We propose and demonstrate experimentally the strong dissipative acousto-optic interaction between a suspended vibrating microfiber and a whispering-gallery microcavity. On the one hand, the dissipative response driven by an external stimulus of acoustic waves is found to be stronger than the dispersive response by 2 orders of magnitude. On the other hand, dead points emerge with the zero dissipative response at certain parameters, promising the potentials in physical sensing such as precise measurements of magnetic field and temperature. The strong dissipative acousto-optic interaction is then explored for ultrasensitive detection of broadband acoustic waves. A noise equivalent pressure as low as 0.81 Pa at 140 kHz in air is demonstrated experimentally, insensitive to cavity $Q$ factors and does not rely on mechanical resonances.

Granular suspensions present a transition from a Newtonian rheology in the Stokes limit to a Bagnoldian rheology when inertia is increased. A custom rheometer that can be run in a pressure- or a volume-imposed mode is used to examine this transition in the dense regime close to jamming. By varying systematically the interstitial fluid, shear rate, and packing fraction in volume-imposed measurements, we show that the transition takes place at a Stokes number of 10 independent of the packing fraction. Using pressure-imposed rheometry, we investigate whether the inertial and viscous regimes can be unified as a function of a single dimensionless number based on stress additivity.

It is of great current interest to establish toy models of ergodicity breaking transitions in quantum many-body systems. Here, we study a model that is expected to exhibit an ergodic to nonergodic transition in the thermodynamic limit upon tuning the coupling between an ergodic quantum dot and distant particles with spin-$1/2$. The model is effectively zero dimensional; however, a variant of the model was proposed by De Roeck and Huveneers to describe the avalanche mechanism of ergodicity breaking transition in one-dimensional disordered spin chains. We show that exact numerical results based on the spectral form factor calculation accurately agree with theoretical predictions, and hence unambiguously confirm existence of the ergodicity breaking transition in this model. We benchmark specific properties that represent hallmarks of the ergodicity breaking transition in finite systems.

It was pointed out in a recent paper that the observed cooling rate of old, cold neutron stars (NS) can provide an upper limit on the transition rate of neutron to mirror neutron ($n-n^{\prime }$). This limit is so stringent that it would preclude any discovery of $n\to n^{\prime }$ oscillation in the current round of terrestrial searches for the process. Motivated by this crucially important conclusion, we critically analyze this suggestion and note an interesting new effect present in nearly exact mirror models for $n\to n^{\prime }$ oscillation, which significantly affects this bound. The new element is the $\beta$ decay $n^{\prime }\to p^{\prime }+e^{\prime }+{\overline{\nu }}_e^{\prime }$, which creates a cloud of mirror particles $n^{\prime }$, $p^{\prime }$, $e^{\prime }$, and $D^{\prime }$ inside the NS core. The $e^{\prime }$ can “rob” the energy generated by the $n\to n^{\prime }$ transition via $e-e^{\prime }$ scattering enabled by the presence of a (minute) millicharge in mirror particles. This energy is emitted as unobserved mirror photons via fast mirror bremsstrahlung leading to a relaxation of this upper limit.

We report on a search for compact binary coalescences where at least one binary component has a mass between $0.2M_{\odot }$ and $1.0M_{\odot }$ in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend our previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio $q\ge 0.1$. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of $0.14{\mathrm{yr}}^{-1}$. This implies an upper limit on the merger rate of subsolar binaries in the range $[220-24200]{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes in the mass range $0.2M_{\odot }<m_{\mathrm{PBH}}<1.0M_{\odot }$ is $f_{\mathrm{PBH}}\equiv {\mathrm{\Omega }}_{\mathrm{PBH}}/{\mathrm{\Omega }}_{\mathrm{DM}}\lesssim 6\%$. This improves existing constraints on primordial black hole abundance by a factor of $\sim 3$. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at $M_{\min }=1M_{\odot }$, where $f_{\mathrm{DBH}}\equiv {\mathrm{\Omega }}_{\mathrm{DBH}}/{\mathrm{\Omega }}_{\mathrm{DM}}\lesssim 0.003\%$. These are the first constraints placed on dissipative dark models by subsolar-mass analyses.

We perform post-Newtonian analysis of double field theory as a test of string theory in gravitational sector against observations. We identify the Eddington-Robertson-Schiff parameters ${\beta }_{\mathrm{PPN}}$, ${\gamma }_{\mathrm{PPN}}$ with the charges of electric $H$ flux and dilaton respectively, and further relate them to stress-energy tensor. We show ${\beta }_{\mathrm{PPN}}=1$ from weak energy condition and argue that the observation of ${\gamma }_{\mathrm{PPN}}\simeq 1$ signifies the ultrarelativistic equation of state in baryons, or the suppression of gluon condensate.

Thin films provide a versatile platform to tune electron correlations and explore new physics in strongly correlated materials. Epitaxially grown thin films of the alkali-doped fulleride ${\mathrm{K}}_{3+x}{\mathrm{C}}_{60}$, for example, exhibit intriguing phenomena, including Mott transitions and superconductivity, depending on dimensionality and doping. Surprisingly, in the trilayer case, a strong electron-hole doping asymmetry has been observed in the superconducting phase, which is absent in the three-dimensional bulk limit. Using density-functional theory plus dynamical mean-field theory, we show that this doping asymmetry results from a substantial charge reshuffling from the top layer to the middle layer. While the nominal filling per fullerene is close to $n=3$, the top layer rapidly switches to an $n=2$ insulating state upon hole doping, which implies a doping asymmetry of the superconducting gap. The interlayer charge transfer and layer-selective metal-insulator transition result from the interplay between crystal field splittings, strong Coulomb interactions, and an effectively negative Hund coupling. This peculiar charge reshuffling is absent in the monolayer system, which is an $n=3$ Mott insulator, as expected from the nominal filling.

Colloidal semiconductor nanoplatelets are excellent optical emitters, which combine a quasi-2D structure with strong in-plane Coulomb interactions. Here, we go beyond the photoexcitation regime and investigate theoretically the effect of charging nanoplatelets with a few interacting fermions (electrons or holes). This introduces severe Coulomb repulsions in the system, enhanced by the inherent dielectric confinement. We predict strong electronic correlations and electron-electron exchange energies (over 20 meV) in type-I ($\mathrm{CdSe}/\mathrm{CdS}$) and type-II ($\mathrm{CdSe}/\mathrm{CdTe}$) nanoplatelets, which give rise to characteristic physical phenomena. These include shell filling spectra deviating from the Aufbau principle, large addition energies which permit deterministic control of the number of charges at room temperature and paramagnetic electron spin configuration activated at cryogenic temperatures.

We study the temperature and magnetic field dependence of the total magnetic moment of large-area permalloy artificial square spin ice arrays. The temperature dependence and hysteresis behavior are consistent with the coherent magnetization reversal expected in the Stoner-Wohlfarth model, with clear deviations due to interisland interactions at small lattice spacing. Through micromagnetic simulations, we explore this behavior and demonstrate that the deviations result from increasingly complex magnetization reversal at small lattice spacing, induced by interisland interactions, and depending critically on details of the island shapes. These results establish new means to tune the physical properties of artificial spin ice structures and other interacting nanomagnet systems, such as patterned magnetic media.

The transfer and control of angular momentum is a key aspect for spintronic applications. Only recently, it was shown that it is possible to transfer angular momentum from the spin system to the lattice on ultrashort timescales. To contribute to the understanding of angular momentum transfer between spin and lattice degrees of freedom we present a scheme to calculate fully relativistic spin-lattice coupling parameters from first principles. In addition to the dipole-dipole interactions often discussed in the literature, these parameters give, in particular, access to the spin-lattice effects controlled by spin-orbit coupling. By treating changes in the spin configuration and atomic positions at the same level, closed expressions for the atomic spin-lattice coupling parameters can be derived in a coherent manner up to any order. Analyzing the properties of these parameters, in particular their dependence on spin-orbit coupling, we find that even in bcc Fe the leading term for the angular momentum exchange between the spin system and the lattice is a Dzyaloshiskii-Moriya-type interaction, which is due to the symmetry breaking distortion of the lattice.

We formulate a hydrodynamic theory of $p$-atic liquid crystals, namely, two-dimensional anisotropic fluids endowed with generic $p$-fold rotational symmetry. Our approach, based on an order parameter tensor that directly embodies the discrete rotational symmetry of $p$-atic phases, allows us to unveil several unknown aspects of flowing $p$-atics, that previous theories, characterized by O(2) rotational symmetry, could not account for. This includes the onset of long-ranged orientational order in the presence of a simple shear flow of arbitrary shear rate, as opposed to the standard quasi-long-ranged order of two-dimensional liquid crystals, and the possibility of flow alignment at large shear rates.

Quantum computers built with superconducting artificial atoms already stretch the limits of their classical counterparts. While the lowest energy states of these artificial atoms serve as the qubit basis, the higher levels are responsible for both a host of attractive gate schemes as well as generating undesired interactions. In particular, when coupling these atoms to generate entanglement, the higher levels cause shifts in the computational levels that lead to unwanted $ZZ$ quantum crosstalk. Here, we present a novel technique to manipulate the energy levels and mitigate this crosstalk with simultaneous off-resonant drives on coupled qubits. This breaks a fundamental deadlock between qubit-qubit coupling and crosstalk. In a fixed-frequency transmon architecture with strong coupling and crosstalk cancellation, additional cross-resonance drives enable a 90 ns CNOT with a gate error of $(0.19\pm 0.02)\%$, while a second set of off-resonant drives enables a novel CZ gate. Furthermore, we show a definitive improvement in circuit performance with crosstalk cancellation over seven qubits, demonstrating the scalability of the technique. This Letter paves the way for superconducting hardware with faster gates and greatly improved multiqubit circuit fidelities.

We study the mixed-state entanglement structure of chaotic quantum many-body systems at late times using the recently developed equilibrium approximation. A rich entanglement phase diagram emerges when we generalize this technique to evaluate the logarithmic negativity for various universality classes of macroscopically thermalized states. Unlike in the infinite-temperature case, when we impose energy constraints at finite temperature, the phase diagrams for the logarithmic negativity and the mutual information become distinct. In particular, we identify a regime where the negativity is extensive but the mutual information is subextensive, indicating a large amount of bound entanglement. When applied to evaporating black holes, these results imply that there is quantum entanglement within the Hawking radiation long before the Page time, although this entanglement may not be distillable into Einstein-Podolsky-Rosen pairs. We claim that at this earlier time, rather than the Page time, information about diaries thrown into the black hole first starts to leak out.

We describe a simple protocol for the single-step generation of $N$-body entangling interactions between trapped atomic ion qubits. We show that qubit state-dependent squeezing operations and displacement forces on the collective atomic motion can generate full $N$-body interactions. Similar to the Mølmer-Sørensen two-body Ising interaction at the core of most trapped ion quantum computers and simulators, the proposed operation is relatively insensitive to the state of motion. We show how this $N$-body gate operation allows for the single-step implementation of a family of $N$-bit gate operations such as the powerful $N$-Toffoli gate, which flips a single qubit if and only if all other $N\text{−}1$ qubits are in a particular state.

As the field of optomechanics advances, quadratic dispersive coupling (QDC) represents an increasingly feasible path toward qualitatively new functionality. However, the leading QDC geometries generate linear dissipative coupling and an associated quantum radiation force noise that is detrimental to QDC applications. Here, we propose a simple geometry that dramatically reduces this noise without altering the QDC strength. We identify optimal regimes of operation, and discuss advantages within the examples of optical levitation and nondestructive phonon measurement.