When the interactions are scale invariant, the quantum dynamics of a quantum gas are strongly constrained by a resultant conformal symmetry. In this Letter we study the expansion dynamics of strongly interacting quantum systems in a shallow harmonic trap in one and three spatial dimensions while interparticle interactions break the scale symmetry explicitly. Our main finding is that in one dimension the dynamics can be strongly constrained by an emergent infrared conformal dynamics (EIRCD) which significantly reduces entropy production, as opposed to three dimensions where there is no EIRCD in the strong coupling limit. We investigate the possibility and signatures of EIRCD in terms of the damping rate of the large amplitude oscillations of the gas, as well as the work done following a two-quench protocol. We find that the damping and the work done are constrained by the EIRCD, and become vanishingly small in the infrared limit when the final harmonic trap frequency is small. Our analysis is based on a close connection between the renormalization group equation flow and expansion dynamics in real space, and as such can be readily applied to a wide range of strongly interacting systems, like one-dimensional (1D) quantum gases and the three-dimensional (3D) unitary Fermi gas.

We explain why and numerically confirm that there are no barren plateaus in the energy optimization of isometric tensor network states (TNS) for extensive Hamiltonians with finite-range interactions, which are, for example, typical in condensed matter physics. Specifically, we consider matrix product states (MPS) with open boundary conditions, tree tensor network states (TTNS), and the multiscale entanglement renormalization ansatz (MERA). MERA are isometric by construction, and for the MPS and TTNS, the tensor network gauge freedom allows us to choose all tensors as partial isometries. The variance of the energy gradient, evaluated by taking the Haar average over the TNS tensors, has a leading system-size independent term and decreases according to a power law in the bond dimension. For a hierarchical TNS (TTNS and MERA) with branching ratio $b$, the variance of the gradient with respect to a tensor in layer $\tau$ scales as ${\left(b\eta \right)}^{\tau }$, where $\eta$ is the second largest eigenvalue of a Haar-average doubled layer-transition channel and decreases algebraically with increasing bond dimension. The absence of barren plateaus substantiates that isometric TNS are a promising route for an efficient quantum-computation-based investigation of strongly correlated quantum matter. The observed scaling properties of the gradient amplitudes bear implications for efficient TNS initialization procedures.

We study an unconventional many-body phase, i.e., a chiral odd-Chern-number lattice supersolid (CLSS) state, in a single-component Rydberg-dressed Fermi gas in an optical lattice. We find that in such a CLSS state, contradicting the common sense that typically the density modulation [charge-density-wave (CDW)] and superfluid (SF) orders compete against each other, there is an essentially different interplay between the coexisting two types of orders. The CDW order not only abnormally enhances the coexisting SF, but also provides a scheme to tune the topology of SS through changing the winding of the phase of SF order along the CDW-modified Fermi surface. It thus can support multiple number-tunable chiral Majorana fermions. We develop a scheme of designing the specially spatial dependence of the effective Rydberg-dressed interaction, which turns out to induce an unveiled odd-Chern-number lattice supersolid state confirmed by both mean-field and Monte Carlo calculations. The result may provide an alternative way for manipulating the chiral Majorana fermions, which would be useful in topological quantum computation.

We investigate pattern formation in two-dimensional Bose-Einstein condensates (BECs) caused by periodic driving of the interatomic interaction. We show that this modulation generically leads to a stable square grid density pattern, due to nonlinear effects beyond the initial Faraday instability. We take the amplitudes of two waves parametrizing the two-dimensional density pattern as order parameters in pattern formation. For these amplitudes, we derive a set of coupled time-evolution equations from the Gross-Pitaevskii equation with a time-periodic interaction. We identify the fixed points of the time evolution and show by stability analysis that the inhomogeneous density exhibits a square grid pattern, which can be understood as a manifestation of a stable fixed point. Our stability analysis establishes the pattern in BECs as a nonequilibrium steady state.

Generating nonclassical states of mechanical systems is a challenge relevant for testing the foundations of quantum mechanics and developing quantum technologies. Significant effort has been made to search for such states in the stationary behavior of cavity optomechanical systems. We focus instead on the transient dynamics. We find that in the single-photon strong-coupling regime the presence of an optical drive causes an initial mechanical coherent state to evolve to a nonclassical state, with a strongly negative Wigner function. An analytical treatment for a weak drive reveals that these states are quantum superpositions of coherent states. A numerical simulation shows that the presence of Wigner negativity is robust against weak dissipation.

We discuss how quantum jumps affect localized regimes in driven-dissipative disordered many-body systems featuring a localization transition. We introduce a deformation of the Lindblad master equation that interpolates between the standard Lindblad and the no-jump non-Hermitian dynamics of open quantum systems. As a platform, we use a disordered chain of hard-core bosons with nearest-neighbor interactions and subject to incoherent drive and dissipation at alternate sites. We probe both the statistics of complex eigenvalues of the deformed Liouvillian and dynamical observables of physical relevance. We show that reducing the number of quantum jumps, achievable through realistic postselection protocols, can promote the emergence of the localized phase. Our findings are based on exact diagonalization and time-dependent matrix-product state techniques.

The use of ancillary quantum systems known as catalysts is known to be able to enhance the capabilities of entanglement transformations under local operations and classical communication. However, the limits of these advantages have not been determined and in particular it is not known if such assistance can overcome the known restrictions on asymptotic transformation rates—notably the existence of bound entangled (undistillable) states. Here we establish a general limitation on entanglement catalysis: we show that catalytic transformations can never allow for the distillation of entanglement from a bound entangled state with positive partial transpose, even if the catalyst may become correlated with the system of interest and even under permissive choices of free operations. This precludes the possibility that catalysis may make entanglement theory asymptotically reversible. Our methods are based on asymptotic bounds for the distillable entanglement and entanglement cost assisted by correlated catalysts.

We perform spin-noise spectroscopy on an unpolarized ${}^{87}\mathrm{Rb}$ vapor in the spin-exchange-relaxation-free (SERF) regime. We observe noise spectral distributions that deviate strongly from Lorentzian models that accurately describe lower-density regimes. For example, at magnetic fields of $\sim 1 \mu \mathrm{T}$ and ${}^{87}\mathrm{Rb}$ densities of $\gtrsim 1\times {10}^{14}$ atoms/${\mathrm{cm}}^3$ we observe an asymmetric spin-noise distribution in which the resonance line is depleted by about half its power, with the diverted power becoming a broad spectral component that could be mistaken for optical shot noise. The results are in good agreement with recent models accounting for correlations between the ground hyperfine states. We discuss implications for quantum sensing and absolute noise calibration in spin squeezing and entanglement detection. The results suggest similarly anomalous spectra for other noise spectroscopies, when noise mechanisms are not aligned with system dynamics.

Fast and high-fidelity qubit measurement is essential for realizing quantum error correction, a key ingredient to universal quantum computing. For electron spin qubits, fast readout is one of the significant challenges toward error correction. Here we examine the dispersive readout of a single spin in a semiconductor double quantum dot coupled to a microwave resonator. We show that using displaced squeezed vacuum states for the probing photons can improve the qubit readout fidelity and speed. With proper phase matching, moderate squeezing can enhance both the signal-to-noise ratio and the fidelity of the qubit readout, and the optimal readout time can be shortened to the submicrosecond range with above $97\%$ fidelity. These enhancements are achieved at low probing microwave intensity, ensuring nondemolition qubit measurement.

We revisit the study of amplitude oscillations in a pair condensate of fermions after an interaction quench, and generalize it to nonzero temperature. For small variations of the order parameter, we show that the energy transfer during the quench determines both the asymptotic pseudoequilibrated value of the order parameter and the magnitude of the oscillations, after multiplication by, respectively, the static response of the order parameter and spectral weight of the pair-breaking threshold. Since the energy transferred to the condensed pairs decreases with temperature as the superfluid contact, the oscillations eventually disappear at the critical temperature. For deeper quenches, we generalize the regimes of persistent oscillations and monotonic decay to nonzero temperatures, and explain how they become more abrupt and are more easily entered at high temperatures when the ratio of the initial to final gap either diverges, when quenching toward the normal phase, or tends to zero, when quenching toward the superfluid phase. Our results are directly relevant for existing and future experiments on the nonequilibrium evolution of Fermi superfluids near the phase transition.

Nonstabilizerness, also colloquially referred to as magic, is a resource for advantage in quantum computing and lies in the access to non-Clifford operations. Developing a comprehensive understanding of how nonstabilizerness can be quantified and how it relates to other quantum resources is crucial for studying and characterizing the origin of quantum complexity. In this work, we establish a direct connection between nonstabilizerness and entanglement spectrum flatness for a pure quantum state. We show that this connection can be exploited to efficiently probe nonstabilizerness even in the presence of noise. Our results reveal a direct connection between nonstabilizerness and entanglement response, and define a clear experimental protocol to probe nonstabilizerness in cold atom and solid-state platforms.

Positron binding energies in halogenated hydrocarbons are calculated ab initio using many-body theory. For chlorinated molecules, including planars for which the interaction is highly anisotropic, very good to excellent agreement with experiment and recent density-functional-theory-based model-potential calculations is found. Predictions for fluorinated and brominated molecules are presented. The comparative effect of fluorination, chlorination, and bromination is elucidated by identifying trends within molecular families including dihaloethylenes and halomethanes based on global molecular properties (dipole moment, polarizability, ionization energy). It is shown that relative to brominated and chlorinated molecules, fluorinated molecules generate a less attractive positron-molecule potential due to larger ionization energies and smaller density of molecular orbitals close to the highest occupied molecular orbital, resulting in very weak, or in most cases loss of, positron binding. Overall, however, it is shown that the global molecular properties are not universal predictors of binding energies, exemplified by consideration of ${\mathrm{CH}}_3\mathrm{Cl}$ vs cis-${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{F}}_2$: Despite the latter having a larger dipole moment, lower ionization energy, and similar polarizability, its binding energy is significantly smaller (25 vs 3 meV, respectively), owing to the important contribution of multiple molecular orbitals to, and the anisotropy of, the positron-molecule correlation potential.

Quantum jumps induced by gain and loss have different quantum behaviors in non-Hermitian photonics. However, the jump effect on global quantum $\mathcal{PT}$ properties has not been comprehensively understood yet. Here, with considering quantum jump of loss and gain in a photonic dimer structure, we analytically obtained the $\mathcal{PT}$-phase diagram under the steady-state condition and defined a Hermitian exchange operator to characterize the $\mathcal{PT}$-symmetry or -broken phase. When we input Fock states into a $\mathcal{PT}$-broken bi-waveguide splitting system, most photons will concentrate in the dominant waveguide with some state distributions. Especially in Hong-Ou-Mandel interferences, if gain is added, whether loss exists or not, $g^{\left(2\right)}$ is always larger than zero because loss cannot compensate gain as their different quantum jump effects. The quantum $\mathcal{PT}$-phase diagram paves the way to the quantum state engineering, quantum interferences, and logic operations in non-Hermitian photonic systems.

We study a system tuned to an absorbing exceptional point and explore its use to efficiently receive and store an incoming wave with an envelope different from the absorbing-eigenmode envelope. Specifically, while absorbing states of lossless resonators have an exponentially increasing envelope, we focus on capturing naturally emitted waves with an exponentially decreasing envelope. We find that, when tuning a cavity to an $n\mathrm{th}$-order absorbing exceptional point (EP), $n+1$ temporal orders of any incoming waveform can be perfectly captured, leading to significantly less scattering and increasing the overall absorption efficiency for general waveforms. We present an approach to tune a cavity to an EP and demonstrate less scattering by an order of magnitude for a decaying incoming waveform. Our results may be used for efficient passive state transfer and detection of spontaneous emission.

In any known description of nature, two physical systems are considered independent of each other if any action on one of the systems does not change the other system. From our classical intuitions about the world, we further conclude that these two systems are not affecting each other in any possible way, and thus these two systems are causally disconnected or they do not influence each other. Building on this idea, we show that in quantum theory such a notion of “classical independence” is not satisfied, that is, two quantum systems can still influence each other even if any operation on one of the systems does not create an observable effect on the other. For our purpose, we consider the framework of quantum networks and construct a linear witness utilizing the Clauser-Horne-Shimony-Holt inequality. We also discuss one of the interesting applications resulting from the maximal violation of classical independence towards device-independent certification of quantum states and measurements.

We propose a spectral-averaging procedure that enables the computation of bandwidth-integrated local density of states (LDOS) from a single scattering calculation, and exploit it to investigate the minimum extinction achievable from dipolar sources over nonzero bandwidths in structured media. Structure-agnostic extinction bounds are derived, providing analytical insights into scaling laws and fundamental design tradeoffs with implications to bandwidth and material selection. We find that perfect LDOS suppression over a nonzero bandwidth $\mathrm{\Delta }\omega$ is impossible. Inspired by limits which predict nontrivial $\sqrt{\mathrm{\Delta }\omega }$ scaling in systems with material dissipation, we show that the pseudogap edge states of quasi-one-dimensional bullseye gratings can—by simultaneously minimizing material absorption and radiation—yield arbitrarily close to perfect LDOS suppression in the limit of vanishing bandwidth.

We employ two-band density-matrix equations and time-dependent density-functional theory to calculate high-order harmonic generation (HHG) in graphene under femtosecond laser irradiation. Our investigation uncovers a striking harmonic enhancement structure (HES) in the HHG spectrum. We find that the HES is associated with the bunching of multiple interband electron-hole recombination trajectories, in analogy to the focusing behavior of the light rays known as caustics. In contrast to the atom situation, where the caustic effects are confined to a narrow energy regime around the HHG cutoff energy, for graphene, the caustic effects can dominate the entire interband harmonic generation regime. The magnitude of enhancement is significant and can be estimated to be on the order of $\sim N^{2/3}$, with $N$ representing the harmonic order, according to catastrophe theory.

We study transverse spin dynamics on a microscopic level by measuring energy-resolved spin correlations in weakly interacting Fermi gases (WIFGs). The trapped cloud behaves as a many-body spin lattice in energy space with effective long-range interactions, simulating a collective Heisenberg model. We observe the flow of correlations in energy space in this quasi-continuous system, revealing the connection between the evolution of the magnetization and the localization or spread of correlations. This work highlights energy-space correlation as an observable in quantum phase transition studies of WIFGs, decoding system features that are hidden in macroscopic measurements.

Nonlinear interference in the interaction of intense laser pulses with atoms profoundly affects the photoelectron momentum distribution (PMD). We theoretically show that the interference pattern in the PMD arises from the interaction of electrons with the fundamental frequencies concealed within the pulse. Nonlinear interference also imprints distinctive features on the ionization spectrum, providing valuable information about electron dynamics and phase relationships within the laser pulse. Additionally, the augmentation of optical cycles induces a distinct confinement in the PMD.

We argue that it is nonstationary Laguerre-Gaussian (NSLG) states rather than the Landau ones that appropriately describe electrons with orbital angular momentum both in their dynamics at the boundary between a solenoid and vacuum and inside the magnetic field. It is shown that the root mean square (rms) radius of the NSLG state oscillates in time and its period-averaged value can significantly exceed the rms radius of the stationary Landau state. We propose several experimental scenarios to probe this unconventional quantum dynamics in the magnetic fields typical for electron microscopes and particle accelerators.