By using a nonlocal, quantum mechanical response function we study graphene plasmons in a one-dimensional superlattice (SL) potential $V_0\cos G_{0}x$. The SL introduces a quantum energy scale $E_G\sim \hslash v_F{G}_0$ associated with electronic subband transitions. At energies lower than $E_G$, the plasmon dispersion is highly anisotropic; plasmons propagate perpendicularly to the SL axis, but become damped by electronic transitions along the SL direction. These results question the validity of semiclassical approximations for describing low energy plasmons in periodic structures. At higher energies, the dispersion becomes isotropic and Drude-like with effective Drude weights related to the average of the absolute value of the local chemical potential. Full quantum mechanical treatment of the kinetic energy thus introduces nonlocal effects that delocalize the plasmons in the SL, making the system behave as a metamaterial even near singular points where the charge density vanishes.

The absence of information—entirely or partly—is called ignorance. Naturally, one might ask if some ignorance of a whole system will imply some ignorance of its parts. Our classical intuition tells us yes, however quantum theory tells us no: it is possible to encode information in a quantum system so that despite some ignorance of the whole, it is impossible to identify the unknown part [T. Vidick and S. Wehner, Phys. Rev. Lett. 107, 030402 (2011).]. Experimentally verifying this counterintuitive fact requires controlling and measuring quantum systems of high dimension $(d>9)$. We provide this experimental evidence using the transverse spatial modes of light, a powerful resource for testing high-dimensional quantum phenomena.

We propose a realistic cold-atom quantum setting where topological localization induces nonreciprocal pumping. This is an intriguing non-Hermitian phenomenon that illustrates how topology, when assisted with atom loss, can act as a “switch” for the non-Hermitian skin effect (NHSE), rather than as a passive property that is modified by the NHSE. In particular, we present a lattice-shaking scenario to realize a two-dimensional cold-atom platform, where nonreciprocity is switched on only in the presence of both atom loss and topological localization due to time-reversal symmetry breaking. The resultant nonreciprocal pumping is manifested by asymmetric dynamical evolution, detectable by atomic populations along the system edges. Our setup may trigger possible applications in nonreciprocal atomtronics, where loss and topological mechanisms conspire to control atomic transport. Its quantum nature will also facilitate future studies on the interplay between non-Hermiticity and many-body physics.

The propagation of matter waves in curved geometry is relevant for ion transport, atomtronics and electrons in nanowires. Curvature effects are usually addressed within the adiabatic limit and treated via an effective potential acting on the manifold to which the particles are strongly confined. However, the strength of the confinements that can be achieved experimentally are limited in practice, and the adiabatic approximation often appears too restrictive for realistic guides. Here, we work out a design method for 2D sharply bent waveguides beyond this approximation using an exact inverse-engineering technique. The efficiency of the method is confirmed by the resolution of the 2D nonlinear Schrödinger equation in curved geometry. In this way, we realize reflectionless and ultrarobust curved guides, even in the presence of interactions. Here, the transverse stability is improved by several orders of magnitude when compared to circular guides of similar size.

The out-of-time-ordered correlators (OTOC), a fundamental concept for quantifying quantum information scrambling, has recently been suggested to be an order parameter to dynamically detect both equilibrium quantum phase transitions (EQPTs) and dynamical quantum phase transitions (DQPTs). Here we report the first experimental observation of EQPTs and DQPTs in a quantum spin chain via quench dynamics of OTOC on a nuclear magnetic resonance quantum simulator. We observe that the quench dynamics of the OTOC can unambiguously detect the DQPTs and the equilibrium critical point, while conventional order parameters such as the longitudinal magnetization can not. Moreover, we investigate the two-body correlations throughout the quench dynamics, and find that OTOC can extract the equilibrium critical point with higher accuracy and is more robust to decoherence than that of two-body correlation. Our experiment paves a way for experimentally investigating DQPTs through OTOCs and for studying the EQPTs through the nonequilibrium quantum quench dynamics with quantum simulators.

The detection of binary black hole coalescences by LIGO and Virgo has aroused the interest in primordial black holes (PBHs), because they could be both the progenitors of these black holes and a compelling candidate of dark matter (DM). PBHs are formed soon after the enhanced scalar perturbations reenter horizon during the radiation dominated era, which would inevitably induce gravitational waves as well. Searching for such scalar induced gravitational waves (SIGWs) provides an elegant way to probe PBHs. We perform the first direct search for the signals of SIGWs accompanying the formation of PBHs in the North American Nanohertz Observatory for Gravitational waves (NANOGrav) 11-year dataset. No statistically significant detection has been made, and hence we place a stringent upper limit on the abundance of PBHs at 95% confidence level. In particular, less than one part in a million of the total DM mass could come from PBHs in the mass range of $[2\times {10}^{-3},7\times {10}^{-1}]M_{\odot }$.

We introduce an extension of the standard inflationary paradigm on which the big bang singularity is replaced by an anisotropic bounce. Unlike in the big bang model, cosmological perturbations find an adiabatic regime in the past. We show that this scenario accounts for the observed quadrupolar modulation in the temperature anisotropies of the cosmic microwave background, and we make predictions for the polarization angular correlation functions $E\text{−}E$, $B\text{−}B$, and $E\text{−}B$, together with temperature-polarization correlations $T\text{−}B$ and $T\text{−}E$, that can be used to test our ideas. We base our calculations on the bounce predicted by loop quantum cosmology, but our techniques and conclusions apply to other bouncing models as well.

Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p+p$ collisions allow us to understand the production mechanism in terms of perturbative and nonperturbative strong interactions. During 2017, the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$. The large nonzero asymmetries increasing both in longitudinal momentum fraction $x_F$ and transverse momentum $p_T$ have been observed at low transverse momentum $p_T<1\mathrm{GeV}/c$ for the first time, at this collision energy. The asymmetries show an approximate $x_F$ scaling in the $p_T$ region where nonperturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.

We study an array of ultracold atoms in an optical lattice (Mott insulator) excited with a coherent ultrashort laser pulse to a state where single-electron wave functions spatially overlap. Beyond a threshold principal quantum number where Rydberg orbitals of neighboring lattice sites overlap with each other, the atoms efficiently undergo spontaneous Penning ionization resulting in a drastic change of ion-counting statistics, sharp increase of avalanche ionization, and the formation of an ultracold plasma. These observations signal the actual creation of electronic states with overlapping wave functions, which is further confirmed by a significant difference in ionization dynamics between a Bose-Einstein condensate and a Mott insulator. This system is a promising platform for simulating electronic many-body phenomena dominated by Coulomb interactions in the condensed phase.

Time-reversal invariant Dirac and Weyl semimetals in three dimensions (3D) can host open Fermi arcs and spin-momentum locking Fermi loops on the surfaces. We find that when they become superconducting with $s$-wave pairing and the doping is lower than a critical level, straight $\pi$-flux vortex lines terminating at surfaces with Fermi arcs or spin-momentum locking Fermi loops can realize 1D topological superconductivity and harbor Majorana zero modes at their ends. Remarkably, we find that the vortex-generation-associated Zeeman field can open (when the surfaces have only Fermi arcs) or enhance the topological gap protecting Majorana zero modes, which is contrary to the situation in superconducting topological insulators. By studying the tilting effect of bulk Dirac and Weyl cones, we further find that type-I Dirac and Weyl semimetals in general have a much broader topological regime than type-II ones. Our findings build up a connection between time-reversal invariant Dirac and Weyl semimetals and Majorana zero modes in vortices.

We have used neutron spectroscopy to investigate the spin dynamics of the quantum ($S=1/2$) antiferromagnetic Ising chains in ${\mathrm{RbCoCl}}_3$. The structure and magnetic interactions in this material conspire to produce two magnetic phase transitions at low temperatures, presenting an ideal opportunity for thermal control of the chain environment. The high-resolution spectra we measure of two-domain-wall excitations therefore characterize precisely both the continuum response of isolated chains and the “Zeeman-ladder” bound states of chains in three different effective staggered fields in one and the same material. We apply an extended Matsubara formalism to obtain a quantitative description of the entire dataset, Monte Carlo simulations to interpret the magnetic order, and finite-temperature density-matrix renormalization-group calculations to fit the spectral features of all three phases.

The observable properties of topological quantum matter are often described by topological field theories. Here, we demonstrate that this principle extends beyond thermal equilibrium. To this end, we construct a model of two-dimensional driven open dynamics with a Chern insulator steady state. Within a Keldysh field theory approach, we show that under mild assumptions—particle number conservation and purity of the stationary state—an abelian Chern-Simons theory describes its response to external perturbations. As a corollary, we predict chiral edge modes stabilized by a dissipative bulk.

The use of multiplexed atomic quantum memories (MAQM) can significantly enhance the efficiency to establish entanglement in a quantum network. In the previous experiments, individual elements of a quantum network, such as the generation, storage, and transmission of quantum entanglement have been demonstrated separately. Here we report an experiment to show the compatibility and integration of these basic operations. Specifically, we generate photon-atom entanglement from any chosen pair of memory cells in a $6\times 5$ MAQM, convert the spin-wave to time-bin photonic excitation after a controllable storage time, and then store and retrieve the photon in a second MAQM for another controllable storage time. The preservation of quantum information in this process is verified by measuring the state fidelity. We also demonstrate that higher dimension quantum states can be transferred between the two distant MAQMs.

Using $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first measurements of the absolute branching fractions of 14 hadronic $D^{0(+)}$ decays to exclusive final states with an $\eta$, e.g., $D^0\to K^{-}{\pi }^{+}\eta$, $K_S^0{\pi }^0\eta$, $K^{+}{K}^{-}\eta$, $K_S^0{K}_S^0\eta$, $K^{-}{\pi }^{+}{\pi }^0\eta$, $K_S^0{\pi }^{+}{\pi }^{-}\eta$, $K_S^0{\pi }^0{\pi }^0\eta$, and ${\pi }^{+}{\pi }^{-}{\pi }^0\eta$; $D^{+}\to K_S^0{\pi }^{+}\eta$, $K_S^0{K}^{+}\eta$, $K^{-}{\pi }^{+}{\pi }^{+}\eta$, $K_S^0{\pi }^{+}{\pi }^0\eta$, ${\pi }^{+}{\pi }^{+}{\pi }^{-}\eta$, and ${\pi }^{+}{\pi }^0{\pi }^0\eta$. Among these decays, the $D^0\to K^{-}{\pi }^{+}\eta$ and $D^{+}\to K_S^0{\pi }^{+}\eta$ decays have the largest branching fractions, which are $\mathcal{B}(D^0\to K^{-}{\pi }^{+}\eta )=(1.853\pm 0.025_{\text{stat}}\pm 0.031_{\text{syst}})\%$ and $\mathcal{B}(D^{+}\to K_S^0{\pi }^{+}\eta )=(1.309\pm 0.037_{\text{stat}}\pm 0.031_{\text{syst}})\%$, respectively. The charge-parity asymmetries for the six decays with highest event yields are determined, and no statistically significant charge-parity violation is found.

The processes $X(3872)\to D^{*0}{\overline{D}}^0+\mathrm{c}.\mathrm{c}.,\gamma J/\psi ,\gamma \psi (2S)$, and $\gamma D^{+}{D}^{-}$ are searched for in a $9.0{\mathrm{fb}}^{-1}$ data sample collected at center-of-mass energies between 4.178 and 4.278 GeV with the BESIII detector. We observe $X(3872)\to D^{*0}\overline{D^0}+\mathrm{c}.\mathrm{c}.$ and find evidence for $X(3872)\to \gamma J/\psi$ with statistical significances of $7.4\sigma$ and $3.5\sigma$, respectively. No evident signals for $X(3872)\to \gamma \psi (2S)$ and $\gamma D^{+}{D}^{-}$ are found, and the upper limit on the relative branching ratio $R_{\gamma \psi }\equiv \{\mathcal{B}[X(3872)\to \gamma \psi (2S)]\}/\{\mathcal{B}[X(3872)\to \gamma J/\psi ]\}<0.59$ is set at 90% confidence level. Measurements of branching ratios relative to decay $X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$ are also reported for decays $X(3872)\to D^{*0}\overline{D^0}+\mathrm{c}.\mathrm{c}.,\gamma \psi (2S),\gamma J/\psi$, and $\gamma D^{+}{D}^{-}$, as well as the non-$D^{*0}\overline{D^0}$ three-body decays ${\pi }^0{D}^0\overline{D^0}$ and $\gamma D^0\overline{D^0}$.

Gould and Pittalis [Phys. Rev. Lett. 123, 016401 (2019) recently revealed a density-driven (DD) correlation energy that is specific to many-electron ensembles and must be accounted for by approximations. We derive in this Letter a general and simpler expression in terms of the ensemble weights, the ensemble Kohn-Sham (KS) orbitals, and their linear response to variations in the ensemble weights. As no additional state-driven KS systems are needed, its evaluation is greatly simplified. We confirm the importance of DD effects and introduce a direct and promising route to approximations.