Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant $B$ were performed for the $5s^{2}5p6s{}^{1,3}{P}_1^{\mathrm{o}}$ excited states of neutral tin. To probe the sensitivity of $B$ to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the $5s^{2}5p6s{}^{1}P_1^{\mathrm{o}}$ state, the final value of $B/Q=703\left(50\right)$ MHz/b differs by $0.4\%$ from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments $Q$ for tin isotopes in the range ${}^{117-131}\mathrm{Sn}$ from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final $B/Q$ value of the $5s^{2}5p6s{}^{1}P_1^{\mathrm{o}}$ state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant $A$.

Several known processes, such as single-photon double ionization and double Auger decay, result in correlated emission of two electrons from an atom or molecule. The ratio of double to single ionization in these processes usually amounts only to several percent. Recently, an experiment was reported in helium droplets doped with alkali dimers, where double ionization of the dimer after excitation of the helium proceeds via interatomic Coulombic decay and occurs with an efficiency comparable to that of single ionization via the usual interatomic Coulombic decay. Motivated by these experimental results, we investigate here the theory of this double interatomic Coulombic decay (dICD) process. First, we develop an explicit asymptotic formula for the decay width of dICD based on the assumption that the electronically excited system providing the necessary excess energy and its neighbor are spatially well separated. This formula contains only quantities accessible experimentally for the separated entities – the system and its neighbor. Second, we derive a general analytical expression for the decay width of dICD by using many-body perturbation theory. Finally, we investigated the efficiency of dICD for experimentally realizable small atomic and molecular clusters employing the asymptotic formula.

A physical theory is presented for polarized light from an aspect of polarization singularity. This is carried out by analyzing the evolution equation of the Stokes parameters that is derived from the nonlinear Schrödinger type equation. The problem is explored from two aspects: The first is concerning the single-mode Stokes parameter that is described by the propagation distance $z$. The trajectory of the polarization singularities is simply given by the points satisfying a rule, $S_3\left(z\right)=\pm S_0$ and 0 ($S_3$ represents the third component of the Stokes parameters), which form a tubelike surface centered with the $C$ line surrounded by $L$ surfaces in the presence of the linear as well as the nonlinear birefringence. It is pointed out that the optical activity (or chirality) plays an “obstacle” to reveal the polarization singularity. As the other aspect, we consider the field theoretic aspect of the Stokes parameters, for which a special solution, called an optical skyrmion, is constructed to explicate the polarization singularity. The skyrmion forms a tube, the dynamical content of which is briefly discussed. On the basis of the work presented here, further analysis would be expected to reveal hidden aspects of polarization optics.

Kerr soliton frequency-comb generation in microresonators has attracted extensive interest since soliton microcombs offer the potential for integration and can be widely used in many fields, such as spectroscopy, communications, precision metrology, sensing, etc. Here, the mechanism of turnkey soliton generation in a microresonator with an organic material coating is illustrated and investigated in both analytical and numerical ways. In particular, based on the thermal curve under a stable state and soliton power from analytical analysis, the turnkey soliton generation regime is calculated and proved by coupled equations with the split-step Fourier method. In addition, the physical parameters of the hybrid modes in the coated resonators are studied, and a suitable design is given in this paper. This research will be helpful for increasing the accessibility of Kerr solitons and make them easier to integrate.

We examine the optical properties of two different configurations of an ordered liquid crystal film on a catenoid forming coreless disclinations. We find the effective optical metric from which we obtain the geodesics and wave modes characterizing thus the propagation of light on this surface. We show that the optical metric describes a 2D section of the spacetime of a conical wormhole.

Space-time (ST) wave packets are propagation-invariant pulsed optical beams that travel rigidly in linear media without diffraction or dispersion at a potentially arbitrary group velocity. These unique characteristics are a result of spatiotemporal spectral correlations introduced into the field; specifically, each spatial frequency is associated with a single temporal frequency (or wavelength). Consequently, the spatial and temporal bandwidths of ST wave packets are correlated, so that exploiting an optical source with a large temporal bandwidth or achieving an ultralow group velocity necessitate an exorbitantly large numerical aperture. Here we show that spectral recycling can help overcome these challenges. Recycling or reusing each spatial frequency by associating it with multiple distinct but widely separated temporal frequencies allows one to circumvent the proportionality between the spatial and temporal bandwidths of ST wave packets, which has been one of their permanent characteristics since their inception. We demonstrate experimentally that the propagation invariance, maximum propagation distance, and group velocity of ST wave packets are unaffected by spectral recycling. We also synthesize a ST wave packet with group velocity $c/14.3$ ($c$ is the speed of light in vacuum) with a reasonable numerical aperture made possible by spectral recycling.

The no-knowledge quantum feedback was proposed by Szigeti et al. [Phys. Rev. Lett. 113, 020407 (2014)] as a measurement-based feedback protocol for decoherence suppression for an open quantum system. By continuously measuring environmental noises and feeding back controls on the system, the protocol can completely reverse the measurement back-action and therefore suppress the system's decoherence. However, the complete decoherence cancellation was shown only for the instantaneous feedback, which is impractical in real experiments. Therefore, in this work, we generalize the original work and investigate how the decoherence suppression can be degraded with unavoidable delay times, by analyzing non-Markovian average dynamics. We present analytical expressions for the average dynamics and numerically analyze the effects of the delayed feedback for a coherently driven two-level system, coupled to a bosonic bath via a Hermitian coupling operator. We also find that, when the qubit's unitary dynamics does not commute with the measurement and feedback controls, the decoherence rate can be either suppressed or amplified, depending on the delay time.

The universal quantum homogenizer can transform a qubit from any state to any other state with arbitrary accuracy, using only unitary transformations to perform this task. Here we present an implementation of a finite quantum homogenizer using nuclear magnetic resonance (NMR), with a four-qubit system. We compare the homogenization of a mixed state to a pure state and the reverse process. After accounting for the effects of decoherence in the system, we find the experimental results to be consistent with the theoretical symmetry in how the qubit states evolve in the two cases. We analyze the implications of this symmetry by interpreting the homogenizer as a physical implementation of pure state preparation and information scrambling.

Quantum controlled-logic gates, including controlled not gate and Toffoli gate, play critical roles in lots of quantum information processing schemes. We design and experimentally demonstrate deterministic Toffoli gate by utilizing orbital-angular-momentum and polarization degrees of freedom of a single photon. In addition, we generate Bell states by using the controlled not gate. The effective conversion rate of the Toffoli gate in our experiment is $(95.1\pm 3.2)\%$. Furthermore, our experimental setup does not require any auxiliary photons and probabilistic postselections.

Optical-optical double-resonance spectroscopy with a continuous wave pump and frequency comb probe allows measurement of sub-Doppler transitions to highly excited molecular states over a wide spectral range with high frequency accuracy. We report on assessment and characterization of sub-Doppler double-resonance transitions in methane measured using a 3.3-$\mu \mathrm{m}$ continuous wave optical parametric oscillator as a pump and a 1.67-$\mu \mathrm{m}$ frequency comb as a probe. The comb spectra were recorded using a Fourier transform spectrometer with comb-mode-limited resolution. With the pump tuned to nine different transitions in the ${\nu }_3$ fundamental band, we detected 36 ladder-type transitions to the $3{\nu }_3$ overtone band region, and 18 V-type transitions to the $2{\nu }_3$ overtone band. We describe in detail the experimental approach and the pump stabilization scheme, which currently limits the frequency accuracy of the measurement. We present the data analysis procedure used to extract the frequencies and intensities of the probe transitions for parallel and perpendicular relative pump-probe polarization. We compare the center frequencies and relative intensities of the ladder-type transitions to theoretical predictions from the TheoReTS and ExoMol line lists, demonstrating good agreement with TheoReTS.

We study electron and positron exchange without a spin flip in a single collision between two polarized orthopositronium beams. We use angular-momentum coupling and density-matrix techniques to calculate the probabilities of obtaining only parapositronium, both para- and orthopositronium or only orthopositronium, after the collision. The probabilities are functions of the angle between the polarization vectors of the beams and scattering amplitudes labeled with total electron spin and total positron spin. The real parts of the scattering amplitudes and products of the polarization tensors for the beams are given in terms of the probabilities for certain angles and initial spin orientations. We show that quenching probabilities for different transitions and the spin-exchange quenching cross section depend on the angle, but the ratio of the total quenching probability to the total probability for positronium scattering does not.

Resonant inelastic x-ray scattering spectra excited at the ${\pi }^{*}$-resonance of the nitrogen molecule are presented. Well-resolved vibrational excitations in the electronic ground state, and in the $3{\sigma }_g^{-1}1{\pi }_g^1{a}^1{\mathrm{\Pi }}_g$ state are observed. The spectra are analyzed within the Kramers-Heisenberg formalism, and the importance of lifetime-vibrational interference effects is highlighted. In addition, strongly dissociative multiply excited final states populated in radiative electron rearrangement are found in the valence ionization continua. The vibrational wave functions of the core-excited state are imaged on the strongly dissociative final state potentials.

Recently, the YbOH molecule has been suggested as a candidate to search for the electron electric dipole moment (eEDM), which violates spatial parity ($P$) and time-reversal ($T$) symmetries [I. Kozyryev and N. R. Hutzler, Phys. Rev. Lett. 119, 133002 (2017)]. In the present paper, we show that the same system can be used to measure coupling constants of the interaction of electrons and nucleus mediated by axionlike particles. The electron-nucleus interaction produced by the axion exchange can contribute to a $T,P$-violating EDM of the whole molecular system. We express the corresponding $T,P$-violating energy shift produced by this effect in terms of the axion mass and product of the axion-nucleus and axion-electron coupling constants.

In this paper, direct observation of micromotion for multiple ions in a laser-cooled trapped ion crystal is discussed along with a measurement technique for micromotion amplitude. Micromotion is directly observed using a time-resolving, single-photon-sensitive camera that provides both fluorescence and position data for each ion on the nanosecond time scale. Micromotion amplitude and phase for each ion in the crystal are measured, allowing this method to be sensitive to tilts and shifts of the ion chain from the null of the radio-frequency quadrupole potential in the linear trap. Spatial resolution makes this micromotion detection technique suitable for complex ion configurations, including two-dimensional geometries. It does not require any additional equipment or laser beams, and the modulation of the cooling lasers or trap voltages is not necessary for detection as it is in other methods.

We analyze spin squeezing via Rydberg dressing in optical lattice clocks with random fractional filling. We compare the achievable clock stability in different lattice geometries, including unity-filled tweezer clock arrays and fractionally filled lattice clocks with varying dimensionality. We provide practical considerations and useful tools in the form of approximate analytical expressions and fitting functions to aid in the experimental implementation of Rydberg-dressed spin squeezing. We demonstrate that spin squeezing via Rydberg dressing in one-, two-, and three-dimensional optical lattices can provide significant improvements in stability in the presence of random fractional filling.

The gradient ascent pulse engineering (GRAPE) algorithm is a celebrated control algorithm with excellent converging rates, owing to a piecewise-constant ansatz for the control function that allows for cheap objective gradients. However, the computational effort involved in the exact simulation of quantum dynamics quickly becomes a bottleneck limiting the control of large systems. In this paper, we experiment with a modified version of GRAPE that uses Krylov approximations (K-GRAPE) to deal efficiently with high-dimensional state spaces. Even though the number of parameters required by an arbitrary control task scale linearly with the dimension of the system, we find a constant elementary computational effort (the effort per parameter). Since the elementary effort of GRAPE is superquadratic, this speed up allows us to reach dimensions far beyond. The performance of the K-GRAPE algorithm is benchmarked in the paradigmatic $XXZ$ spin-chain model.

Rapidly developing photonics brings many interesting resonant optical phenomena, in which the Fano resonance (FR) always intrigues researchers because of its applications in optical switching and sensing. However, its sensitive dependence on environmental conditions makes it hard to implement in experiments. In this work we suggest a robust FR based on the photonic valley Hall insulators, immune to the system impurities. The robust FR is achieved by coupling the valley-dependent edge states with one double-degenerate cavity. The $\delta$-type photonic transport theory we build reveals that this FR dates from the interference of the two transmissions that are attributed to the two cavity modes. We confirm that the induced Fano line shape of the transmission spectra is robust against the bending domain walls and disorders. Our work may provoke exciting frontiers for manipulating the valley transport and pave a way for the valley photonic devices such as optical switches, low-threshold lasers, and ultrasensitive sensors.