In this paper, we deal with the macroscopic electromagnetic response of a finite size dispersive dielectric object, in unbounded space, in the framework of quantum electrodynamics, using the Heisenberg picture. We keep the polarization and the electromagnetic field distinct to enable the treatment of the polarization and electromagnetic fluctuations on equal footing in a self-consistent QED Hamiltonian. We apply a Hopfield type scheme to account for the dispersion and dissipation of the matter. We provide a general expression of the time evolution of the polarization density field observable as function of the initial conditions of the matter field observables and of the electromagnetic field observables. It is an integral operator whose kernel is a linear combination of the impulse responses of the dielectric object that we obtain within the framework of classical electrodynamics. The electric field observable is expressed in terms of the polarization density field observable by means of the full wave dyadic Green's function for the free space. The statistical functions of the observables of the problem can be expressed through integral operators of the statistics of the initial conditions of the matter field observables and of the electromagnetic field observables, whose kernels are linear or multilinear expressions of the impulse responses of the dielectric object. We expand the polarization density field observable in terms of the static longitudinal and transverse modes of the object to diagonalize the Coulomb and Ampere interaction energy terms of the Hamiltonian in the Coulomb gauge. Few static longitudinal and transverse modes are needed to calculate each element of the impulse response matrix for dielectric objects with sizes of the order up to $\underset{\omega }{min}\{c_0/\left[\omega \sqrt{\left|\chi \right(\omega \left)\right|}\right]\}$, where $\chi \left(\omega \right)$ is the susceptibility of the dielectric. We apply the proposed approach to different scenarios describing the dielectric susceptibility by the Drude-Lorentz model.

We introduce a quantum Monte Carlo method to simulate the reversible dynamics of correlated many-body systems. Our method is based on the Laplace transform of the time-evolution operator, which, as opposed to most quantum Monte Carlo methods, makes it possible to access the dynamics at longer times. The Monte Carlo trajectories are realized through a piecewise stochastic-deterministic reversible evolution where free dynamics is interspersed with two-process quantum jumps. The dynamical sign problem is bypassed via the so-called deadweight approximation, which stabilizes the many-body phases at longer times. We benchmark our method by simulating spin excitation propagation in the one-dimensional (1D) XXZ spin chain, dynamical confinement in the 1D quantum Ising model and quenched magnetization dynamics in the two-dimensional square Ising model. Finally, we also show how to extract dynamical information directly from the Laplace representation.

Intense femtosecond infrared (IR) laser pulses have been used in recent years to study the breakup dynamics of molecules. However, observables such as kinetic energy release and branching ratios of molecular fragments are often difficult to predict by theory, making information of the molecular dynamics difficult to retrieve. In this work, we develop a simple model for sequential double ionization of molecules based on a density-matrix approach. The model describes tunneling ionization of the neutral and the ion as well as laser couplings between the ionic states simultaneously. Population of different doubly charged states can be obtained at a low computational cost. We applied our model to ${\mathrm{N}}_2$ and obtained a good agreement on the kinetic energy release spectrum with a previous experiment. This theoretical development could open up the opportunities to use intense short IR laser pulses with coincidence measurement to probe molecular dynamics.

We report experimental realization of the space-dependent interaction by optical controlled narrow $p$-wave magnetic Feshbach resonance in a ${}^{40}\mathrm{K}$ Fermi gas. A space varied optical field at the tune-out wavelength is applied to illuminate the atomic sample, which drives the bound-to-bound molecular transition to shift the energy of a closed-channel molecule state. Due to the position varied atomic interaction induced by the different laser intensity distribution across the entire Fermi atom cloud, the space-dependent atomic loss rate is observed. This scheme provides a control technique to study the Fermi gas with the space-dependent atomic $p$-wave interaction, and has great potential in quantum simulation.

We report our experiment on sideband cooling with two Raman transitions in a $\mathrm{\Lambda }$ configuration that allows selective coherent population trapping (CPT) of the low-lying motional states. The cooling method is applied to ${}^{87}\mathrm{Rb}$ atoms in a circularly polarized one-dimensional optical lattice. Owing to the vector polarizability, the vibration frequency of a trapped atom depends on its Zeeman quantum number and the CPT resonance for a pair of bound states in the $\mathrm{\Lambda }$ configuration depends on their vibrational quantum numbers. We call this scheme motion-selective coherent population trapping (MSCPT) and it is a trapped-atom analog of the velocity-selective CPT developed for free He atoms. We observe a pronounced dip in temperature near a detuning for the Raman beams to satisfy the CPT resonance condition for the motional ground state. Although the lowest temperature we obtain is ten times the recoil limit owing to the heat load from motion along an axis, which is left uncooled, and the large Lamb-Dicke parameter of 2.3 in our apparatus, the experiment demonstrates that MSCPT enhances the effectiveness of Raman sideband cooling and enlarges the range of its application. Discussions of design parameters optimized for MSCPT on ${}^{87}\mathrm{Rb}$ atoms and opportunities provided by diatomic polar molecules, whose Stark shift shows a strong dependence on the rotational quantum number, are included.

We propose a scheme that combines velocity-selective coherent population trapping (CPT) and Raman sideband cooling (RSC) for subrecoil cooling of optically trapped atoms outside the Lamb-Dicke regime. This scheme is based on an inverted $\mathsf{Y}$ configuration in an alkali-metal atom. It consists of a $\mathrm{\Lambda }$ formed by two Raman transitions between the ground hyperfine levels and the $D$ transition, allowing RSC along two paths and formation of a CPT dark state. Using the state-dependent difference in vibration frequency of the atom in a circularly polarized trap, we can tune the $\mathrm{\Lambda }$ to make only the motional ground state a CPT dark state. We call this scheme motion-selective coherent population trapping (MSCPT). We write the master equations for RSC and MSCPT and solve them numerically for a ${}^{87}\mathrm{Rb}$ atom in a one-dimensional optical lattice when the Lamb-Dicke parameter is 1. Although MSCPT reaches the steady state slowly compared with RSC, the former consistently produces colder atoms than the latter. The numerical results also show that subrecoil cooling by MSCPT outside the Lamb-Dicke regime is possible under a favorable, yet experimentally feasible, condition. We explain this performance quantitatively by calculating the relative darkness of each motional state. Finally, we discuss the application of the MSCPT scheme to an optically trapped diatomic polar molecule whose Stark shift and vibration frequency exhibit large variations depending on the rotational quantum number.

We investigate the open dynamics of a chain of interacting spins using the quantized version of the general equation for the nonequilibrium reversible-irreversible coupling equation from classical out-of-equilibrium thermodynamics. We focus on both equilibrium and nonequilibrium scenarios for chains of different sizes. Whereas in the equilibrium case we demonstrate thermal equilibration to the correct many-body Gibbs density matrix, in the nonequilibrium dynamics we show a ballistic-to-diffusive transition in the steady-state energy current and a scaling that is consistent with Fourier's law of heat transfer.

Nonlocal correlations between a fully characterized quantum system and an untrusted black box device are described by an assemblage of conditional quantum states. These assemblages form a convex set, whose extremal points are relevant in many operational contexts. We give necessary and sufficient conditions for an assemblage to be extremal using linear independence conditions and an algorithm to decompose a generic assemblage into extremal points. A matlab implementation of this algorithm is also provided.

Photonic quantum computers, programed within the framework of the measurement-based quantum computing (MBQC), and gate-based platforms are racing toward useful quantum advantage, and some algorithms have emerged as main candidates to reach this goal in the near term. The majority of these algorithms are only expressed in the gate-based model of computation, which is incompatible with photonic platforms. Methods to translate gate-based algorithms into the MBQC framework exist, but they are not always optimal in terms of resource cost. In our work, we propose an MBQC algorithm to run the quantum approximate optimization algorithm (QAOA). Furthermore, we apply the MBQC-QAOA algorithm to the Max $K$-Cut problem, for all values of $K$, expressing the cost Hamiltonian and its constraints in a form easily implementable in the MBQC model. We conclude by analyzing the resource cost of our algorithm, compared to the case of translating a gate-based QAOA algorithm into MBQC rules, and show up to a 30-fold improvement. With our work, we contribute to closing the gap between gate-based and MBQC near-term algorithms, a gap not reflecting the current status of the hardware development.

Nonorthogonal quantum state discrimination (QSD) plays an important role in quantum information and quantum communication. In addition, compared to Hermitian quantum systems, parity-time-($\mathcal{PT}$-)symmetric non-Hermitian quantum systems exhibit novel phenomena and have attracted considerable attention. Here, we experimentally demonstrate QSD in a $\mathcal{PT}$-symmetric system (i.e., $\mathcal{PT}$-symmetric QSD), by having quantum states evolve under a $\mathcal{PT}$-symmetric Hamiltonian in a lossy linear optical setup. We observe that two initially nonorthogonal states can rapidly evolve into orthogonal states and the required evolution time can even be vanishing provided the matrix elements of the Hamiltonian become sufficiently large. We also observe that the cost of such a discrimination is a dissipation of quantum states into the environment. Furthermore, by comparing $\mathcal{PT}$-symmetric QSD with optimal strategies in Hermitian systems, we find that at the critical value, $\mathcal{PT}$-symmetric QSD is equivalent to the optimal unambiguous state discrimination in Hermitian systems. We also extend the $\mathcal{PT}$-symmetric QSD to the case of discriminating three nonorthogonal states. The QSD in a $\mathcal{PT}$-symmetric system opens a new door for quantum state discrimination, which has important applications in quantum computing, quantum cryptography, and quantum communication.

The weak-value-amplification (WVA) technique has been extensively considered and debated in the field of quantum precision measurement, largely owing to the reduced Fisher information caused by the low probability of successful postselection. In this work we show that, rather than the transverse-spatial-wave-function meter typically considered, using the optical coherent state as a meter, the WVA measurement can outperform the conventional measurement not involving the strategy of postselection. We also show that the postselection procedure involved in the WVA scheme can make a mixture of coherent states work better than a pure coherent state with identical average photon numbers. This is in contrast to the main result proved in the absence of postselection. The postselection strategy can also result in the precision of Heisenberg scaling with the photon numbers without using expensive quantum resources. The present work may stimulate further interest in postselection strategy for quantum precision measurements.

The eight-port homodyne detector is an optical circuit designed to perform the monitoring of two quadratures of an optical field: the signal. By using quantum Bose fields and quantum stochastic calculus, we give a complete quantum description of this apparatus, when used as quadrature detector in continuous time. We can treat either the traveling waves in the optical circuit or the observables involved in the detection part: two couples of photodiodes, postprocessing of the output currents…. The analysis includes imperfections, such as not perfectly balanced beam splitters, detector efficiency, electronic noise, phase and intensity noise in the laser acting as local oscillator; this last noise is modeled by using mixtures of field coherent states as statistical operator of the laser component. Due to the monitoring in continuous time, the output is a stochastic process and its full probability distribution is obtained. When the output process is sampled at discrete times, the quantum description can be reduced to discrete mode operators, but at the price of having random operators, which contain also the noise of the local oscillator. Consequently, the local oscillator noise has a very different effect on the detection results with respect to an additive noise, such as the noise in the electronic components. As an application, the problem of secure random-number generation is considered, based on the local oscillator shot noise. The rate of random bits that can be generated is quantified by the min-entropy; the possibility of classical and quantum side information is taken into account by suitable conditional min-entropies. The final rate depends on which parts of the apparatus are considered to be secure and on which ones are considered to be exposed to the intervention of an intruder. In some experimentally realistic situations, the entropy losses are computed, depending on the values of the parameters quantifying the imperfections.

We present relativistic many-body calculations of atomic and molecular Schiff-moment interaction constants including interelectron correlation effects using atomic Gaussian basis sets specifically optimized for the Schiff interaction. Our present best results employing a Gaussian nuclear density function are ${\alpha }_{\text{SM}}=(0.362\pm 0.025)\times {10}^{-17}\frac{e\text{cm}}{e{\text{fm}}^3}$ for atomic ${}^{129}\mathrm{Xe}, {\alpha }_{\text{SM}}=(-2.26\pm 0.23)\times {10}^{-17}\frac{e\text{cm}}{e{\text{fm}}^3}$ for atomic ${}^{199}\mathrm{Hg}$, and $W_{\text{SM}}=(39967\pm 3600)$ a.u. for the thallium nucleus in the molecule ${}^{205}\mathrm{TlF}$. We discuss agreements and discrepancies between our present results and those from earlier calculations on the atoms ${}^{129}\mathrm{Xe}$ and ${}^{199}\mathrm{Hg}$. Using the most recent measurements of $\mathcal{P},\mathcal{T}$-odd electric dipole moments and the present interaction constants, reliable upper bounds on the Schiff moments of the ${}^{199}\mathrm{Hg}$ and ${}^{205}\mathrm{Tl}$ nuclei are determined in the context of a single-source assumption.

High-order harmonic generation by two linearly polarized fields that enclose an arbitrary crossing angle $\theta$ is investigated using the strong-field approximation. We investigate the combinations with frequency ratios $s/r=2$ and 3 with integer $r$ and $s$. In the former case, the emitted harmonics are elliptically polarized unless $\theta =0^{\circ }$ or ${90}^{\circ }$, while in the latter they are always elliptically polarized except for $\theta =0^{\circ }$. The possibility to control the intensity and ellipticity of the emitted harmonics by variation of the relative phase $\phi$ between the field components and the crossing angle $\theta$ is explored. There are regions with large harmonic ellipticity and appreciable intensity in the relative-phase–harmonic-order plane and they are more extended for values of the crossing angle closer to ${90}^{\circ }$. The overall shape of the spectra (smooth, oscillatory, or erratic) for different values of $\theta$ and $\phi$ is explained using the saddle-point method and quantum-orbit theory. The simple-man model is utilized to assess the regions with large harmonic intensity and to predict the position of the cutoff. For the frequency ratio $s/r=2$, the harmonic ellipticity is significant even for extremely small deviations of the crossing angle $\theta$ from ${90}^{\circ }$.

We numerically investigated the pulse dynamics of soliton macromolecules (SMs) in erbium-doped fiber lasers mode-locked using a nonlinear optical loop mirror (NOLM) with a sinusoidal spectral filter (SSF). SM regimes with various pulse intervals were proposed by modulating the saturation energy and filter period, distributed discretely owing to the restriction of the cavity length and pulse-to-pulse interaction. Several SM properties were discovered in stable SM states with filter periods of 1.3 and 1.95 nm, including the $\pi \text{−}\mathrm{phase}$ difference between adjacent pulses, Kelly sidebands in optical spectra, and the alternating change of phases against round trips. The laser worked in transition regimes, such as pulse splitting and pulsating to a stable SM, by increasing the saturation energy with certain filter periods. In pulsating SM regimes, soliton collisions and periodic variations of pulse intervals and peak powers occurred, accompanied by energy transfer between different spectrum components or spectrum shifts. This study reveals that the SSF-based NOLM enables SM generation and provides a method for controlling the SM dynamics in fiber lasers.

In solid quantum systems, strong phonon-phonon repulsive or attractive interactions are difficult to achieve. The highly adjustable phonon-phonon interactions created by silicon-vacancy (SiV) centers in a one-dimensional chiral phononic waveguide are investigated in this paper. Under specific situations, phonon-phonon attractive or repulsive interactions between the chiral transport phonons are created when they are scattered by two-level or three-level structural SiV centers. Furthermore, by modulating the laser Rabi frequencies and detunings, the resultant attractive or repulsive interactions between phonons can be adjusted over a large frequency range. Single-phonon creation and phonon manipulation in solid acoustic quantum information processing could benefit from the tunable phonon-phonon interactions.