Preserving quantum coherence with the increase of a system's size and complexity is a major challenge. Molecules, with their diverse sizes and complexities and many degrees of freedom, are an excellent platform for studying the transition from quantum to classical behavior. While most quantum-control studies of molecules focus on vibrations and rotations, we focus here on creating a quantum superposition between two nuclear-spin isomers of the same molecule. We present a scheme that exploits an avoided crossing in the spectrum to create strong coupling between two uncoupled nuclear-spin-isomer states, hence creating an isomeric qubit. We model our scheme using a four-level Hamiltonian and explore the coherent dynamics in the different regimes and parameters of our system. Our four-level model and approach can be applied to other systems with a similar energy-level structure.

We study the quantum Hall effect (QHE) in the three-dimensional topological insulator HgTe, which features topological Dirac-type surface states in a bulk gap opened by strain. Despite the coexistence of multiple carrier subsystems, the system exhibits perfectly quantized Hall plateaus at high magnetic fields. Here we study the system using three different experimental techniques: Transport experiments, capacitance measurements including the quantum capacitance, and current distribution measurements using electrostatically sensitive scanning probe microscopy. Our key finding is that at sufficiently high magnetic fields, the different electronic subsystems merge into one, and the current in a quantum Hall plateau is distributed across the entire width of the Hall bar device.

Easy-plane quantum magnets are strikingly similar to superconductors, allowing for spin supercurrent and an effective superconducting phase stemming from their $U\left(1\right)$ rotation symmetry around the $z$ axis. We uncover a generalized fractional Josephson effect with a periodicity that increases linearly with system size in one-dimensional spin-$1/2$ chains at selected anisotropies and phase-fixing boundary fields. The effect combines arbitrary integer periodicities in a single system, exceeding the $4\pi$ and $8\pi$ periodicity of superconducting Josephson effects of Majorana zero modes and other exotic quasiparticles. We reveal a universal energy-phase relation and connect the effect to the recently discovered phantom helices.

A potential phase transition between a normal ground state and a photon-condensed ground state in many-dipole light-matter systems is a topic of considerable controversy, exacerbated by conflicting no-go and counter no-go theorems and often ill-defined models. We contribute to the clarification of this long-lasting debate by analyzing two specific arrangements of atoms, including a three-dimensional cubic lattice and a cavity-embedded square lattice layer—which provides a physical model for single-mode cavity QED with coupled dipoles in the thermodynamic limit. These models are shown to significantly differ from the standard Dicke model and, in the thermodynamic limit, give rise to renormalized Hopfield models. We show that a ferroelectric phase transition can, in principle, still occur and the description of the abnormal phase beyond the critical point requires the inclusion of nonlinear terms in the Holstein-Primakoff mapping. We also demonstrate how our model agrees with recent experiments.

The Grobe-Eberly doublet phenomenon occurs in photoelectron distributions when a field dresses the remaining ion. Its manifestation is due to entanglement between a free electron and a hybrid state of light and matter. Direct detection of such entanglement is however not possible by coincidence schemes due to the dressing mechanism having an inconspicuous phase-correlation effect on the ion. Here, it is shown that odd envelopes fundamentally alter the entanglement, such that channel-resolved photoelectron distributions become identifiable in coincidence with the internal state of the field-free ion. This constitutes a first usage of the parity of time symmetry in strong-field interactions.

Although gut microbiomes exhibit host-specific complexity, it is becoming clear that their dynamics are governed by common rules. In this paper, we empirically show that three key statistical laws—the fat-tailed species abundance distribution, the scaling law of fluctuations, and the tent-shaped log growth rate distribution—are quantitatively universal across humans and mice. We further propose a simple stochastic model that comprehensively reproduces these statistical laws. The model is based on a microscopic model representing the dynamics of each species at local sites on the gut wall, modeled as a random multiplicative process. By introducing coarse-grained time and spatial scales that reflect real-world sampling processes, the model provides a physical interpretation of the dynamic properties of the empirical data, including timescales and temporal stochasticity. Furthermore, incorporation of diffusion effects predicts a heterogeneous spatial distribution on the gut wall. This model serves as a fundamental framework for the unified analysis of the spatiotemporal patterns of the gut microbiome.

Entanglement has been extensively used to characterize the structure of strongly correlated many-body systems. Most of these analyses focus on either spatial properties of entanglement or its temporal behavior. Negativity, as an entanglement measure, quantifies entanglement between different noncomplementary blocks of a many-body system. Here, we consider a combined spatial-temporal analysis of entanglement negativity in a strongly correlated many-body system to characterize complex formation of correlations through nonequilibrium dynamics of such systems. A bond defect is introduced through a local quench at one of the boundaries of a uniform Heisenberg spin chain. Using negativity and entanglement entropy, computed by the time-dependent density-matrix renormalization group, we analyze the extension of entanglement in the model as a function of time. We find that an entanglement cloud is formed, detached from the boundary spin and composed of spins with which it is highly entangled. The cloud travels ballistically in the chain until it reaches the other end where it reflects back and the cycle repeats. The revival dynamics exhibits an intriguing contraction (expansion) of the cloud as it moves away from (towards) the boundary spin.

Magnetized collisionless shocks drive particle acceleration broadly in space and astrophysics. We perform the first large-scale particle-in-cell simulations with realistic laboratory parameters (density, temperature, and velocity) to investigate the magnetized shock and of the associated ion acceleration in head-on colliding plasmas. It is shown that a perpendicular collisionless shock is formed with about fourfold density jump when two plasma flows collide. This shock is also characterized by a rapid increase of neutron yield and alteration of neutron velocity shift with respect to the emitted angle, both of which are prompted by the beam-beam nuclear reactions between upstream injected deuterons and ones reflected by the shock. Distinct from the shocks arising from the interaction of a piston with a magnetized ambient plasma, the self-generated magnetic field in this colliding plasmas experiences a significant amplification due to the intensifying diamagnetic current. Moreover, we find that ions, regardless of whether they pass through or are reflected by the shock, can gain energy by the convective electric field, generating a power-law energy spectrum.

Electronic supercrystals can form in spatial or temporal dimensions where traditional mechanisms usually require many-body interactions, such as Wigner crystals or discrete time crystals. We propose an approach for electronic supercrystals in $1+1\text{D}$ without requiring many-body interactions, but arising from the competition between characteristic space-time areas in periodically driven Su-Schrieffer-Heeger lattices under electric fields. Utilizing the non-Abelian dynamical symmetries described by the electric translation group, the area competition is characterized by fractal spectra and replicated bands, furnished with eigenstates crystallized in enlarged space-time unit cells forming space-time supercrystals under perturbations. We also report robust dynamical localization of electrons arising from the static topology of the SSH lattice.

Classical information loading is an essential task for many processing quantum algorithms, constituting a cornerstone in the field of quantum machine learning. In particular, the embedding techniques based on Hamiltonian simulation techniques enable the loading of matrices into quantum computers. A representative example of these methods is the Lloyd-Mohseni-Rebentrost (LMR) protocol, which efficiently implements matrix exponentiation when multiple copies of a quantum state are available. However, this is a quite ideal setup, and in a realistic scenario, the copies are limited and the noncloning theorem prevents one from producing more exact copies in order to increase the accuracy of the protocol. Here, we propose a method to circumvent this limitation by introducing imperfect quantum copies, which significantly improve the performance of the LMR when the eigenvectors are known.

Nonunitary state preparation protocols such as imaginary time evolution (ITE) offer substantial advantages relative to unitary ones, including the ability to prepare certain long-range correlated states more efficiently. Here, we ask whether such protocols are also robust to noise arising due to coupling to the environment. We consider a nonunitary ITE “circuit” subjected to a variety of noise models and investigate whether the resulting steady state remains in the same phase as the target state of the ITE at finite noise strength. Taking the one-dimensional quantum Ising model as a concrete example, we find that the ground-state order and associated phase transition persist in the presence of noise, provided the noise does not explicitly break the symmetry that protects the phase transition. That is, the noise must possess the protecting symmetry in a weak (or average) form. Our analysis is facilitated by a mapping to an effective Hamiltonian picture in a doubled Hilbert space. We discuss possible implications of these findings for quantum simulation on noisy quantum hardware.

We introduce a control scheme able to steer the evolution of networked reaction-diffusion systems toward any intended dynamics. Specifically, we consider simplicial complexes of reaction-diffusion systems that can be collapsed into weighted complex networks by leveraging the linear relationship between the Laplacian matrix of the simplicial complex and the Laplacian matrix of each order simplex. The method integrates reaction and network-based diffusion controls and, as far as effectiveness and cost are concerned, features a significantly improved performance over traditional single-variable control methods. Numerical simulations using the FitzHugh-Nagumo and susceptible-infected-removed models demonstrate the resilience of the proposed mixed control across diverse systems, highlighting the potential of the method for complex system management and intervention strategies.

This work aims at exploring whether the nonlocal correlations due to quantum entanglement could exist without nonlocal causation. This is done with the aid of a toy model to investigate whether the ability of two quantum entangled particles to “correlate” their behaviors even at very large distances and in the absence of any physical connection can be seen as due to an exchange of information through an extra-temporal dimension. Since superluminal information exchange is forbidden in our (3,1) spacetime, an extra-temporal dimension is needed to recover the physical picture of finite velocity information exchange between entangled entities. Assuming that the geometry of spacetime of dimension (3,2) is described by a metric containing a warping factor, the confinement of the massive particles in the extra time dimension follows. Therefore why we do not experience an infinitely large extra time dimension can be explained. The toy model proposed here is defined by borrowing Bohm-Bub's proposal to describe the wave function collapse using nonlinear (nonunitary) dynamical equations and then elaborating this approach for an entangled system. The model thus obtained aims to be a first step into unexplored territory, certainly a model that can be improved, but which already satisfies the purpose of giving the possibility to the hypotheses formulated above to be experimentally verified. The required experimental test has to resort to an unusual experiment which would otherwise be immediately dismissed as manifestly trivial. The proposed experiment would consist of checking the possible violation of Bell's inequality between two identical but independent systems under appropriate conditions. Beyond its theoretical interest, entanglement is a key topic in quantum computing and quantum technologies, so any attempt to gain a deeper understanding of it could be useful.