We consider the Fermi polaron problem of an impurity hopping around a two-dimensional square lattice and interacting with a sea of fermions at given filling factor. When the interaction is attractive, we find standard Fermi polaron quasiparticles, categorized as attractive polarons and repulsive polarons. When the interaction becomes repulsive, interestingly, we observe an unconventional highly excited polaron quasiparticle, sharply peaked at the corner of the first Brillouin zone with momentum $\mathbf{k}=(\pm \pi ,\pm \pi )$. This super Fermi polaron branch arises from the dressing of the impurity's motion with holes, instead of particles of fermions. We show that super Fermi polarons become increasingly well defined with increasing impurity-fermion repulsions and might be considered as a precursor of Nagaoka ferromagnetism, which would appear at sufficiently large repulsions and at large filling factors. We also investigate the temperature dependence of super Fermi polarons and find that they are thermally robust against the significant increase in temperature.

Electro-optic control of quantum dots embedded in plasmonic nanocavities enables active tuning of photonic devices for emerging applications in quantum optics such as quantum information processing, entanglement, and ultrafast optical switching. Here, we demonstrate the coherent control of plexcitonic states in (i) off-resonant and (ii) resonant coupled quantum systems through the optical Stark effect. We analyze a hybrid plasmon-emitter system which exhibits tunable photoluminescence, Stark-induced transparency, and vacuum Rabi splitting due to a quadratic Stark shift in the degenerate states of a quantum emitter (QE). In addition, a resonantly coupled system shows path interference of hybrid plexcitonic states due to Stark-induced splitting in a two-level QE. Our study shows that the Stark tuning of plexcitons not only mitigates decoherence in the quantum system but it also stimulates the on/off switching of spontaneous photon emission in the visible regime. Such tunable systems can be used to operate photonic integrated circuits for applications in quantum computing and information processing.

Microcavities stand out as competitive tools in the development of quantum frequency combs (QFCs) for multiphoton entanglement sources, frequency-multiplexed single-photon sources, and the generation of high-dimensional entangled states. However, the presence of waveguide dispersion hinders the creation of broadband QFCs, an issue that becomes increasingly critical as the quality factor of the microcavity increases. Here, we present a scheme to enhance the spectral range of QFCs by selectively manipulating the pump resonance via parity-time symmetry. We show that by using pulsed pump light to cover the pump resonance, frequency-matching conditions can be relaxed and the spectral range of QFCs can thus be significantly extended near the exceptional point. The proposed method offers a simple, effective, and robust approach to increase the dimension of QFCs, without severely sacrificing nonlinear efficiency.

We explore the role of exceptional points and complex eigenvalues on the occurrence of the quantum Mpemba effect. To this end, we study a two-level driven dissipative system subjected to an oscillatory electric field and dissipative coupling with the environment. We find that both exceptional points and complex eigenvalues can lead to multiple quantum Mpemba effect. It occurs in an observable when time-evolved copies corresponding to two different initial conditions, one initially having higher observable value compared to the other and both relaxing towards the same steady state, intersect each other more than once during their relaxation process. Each of the intersections denotes a quantum Mpemba effect and marks the reversal of identities between the two copies, i.e., the copy with higher observable value before the intersection becomes the lower-valued copy (and vice versa) after the intersection. Such multiple intersections originate from additional algebraic time dependence at the exceptional points and due to oscillatory relaxation in the case of complex eigenvalues. We provide analytical results for quantum Mpemba effect in the density matrix in presence of coherence. Depending on the control parameters (drive and dissipation), observables such as energy, von Neumann entropy, temperature, etc., exhibit either single or multiple quantum Mpemba effect. However, the distance from steady state measured in terms of the Kullback-Leibler divergence shows only single quantum Mpemba effect although the corresponding speed gives rise to either single or multiple quantum Mpemba effect.

Monitored quantum systems evolve along stochastic trajectories correlated with the observer's knowledge of the system's state. Under such dynamics, certain quantum resources like entanglement may depend on the observer's state of knowledge. Here, we quantify the entanglement for a particle on a one-dimensional (1D) quantum random walk under inefficient monitoring using a mixed state-entanglement measure: the configuration coherence. We find that the system's maximal mean entanglement at the measurement-induced quantum-to-classical crossover is suppressed in different ways by the measurement strength and inefficiency. In principle, strong measurements can lower the amount of entanglement indefinitely. However, at a given measurement strength, efficient readout can crucially increase the system entanglement, making high-fidelity detectors essential for successful quantum computing. Our results bear impact for a broad range of fields, ranging from quantum simulation platforms of random walks to questions related to measurement-induced phase transitions.

Algorithmic cooling (AC) protocols have been predominantly studied for their cooling capabilities, with limited attention paid to their thermodynamic properties. This work explores an alternative perspective by analyzing a broad family of AC protocols from a thermodynamic standpoint. First, we give an in-depth review and formal classification of standard AC protocols. Leveraging the transfer matrix formalism, we achieve a consistent calculation of performance metrics, encompassing both cooling limits and target state evolution. We obtained a unification of these diverse cooling limits into a single, coherent mathematical expression, streamlining comparative analyses. Then, to assess the efficiency of coherent cooling protocols, we introduce two generic metrics: the coefficient of performance $K$ and Landauer's Ratio $R_L$, and establish a direct interrelation. Applying these metrics, we thoroughly evaluate selected AC protocols, highlighting their relative strengths. Finally, we propose improved versions of AC protocols that exhibit enhanced thermodynamic performance, achieving desired target temperatures with lower work inputs. This research contributes to a deeper understanding of AC protocols and provides valuable insights for designing efficient cooling strategies in various applications.

The probability density of a quantum particle moving freely within a circular ring can exhibit local flow patterns inconsistent with its angular momentum, a phenomenon known as quantum backflow. In this study, we examine a quantum particle confined to a ring and prepared in a state composed of a fixed (yet arbitrary) number of lowest-energy eigenstates with nonnegative angular momentum. We investigate the time-dependent behavior of the probability current at a specified point along the ring's circumference. We establish precise lower and upper bounds for this probability current, thereby delineating the exact scope of the quantum backflow effect. We also present an analytical expression for a quantum state that yields a record-high backflow probability transfer, reaching over $95\%$ of the theoretical bound. Furthermore, our investigation yields compelling numerical and analytical evidence supporting the conjecture that the current-versus-time function associated with states maximizing backflow probability transfer forms a fractal curve with a dimension of $7/4$. The observed fractality may provide a characteristic, experimentally relevant signature of quantum backflow near the probability-transfer bound.

We investigate violations of Leggett-Garg inequalities (LGIs) for a harmonic oscillator and a $(1+1)$-dimensional chiral scalar field with coherent-state projectors, which is equivalent to a heterodyne-type measurement scheme. For the harmonic oscillator, we found that the vacuum and thermal states violated the LGIs by evaluating the two-time quasiprobability distribution function. In particular, we demonstrate that the value of the two-time quasiprobability reaches $-0.123$ for a squeezed coherent-state projector, which is equivalent to $98\%$ of the Lüders bound corresponding to the maximal violation of the LGIs. We also find a violation of the LGIs for the local mode of a quantum chiral scalar field by constructing a coherent-state projector similar to the harmonic-oscillator case. In contrast with the harmonic oscillator, the periodicity in the time direction of the quasiprobability disappears, which is related to the existence of quantum entanglement between the local mode and its complementary degrees of freedom.

The symplectic invariance property of the Wigner-Rényi entropies family is used to estimate the interaction time for the propagating Schrödinger cat state that interacts with the periodically changing potential. With the help of this property, the hierarchy of the interaction times is specified for the quantum dynamics of the periodically driven system. It is also demonstrated that the lower and upper bounds of the interaction time are determined by the Wigner-Rényi entropies corresponding to increasing Rényi index values, respectively. The interpretation of the presented results is supported by calculations of the dynamical transmission and capture coefficients, which give a clear insight into the scattering of the non-Gaussian state on the periodically changing potential, which switches between the Gaussian potential barrier and the well.

Quantum simulation of lattice gauge theories is a promising tool for the study of many complicated problems including ones with real-time dynamics. For gauge theories, however, there is a major challenge in maintaining gauge invariance during time evolution. Such theories have a full Hilbert space that is larger than the physical space—the set of states which are gauge invariant or equivalently respect the Gauss law. While an exact implementation of Hamiltonian dynamics starting in the physical Hilbert space will keep the system in the physical space, various types of errors will inevitably produce components outside of it. This work proposes a method of suppressing this gauge drift via the Zeno effect. As in the standard picture of the Zeno effect, our method relies on frequent projection onto the physical subspace. Additionally, a technique is discussed to reduce the speed of the gauge drift, which helps to reduce the required frequency of projections. We demonstrate our method on a ${\mathbb{Z}}_2$ gauge theory toy model.

Topological quantum computation based on Majorana objects is subject to a significant challenge because at least some of the two-qubit quantum gates rely on the fermion (either charge or spin) parity of the qubits. This dependency renders the quantum operations involving these gates probabilistic when attempting to advance quantum processes within the quantum circuit model. Such an approach leads to significant information loss whenever measurements yield the undesired fermion parity. To resolve the problem of wasting information, we devise topological operations that allow for the nondissipative correction of information from undesired fermion parity to the desired one. We will use the sparse-dense mixed encoding process for the controlled-NOT gate as an example to explain how corrections can be implemented without affecting the quantum information carried by the computational qubits. This correction process can be applied to either the undesired input qubits or the fermion parity-dependent quantum gates, and it works for both Majorana-zero-mode-based and Majorana-edge-mode-based topological quantum computation.

The twist-and-turn dynamics of spin squeezing results from the interplay of the one-axis-twisting (nonlinear in the collective-spin operators) and the transverse-field turning (linear) term in the underlying Lipkin-Meshkov-Glick-type Hamiltonian, both with constant (time-independent) prefactors. Using shortcuts to adiabaticity (STA) and the recently developed enhanced version thereof (eSTA), we demonstrate here that dynamics of this type can be utilized for a fast and robust preparation of spin-squeezed states in internal bosonic Josephson junctions, i.e., condensates of cold bosonic atoms in two different internal (hyperfine) states (single-boson modes) coupled through Rabi rotations. Assuming that the initial state of this system is its ground state for a given initial value of the (time-dependent) linear coupling strength and that the nonlinear coupling strength remains constant, we set out to determine the time dependence of the linear (Rabi) coupling strength that allows for the generation of spin-squeezed states using the STA- and eSTA-based approaches. We then characterize the modified twist-and-turn dynamics of this system by evaluating the coherent spin-squeezing and number-squeezing parameters, as well as the fidelity of the target spin-squeezed states. In this way, we show that the eSTA approach allows for a particularly robust realization of strongly spin-squeezed states in this system, consistently outperforming its adiabatic and STA-based counterparts, even for systems with several hundred particles. Our method could also be employed for the generation of metrologically-useful non-Gaussian states.

The fluorescence decay rate of $2 {}^3{P}_J$ positronium (Ps) atoms $\left[{\mathrm{\Gamma }}_{\mathrm{fl}}\right]$ has been experimentally determined using a Stark-mixing technique. Ground-state Ps atoms were optically excited in an electric field to states containing both $2 {}^3{P}_J$ and $2{}^3{S}_1$ components. The relative state populations were controlled via an applied mixing electric field, and a larger, pulsed, electric field was used to induce rapid quenching of the system after a fixed time delay. The dependence of the quenching signal on the mixing field strength was used to determine the relative S and P populations of the mixed states, whose decay rates are determined by the intrinsic self-annihilation and fluorescence decay rates. The measurements were compared to a trajectory simulation and Stark-mixing model, using the fluorescence decay rate as a free parameter. By finding the best agreement between the data and simulations we obtain ${\mathrm{\Gamma }}_{\mathrm{fl}}=299\pm 25\mu {\mathrm{s}}^{-1}$, which is consistent with the mean theoretical value of $313.343\pm 0.003\mu {\mathrm{s}}^{-1}$.

The low-energy electron-molecule collisions have several implications for the behavior of microscopic and macroscopic environments. One of the most important consequences of this event is molecular ionization due to the electron impact. Since the inclusion of ionization effects through ab initio methods is challenging, we implemented a negative imaginary potential to act as a sinkhole of probability flux to mimic the ionization effects in electron-molecule collisions. We employed an iterative procedure to reproduce the total ionization cross sections computed with the binary-encounter-Bethe model and investigated some Gaussian distributions representing the model potential. Also, in light of obtaining a model with a reasonable physical significance and avoiding arbitrariness, we performed calculations using the probability density as an imaginary potential. Our main goal is to investigate the effect of an absorption potential in the elastic and inelastic channels in ab initio calculations using the Schwinger multichannel method. The results obtained in this study using ${\mathrm{H}}_2$ as a test case are encouraging, since the absorption channel disputes flux probability with other channels.

This paper reports the structure and intermolecular potential energy curve (PEC) of heteroaromatic thiophene dimers obtained using a cold-target recoil-ion momentum spectroscopy reaction microscope. The three-dimensional momenta and kinetic energy release (KER) of the ${\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{S}}^{+}+{\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{S}}^{+}$ ion pairs are obtained by coincident momentum measurement. The two-body dissociation channel is initiated either by the rapid removal of one outer-valence electron from each thiophene molecule via sequential ionization or by intermolecular Coulombic decay (ICD). Our analysis of the absolute cross sections indicates that the ${\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{S}}^{+}+{\mathrm{C}}_4{\mathrm{H}}_4{\mathrm{S}}^{+}$ ion pair is preferentially formed by the ICD process. The measured KER and PEC, accompanied by ab initio molecular dynamics simulations for three different types of conformers, enable us to clarify the minimum energy configuration of thiophene dimers in the gas phase. These results are helpful for our understanding of $\pi \text{−}\pi$ and $\sigma \text{−}\pi$ interactions within heteroaromatic ring complexes.

Conformal symmetry heavily constrains the dynamics of nonrelativistic quantum gases tuned to a nearby quantum critical point. One important consequence of this symmetry is that entropy production can be absent in far-away-from-equilibrium dynamics of strongly interacting three-dimensional (3D) and one-dimensional (1D) quantum gases placed inside an adjustable harmonic trapping potential. This can lead to an oscillatory fully revivable many-body dynamic state, which is reflected in many physical observables. In this article we further investigate the consequences of conformal symmetry on (a) the zero-temperature autocorrelation function, (b) the Wigner distribution function, and (c) the von Neumann entanglement entropy. A direct calculation of these quantities for generic strongly interacting systems is usually extremely difficult. However, we have derived the general structures of these functions in the nonequilibrium dynamics when their dynamics are constrained by conformal symmetry. We obtain our results for (a) by utilizing an operator-state correspondence which connects the imaginary time evolution of primary operators to different initial states of harmonically trapped gases, while the dynamics of the functions in (b) and (c) are derived from conformal invariant density matrices.

Coupled-mode theory (CMT) is a widely used approach for describing resonances and eigenmodes in various photonic structures. Here, we propose a formulation of the CMT describing resonant multilayer structures. In particular, we revisit the conventional Fabry-Pérot resonator and describe its optical properties from the point of view of the spatiotemporal formulation of the CMT. This formulation provides partial differential equations describing both temporal and spatial evolution of the field distribution, thus generalizing the conventional temporal and spatial versions of the CMT. The developed CMT takes into account the symmetry of the considered structure, energy conservation law, reciprocity, and causality. By considering the parameters of the developed CMT to be spatially dependent, we apply it to describe the optical properties of linear variable filters (LVFs) comprising two Bragg mirrors separated by a wedge-shaped (tapered) layer. In good agreement with the results of the rigorous numerical solution of Maxwell's equations, the proposed CMT accurately reproduces the broadening of the resonant peak and the appearance of Fizeau fringes when increasing the wedge angle of the LVF.

Spin-orbit interaction (SOI) due to the tight focusing of light in optical tweezers has led to exciting and exotic avenues towards inducing rotation in microscopic particles. However, instances where the back action of the particles influences and modifies SOI effects so as to induce rotational motion are rarely known. Here we tightly focus a vector beam having radial/azimuthal polarization carrying no intrinsic angular momentum into a refractive index stratified medium and observe the orbital rotation of birefringent particles around the beam propagation axis. In order to validate our experimental findings, we perform numerical simulations of the governing equations. Our simulations reveal that the interaction of light with a birefringent particle gives rise to inhomogeneous spin currents near the focus, resulting in a finite spin momentum. This spin momentum combines with the canonical momentum to finally generate an origin-dependent orbital angular momentum, which is manifested in the rotation of the birefringent particles around the beam axis. Our study describes a unique modulation of the SOI of light due to its interaction with anisotropic particles that can open up new avenues for exotic and complex particle manipulation in optical tweezers.

We investigate the optical soliton and patterns within a system exhibiting a ladder-type Rydberg electromagnetically induced transparency configuration, controlled by a moiré lattice potential. By designing theoretically the optical moiré lattice, we study its localization-delocalization transition and numerically demonstrate the conditions for stable high-dimensional solitons in a commensurate and an incommensurate moiré lattice, respectively. Through modulation instability analysis and numerical simulations, on the one hand, we find that the solitons and vortices exhibit exceptional stability in the self-focusing Kerr nonlinear system. On the other hand, our simulations further reveal the emergence of various extended structures, including polygonal, hexagonal, square, annular, and droplet patterns in self-defocusing Kerr nonlinear system. We also demonstrate various structural phase transitions of the optical patterns by actively manipulating the moiré lattice constant and the strength of nonlinear interactions, resulting in a diverse range of ground-state patterns. Our paper provides a versatile platform for manipulating and controlling light-matter interactions in Rydberg atomic ensembles, opening avenues for future research in designing and controlling complex light structures using Rydberg atomic systems.