Laser pulses can break the electronic structure symmetry of atoms and molecules by preparing a superposition of states with different irreducible representations. Here, we discover the reverse process, symmetry restoration, by means of two circularly polarized laser pulses. The laser pulse for symmetry restoration is designed as a copy of the pulse for symmetry breaking. Symmetry restoration is achieved if the time delay is chosen such that the superposed states have the same phases at the temporal center. This condition must be satisfied with a precision of a few attoseconds. Numerical simulations are presented for the ${\mathrm{C}}_6{\mathrm{H}}_6$ molecule and ${}^{87}\mathrm{Rb}$ atom. The experimental feasibility of symmetry restoration is demonstrated by means of high-contrast time-dependent Ramsey interferometry of the ${}^{87}\mathrm{Rb}$ atom.

We report on a quantitative experimental determination of the laser-induced frequency shift rate of the ultracold cesium molecules formed via photoassociation (PA) by means of the trap loss measurement of the losses of trapped atoms in a standard magneto-optical trap. The experiment was directly performed by varying the photoassociation laser intensity without any additional frequency monitor technologies. Our experimental method utilized dependences of the losses on the laser-induced frequency shift rate based on the conditions of the identified photoassociation spectral shape. We demonstrated that the method is sensitive enough to determine small frequency shifts of rovibrational levels of ultracold cesium molecules.

We propose a high-fidelity quantum control framework based on the quasi-topological number (νqua), which extends the traditional Chern number to characterize geometric responses in non-closed paths. By introducing an Adiabatic Gauge Potential that dynamically suppresses non-adiabatic transitions and reconstructs path curvature, we demonstrate that νqua—a relative homotopy invariant of compact manifolds in parameter space—quantifies the robustness of geometric phases during open-path quantum evolution. This integer invariant ensures gauge-invariant suppression of decoherence errors arising from dynamical phase coupling. Numerical simulations in the Kitaev superconducting chain and 2D transverse field Ising model confirm that our protocol achieves high quantum gate fidelity. We bridge geometric quantum control with topological protection, offering a universal approach to obtain high-fidelity and robust quantum gates.

In advanced spectroscopy, the classical symmetric optical frequency comb is limited in temporal flexibility and selection freedom, which constrains the efficiency and stability of quantum manipulation. To overcome this limitation, we propose a method to realize precise energy-level manipulation using a femtosecond non-temporally symmetric optical frequency comb in the semiclassical three-level system. Numerical calculations show that the fall time of the pulse is the key parameter to realize the precise manipulation, and a shorter fall time contributes to the efficient accumulation of population. By optimizing the pulse parameters, 99.15% accumulation of population in the target state can be successfully achieved and stably maintained using an asymmetric slowly turned-on and rapidly turned-off (STRT) pulse train. Our demonstration of the non-temporally symmetric optical frequency comb provides a promising approach to efficient quantum-state preparation using spectral modulation.

Nonlinear dynamics plays a significant role in interdisciplinary fields spanning biology, engineering, mathematics, and physics. Under small-amplitude approximations, certain nonlinear systems can be effectively described by the linear Mathieu equation. Within the Lagrangian mechanics framework, here we systematically investigate nonlinear dynamics and parametric resonance phenomena in a collision-coupled double pendulum system. The complete dynamical model successfully captures the system’s nonlinear behavior under large angular displacements. Numerical simulations and experimental validations demonstrate parametric resonance within specific frequency ratio ranges, with resonance boundaries showing good agreement with theoretical predictions. The collision coupling mechanism enables unique energy transfer properties, while system nonlinearity ultimately leads to amplitude saturation. Notably, frequency modulation techniques achieve perturbation-free excitation of parametric resonance. We propose a novel example in nonlinear dynamics, with a methodological framework applicable to broader collision-coupled systems.

We present the observation of high-precision direct frequency comb spectroscopy excited by an optical frequency comb and a diode laser when each of them drives one step of the two-photon transitions in a rubidium vapor system. We demonstrate a stable and low noise system by directly locking the frequency of continuous-wave laser to rubidium two-photon transitions. The frequency stabil ity of diode laser via two-photon transitions locking technique is 8*10−11 for a 1-s gate time and 3*10−12 for 1000-s. It proves a potential technique to locking the diode laser with high stability. We choice the suitable optical frequency comb pulse and the frequency of diode laser to fulfill the double-resonance condition. These techniques eliminate spectrum lines overlap would benefit spectroscopy measurement.