We demonstrate a novel method that integrates quantum state preparation of polar molecular ions and the detection of spatially resolved fluorescence in specific regions to study the high-precision spectroscopy of ${\mathrm{HD}}^{+}$ molecular ions in traps. The detection technique not only enables real-time signal measurement but also suppresses common-mode noise arising from fluorescence fluctuations and reduces the state redistribution induced by blackbody radiation. Thus, this method overcomes the key limitations encountered during quantum state preparation of polar molecules through resonance-enhanced threshold photoionization. By utilizing this approach, we measured the ($v, N$): $(0,0)\to (6,1)$ rovibrational transition of ${\mathrm{HD}}^{+}$ ions, with an unperturbed frequency of 303.396 506 7(20) THz. This value is in excellent agreement with the predictions of quantum electrodynamics (QED). Looking forward, our method could be extended to detect hot-band transitions of $\mathrm{H}{\mathrm{D}}^{+}$ excited from highly excited rovibrational states. This provides high-precision tools for determining fundamental constants such as the proton-to-electron mass ratio and for exploring the unknown contributions of QED.

We study continuous interaction of a trapped two-component Bose-Einstein condensate with light fields in a $\mathrm{\Lambda }$-type configuration. Using light beams with orbital angular momentum, we theoretically show how to create a stable, pinned vortex configuration, where the rotating component is confined to the region surrounded by the second, nonrotating component. The atoms constituting this vortex can be localized in volumes much smaller than the volume occupied by the second component. We also show that the vortex position can be changed dynamically by moving the laser beams, provided the beams' movement speed remains below the speed of sound. This allows us to use the localized vortex to stir the second component, and to determine the superfluid flow's critical velocity.

We have experimentally investigated the nonlinear nature of massive particle dynamics in a quadrupole trap under atmospheric pressure. We have studied our levitated system over a wide range of trapping parameters and determined four distinct dynamical states of the trapped particle motion, which are associated with the retaining force and drag force nonlinearities. Like any other nonlinear system, the considered one possesses a phase transition in its behavior that demarcates linear and nonlinear regimes of motion. The nonlinear regime manifests itself as the formation of a specific limit cycle of the trapped particle motion also known as an extended orbit. We have shown that the birth of the extended orbits is foretold by the appearance of half-integer trapping frequency multiples in the particle motion oscillation. These half-integer multiples are highly sensitive to trapping parameters and external perturbation. We have demonstrated that the phase transition is a continuous process over a range of system parameters and can be exploited to detect small influences on the levitated system. We have tested the system response in the transient state to the external optical perturbation. The strong sensitivity to perturbation laser power has been shown for both the spectral composition of the trapped particle translational oscillations and extended orbit formation point. We believe in the potential to apply the nonlinear state of the levitodynamic system with massive particles to the field of precision measurements and nonequilibrium physics investigation.

Long-range propagation of laser pulses in the atmosphere is of interest in free-space communication, remote detection, and directed energy, among others. We analyze and numerically simulate the propagation and stability of laser pulses propagating in the vertical direction. Stability of the dynamic equilibrium of the laser pulse is analyzed and numerically simulated, taking into account the variation of the air density, linear and nonlinear dispersion, and turbulence level, as a function of altitude. In the dynamic equilibrium, the spot size, pulse duration, wave-front curvature, phase, and chirp evolve self-consistently along the propagation path. Significant intensity enhancement at remote distances is achieved by tailoring the laser parameters in such a way that the transverse and longitudinal focal points nearly coincide. In addition, the hybrid filamentation-modulation instability is analyzed and simulated, indicating that the beam breaks up transversely and longitudinally. Our model enables laser pulse propagation studies over distances that ordinarily would be computationally challenging.

Thermal light by nature exhibits the well-known photon bunching effect with the zero-delay second-order correlation coefficient $g^{\left(2\right)}$ ideally equal to 2. The Photon extra-bunching effect, as a special class of the superbunching effect ($g^{\left(2\right)}>2$), describes the enhanced photon correlation ($g^{\left(2\right)}=3$) through the interference of bright twin beams produced in the spontaneous parametric down-conversion. In this work, we report that this effect can exist in classical beams and that $g^{\left(2\right)}$ can approach 4 in some extended extreme models. We experimentally demonstrate the nontrivial extra-bunching correlation ($\sim 1.4\times$ gain) in pairwise-generated holographic thermal light beams with a Dove prism-embedded balanced Mach-Zehnder interferometer. The interaction of such a pair of conjugated thermal light beams can generate a pair of uncorrelated superthermal light beams, enabling ghost imaging and Young's intensity interference with enhanced visibility. The quantum-inspired interference-induced spatial extra-bunching effect provides novel insights into inducing superbunching correlation in classical light and holds the potential for application in the coherent two-photon Lidar system to enhance sensitivity.

We investigate the coupling of the fully degenerate triple-photon state generated by three-mode spontaneous parametric down-conversion with the vacuum at a beam splitter via numerical modeling. By using fully degenerate triple-photon states with distinct pump phases as input states, four different squeezed states are extracted at the output, which can be referred to as zero-phase, $\pi /2$-phase, $\pi$-phase, and $3\pi /2$-phase positive Wigner squeezed states. The non-Gaussianity evolution during the coupling process is quantitatively analyzed via quantum relative entropy, and the entanglement between the two output modes is confirmed from an entropic perspective. Furthermore, the entanglement properties of the zero-phase and $\pi$-phase positive Wigner squeezed states at the third- and sixth-order moments are revealed by applying the partial transpose positive criterion based on the higher-order covariance matrix. In particular, it is found that the steerability of the two output modes at the third- and sixth-order moments can be dynamically controlled by adjusting the intensity of the input light and the transmission of the beam splitter. These results enrich the repertoire of squeezed states in quantum optics and offer a feasible approach for the deterministic preparation of non-Gaussian entanglement via coupling fully degenerate triple-photon states with vacuum.

Recent advances have significantly enhanced the coherence times of superconducting qubits. However, high-fidelity storage of multiqubit quantum states in large-scale circuits is still limited by factors such as the flux noise and crosstalk. We propose an X-iSwap decoupling sequence combining single-qubit $X_{\pi }$ gates and two-qubit iSwap gates to effectively mitigate dephasing from the low-frequency flux noise and eliminate crosstalk between qubits. Numerical simulations of noisy random evolution show excellent agreement with the theoretical models. In quantum memory applications, our method substantially extends the decay time of two-qubit fidelity and eliminates fidelity oscillations caused by the ZZ crosstalk. Compared to the traditional decoupling methods based on single-qubit gates, the X-iSwap sequence exhibits superior robustness against small system errors, which holds promise for widespread application in two-qubit systems and large-scale quantum processors for tasks such as long-term quantum memory and entanglement protection.

We propose a novel pulsed optical method based on saturated absorption spectroscopy, where the pump beam is periodically switched on and off using pulse amplitude modulation. This periodic alternation enables time-division multiplexing of the same probe beam into both probe and reference signals, achieving differential Doppler-free spectroscopy with a deterministic zero background. This method effectively mitigates Doppler broadening and common-mode optical noise by addressing disturbances such as nonuniform background absorption and environmental noise, thereby offering enhanced accuracy and robustness. Using this technique, we measured the transition frequency of ${\mathrm{Yb}}^{+}$ isotopes in the ${}^{2}S_{1/2}\to {}^{2}P_{1/2}$ transition. By employing an error signal derived from the dispersive signal of ${}^{174}\mathrm{Yb}^{+}$, we achieved efficient stabilization of a 369.5-nm ultraviolet diode laser, demonstrating a frequency stability of $3\times {10}^{-11}$ (26 kHz) over a 1500-s averaging period and a locking point standard deviation of 850 kHz sustained over 10 days. Furthermore, we report the first in situ observation of Doppler-free Zeeman sublevel spectra in a hot ion system, highlighting the precision of this method and its potential application in measuring magnetic field gradients.

With the growing interest in non-Hermitian quantum systems, the concepts of geometric phase such as Berry phase, adiabatic non-Abelian geometric phase, and nonadiabatic Abelian geometric phase have been gradually extended from Hermitian to non-Hermitian quantum systems. However, extending the most general form, the nonadiabatic non-Abelian geometric phase, to non-Hermitian systems has remained an open problem. In this paper, we address this issue by proposing a formalism of the nonadiabatic non-Abelian geometric phase in non-Hermitian quantum systems. Our formalism is consistent with the previous extensions in non-Hermitian quantum systems, and can also naturally revert to the concepts of geometric phase in Hermitian quantum systems. It provides a general formulation of geometric phase for both Hermitian and non-Hermitian quantum systems.

We use support vector regression based on a projected-quantum-kernel method to predict the density structure of one-dimensional fermionic systems of interest in quantum chemistry and quantum matter. The kernel is built upon with the observables of a quantum reservoir implementable with interacting Rydberg atoms. Training and test data of the fermionic system are generated using a density-functional theory approach. We test the performance of the method for several Hamiltonian parameters, finding a general common behavior of the error as a function of measurement time. At sufficiently long measurement times, we find that the method outperforms the classical linear kernel method and becomes competitive with the radial basis function method.

We report a detailed study of postcollision interaction (PCI) in a liquid medium. We investigate PCI for the Auger KLL electrons of solvated ${\mathrm{Cl}}^{-}, {\mathrm{K}}^{+}$, and ${\mathrm{Ca}}^{2+}$. All three isoelectronic ions exhibit a very similar PCI behavior, which is little affected by changing the solvent from water to methanol or ethanol. The two main factors modifying the PCI interaction in condensed media are the screening of Coulombic interactions and scattering of the electrons. The experimental results are compared with the predictions of a previously reported semiclassical PCI theory modified to account for screening and scattering. We show that a better agreement with experiment can be obtained by instead modeling scattering using electron transport Monte Carlo simulations. We suggest that, in turn, PCI experimental data could be used as another experimental constraint to refine the currently insufficiently well-known scattering parameters of low-energy electrons in water, which are crucial in many fields.

Optical lattice clocks based on the narrow $(5s^2){}^{1}S_0\text{−}\left(5s5p\right){}^{3}P_0$ transition in neutral strontium (Sr) are among the most precise and accurate measurement devices in existence. Although this transition is completely forbidden by selection rules, state mixing from the hyperfine interaction in ${}^{87}\mathrm{Sr}$ provides a weakly allowed transition that can be coherently driven with practical clock laser intensities. While the coherent interrogation times of optical clocks are typically set by the linewidth of the probe laser, this limitation can be overcome in synchronous differential comparisons between ensembles. In such measurements the natural lifetime of the ${}^{1}S_0–{}^{3}P_0$ clock transition becomes the fundamental limiting factor to the duration of a single run of the experiment. However, a direct measurement of the decay rate of the clock excited state is quite challenging due to the competing effects of other loss channels such as Raman scattering, inelastic collisions, and atom loss due to background gas. In this work, we monitor the decay of Sr atoms trapped in an optical lattice and initialized in the ${}^{3}P_0$ state. By making measurements of high and low density ensembles of both ${}^{87}\mathrm{Sr}$ and ${}^{88}\mathrm{Sr}$ across varying lattice trap depths, we isolate radiative decay, which accounts for a significant fraction of the observed decays at low depths. We obtain a natural radiative decay lifetime of ${167}_{-40}^{+79}$ s for the ${}^{3}P_0$ clock state in ${}^{87}\mathrm{Sr}$, a value that is consistent with previously reported measurements and theoretical predictions. We also introduce an additional measurement scheme that involves repeated measurements of the ground-state population within a single experimental sequence, validating our model and the consistency of the measured rates. We expect that the techniques introduced in this work are applicable to lifetime measurements of long-lived metastable states in other atoms and ions used for clocks and quantum computing. The results presented in this work inform performance estimates of proposed gravitational wave detectors and long-baseline atom interferometers making use of ${}^{87}\mathrm{Sr}$.

We develop a theoretical approach for the full analytical description of dissipative optical solitons, which takes into account all relaxation processes in the medium. Most analytical solutions available today for ultrashort optical solitons are obtained upon neglecting a number of relaxation terms in the governing equations for the medium response. The suggested method is based on finding explicit analytical expressions for the extended soliton tails distant enough from the soliton central part, when taking into consideration all relaxation processes. These soliton tails can be described by the linearized equations for the medium response both at the soliton leading and trailing edges. Afterwards, the analytical expressions for the soliton tails and its central part can be matched to yield the full analytical description of ultrashort dissipative solitons with all relaxation processes in the resonant medium properly treated. The proposed approach is demonstrated for ultrashort dissipative solitons in a resonant medium consisting either of only amplifying resonant two-level centers or of a mixture of amplifying and absorbing two-level centers.

We establish a connection between the thermal relaxation rate of optical beams in weakly nonlinear multimoded systems and the spatial correlations among the system's linear supermodes. We implement this methodology for tailored network arrangements supporting various spatial mode profiles. For critical disorder configurations giving rise to metal-insulator transitions, fractal supermodes extremize the correlations, inflating the relaxation rates. Our results inform a design of the physical platforms (their topology, disorder, etc.) supporting targeted relaxation rates.

We present an analytical and numerical investigation into the phenomenon of filter-induced modulation instability in passive hybrid optical resonators exhibiting quadratic and cubic nonlinearity. We show that asymmetric spectral losses, with respect to the continuous-wave solution frequency, can trigger sideband amplification in the normal dispersion regime. We calculate the parametric gain and demonstrate the associated pattern formation process. We furthermore show how this parametric process can be exploited to generate optical frequency combs with a tunable repetition rate.

We investigate the steady-state optical response of a Laguerre-Gaussian vortex cavity system integrated with cold atoms featuring a double-$\mathrm{\Lambda }$ energy level structure. Within this hybrid system, the atoms are driven by a cavity mode and three coherent vortex beams, each carrying independent orbital angular momentum. We first check the steady-state output spectrum of the hybrid system in the passive (active) case [without (with) external cavity driving]. Our findings reveal that the optomechanically induced transparency spectrum is modulated by the orbital angular momentum difference $\left(\mathrm{\Delta }\ell \hslash \right)$ from the atomic component throughout the four-wave-mixing process. The resulting loop phase (${\ell }_{\mathrm{\Theta }}\theta$) can achieve a switching effect on the absorption and gain behavior of the hybrid system for the probe beam. Additionally, the group delay, indicative of fast or slow light phenomena, is also tuned by $\mathrm{\Delta }\ell$. We further display how the atomic orbital angular momentum modulates the periodicity of the output spot pattern in the hybrid system. This research provides valuable insights into the modulation of optical responses in Laguerre-Gaussian vortex cavity systems.