Accurate simultaneous estimation of temperature and effective detuning is crucial for understanding, controlling, and optimizing optomechanical systems. Temperature characterizes the thermal state and mechanical properties, while detuning governs the light-motion interaction, influencing stability and enabling diverse quantum applications. Precise estimates of these parameters are therefore essential to exploit the full potential of such systems in high-precision metrology and the exploration of macroscopic quantum phenomena. In this work we investigate the simultaneous estimation of the effective detuning $\mathrm{\Delta }$ and the mirror temperature $T$ in a Fabry-Pérot cavity system, with a particular focus on the performance of heterodyne detection. Using analytical expressions for the quantum Fisher information matrices (QFIM) derived from the symmetric logarithmic derivative (SLD) and the right logarithmic derivative (RLD), we demonstrate that the quantum Cramér-Rao bound associated with the RLD is consistently lower than that based on the SLD, highlighting superior estimation precision. This gap between the SLD- and RLD-based bounds becomes especially pronounced in certain physical regimes, emphasizing the relevance of choosing the appropriate formalism in noncommutative estimation scenarios. From a physical perspective, the improved estimation performance stems from the fact that temperature directly influences thermal fluctuations in the mechanical mode, while the effective detuning modulates the strength of the optomechanical interaction, shaping the information exchange between optical and mechanical subsystems. We showed that using higher optical power, greater cavity decay rate, increased photon and phonon numbers, and reduced coupling strength improves the precision of both parameter estimates. These physical mechanisms affect the available quantum resources in the system—such as squeezing, entanglement, and state purity—which in turn determine the ultimate sensitivity achievable. Furthermore, our analysis shows that heterodyne detection can, under certain conditions, approach the ultimate precision set by the QFIM. Thus, a measurement strategy based on heterodyne detection could enable the efficient estimation of temperature, achieving performance close to that of ideal quantum-limited strategies.

The negative ion of lanthanum has one of the richest bound-state spectra observed for an atomic negative ion and it has been proposed as a promising candidate for laser cooling, which has not yet been achieved for any negatively charged system. In the present study, radiative decays of low-lying excited states of ${\mathrm{La}}^{-}$ were experimentally investigated at the DESIREE cryogenic electrostatic ion-beam storage ring facility using state-selective photodetachment over storage times of up to 800 s. Independently, the transition rates for the relevant states were calculated using a high-precision hybrid theoretical approach. The measured lifetime of the lowest excited state of ${\mathrm{La}}^{-}$ $\left({}^3{F}_3^e\right)$ of 132(20) s agrees very well with the theoretical calculations and previous predictions. However, a puzzling discrepancy exists for the next-higher state ${}^3{F}_4^e$, with the experiments yielding a lifetime $\sim 4$ times shorter than calculated, highlighting the challenges for this complex ion. The results provide valuable insights into the prospects for laser cooling ${\mathrm{La}}^{-}$.

An electronically variational approach to the calculation of atomic hyperfine structure transition energies under the influence of static external electric fields is presented. The method avoids the calculation of intermediate atomic states entirely and requires only the wave functions of the electronic states involved in the respective hyperfine levels. These wave functions are obtained through relativistic general-excitation-rank configuration-interaction theory. A variant of the method also enables calculations on atoms with the most complicated of shell structures. Applications to ${}^{87}\mathrm{Rb}, {}^{133}\mathrm{Cs}$, and a specific clock transition in ${}^{169}\mathrm{Tm}$ are presented. The final results $k_{\text{Rb}}=-1.234\pm 0.023[{10}^{-10}\mathrm{Hz}/{(\mathrm{V}/\mathrm{m})}^2]$ and $k_{\text{Cs}}=-2.347\pm 0.084[{10}^{-10}\mathrm{Hz}/{(\mathrm{V}/\mathrm{m})}^2]$ obtained under inclusion of up to quintuple excitations in the atomic wave-function expansion are compatible with previous calculations and, in the case of Cs, confirm that one of the earlier experimental measurements is not reliable. For ${}^{169}\mathrm{Tm}$ that is used in the development of atomic clocks the differential static scalar electric dipole polarizability between ground levels $J=\frac{7}{2}$ and $\frac{5}{2}$ is calculated to be $\mathrm{\Delta }{\alpha }_0^s=-0.134\pm 0.122$ a.u. This result from a pure ab initio calculation supports the result of $\mathrm{\Delta }{\alpha }_0^s=-0.{063}_{-0.005}^{+0.01}$ a.u. obtained recently [A. Golovizin, E. Fedorova, D. Tregubov, D. Sukachev, K. Khabarova, V. Sorokin, and N. Kolachevsky, Nat. Commun. 10, 1724 (2019)] where a combination of measurement and theoretical modeling has been used.

Accurate ab initio potential energy surfaces are essential to understand and predict collisional outcomes in ultracold molecular systems. In this study, we explore the intermolecular interactions between two laser-cooled CaF molecules, in both their ground and excited electronic states, aiming to understand the mechanisms behind the observed collisional losses on the nonreactive, spin-polarized surface of the $\mathrm{CaF}+\mathrm{CaF}$ system. Using state-of-the-art ab initio methods, we compute 12 electronic states of the ${\mathrm{Ca}}_2{\mathrm{F}}_2$ complex within the rigid rotor approximation applied to CaF. Calculating the potential energy surfaces for the excited electronic states of ${\mathrm{Ca}}_2{\mathrm{F}}_2$ is challenging and computationally expensive. Our approach employs the multireference configuration interaction method, restricted to single and double excitations, along with a reasonably large active space to ensure the convergence in the excited states. We also compute the spin-orbit coupling between the ground state and the lowest spin-polarized triplet state, as well as the spin-spin coupling within the lowest triplet state (1) ${}^3{\mathrm{A}}^{\prime }$. Additionally, we determine the electric transition dipole moments for the (1) ${}^3{\mathrm{A}}^{\prime }$–(2) ${}^3{\mathrm{A}}^{\prime }$ and (1) ${}^3{\mathrm{A}}^{\prime }$–(1) ${}^3{\mathrm{A}}^{″}$ transitions. Notably, we find that the lowest spin-polarized state (1) ${}^3{\mathrm{A}}^{\prime }$, shifted by 1064 nm of laser light from the optical dipole trap, intersects several electronically excited states. Finally, by analyzing the potential energy surfaces, we discuss two plausible pathways that may account for the observed collisional losses on the spin-polarized surface of the $\mathrm{CaF}+\mathrm{CaF}$ system.

Positronic lithium, the first theoretically predicted positronic atom, has yet to be observed experimentally due to its weakly bound nature and short lifetime. Consequently, studies of its structural and annihilation properties can provide valuable guidance for future experimental efforts. In this work, we investigate the relativistic effects on positron binding to atomic lithium by evaluating the expectation values of relativistic operators. Our calculations show that while the total relativistic correction of positronic lithium is comparable in magnitude to the binding energy, the corrections for the bound and dissociated states are nearly identical and largely cancel each other, resulting in only a minor effect on the binding energy. Specifically, the inclusion of relativistic corrections alters the binding energy of positronic lithium and its isotopes by less than 0.13% for spin-triplet states and 0.04% for spin-singlet states. We also calculate the annihilation rates and lifetimes for both spin-triplet and spin-singlet states of positronic lithium.

Rescattering of the photoelectron at its parent ion underlies a number of phenomena in intense laser field interaction with matter, such as high harmonic generation, attosecond pulse production, nonsequential double ionization, and others. These processes are unavoidably accompanied by the medium photoionization. The interaction of the laser pulse with the photoionization-induced plasma excites wakefield waves, which are self-consistently coupled plasma density and Langmuir waves. We study theoretically the effect of the electric field of the plasma wave on the rescattering processes. We show that this field can compensate for the magnetic drift of the rescattering electron, which otherwise dramatically suppresses the rescattering efficiency in intense low-frequency laser fields. Moreover, the presence of the plasma-wave field leads to new lines in the spectrum emitted due to the XUV free-induction decay (XFID). Observation of these lines can allow, in particular, the detection of forbidden transition frequencies, thus providing new perspectives for XFID spectroscopy.

An optical centrifuge is a laser pulse which enables controlled rotational excitation of molecules. Centrifuged molecules rotating with well-defined angular frequencies are ideal candidates to probe many-body quantum systems at the nanoscale. Because the interaction with the quantum environment increases the effective moment of inertia of the embedded molecular probes, the required rotational acceleration of the optical centrifuge must be lowered to accommodate adiabatic spinning. We demonstrate a design of an optical centrifuge, based on the method of spectral focusing, which enables extremely low, down to zero, rotational accelerations. We discuss the potential of using such constant-frequency centrifuge to investigate molecular rotation inside helium nanodroplets.

Recent advances in generating high-energy, few-cycle, carrier-envelope phase (CEP)-stabilized vortex lasers has opened the possibility of producing novel vortex light sources in the extreme ultraviolet (XUV) and soft x-ray regions via high-order harmonic generation (HHG) in gases. However, this area remians underexplored and poorly understood, both experimentally and theoretically. In this work, we investigate the characteristics of vortex high harmonics driven by few-cycle Laguerre-Gaussian (LG) beams using an improved three-dimensional propagation model in which the nonlinear polarization is efficiently computed via a two-dimensional interpolation method. We demonstrate that the intensity profiles of generated vortex high harmonics exhibit discontinuous bright-spot patterns along the azimuthal direction, and the orbital angular momentum (OAM) carried by the $q\mathrm{th}$ harmonic contains multiple modes with topological charges $\ge q{l}_0$, where $l_0$ is the topological charge of the fundamental laser. These features are distinctly different from those observed with long-duration LG beams. Such phenomena arise from the strong CEP dependence of few-cycle laser waveforms, which induces variations in the quantum-trajectory phase accumulated during electron ionization and recombination, effects that are especially pronounced for long trajectories. Additionally, we show that the harmonic intensity profiles, OAM spectra, and helical attosecond pulses depend sensitively on the position of the gas medium. We expect that this work will stimulate further experimental and theoretical investigations into strong-field phenomena driven by few-cycle vortex laser pulses.

We investigate the dynamical instabilities of a one-dimensional ultracold Bose-Bose mixture with long-range dipole-dipole interactions, trapped in deep optical lattices and subject to periodically varying contact interaction. The effect of beyond-mean-field corrections due to quantum fluctuations is considered. In the tight-binding regime, we employ Wannier functions to derive a discrete nonlinear Schrödinger equation that captures the dynamics of the system. Using linear stability analysis coupled to multiple scale expansion, we systematically study the modulational and parametric instabilities of the system in the miscible regime, identifying the conditions under which these instabilities emerge. The corresponding instability domains are found and examined. The roles of long-range interactions and quantum fluctuations are highlighted, demonstrating their significant impact on the stability and dynamics of the lattice system. Our analytical predictions are validated through direct numerical simulations, which confirm the instability diagrams through the effective onset of instabilities and reveal the intricate interplay between interaction strength, quantum fluctuation, and the long-range nature of the dipole-dipole forces. This work provides insights into the control and manipulation of ultracold quantum gases in optical lattices, which have potential applications in quantum simulation and condensed-matter physics.

We investigate a non-Hermitian extension of the Su-Schrieffer-Heeger model that incorporates spin-dependent SU(2) gauge fields, represented by non-Abelian couplings between lattice sites, as well as independent nonreciprocal hopping amplitudes. This framework gives rise to a rich phase structure characterized by complex-energy braiding and tunable non-Hermitian skin effects. By employing the generalized Brillouin zone approach, we analyze the bulk-boundary correspondence and identify topological transitions protected by chiral symmetry. Notably, we demonstrate that non-Abelian gauge fields significantly enhance the dynamical resilience of the system, enabling robust self-healing under a moving scattering potential. These results clarify the role of SU(2) gauge fields in stabilizing non-Hermitian topological phases and indicate that the proposed model can be realized with currently available photonic, atomic, and superconducting experimental platforms.

The non-Hermitian skin effect (NHSE) is a novel localization phenomenon, in which all bulk states in a non-Hermitian system under certain conditions are localized at the edge of the system. Conventionally, most studies of NHSE have dealt with discrete lattice systems with nonreciprocal couplings. However, in recent years, NHSE in a reciprocal two-dimensional continuous medium, such as photonic crystal systems, has also been reported. In particular, we have previously shown that NHSE also occurs in two-dimensional uniform media. In such two-dimensional systems, skin modes propagate in a direction perpendicular to the localization direction and, in particular, they have the property of propagating in only one direction. In this paper, we show numerically an intriguing scattering phenomenon: when a scatterer is placed in the path of a skin mode, the scattering causes the skin mode to hop between opposing edges. In addition, we propose a unique method of generating circulating modes with orbital angular momentum (OAM) using this scattering phenomenon. Our work paves the way for more applications of NHSE as microsized optical devices manipulating or generating OAM.

Future laser-electron colliders will reach quantum parameters $\chi$ well in excess of unity, enabling studies of strong-field QED in extreme regimes. However, statistical inference in such experiments requires mitigating premature radiative losses of electrons to enable high-$\chi$ QED events, as well as separating the detectable signal of these events from that of lower-$\chi$ particles and photons produced by QED cascades. We propose a collider geometry in which electrons traverse the waist of two or four perpendicularly propagating, tightly focused laser pulses. This configuration suppresses both outlined difficulties by leveraging the short interaction length of the waist, rather than relying on the more technically demanding reduction of pulse duration. Moreover, altering the phase and polarization of each pulse causes the electrons to undergo helical motion where the deflection angle is correlated with the field strength, permitting an angle-based discrimination of the signal from high-$\chi$ events. Analysis and simulations show that the case of four circularly polarized pulses uniquely permits achieving helical motion throughout the entire focal region, leading to near-perfect high-$\chi$ angle-discrimination and thereby high signal-to-noise ratio. These findings support the consideration of the proposed concept as a viable layout for future experiments at PW laser facilities.

We theoretically propose a scheme to generate strong genuine tripartite entanglement among three mechanical oscillators in a multimode optomechanical system. In our setup, each mechanical oscillator is independently coupled to three optical modes supported by a single optical cavity, with each optical mode driven by a six-tone driving field. By appropriately tailoring the amplitudes of the driving fields, the mechanical steady state can be engineered into a three-mode squeezed vacuum state exhibiting significant genuine tripartite entanglement. We further investigate the effects of mechanical thermal reservoirs and demonstrate that the entanglement generated by our scheme persists at a significant level even at dilution refrigerator temperatures. Our results offer a feasible route toward the generation and utilization of multipartite entanglement in quantum optomechanical platforms, with potential applications in quantum devices.

Temporal optics has attracted much attention due to its ability for lossless stretching of ultrafast temporal pulses. Concurrently, spatial SU(1,1) interferometers (SUIs) are widely utilized due to their high sensitivity to phase changes. Building on these concepts, we investigate a temporal SUI based on a temporal Fourier transform system, injecting broadband squeezed light for characterization. Our results show that the output spectral characteristics of the interferometer depend on the ratio of the focal group delay dispersion values of the two time lenses (defined as the scaling factor $M$) and the derivative of the applied phase. The scaling factor $M$ strongly influences both the bandwidth and the degree of squeezing in the output spectrum. Meanwhile, the phase derivative induces a frequency shift proportional to its magnitude. Furthermore, the output squeezed-state spectrum exhibits concentrated squeezing at both the center frequency and the shifted frequencies. As the scaling factor $M$ increases, the proportion of squeezing concentrated at the center frequency increases correspondingly. We also theoretically analyze and numerically calculate the phase sensitivity with respect to the phase derivative and the scaling factor $M$, under both lossless and lossy conditions. This temporal SUI architecture opens new avenues for the control of nonclassical fields in the time-frequency domain and quantum information processing applications.

We theoretically investigate the collective emission of one and two circular arrays of two-level atoms surrounding an optical nanofiber. We show that the radiation eigenmodes of a single ring selectively couple to specific guided modes of the fiber, according to their symmetry, and study how the physical parameters of the system control their nature. In particular, we identify situations in which the emission toward radiation modes is highly suppressed with respect to fiber guided modes while the lifetime of the atomic excitation is enhanced. We further address the case of two identical rings positioned at a distance from each other along the nanofiber. By contrast to free-space configurations, the rings can exchange an excitation even at large separation through nanofiber guided modes resulting in enhanced sub- and supper-radiance with respect to the single-ring case. Our findings suggest that the ring configuration is promising for the implementation of efficient and versatile light-matter nanofiber-based interfaces and the achievement of waveguide quantum electrodynamics.

We investigate the topological phase transitions and edge-state properties of a time-multiplexed nonunitary quantum walk with sublattice symmetry. By constructing a Floquet operator incorporating tunable gain and loss, we systematically analyze both unitary and nonunitary regimes. In the unitary case, the conventional bulk-boundary correspondence (BBC) is preserved, with edge modes localized at opposite boundaries as predicted by topological invariants. In contrast, the nonunitary regime exhibits non-Hermitian skin effects, leading to a breakdown of the conventional BBC. By applying non-Bloch band theory and generalized Brillouin zones, we restore a generalized BBC and reveal a transfer phenomenon, where edge modes with different sublattice symmetries can become localized at the same boundary. Furthermore, we demonstrate that the structure of the spectral loops in the complex quasienergy plane provides a clear signature for these transfer behaviors. Our findings deepen the understanding of nonunitary topological phases and offer valuable insights for the experimental realization and control of edge states in non-Hermitian quantum systems.

We investigated harmonic generation in preionized liquid ethanol and water driven by linearly polarized midinfrared (MIR) pulses at a center wavelength of 3100 nm. The liquid targets were preionized by a near-infrared pump pulse at 800 nm, enabling systematic control of the electron density in the liquids. At low pump intensities, the harmonic spectra remain unchanged. In contrast, at intermediate pump intensities, the spectra exhibit pronounced target- and delay-dependent modifications, reflecting changes in the optical properties of the ionized liquids. At high intensities, where the electron density exceeds the critical plasma density for MIR light, harmonic yields are strongly suppressed and spectral broadening disappears. Numerical simulations based on the nonlinear propagation model, incorporating plasma and Kerr effects, qualitatively reproduce the experimental observations above the critical plasma density and confirm the significant role of plasma shuttering in harmonic generation. The observation of narrow harmonic spectra provides clear evidence of evanescent-field-induced harmonic generation in preionized liquids. This highlights the potential of ionized liquid plasmas as a robust platform for exploring strong-field phenomena driven by intense and spatially nonuniform fields, beyond the damage thresholds of conventional materials.

Given a finite lifetime, a ubiquitous challenge in quantum systems is how to prepare a target state in the shortest possible time. This issue is particularly relevant for Rydberg-atom arrays in optical tweezers, where the dephasing time is typically restricted to a few microseconds. In this work, we develop a rapid passage to ordered many-body states in a Rydberg-atomic chain, which allows the transition of the system to various ordered phases in the phase diagram, such as the ${\mathrm{Z}}_2$-, ${\mathrm{Z}}_3$-, and ${\mathrm{Z}}_4$-ordered antiferromagnetic states. Our scheme ramps the parameter in a “nonadiabatic to quasi-adiabatic to nonadiabatic (NQN)” manner. The NQN configuration significantly reduces the time cost required for the state preparation using entirely adiabatic methods and is generally applicable to a sizable number of atoms. Moreover, we experimentally validate the NQN scheme on the neutral-atom quantum cloud computer Aquila.

The exotic entanglement dynamics associated with exceptional points (EP) have been explored in a ring mechanical system, which consists of a phase-dependent phonon-hopping interaction and two phonon-squeezing interactions. By modulating the gauge-invariant phase of the system, the spontaneous $\mathcal{PT}$-symmetry breaking can be generated, enabling the realization of higher-order EPs, such as second- and third-order EPs. The entanglement dynamics are strongly dependent on the orders of the EP. Specifically, both bipartite and tripartite entanglements emerge near the second-order EP, while the third-order EP leads to optimal bipartite entanglement with vanishing tripartite entanglement. Moreover, the asymmetric feature of the bipartite entanglement can be controlled by tuning the parity of the third-order EP through modulation of the system's gauge-invariant phase. The work indicates that the entanglement dynamics associated with EPs may provide a useful platform for realizing non-Hermiticity-enhanced quantum information processing.

Non-Hermiticity incorporating gain and loss allows new symmetries, enriching the fundamental topological classification. While various non-Hermitian topological phases have been uncovered, the interplay between multigap topology and non-Hermiticity remains to be explored. Here we investigate the topological states of a multiband tetramerized superlattice by introducing three distinct gain-loss patterns: $(ig,$ $-ig,$ $ig,$ $-ig)$, $(ig,$ $ig,$ $-ig,$ $-ig)$, and $(ig,$ $-ig,$ $-ig,$ $ig)$. We uncover the unique effects of each configuration on the multigap topological edge states. Specifically, we find that the non-Hermiticity in the first configuration does not affect the multigap topological phases. Interestingly, it leads to a multiple reemergence behavior of the midgap defect state. For the second one, the gain-loss induces a topological phase transition in the midgap from nontrivial to trivial. Additionally, it results in the emergence of trivial edge states when the nonmidgap is initially trivial. The non-Hermiticity in the third one drives a topological phase transition in the midgap from trivial to nontrivial, while simultaneously destroying the localized topological edge states in the nonmidgap. Our results show a rich synergy between non-Hermiticity and multigap topology, introducing avenues for controlling multigap topological edge modes, which may have potential applications in multifrequency topological devices.