We report a novel source of twin beams based on modulational instability in high-pressure argon-filled hollow-core kagome-style photonic-crystal fiber. The source is Raman-free and manifests strong photon-number correlations for femtosecond pulses of squeezed vacuum with a record brightness of $\sim 2500$ photons per mode. The ultra-broadband ($\sim 50\mathrm{THz}$) twin beams are frequency tunable and contain one spatial and less than 5 frequency modes. The presented source outperforms all previously reported squeezed-vacuum twin-beam sources in terms of brightness and low mode content.

Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realizations of photonic quantum information technologies due to the ease of performing single qubit manipulations, the availability of polarization-entangled photon-pair sources, and the possibility of leveraging existing fiber-optic links for distributing qubits over long distances. An optical quantum memory compatible with this platform could serve as a building block for these technologies. Here we present the first experimental demonstration of an atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of freedom of a telecom-wavelength photon. We show that heralded polarization qubits at a telecom wavelength are stored and retrieved with near-unity fidelity by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing.

We present the first measurement of elliptic ($v_2$) and triangular ($v_3$) flow in high-multiplicity ${}^3\mathrm{He}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in ${}^3\mathrm{He}+\mathrm{Au}$ and in $p+p$ collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the ${}^3\mathrm{He}+\mathrm{Au}$ system. The collective behavior is quantified in terms of elliptic $v_2$ and triangular $v_3$ anisotropy coefficients measured with respect to their corresponding event planes. The $v_2$ values are comparable to those previously measured in $d+\mathrm{Au}$ collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three ${}^3\mathrm{He}$ nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.

Cold magnetized plasma possesses an anisotropic permittivity tensor with a unique dispersion relation that for adequate electron density and magnetic field results in anomalous diffraction of a right-hand circularly polarized beam. In this work, we demonstrate experimentally anomalous diffraction of a microwave beam in plasma. Additionally, decreasing the electron density enables observation of the transition of the material from a hyperbolic to a standard material. Manipulation of the control parameters will enable plasma to serve as a reconfigurable metamaterial-like medium.

The de Haas–van Alphen effect (dHvAE), describing oscillations of the magnetization as a function of magnetic field, is commonly assumed to be a definite sign for the presence of a Fermi surface (FS). Indeed, the effect forms the basis of a well-established experimental procedure for accurately measuring FS topology and geometry of metallic systems, with parameters commonly extracted by fitting to the Lifshitz-Kosevich (LK) theory based on Fermi liquid theory. Here we show that, in contrast to this canonical situation, there can be quantum oscillations even for band insulators of certain types. We provide simple analytic formulas describing the temperature dependence of the quantum oscillations in this setting, showing strong deviations from LK theory. We draw connections to recent experiments and discuss how our results can be used in future experiments to accurately determine, e.g., hybridization gaps in heavy-fermion systems.

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low $T_c$. We report the occurrence of high $T_c$ superconductivity in the bilayer ${\mathrm{CaCuO}}_2/{\mathrm{SrTiO}}_3$, where both the constituent oxides are insulating. In order to obtain a superconducting state, the ${\mathrm{CaCuO}}_2/{\mathrm{SrTiO}}_3$ interface must be realized between the Ca plane of ${\mathrm{CaCuO}}_2$ and the ${\mathrm{TiO}}_2$ plane of ${\mathrm{SrTiO}}_3$. Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the ${\mathrm{CuO}}_2$ planes. A detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O $K$ edge, clearly showing that the (super)conductivity is confined to about 1–2 ${\mathrm{CaCuO}}_2$ unit cells close to the interface with ${\mathrm{SrTiO}}_3$. The results obtained for the ${\mathrm{CaCuO}}_2/{\mathrm{SrTiO}}_3$ interface can be extended to multilayered high $T_c$ cuprates, contributing to explaining the dependence of $T_c$ on the number of ${\mathrm{CuO}}_2$ planes in these systems.

There is great interest in finding materials possessing quasiparticles with topological properties. Such materials may have novel excitations that exist on their boundaries which are protected against disorder. We report experimental evidence that magnons in an insulating kagome ferromagnet can have a topological band structure. Our neutron scattering measurements further reveal that one of the bands is flat due to the unique geometry of the kagome lattice. Spin wave calculations show that the measured band structure follows from a simple Heisenberg Hamiltonian with a Dzyaloshinkii-Moriya interaction. This serves as the first realization of an effectively two-dimensional topological magnon insulator—a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes.

Using neutron spin echo spectroscopy, we show that the segmental dynamics of polymer rings immersed in linear chains is completely controlled by the host. This transforms rings into ideal probes for studying the entanglement dynamics of the embedding matrix. As a consequence of the unique ring topology, in long chain matrices the entanglement spacing is directly revealed, unaffected by local reptation of the host molecules beyond this distance. In shorter entangled matrices, where in the time frame of the experiment secondary effects such as contour length fluctuations or constraint release could play a role, the ring motion reveals that the contour length fluctuation is weaker than assumed in state-of-the-art rheology and that the constraint release is negligible. We expect that rings, as topological probes, will also grant direct access to molecular aspects of polymer motion which have been inaccessible until now within chains adhering to more complex architectures.

The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states $P_c(4380)$ and $P_c(4450)$. These two hidden-charm states are interpreted as the loosely bound ${\mathrm{\Sigma }}_c(2455)D^{*}$ and ${\mathrm{\Sigma }}_c^{*}(2520)D^{*}$ molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of $P_c(4450)$ is much narrower than that of $P_c(4380)$. The discovery of the new resonances $P_c(4380)$ and $P_c(4450)$, indeed, opens a new page for hadron physics. The partners of $P_c(4380)$ and $P_c(4450)$ should be pursued in future experiments.

We report on the observation of a helical Luttinger liquid in the edge of an $\mathrm{InAs}/\mathrm{GaSb}$ quantum spin Hall insulator, which shows characteristic suppression of conductance at low temperature and low bias voltage. Moreover, the conductance shows power-law behavior as a function of temperature and bias voltage. The results underscore the strong electron-electron interaction effect in transport of $\mathrm{InAs}/\mathrm{GaSb}$ edge states. Because of the fact that the Fermi velocity of the edge modes is controlled by gates, the Luttinger parameter can be fine tuned. Realization of a tunable Luttinger liquid offers a one-dimensional model system for future studies of predicted correlation effects.

The fabrication of small scale, fixed structure fluidic diodes for simple fluids is quite challenging and has not yet been achieved. Here, we fabricate a moving part-free nanofluidic diode for simple fluids using heterogeneous nanochannels, half of which is hydrophilic and the other half is hydrophobic. It accepts water flows in the forward (from hydrophilic to hydrophobic) direction, while the flows in the backward direction are blocked for pressure drop range $0<\mathrm{\Delta }P<0.63\mathrm{MPa}$. The diode is ensured by a potential energy barrier at the channel entrance on the hydrophobic side due to the molecular interactions between the water and channel surface. As the upstream pressure becomes higher than 0.63 MPa, the fluidic diode turns to be a rectifier, which allows flows in both the forward and backward directions but with different flow rates. At sufficiently high driving pressures, the fluidic system fails in flow rectification, analogous to the breakdown of electronic diodes. The three different flow modes (diode, rectifier, and breakdown) of the fluidic chip and the underlying rectification mechanisms are confirmed by molecular dynamics simulations.

We report scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements of monolayer and bilayer ${\mathrm{WSe}}_2$. We measure a band gap of $2.21\pm 0.08\mathrm{eV}$ in monolayer ${\mathrm{WSe}}_2$, which is much larger than the energy of the photoluminescence peak, indicating a large excitonic binding energy. We additionally observe significant electronic scattering arising from atomic-scale defects. Using Fourier transform STS, we map the energy versus momentum dispersion relations for monolayer and bilayer ${\mathrm{WSe}}_2$. Further, by tracking allowed and forbidden scattering channels as a function of energy we infer the spin texture of both the conduction and valence bands. We observe a large spin-splitting of the valence band due to strong spin-orbit coupling, and additionally observe spin-valley-layer coupling in the conduction band of bilayer ${\mathrm{WSe}}_2$.

Multistage Zeeman deceleration was used to generate a slow, dense beam of translationally cold ${\mathrm{He}}_2$ molecules in the metastable $a\hspace{0.17em}{}^3{\mathrm{\Sigma }}_u^{+}$ state. Precision measurements of the Rydberg spectrum of these molecules at high values of the principal quantum number $n$ have been carried out. The spin-rotational state selectivity of the Zeeman-deceleration process was exploited to reduce the spectral congestion, minimize residual Doppler shifts, resolve the Rydberg series around $n=200$ and assign their fine structure. The ionization energy of metastable ${\mathrm{He}}_2$ and the lowest rotational interval of the $X^{+}\hspace{0.17em}{}^2{\mathrm{\Sigma }}_u^{+}$ (${\nu }^{+}=0$) ground state of ${}^4{{\mathrm{He}}_2}^{+}$ have been determined with unprecedented precision and accuracy by Rydberg-series extrapolation. Comparison with ab initio predictions of the rotational energy level structure of ${}^4{{\mathrm{He}}_2}^{+}$ [W.-C. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012)] enabled us to quantify the magnitude of relativistic and quantum-electrodynamics contributions to the fundamental rotational interval of ${{\mathrm{He}}_2}^{+}$.

We present density functional theory based atomistic calculations predicting that slow fracturing of silicon is possible at any chosen crack propagation speed under suitable temperature and load conditions. We also present experiments demonstrating fracture propagation on the Si(110) cleavage plane in the $\sim 100\mathrm{m}/\mathrm{s}$ speed range, consistent with our predictions. These results suggest that many other brittle crystals could be broken arbitrarily slowly in controlled experiments.

We investigate the decoherence of ${}^{40}\mathrm{K}$ impurities interacting with a three-dimensional Fermi sea of ${}^6\mathrm{Li}$ across an interspecies Feshbach resonance. The decoherence is measured as a function of the interaction strength and temperature using a spin-echo atom interferometry method. For weak to moderate interaction strengths, we interpret our measurements in terms of scattering of K quasiparticles by the Fermi sea and find very good agreement with a Fermi liquid calculation. For strong interactions, we observe significant enhancement of the decoherence rate, which is largely independent of temperature, pointing to behavior that is beyond the scattering of quasiparticles in the Fermi liquid picture.

The large available Hilbert space and high coherence of cavity resonators make these systems an interesting resource for storing encoded quantum bits. To perform a quantum gate on this encoded information, however, complex nonlinear operations must be applied to the many levels of the oscillator simultaneously. In this work, we introduce the selective number-dependent arbitrary phase (snap) gate, which imparts a different phase to each Fock-state component using an off-resonantly coupled qubit. We show that the snap gate allows control over the quantum phases by correcting the unwanted phase evolution due to the Kerr effect. Furthermore, by combining the snap gate with oscillator displacements, we create a one-photon Fock state with high fidelity. Using just these two controls, one can construct arbitrary unitary operations, offering a scalable route to performing logical manipulations on oscillator-encoded qubits.

What is the spatiotemporal limit of a macroscopic model that describes the optoelectronic interaction at the interface between different media? This fundamental question has become relevant for time-dependent photoemission from solid surfaces using probes that resolve attosecond electron dynamics on an atomic length scale. We address this fundamental question by investigating how ultrafast electron screening affects the infrared field distribution for a noble metal such as Cu(111) at the solid-vacuum interface. Attosecond photoemission delay measurements performed at different angles of incidence of the light allow us to study the detailed spatiotemporal dependence of the electromagnetic field distribution. Surprisingly, comparison with Monte Carlo semiclassical calculations reveals that the macroscopic Fresnel equations still properly describe the observed phase of the IR field on the Cu(111) surface on an atomic length and an attosecond time scale.

For a mixture of alkali-earth atomic gas in the long-lived excited state ${}^3{P}_0$ and the ground state ${}^1{S}_0$, in addition to nuclear spin, another “orbital” index is introduced to distinguish these two internal states. In this Letter we propose a mechanism to induce Feshbach resonance between two atoms with different orbital and nuclear spin quantum numbers. Two essential ingredients are the interorbital spin-exchange process and orbital dependence of the Landé $g$ factors. Here the orbital degrees of freedom plays a similar role as the electron spin degree of freedom in magnetic Feshbach resonance in alkali-metal atoms. This resonance is particularly accessible for the ${}^{173}\mathrm{Yb}$ system. The BCS-BEC crossover in this system requires two fermion pairing order parameters, and displays a significant difference compared to that in an alkali-metal system.

While numerous methods have been proposed to produce semiconducting graphene, a significant band gap has never been demonstrated. The reason is that, regardless of the theoretical gap formation mechanism, subnanometer disorder prevents the required symmetry breaking necessary to make graphene semiconducting. In this work, we show for the first time that semiconducting graphene can be made by epitaxial growth. Using improved growth methods, we show by direct band measurements that a band gap greater than 0.5 eV can be produced in the first graphene layer grown on the SiC(0001) surface. This work demonstrates that order, a property that remains lacking in other graphene systems, is key to producing electronically viable semiconducting graphene.

We propose that “standard pings,” brief broadband radio impulses, can be used to study the three-dimensional clustering of matter in the Universe even in the absence of redshift information. The dispersion of radio waves as they travel through the intervening plasma can, like redshift, be used as a cosmological distance measure. Because of inhomogeneities in the electron density along the line of sight, dispersion is an imperfect proxy for radial distance and we show that this leads to calculable dispersion-space distortions in the apparent clustering of sources. Fast radio bursts (FRBs) are a new class of radio transients that are the prototypical standard ping and, due to their high observed dispersion, have been interpreted as originating at cosmological distances. The rate of fast radio bursts has been estimated to be several thousand over the whole sky per day and, if cosmological, the sources of these events should trace the large-scale structure of the Universe. We calculate the dispersion-space power spectra for a simple model where electrons and FRBs are biased tracers of the large-scale structure of the Universe, and we show that the clustering signal could be measured using as few as 10 000 events. Such a survey is in line with what may be achieved with upcoming wide-field radio telescopes.