At supranuclear densities, explored in the core of neutron stars, a strong phase transition from hadronic matter to more exotic forms of matter might be present. To test this hypothesis, binary neutron-star mergers offer a unique possibility to probe matter at densities that we cannot create in any existing terrestrial experiment. In this work, we show that, if present, strong phase transitions can have a measurable imprint on the binary neutron-star coalescence and the emitted gravitational-wave signal. We construct a new parametrization of the supranuclear equation of state that allows us to test for the existence of a strong phase transition and extract its characteristic properties purely from the gravitational-wave signal of the inspiraling neutron stars. We test our approach using a Bayesian inference study simulating 600 signals with three different equations of state and find that for current gravitational-wave detector networks already 12 events might be sufficient to verify the presence of a strong phase transition. Finally, we use our methodology to analyze GW170817 and GW190425 but do not find any indication that a strong phase transition is present at densities probed during the inspiral.

In the quantum Zeno effect, quantum measurements can block the coherent oscillation of a two level system by freezing its state to one of the measurement eigenstates. The effect is conventionally controlled by the measurement frequency. Here we study the development of the Zeno regime as a function of the measurement strength for a continuous partial measurement. We show that the onset of the Zeno regime is marked by a cascade of transitions in the system dynamics as the measurement strength is increased. Some of these transitions are only apparent in the collective behavior of individual quantum trajectories and are invisible to the average dynamics. They include the appearance of a region of dynamically inaccessible states and of singularities in the steady-state probability distribution of states. These predicted dynamical features, which can be readily observed in current experiments, show the coexistence of fundamentally unpredictable quantum jumps with those continuously monitored and reverted in recent experiments.

Weyl metals host relativistic chiral quasiparticles, which display quantum anomalies in the presence of external electromagnetic fields. Here, we study the manifestations of chiral anomalies in the longitudinal and planar magnetotransport coefficients of Weyl metals, in the presence of a quantizing magnetic field. We present a general framework for calculating all the transport coefficients in the regime where multiple Landau levels are occupied. We explicitly show that all the longitudinal and planar transport coefficients show quantum oscillations which are periodic in $1/B$. Our calculations recover the quadratic-$B$ dependence in the semiclassical regime and predict a linear-$B$ dependence in the ultraquantum limit for all the transport coefficients.

Linear-in-wave-vector $K$ terms of an electron Hamiltonian play an important role in topological insulators and spintronic devices. Here we demonstrate how an external electric field can control the magnitude of a linear-in-$K$ term in the exciton Hamiltonian. The effect of the electric field on interference of exciton polaritons in a high-quality structure with a wide GaAs quantum well was experimentally studied by means of the differential reflection spectroscopy. It is found that the interference pattern is strongly suppressed at certain electric field and then it is reinstalled, but with an inverted phase, at the further increase of the field. This behavior of the pattern is successfully explained by the electric-field-induced linear-in-$K$ terms in the Hamiltonian of the exciton propagating across the quantum well. An excellent agreement between the experimental data and the results of calculations using semiclassical nonlocal dielectric response model confirms the validity of the method and paves the way for the realization of excitonic Datta-Das transistors. In full analogy with the spin-orbit transistor proposed by Datta and Das [Appl. Phys. Lett. 56, 665 (1990)], the switch between positive and negative interference of exciton polaritons propagating forward and backward in a GaAs film is achieved by application of an electric field having a nonzero component in the plane of the quantum well layer.

We propose to generate localized artificial magnetic fields using two thin Raman laser beams intersected at a narrow region of a two-leg ladder, where the frequency difference must approximately match the energy offset between the two legs. Based on this method, we investigate the single-atom transport in a two-leg ladder with only two rungs, which, together with the legs, enclose a localized artificial magnetic flux. Here, the atoms on the two legs (channels) possess different onsite energies that produce another energy offset. We find that the atom incoming from the left channel can experience from blockade to transparency via modifying the onsite energy, tunneling strength, or magnetic flux, which can be potentially used for a quantum switcher. Furthermore, the atom incoming from the left channel can also be perfectly routed into the right leg, when, intriguingly, the outgoing atom in the right channel possesses a quasimomentum that can be modulated by the magnetic flux. The result may be potentially used for the interface that controls the communication between two individual quantum devices of cold atoms. The method can also be generalized to other artificial quantum systems, such as superconducting quantum circuit systems, optical systems, etc.

Neutron scattering, specific-heat, and magnetization measurements on both powders and single crystals reveal that ${\mathrm{Dy}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ realizes the fragmented monopole crystal state in which antiferromagnetic order and a Coulomb phase spin liquid coinhabit. The measured residual entropy is that of a hard-core dimer liquid, as predicted. Inclusion of Coulomb interactions allows for a quantitative description of both the thermodynamic data and the magnetization dynamics, with the energy scale given by deconfined defects in the emergent ionic crystal. Our data reveal low-energy excitations, as well as a large distribution of energy barriers down to low temperatures, while the magnetic response to an applied field suggests that domain wall pinning is important, results that call for further theoretical modeling.

The anisotropy and magnetic ground state of hyperkagome dysprosium gallium garnet ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ are investigated, along with that of its closest structural analog and archetypal Ising multiaxis antiferromagnet, dysprosium aluminum garnet ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, using a combination of neutron scattering techniques, including polarized neutron powder diffraction. Results show a dramatic change from an Ising-like anisotropy in ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, to a quasiplanar one in ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$. According to a point charge modeling, this is due to small variations of the oxygen positions surrounding ${\mathrm{Dy}}^{3+}$ ions. The magnetic ground state of ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ is investigated for the first time and is found to be similar to that of ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, yet with a much lower $T_{\mathrm{N}}$. Mean-field calculations show that the dipolar interaction favors distinct magnetic ground states, depending on the anisotropy tensor: a multiaxis antiferromagnetic state is favored in the case of strong Ising-like anisotropy, like in ${\mathrm{Dy}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$, whereas a complex ferrimagnetic state is stabilized in the case of planar anisotropy. The ${\mathrm{Dy}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ crystal field parameters locate the latter close to the boundary between those two ground states, which, alongside competition between dipolar and a small but finite magnetic exchange, may explain its low $T_{\mathrm{N}}$. To widen the scope of these experimental results, we performed mean-field calculations to generate the magnetic phase diagram of an effective anisotropic pseudospin $S=1/2$, characterized by general $g_{xx}$, $g_{yy}$, and $g_{zz}$ Landé factors. A very rich magnetic phase diagram, encompassing complex phases, likely disordered, is evidenced when magnetic anisotropy departs from the strong Ising case. With magnetic anisotropy being controllable through appropriate tuning of the rare-earth oxygen environment, these results emphasize the potential of rare-earth hyperkagome networks for the exploration of new magnetic phases.

We propose a definition of externally measurable quantum work in driven systems. Work is given as a quantum observable on a control device which is forcing the system and can be determined without knowledge of the system Hamiltonian ${\widehat{H}}_{\mathcal{S}}$. We argue that quantum work fluctuation theorems which rely on the knowledge of ${\widehat{H}}_{\mathcal{S}}$ are of little practical relevance, contrary to their classical counterparts. Using our framework, we derive a fluctuation theorem which is operationally accessible and could in principle be implemented in experiments to determine bounds on free energy differences of unknown systems.

The main feature of amorphous materials is the presence of excess vibrational modes at low energies, giving rise to the so-called “boson peak” in neutron and optical spectroscopies. These same modes manifest themselves as two-level systems (TLSs) causing noise and decoherence in qubits and other sensitive devices. Here, we present an experiment that uses the spin relaxation of dangling bonds at the $\mathrm{Si}/\left(\mathrm{amorphous}\right){\mathrm{SiO}}_2$ interface as a probe of TLSs. We introduce a model that is able to explain the observed nonexponential electron spin inversion recovery and provides a measure of the degree of spatial localization and concentration of the TLSs close to the interface, their maximum energy, and its temperature dependence.

We theoretically study the structure of a stationary soliton in the polar phase of spin-1 Bose–Einstein condensate in the presence of quadratic Zeeman effect at zero temperature. The phase diagram of such solitons is mapped out by finding the states of minimal soliton energy in the defining range of polar phase. The states are assorted into normal, antiferromagnetic, broken-axisymmetry, and ferromagnetic phases according to the particle and spin densities in the core. The order of phase transitions between different solitons and the critical behavior of relevant continuous transitions are proved within the mean-field theory.

We present a method for calculating Rényi entanglement entropies for fermionic field theories originating from microscopic Hamiltonians. The method builds on an operator identity, which leads to the representation of traces of operator products, and thus Rényi entropies of a subsystem, in terms of fermionic-displacement operators. This allows for a very transparent path-integral formulation, both in and out of equilibrium, having a simple boundary condition on the fermionic fields. The method is validated by reproducing well-known expressions for entanglement entropy in terms of the correlation matrix for noninteracting fermions. We demonstrate the effectiveness of the method by explicitly formulating the field theory for Rényi entropy in a few zero- and higher dimensional large-$N$ interacting models akin to the Sachdev-Ye-Kitaev (SYK) model and for the Hubbard model within the dynamical mean field theory (DMFT) approximation. We use the formulation to compute Rényi entanglement entropy of interacting Fermi liquid (FL) and non-Fermi liquid (NFL) states in the large-$N$ models and compare the results successfully with those obtained via exact diagonalization for finite $N$. We elucidate the connection between Rényi entanglement entropy and residual entropy of the NFL ground state in the SYK model and extract sharp signatures of quantum phase transition in the entanglement entropy across an NFL to FL transition. Furthermore, we employ the method to obtain nontrivial system-size scaling of entanglement in an interacting diffusive metal described by a chain of SYK dots.

The states generated by the two-spin generalization of the two-axis countertwisting Hamiltonian are examined. We analyze the behavior at both short and long timescales, by calculating various quantities such as squeezing, spin expectation values, probability distributions, entanglement, Wigner functions, and Bell correlations. In the limit of large spin ensembles and short interaction times, the state can be described by a two-mode squeezed vacuum state; for qubits, Bell state entanglement is produced. We find that the Hamiltonian approximately produces two types of spin Einstein-Podolsky-Rosen (EPR) states, and the time evolution produces aperiodic oscillations between them. In a similar way to the basis invariance of Bell states and two-mode squeezed vacuum states, the Fock state correlations of spin EPR states are basis invariant. We find that it is possible to violate a Bell inequality with such states, although the violation diminishes with increasing ensemble size. Effective methods to detect entanglement are also proposed, and formulas for the optimal times to enhance various properties are calculated.

The orbital degree of freedom of electrons greatly influences the physical properties of materials such as magnetic order and unconventional superconductivity. An orbital is a minimal unit of “shape,” and the orbital state can be unraveled by observing the spatial anisotropic distribution of electrons. However, it is difficult to experimentally extract the orbital information in a crystal because of various technical problems. Here, the $\mathrm{Ti}\text{−}3d$ orbital state in perovskite-type oxides $R\mathrm{Ti}{\mathrm{O}}_3$ ($R=\mathrm{Y}$, Sm, and La) is directly determined by a core differential Fourier synthesis (CDFS) method using synchrotron x-ray diffraction. The valence electron-density distribution, including information on the anisotropy and the hybridization between atomic orbitals, can be extracted from the CDFS analysis. Our study not only demonstrates the relationship between the magnetic- and orbital-ordered states called the Kugel-Khomskii model, but also provides a nontrivial picture of the orbital state reconstructed by the orbital hybridization.

Electromagnetic pulses (EMP) present a serious threat for operation of high-power, high-energy laser facilities. Here, we present an efficient strategy for EMP mitigation with a resistive and inductive holder, which is supported by extended numerical simulations and validated in dedicated experiments at the kilojoule/picosecond (kJ/ps) Petawatt Aquitaine Laser (PETAL) facility. Moreover, we demonstrate how a combination of PETAL with the tens of kJ/ns Laser MegaJoule (LMJ) beams may suppress the EMP emission. This method opens another efficient way for the EMP control on high-power, high-energy laser facilities.

Most of our quantitative understanding of disorder-induced metal-insulator transitions comes from numerical studies of simple noninteracting tight-binding models, like the Anderson model in three dimensions. An important outstanding problem is the fate of the Anderson transition in the presence of additional Hubbard interactions of strength $U$ between particles. Based on large-scale numerics, we compute the position of the mobility edge for a system of two identical bosons or two fermions with opposite spin components. The resulting phase diagram in the interaction-energy-disorder space possesses a remarkably rich and counterintuitive structure, with multiple metallic and insulating phases. We show that this phenomenon originates from the molecular or scatteringlike nature of the pair states available at given energy $E$ and disorder strength $W$. The disorder-averaged density of states of the effective model for the pair is also investigated. Finally, we discuss the implications of our results for ongoing research on many-body localization.

We systematically derive low-energy effective Hamiltonians for molecular solids ${\beta }^{\prime }\text{−}X{\left[\mathrm{Pd}{\left(\mathrm{dmit}\right)}_2\right]}_2$ ($X$ represents a cation) using ab initio density functional theory calculations and clarify how the cation controls the interdimer transfer integrals and the interaction parameters. The effective models are solved using the exact diagonalization method and the antiferromagnetic ordered moment is shown to be significantly suppressed around the spin-liquid candidate of $X=\mathrm{Et}{\mathrm{Me}}_3\mathrm{Sb}$, which is reported in experiments. We also show that both the geometrical frustration and the off-site interactions play essential roles in the suppression of antiferromagnetic ordering. This systematic derivation and analysis of the low-energy effective Hamiltonians offers a firm basis to clarify the nature of the quantum spin liquid found in ${\beta }^{\prime }\text{−}\mathrm{Et}{\mathrm{Me}}_3\mathrm{Sb}{\left[\mathrm{Pd}{\left(\mathrm{dmit}\right)}_2\right]}_2$.

Micron-size charged particles can be easily levitated in low-density plasma environments. At low pressures, suspended particles have been observed to spontaneously oscillate around an equilibrium position. In systems of many particles, these oscillations can catalyze a variety of nonequilibrium, collective behaviors. Here, we report spontaneous oscillations of single particles that remain stable for minutes with striking regularity in amplitude and frequency. The oscillation amplitude can also exceed 1 cm, nearly an order of magnitude larger than previously observed. Using an integrated experimental and numerical approach, we show how the motion of an individual particle can be used to extract the electrostatic force and equilibrium charge variation in the plasma sheath. Additionally, using a delayed-charging model, we are able to accurately capture the nonlinear dynamics of the particle motion, and estimate the particle's equilibrium charging time in the plasma environment.

We introduce interpretable siamese neural networks (SNNs) for similarity detection to the field of theoretical physics. More precisely, we apply SNNs to events in special relativity, the transformation of electromagnetic fields, and the motion of particles in a central potential. In these examples, SNNs learn to identify data points belonging to the same event, field configuration, or trajectory of motion. We demonstrate that in the process of learning which data points belong to the same event or field configuration, these SNNs also learn the relevant symmetry invariants and conserved quantities. Such SNNs are highly interpretable, which enables us to reveal the symmetry invariants and conserved quantities without prior knowledge.

The dimensionality of a thermometer is key in the design of quantum thermometry schemes. In general, the phenomenology that is typical of qubit-based quantum thermometry does not apply to infinite-dimensional ones. We analyze the dynamical and metrological features of nonequilibrium Gaussian quantum thermometers: On one hand, we highlight how quantum entanglement can enhance the readiness of composite Gaussian thermometers; on the other hand, we show that nonequilibrium conditions do not guarantee the best sensitivities in temperature estimation, thus suggesting the reassessment of some of the working principles underpinning quantum thermometry.

Nonequilibrium states of quantum systems in contact with thermal baths help distinguishing between environments with different temperatures or different statistics. We extend these studies to a more generic problem that consists in discriminating between two baths with disparate constituents at unequal temperatures. Notably there exist temperature regimes in which the presence of coherence in the initial state preparation is beneficial for the discrimination capability. We also find that nonequilibrium states are not universally optimal and detail the conditions in which it becomes advantageous to wait for complete thermalization of the probe. These concepts are illustrated in a linear-optical simulation.