserving perturbations. Utilizing the proposed glide and time-reversal symmetries, we theoretically design and experimentally verify an acoustic crystal of two frequency-isolated three-dimensional Dirac points with $Z_2$ monopole charges and four gapless helicoid surface states.

In recent years, many $\gamma$-ray sources have been identified, yet the unresolved component hosts valuable information on the faintest emission. In order to extract it, a cross-correlation with gravitational tracers of matter in the Universe has been shown to be a promising tool. We report here the first identification of a cross-correlation signal between $\gamma$ rays and the distribution of mass in the Universe probed by weak gravitational lensing. We use data from the Dark Energy Survey Y1 weak lensing data and the Fermi Large Area Telescope 9-yr $\gamma$-ray data, obtaining a signal-to-noise ratio of 5.3. The signal is mostly localized at small angular scales and high $\gamma$-ray energies, with a hint of correlation at extended separation. Blazar emission is likely the origin of the small-scale effect. We investigate implications of the large-scale component in terms of astrophysical sources and particle dark matter emission.

We report the first experimental observation of a strong-coupling effect in a one-dimensional moiré superlattice. We study one-dimensional double-wall carbon nanotubes (DWCNTs) in which van der Waals–coupled two single nanotubes form a one-dimensional moiré superlattice. We experimentally combine Rayleigh scattering spectroscopy and electron beam diffraction on the same individual DWCNTs to probe the optical transitions of the structure-identified DWCNTs in the visible spectral range. Among more than 30 structure-identified DWCNTs examined, we experimentally observed and identified a drastic change of the optical transition spectrum in a DWCNT with chirality (12,11)@(17,16). The origin of the marked change is attributed to the strong intertube coupling effect in the moiré superlattice formed by two nearly armchair nanotubes. Our numerical simulation is consistent with the experimental findings.