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Higher-order topological insulators (HOTIs), a new horizon of topological phases of matter, host lower-dimensional corner or hinge states, providing important stepping stones to the realization of robust topological waveguides in higher dimensions. The nontrivial band topology that gives rise to the corner or hinge states is usually enabled by certain crystalline symmetries. As a result, higher-order topological boundary states are tied to specific corners or hinges, lacking the flexibility of switching and selecting. Here, we report the experimental realization of topologically switchable and valley-selective corner states in a two-dimensional sonic crystal. Such intriguing properties are enabled by exploiting the higher-order topology assisted with the valley degree of freedom. For this purpose, we realize a valley HOTI of second-order topology characterized by the nontrivial bulk polarization. Interestingly, the hosted corner states are found to be valley dependent and therefore enable flexible control and manipulation on the wave localization. Topological switch on or off and valley selection of the corner states are directly observed through spatial scanning of the sound field. We further design an arbitrary structure of complex patterns containing corners with various intersection angles, among which selected corners can be illuminated or darkened upon valley selection. The reported valley HOTI and the valley-selective corner states provide fundamental understanding on the interplay between higher-order topology and valley degree of freedom and pave the way for lower-dimensional valleytronics, which may find potential applications in integrated acoustics and photonics.Tremendous progress has been made experimentally in the hadron spectrum containing heavy quarks in the last two decades. It is surprising that many resonant structures are around thresholds of a pair of heavy hadrons. There should be a threshold cusp at any S-wave threshold. By constructing a nonrelativistic effective field theory with open channels, we discuss the generalities of threshold behavior, and offer an explanation of the abundance of near-threshold peaks in the heavy quarkonium regime. learn more We show that the threshold cusp can show up as a peak only for channels with attractive interaction, and the width of the cusp is inversely proportional to the reduced mass relevant for the threshold. We argue that there should be threshold structures at any threshold of a pair of heavy-quark and heavy-antiquark hadrons, which have attractive interaction at threshold, in the invariant mass distribution of a heavy quarkonium and light hadrons that couple to that open-flavor hadron pair. The structure becomes more pronounced if there is a near-threshold pole. Predictions of the possible pairs are also given for the ground state heavy hadrons. Precisely measuring the threshold structures will play an important role in revealing the heavy-hadron interactions, and thus understanding the puzzling hidden-charm and hidden-bottom structures.Topological phases, including the conventional first-order and higher-order topological insulators and semimetals, have emerged as a thriving topic in the fields of condensed-matter physics and materials science. Usually, a topological insulator is characterized by a fixed order topological invariant and exhibits associated bulk-boundary correspondence. Here, we realize a new type of topological insulator in a bilayer phononic crystal, which hosts simultaneously the first-order and second-order topologies, referred to here as the hybrid-order topological insulator. The one-dimensional gapless helical edge states, and zero-dimensional corner states coexist in the same system. The new hybrid-order topological phase may produce novel applications in topological acoustic devices.Squeezed states of harmonic oscillators are a central resource for continuous-variable quantum sensing, computation, and communication. Here, we propose a method for the generation of very good approximations to highly squeezed vacuum states with low excess antisqueezing using only a few oscillator-qubit coupling gates through a Rabi-type interaction Hamiltonian. This interaction can be implemented with several different methods, which has previously been demonstrated in superconducting circuit and trapped-ion platforms. The protocol is compatible with other protocols manipulating quantum harmonic oscillators, thus facilitating scalable continuous-variable fault-tolerant quantum computation.We prepare mixtures of ultracold CaF molecules and Rb atoms in a magnetic trap and study their inelastic collisions. When the atoms are prepared in the spin-stretched state and the molecules in the spin-stretched component of the first rotationally excited state, they collide inelastically with a rate coefficient k_2=(6.6±1.5)×10^-11 cm^3/s at temperatures near 100 μK. We attribute this to rotation-changing collisions. When the molecules are in the ground rotational state we see no inelastic loss and set an upper bound on the spin-relaxation rate coefficient of k_2 less then 5.8×10^-12 cm^3/s with 95% confidence. We compare these measurements to the results of a single-channel loss model based on quantum defect theory. The comparison suggests a short-range loss parameter close to unity for rotationally excited molecules, but below 0.04 for molecules in the rotational ground state.Clouds of ultralight bosons-such as axions-can form around a rapidly spinning black hole, if the black hole radius is comparable to the bosons' wavelength. The cloud rapidly extracts angular momentum from the black hole, and reduces it to a characteristic value that depends on the boson's mass as well as on the black hole mass and spin. Therefore, a measurement of a black hole mass and spin can be used to reveal or exclude the existence of such bosons. Using the black holes released by LIGO and Virgo in their GWTC-2, we perform a simultaneous measurement of the black hole spin distribution at formation and the mass of the scalar boson. We find that the data strongly disfavor the existence of scalar bosons in the mass range between 1.3×10^-13 and 2.7×10^-13 eV. Our mass constraint is valid for bosons with negligible self-interaction, that is, with a decay constant f_a≳10^14 GeV. The statistical evidence is mostly driven by the two binary black holes systems GW190412 and GW190517, which host rapidly spinning black holes.
Read More: https://www.selleckchem.com/products/gc376-sodium.html
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