We report the observation of the thermalization of the Fermi-Pasta-Ulam-Tsingou recurrence process in optical fibers. We show the transition from a reversible regime to an irreversible one, revealing a spectrally thermalized state. To do so, we actively compensate the fiber loss to make the observation of several recurrences possible. We inject into the fiber a combination of three coherent continuous waves, which we call Fourier modes, and a random noise. We enhance the noise-driven modulation instability process against the coherent one by boosting the input noise power level to speed up the evolution to the thermalization. The distributions of the Fourier modes' power along the fiber length are recorded thanks to a multiheterodyne time-domain reflectometer. At low input noise levels, we observe up to four recurrences. Whereas, at higher noise levels, the Fourier modes fade into the noise-driven modulation instability spectrum, revealing that the process reached an irreversible thermalized state.

Using an extended Tavis-Cummings model, we study the effect of the spin-orbit coupling between the singlet and the triplet molecular excitons in organic microcavities in the strong-coupling regime. The model is solved in the single excitation space for polaritons, which contains the bright (permutation symmetric) singlet and triplet excitons, as well as the dark bands consisting of the nonsymmetric excitons of either type. We find that the spin-orbit coupling splits the lower polariton into two branches, and also creates a triplet polariton when the cavity mode is in resonance with the triplet excitons. The optical absorption spectrum of the system that can reveal this splitting in experiments is presented and the effect of disorder in exciton energies and couplings is explored. An important consequence of the disorder in the spin-orbit coupling—a weak coupling between the otherwise decoupled bright and dark sectors—is explored and detailed calculations of the squared transition matrix elements between the dark bands and polaritons are presented along with derivation of some approximate yet quite accurate analytical expressions. This relaxation channel for the dark states contains an interference between two transition paths that, for a given polariton state, suppresses the relaxation of one dark band and enhances it for the other.

Understanding and manipulating the excitation transport lie in the center of the research of various mesoscopic quantum devices. Here, we study the exciton transport in a one-dimensional two-level systems chain described by the Su-Schrieffer-Heeger Hamiltonian. Without cavity, the dimerization-assisted transport occurs for both odd and even chains. It is proved that such an effect is the result of competition between localization and delocalization of the modes near zero energy. In the presence of a cavity, both the localized edge modes of the even chain can be dressed by the cavity by the loss of their parities induced by the driving field. The exciton transport can be significantly enhanced through the polaritonic states formed by the strong coupling of edge states and the cavity. The polaritonic channels originating from edge modes with different parities compete with each other and can each dominate the transport at different exciton-cavity coupling strengths. Our work provides possible avenues for the enhancement and control of exciton transport for excitonic devices.

There is a pressing need to develop new rechargeable battery technologies that can offer higher energy storage, faster charging, and lower costs. Despite the success of existing methods for the simulation of battery materials, they can sometimes fall short of delivering accurate and reliable results. Quantum computing has been discussed as an avenue to overcome these issues, but only limited work has been done to outline how it may impact battery simulations. In this work, we provide a detailed answer to the following question: how can a quantum computer be used to simulate key properties of a lithium-ion battery? Based on recently introduced first-quantization techniques, we lay out an end-to-end quantum algorithm for calculating equilibrium cell voltages, ionic mobility, and thermal stability. These can be obtained from ground-state energies of materials, which are the core calculations executed by the quantum computer using qubitization-based quantum phase estimation. The algorithm includes explicit methods for preparing approximate ground states of periodic materials in first quantization. We bring these insights together to estimate the resources required to implement a quantum algorithm for simulating a realistic cathode material, dilithium iron silicate.

The increasing success of classical generative adversarial networks (GANs) has inspired several quantum versions of GANs. Fully quantum mechanical applications of such quantum GANs have been limited to one- and two-qubit systems. In this paper, we investigate the entangling quantum GAN (EQ-GAN) for multiqubit learning. We show that the EQ-GAN can learn a circuit more efficiently compared with a swap test. We also consider the EQ-GAN for learning eigenstates that are variational quantum eigensolver (VQE) approximated and find that it generates excellent overlap matrix elements when learning VQE states of small molecules. However, this does not directly translate into a good estimate of the energy due to a lack of phase estimation. Finally, we consider random state learning with the EQ-GAN for up to six qubits, using different two-qubit gates, and show that it is capable of learning completely random quantum states, something which could be useful in quantum state loading.

Quantum teleportation provides a way to transfer unknown quantum states from one system to another via an entangled state as a quantum channel without physical transmission of the object itself. The entangled channel, measurement performed by the sender (Alice), and classical information sent to the receiver (Bob) are three key ingredients in the procedure, which need to cooperate with each other. To study the relationship among the three parts, we propose a scheme for perfect teleportation of a qubit through a high-dimensional quantum channel in a pure state with two equal largest Schmidt coefficients. The scheme requires less entanglement of Alice's measurement but more classical bits than the original scheme via a Bell state. The two quantities increase with the entanglement of the quantum channel when its dimension is fixed and thereby can be regard as Alice's necessary capabilities to use the quantum channel. And the two capabilities appear complementary to each other.

Fault-tolerant quantum computation relies on scaling up quantum error correcting codes in order to suppress the error rate on the encoded quantum states. Topological codes, such as the surface code or color codes, are leading candidates for practical scalable quantum error correction and require efficient and scalable decoders. In this work, we propose and study the efficiency of a decoder for two-dimensional topological color codes on the 4.8.8 lattice (also known as the square-octagon code), by building on the work of Sarvepalli and Raussendorf [Phys. Rev. A 85, 022317 (2012)], for color codes on hexagonal lattices. The decoder is based on a rescaling approach, in which syndrome information on a part of the qubit lattice is processed locally, and then the lattice is rescaled iteratively to smaller sizes. We find a threshold of 6.0% for code capacity noise.

A two-dimensional Fock-state lattice (FSL) is constructed from the many-body states of two interacting two-mode quantum gases. By periodically driving the interspecies interactions and pulsing the tunneling between the two modes of each gas, a synthetic gauge field is generated. We derive an effective Hamiltonian in the short pulse limit which resembles the Harper-Hofstadter Hamiltonian where the magnetic flux per plaquette is controlled by the ratio of the interaction energy and the driving frequency. The quasispectrum of the Floquet operator of the driving sequence shows the celebrated Hofstadter's butterfly pattern as well as the existence of edge states. From the calculation of the local Chern marker, we establish that the FSL has nontrivial topology and by simulating the dynamics of the edge states, show that they exhibit chirality. Finally, the inclusion of intraspecies interactions creates an overall harmonic trap in the lattice and introduces the nonlinear effect of macroscopic quantum self-trapping, which is shown to hinder movement along the edges of the lattice. This work introduces an avenue to explore synthetic gauge fields and the link between condensed matter systems and quantum gases.

Optical forces in dielectric structures are typically analyzed by utilizing either the Maxwell stress tensor or energy-based methods from which they can be derived by means of the eigenfrequencies and the effective refractive indices involved. While the equivalence of these two methods has been discussed in several studies, it would seem that a general electrodynamic proof of this aspect is still lacking. In this work, we provide a rigorous electrodynamic derivation based on the Minkowski-Helmholtz formula and the electromagnetic variation theorem, from which one can directly conclude that under Hermitian conditions these two approaches are formally equivalent to each other. The results of our study universally apply to any dielectric waveguide or cavity configuration. In addition, this methodology can be employed in graded index systems that do not exhibit sharp interfaces. Importantly, our analysis offers a straightforward route for predicting optical forces in a variety of photonic arrangements, including dielectric scatterers and multielement array configurations.

Bell nonlocality represents one of the most striking departures of quantum mechanics from classical physics. It shows that correlations between spacelike separated systems allowed by quantum mechanics are stronger than those present in any classical theory. In a recent work [A. Tavakoli, M. Farkas, D. Rosset, J.-D. Bancal, and J. Kaniewski, Sci. Adv. 7, eabc3847 (2021)], a family of Bell functionals tailored to mutually unbiased bases (MUBs) was proposed. For these functionals, the maximal quantum violation is achieved if the two measurements performed by one of the parties are constructed out of MUBs of a fixed dimension. Here, we generalize this construction to an arbitrary incompatible pair of rank-one projective measurements. By constructing a new family of Bell functionals, we show that for any such pair there exists a Bell inequality that is maximally violated by this pair. Moreover, when investigating the robustness of these violations to noise, we demonstrate that the realization which is most robust to noise is not generated by MUBs.

Observation of vibrational Feshbach resonances in the annihilation spectra of positrons on molecules provides a direct measurement of the positron-molecule binding energy ${\varepsilon }_B$. Annihilation measurements are presented for ring hydrocarbons with different numbers of $\pi$ bonds, for which it is observed that the presence of $\pi$ bonds generally increases the positron binding energies. These molecules were chosen because other global molecular parameters (e.g., polarizability, dipole moment, and geometry) are approximately constant, so the observed differences in ${\varepsilon }_B$ can be related to changes in the nature of the bonds. The molecular ionization potential $E_{\mathrm{i}}$ is an exception: for these molecules, the inclusion of $\pi$ bonds tends to decrease $E_{\mathrm{i}}$, and the number of $\pi$ bonds also exhibits a correlation with ${\varepsilon }_B$. Comparison with other molecules with $\pi$ bonds indicates that the changes in ${\varepsilon }_B$ are better correlated with the changing electronic structure of the bonds rather than with a direct dependence of ${\varepsilon }_B$ on $E_{\mathrm{i}}$. The relationship between the dependence of ${\varepsilon }_B$ on the number of $\pi$ bonds and electron-positron correlation effects (such as virtual positronium formation) is discussed.

We report measurements of the absolute photoionization cross sections of magnesiumlike ${\mathrm{S}}^{4+}$ over the 158–280 eV photon energy range. The experiments were performed with the multianalysis ion apparatus at the SOLEIL synchrotron radiation facility. Single- and double-ionization ion yields produced by the photoionization of the $2p$ subshell of the ${\mathrm{S}}^{4+}$ both from the $2p^{6}3s^2{}^1{S}_0$ ground state and the $2p^{5}3s3p{}^3{P}_{0,1,2}$ metastable levels were observed, as well as $2s$ excitations. Theoretical calculations of the photoionization cross sections were carried out using multiconfiguration Dirac-Fock and $R$-matrix computer codes and the results are compared with the experimental data. While in general reasonably good agreement was found, notable differences in the strengths and positions of predicted resonances were observed and significant systematic energy shifts of the theoretical predictions were required.

Postcollision-interaction (PCI) effects involving multistep decay processes following Ar $1s$ photoionization has been studied by Auger electron spectroscopy. The experiment focused on $LMM$ Auger electrons measured in small photon energy steps across the Ar $1s$ photoionization threshold. Decay pathways that we studied include (1) the ${\mathrm{Ar}}^{+*}2p^{–1}\to {\mathrm{Ar}}^{2+}3p^{–2}$ LMMα Auger process due to a single $L$ hole created by $KL$ fluorescence, (2) the ${\mathrm{Ar}}^{2+*}2p^{–2}\to {\mathrm{Ar}}^{3+*}2p^{–1}3p^{–2}$ ${LMM}_1$ Auger process following double $L$ shell hole states produced by a $KLL$ Auger processes, and (3) the subsequent ${\mathrm{Ar}}^{3+*}2p^{–1}3p^{–2}\to {\mathrm{Ar}}^{4+}3p^{–4}$ ${LMM}_2$ Auger transitions. Particularly pronounced PCI shifts and unusual line shapes compared to the ordinary one-step PCI process were found in the spectra of Auger processes following a $KLL$ Auger first step. The experimental results were compared with calculations based on the semiclassical approach to PCI. Good agreement was found between the calculated and experimental PCI shifts. The result opens possibilities for further studies of the multielectron dynamics between Auger electrons mediated through the photoelectron in these and similar systems.

The complicated collisional processes inside a femtosecond laser-induced plasma column can show a great impact on the light emissions from it. A known example is that the lifetime of noncoherent fluorescence emitting from gas plasma can be greatly decreased due to the fierce ultrafast plasma collisions. However, for coherent stimulated emissions in plasma surrounding, to what extent it can be influenced by the collisional process has not been fully understood. Herein, we report an experimental spectral width analysis on coherent ${\mathrm{N}}_2^{+}$ lasing that is generated in weakly ionized gas plasma with a frequently adopted pump-probe scheme. It is found unexpectedly that the spectral width of ${\mathrm{N}}_2^{+}$ lasing evidently shortens with the increasing delay between the pump and the probe pulses at a pressure of 40 mbars, whereas an invariable spectral width appears when the gas pressure is decreased below 10 mbars. Moreover, it was also observed that the spectral width narrows with the increment of polarization angle between the pump and the probe pulses. These observations update the understandings of molecular spectral manipulation on the basis of the previous that the spectral modulations mainly occur in the vicinity of molecular alignment. Our results indicate that by combining the spectral width and intensity analysis, a more comprehensive understanding regarding the impact of ultrafast electronic plasma-ion collisions on the ${\mathrm{N}}_2^{+}$ lasing generation can be obtained. These findings also shed light on the spectral manipulation for coherent irradiations produced during strong laser-matter interaction.

We investigate theoretically the photoelectron holography in strong-field ionization by a few-cycle chirped laser pulse. It is shown that the numerical results by solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) are in agreement with that by using the semiclassical two-step (SCTS) model. The opening and the closing of the ionization channel can be controlled precisely by a few-cycle chirped laser pulse and the holographic interference structure can be isolated by adjusting the chirp parameters. This holographic interference structure is related to the rescattered electron wave packet (EWP) which released within an attosecond timescale. We demonstrate that the chirped laser pulse can be used to coherently control the recollision process. By analyzing the rescattered trajectory, we illustrate that the travel time of the rescattered electron is increased and the rescattered electron can obtain high return energy in a negatively chirped laser pulse. In addition, we also illustrate that the photoelectron momentum distributions (PMDs) are very sensitive to the carrier-envelope phase.

We show that the higher-order soliton evolution can be considerably affected by the relative positions of the zero-nonlinearity wavelength (ZNW) and zero-dispersion wavelength (ZDW) with respect to the input wavelength in photonic crystal fibers (PCFs) with frequency-dependent Kerr nonlinearity. By regulating the magnitude of nonlinear dispersion, the position of the ZNW and the strength of the doping Kerr nonlinearity can vary to a large extent, which significantly changes the general process of higher-order soliton evolution in the PCFs. Particularly, some interesting phenomena observed numerically in the PCFs with one ZDW and one ZNW are as follows: the formation of a blueshifted fundamental soliton that satisfies the phase-matching and group-velocity-matching conditions with a redshifted fundamental soliton, the tunneling effect of a fundamental soliton that transfers from one solitonic region to another one through a spectrally limited nonsolitonic region, and the generation of the high-intensity blueshifted dispersive wave and redshifted dispersive wave.

A model of charge separation in quantum photosynthesis as a model of quantum feedback control in a system of interacting excitons and vibrons is introduced. In this approach quantum feedback induces a nonlinear evolution equation which describes the Landau-Zener transition with decoherence and can be considered a quantum ratchet. It explains both the irreversibility in the process of charge separation for quantum photosynthesis (for this model direct transitions have probabilities close to 1, and reverse transitions have probabilities close to zero) and coincidence of the energy of the vibron paired to the transition and the Bohr frequency of the transition.