Among the key insights into the glass transition has been the identification of a nonequilibrium phase transition in trajectory space which reveals phase coexistence between the normal supercooled liquid (active phase) and a glassy state (inactive phase). Here, we present evidence that such a transition occurs in experiments. In colloidal hard spheres, we find a non-Gaussian distribution of trajectories leaning towards those rich in locally favored structures (LFSs), associated with the emergence of slow dynamics. This we interpret as evidence for a nonequilibrium transition to an inactive LFS-rich phase. Reweighting trajectories reveals a first-order phase transition in trajectory space between a normal liquid and a LFS-rich phase. We also find evidence for a purely dynamical transition in trajectory space.

Efficient bacterial chromosome segregation typically requires the coordinated action of a three-component machinery, fueled by adenosine triphosphate, called the partition complex. We present a phenomenological model accounting for the dynamic activity of this system that is also relevant for the physics of catalytic particles in active environments. The model is obtained by coupling simple linear reaction-diffusion equations with a proteophoresis, or “volumetric” chemophoresis, force field that arises from protein-protein interactions and provides a physically viable mechanism for complex translocation. This minimal description captures most known experimental observations: dynamic oscillations of complex components, complex separation, and subsequent symmetrical positioning. The predictions of our model are in phenomenological agreement with and provide substantial insight into recent experiments. From a nonlinear physics view point, this system explores the active separation of matter at micrometric scales with a dynamical instability between static positioning and traveling wave regimes triggered by the dynamical spontaneous breaking of rotational symmetry.

Single nanoparticles are shown to develop a localized acoustic resonance, the bouncing mode, when placed on a substrate. If both substrate and nanoparticle are noble metals, plasmonic coupling of the nanoparticle to its image charges in the film induces tight light confinement in the nanogap. This yields ultrastrong “acoustoplasmonic” coupling with a figure of merit 7 orders of magnitude higher than conventional acousto-optic modulators. The plasmons thus act as a local vibrational probe of the contact geometry. A simple analytical mechanical model is found to describe the bouncing mode in terms of the nanoscale structure, allowing transient pump-probe spectroscopy to directly measure the contact area for individual nanoparticles.

The dipole coupling strength $g$ between cavity photons and quantum well excitons determines the regime of light matter coupling in quantum well microcavities. In the strong coupling regime, a reversible energy transfer between exciton and cavity photon takes place, which leads to the formation of hybrid polaritonic resonances. If the coupling is further increased, a hybridization of different single exciton states emerges, which is referred to as the very strong coupling regime. In semiconductor quantum wells such a regime is predicted to manifest as a photon-mediated electron-hole coupling leading to different excitonic wave functions for the two polaritonic branches when the ratio of the coupling strength to exciton binding energy $g/E_B$ approaches unity. Here, we verify experimentally the existence of this regime in magneto-optical measurements on a microcavity characterized by $g/E_B\approx 0.64$, showing that the average electron-hole separation of the upper polariton is significantly increased compared to the bare quantum well exciton Bohr radius. This yields a diamagnetic shift around 0 detuning that exceeds the shift of the lower polariton by 1 order of magnitude and the bare quantum well exciton diamagnetic shift by a factor of 2. The lower polariton exhibits a diamagnetic shift smaller than expected from the coupling of a rigid exciton to the cavity mode, which suggests more tightly bound electron-hole pairs than in the bare quantum well.

In a seminal paper [D. N. Page, Phys. Rev. Lett. 71, 1291 (1993)], Page proved that the average entanglement entropy of subsystems of random pure states is $S_{\text{ave}}\simeq \ln {\mathcal{D}}_{\mathrm{A}}-(1/2){\mathcal{D}}_{\mathrm{A}}^2/\mathcal{D}$ for $1\ll {\mathcal{D}}_{\mathrm{A}}\le \sqrt{\mathcal{D}}$, where ${\mathcal{D}}_{\mathrm{A}}$ and $\mathcal{D}$ are the Hilbert space dimensions of the subsystem and the system, respectively. Hence, typical pure states are (nearly) maximally entangled. We develop tools to compute the average entanglement entropy $⟨S⟩$ of all eigenstates of quadratic fermionic Hamiltonians. In particular, we derive exact bounds for the most general translationally invariant models $\ln {\mathcal{D}}_{\mathrm{A}}-(\ln {\mathcal{D}}_{\mathrm{A}}{)}^2/\ln \mathcal{D}\le ⟨S⟩\le \ln {\mathcal{D}}_{\mathrm{A}}-[1/(2\ln 2)](\ln {\mathcal{D}}_{\mathrm{A}}{)}^2/\ln \mathcal{D}$. Consequently, we prove that (i) if the subsystem size is a finite fraction of the system size, then $⟨S⟩<\ln {\mathcal{D}}_{\mathrm{A}}$ in the thermodynamic limit; i.e., the average over eigenstates of the Hamiltonian departs from the result for typical pure states, and (ii) in the limit in which the subsystem size is a vanishing fraction of the system size, the average entanglement entropy is maximal; i.e., typical eigenstates of such Hamiltonians exhibit eigenstate thermalization.

Nonergodic dynamical systems display anomalous transport properties. Prominent examples are integrable quantum systems, whose exceptional properties are diverging dc conductivities. In this Letter, we explain the microscopic origin of ideal conductivity by resorting to the thermodynamic particle content of a system. Using group-theoretic arguments we rigorously resolve the long-standing controversy regarding the nature of spin and charge Drude weights in the absence of chemical potentials. In addition, by employing a hydrodynamic description, we devise an efficient computational method to calculate exact Drude weights from the stationary currents generated in an inhomogeneous quench from bipartitioned initial states. We exemplify the method on the anisotropic Heisenberg model at finite temperatures for the entire range of anisotropies, accessing regimes that are out of reach with other approaches. Quite remarkably, spin Drude weight and asymptotic spin current rates reveal a completely discontinuous (fractal) dependence on the anisotropy parameter.

The phase transition responsible for axion dark matter (DM) production can create large amplitude isocurvature perturbations, which collapse into dense objects known as axion miniclusters. We use microlensing data from the EROS survey and from recent observations with the Subaru Hyper Suprime Cam to place constraints on the minicluster scenario. We compute the microlensing event rate for miniclusters, treating them as spatially extended objects. Using the published bounds on the number of microlensing events, we bound the fraction of DM collapsed into miniclusters $f_{\mathrm{MC}}$. For an axion with temperature-dependent mass consistent with the QCD axion, we find $f_{\mathrm{MC}}<0.083(m_a/100\mu \mathrm{eV}{)}^{0.12}$, which represents the first observational constraint on the minicluster fraction. We forecast that a high-efficiency observation of around ten nights with Subaru would be sufficient to constrain $f_{\mathrm{MC}}\lesssim 0.004$ over the entire QCD axion mass range. We make various approximations to derive these constraints, and dedicated analyses by the observing teams of EROS and Subaru are necessary to confirm our results. If accurate theoretical predictions for $f_{\mathrm{MC}}$ can be made in the future, then microlensing can be used to exclude or discover the QCD axion. Further details of our computations are presented in a companion paper [M. Fairbairn, D. J. E. Marsh, J. Quevillon, and S. Rozier (to be published)].

Continuous symmetry breaking (CSB) in low-dimensional systems, forbidden by the Mermin-Wagner theorem for short-range interactions, may take place in the presence of slowly decaying long-range interactions. Nevertheless, there is no stringent bound on how slowly interactions should decay to give rise to CSB in 1D quantum systems at zero temperature. Here, we study a long-range interacting spin chain with $U(1)$ symmetry and power-law interactions $V(r)\sim 1/r^{\alpha }$. Using a number of analytical and numerical techniques, we find CSB for $\alpha$ smaller than a critical exponent ${\alpha }_c(\le 3)$ that depends on the microscopic parameters of the model. Furthermore, the transition from the gapless $XY$ phase to the gapless CSB phase is mediated by the breaking of conformal and Lorentz symmetries due to long-range interactions, and is described by a universality class akin to, but distinct from, the Berezinskii-Kosterlitz-Thouless transition. Signatures of the CSB phase should be accessible in existing trapped-ion experiments.

We report the first observation of an excited quadrupole-bound state (QBS) in an anion. High-resolution photoelectron imaging of cryogenically cooled 4-cyanophenoxide ($4{\mathrm{CP}}^{-}$) anions yields an electron detachment threshold of $24927{\mathrm{cm}}^{-1}$. The photodetachment spectrum reveals a resonant transition $20{\mathrm{cm}}^{-1}$ below the detachment threshold, which is attributed to an excited QBS of $4{\mathrm{CP}}^{-}$ because neutral 4CP has a large quadrupole moment with a negligible dipole moment. The QBS is confirmed by observation of seventeen above-threshold resonances due to autodetachment from vibrational levels of the QBS.

Here we show that, in single perovskite ${\mathrm{CsPbI}}_3$ nanocrystals synthesized from a colloidal approach, a bright-exciton fine-structure splitting as large as hundreds of $\mu \mathrm{eV}$ can be resolved with two orthogonally and linearly polarized photoluminescence peaks. This doublet could switch to a single peak when a single ${\mathrm{CsPbI}}_3$ nanocrystal is photocharged to eliminate the electron-hole exchange interaction. The above findings have prepared an efficient platform suitable for probing exciton and spin dynamics of semiconductor nanostructures at the visible-wavelength range, from which a variety of practical applications such as in entangled photon-pair source and quantum information processing can be envisioned.

The emergence of structure through aggregation is a fascinating topic and of both fundamental and practical interest. Here we demonstrate that self-generated solvent flow can be used to generate long-range attractions on the colloidal scale, with subpiconewton forces extending into the millimeter range. We observe a rich dynamic behavior with the formation and fusion of small clusters resembling molecules. The dynamics of this assembly is governed by an effective conservative energy that for large separations $r$ decays as $1/r$. Breaking the flow symmetry, these clusters can be made active.

Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic $\mathrm{\Lambda }$ system and quantum erasure of the Raman-photon path information. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for $|{\psi }^{(+)}⟩$ and $|{\psi }^{(-)}⟩$ states of $61.6\pm 2.3\%$ and a record-high entanglement generation rate of 7.3 kHz between distant qubits.

The generalization of the multiscale entanglement renormalization ansatz (MERA) to continuous systems, or cMERA [Haegeman et al., Phys. Rev. Lett. 110, 100402 (2013)], is expected to become a powerful variational ansatz for the ground state of strongly interacting quantum field theories. In this Letter, we investigate, in the simpler context of Gaussian cMERA for free theories, the extent to which the cMERA state $|{\mathrm{\Psi }}^{\mathrm{\Lambda }}⟩$ with finite UV cutoff $\mathrm{\Lambda }$ can capture the spacetime symmetries of the ground state $|\mathrm{\Psi }⟩$. For a free boson conformal field theory (CFT) in $1+1$ dimensions, as a concrete example, we build a quasilocal unitary transformation $V$ that maps $|\mathrm{\Psi }⟩$ into $|{\mathrm{\Psi }}^{\mathrm{\Lambda }}⟩$ and show two main results. (i) Any spacetime symmetry of the ground state $|\mathrm{\Psi }⟩$ is also mapped by $V$ into a spacetime symmetry of the cMERA $|{\mathrm{\Psi }}^{\mathrm{\Lambda }}⟩$. However, while in the CFT, the stress-energy tensor $T_{\mu \nu }(x)$ (in terms of which all the spacetime symmetry generators are expressed) is local, and the corresponding cMERA stress-energy tensor $T_{\mu \nu }^{\mathrm{\Lambda }}(x)=V{T}_{\mu \nu }(x)V^{†}$ is quasilocal. (ii) From the cMERA, we can extract quasilocal scaling operators $O_{\alpha }^{\mathrm{\Lambda }}(x)$ characterized by the exact same scaling dimensions ${\mathrm{\Delta }}_{\alpha }$, conformal spins $s_{\alpha }$, operator product expansion coefficients $C_{\alpha \beta \gamma }$, and central charge $c$ as the original CFT. Finally, we argue that these results should also apply to interacting theories.

Neutral-current production of $K^{+}$ by atmospheric neutrinos is a background in searches for the proton decay $p\to K^{+}\overline{\nu }$. Reactions such as $\nu p\to \nu K^{+}\mathrm{\Lambda }$ are indistinguishable from proton decays when the decay products of the $\mathrm{\Lambda }$ are below detection threshold. Events with $K^{+}$ are identified in MINERvA by reconstructing the timing signature of a $K^{+}$ decay at rest. A sample of 201 neutrino-induced neutral-current $K^{+}$ events is used to measure differential cross sections with respect to the $K^{+}$ kinetic energy, and the non-$K^{+}$ hadronic visible energy. An excess of events at low hadronic visible energy is observed relative to the prediction of the neut event generator. Good agreement is observed with the cross section prediction of the genie generator. A search for photons from ${\pi }^0$ decay, which would veto a neutral-current $K^{+}$ event in a proton decay search, is performed, and a $2\sigma$ deficit of detached photons is observed relative to the genie prediction.

We report the first measurements of the perturbation amplitude in the converging Richtmyer-Meshkov instability in a semiannular shock tube. At early stages, the amplitude growth agrees well with the impulsive model considering the geometrical convergence effect. A quick decrease of the growth rate at late time, even to be negative, before the reshock is observed for the first time. The reduction of the growth rate is ascribed to the Rayleigh-Taylor stabilization caused by the interface deceleration motion only presented in the converging circumstance. By reasonably evaluating the Rayleigh-Taylor stabilization, a modified model based on the Bell equation is proposed, which well predicts the perturbation growth in a converging geometry from early to late stages before the reshock. It is also found that the flow compressibility is significant in the converging Richtmyer-Meshkov instability.