We have completed measurements of two low-lying excited-state electric-dipole (E1) transition amplitudes in lead. Our measured reduced matrix elements of the $\left(6s^{2}6p^2\right){}^{3}P_1\to \left(6s^{2}6p7s\right){}^{3}P_0$ transition at 368.3 nm and the 405.8-nm $\left(6s^{2}6p^2\right){}^{3}P_2\to \left(6s^{2}6p7s\right){}^{3}P_1$ transition are 1.90(1) and 3.01(2) a.u., respectively, both measured to sub-1% precision and both in excellent agreement with the latest ab initio lead wave-function calculations. These measurements were completed by comparing the low-field Faraday optical rotation spectra of each E1 transition in turn with that of the ground-state ${}^{3}P_0-{}^{3}P_1$ M1 transition under identical experimental conditions. Our spectroscopy technique involves polarization modulation and lock-in detection yielding microradian-level optical rotation resolution. At temperatures where direct absorption was significant for both E1 and M1 transitions, we also extracted matrix element values from a direct optical absorption depth comparison. As part of this work we designed an interaction region within our furnace which allows precise measurement of our quartz vapor cell sample temperature and thus accurate determination of the Boltzmann thermal population of the low-lying excited states that were studied.

Radiative corrections to electronic structure are characterized by perturbative expansions in $\alpha$ and $Z\alpha$, where $\alpha$ is the fine-structure constant and $Z$ is the nuclear charge. A formulation of the leading-order $\alpha \left(Z\alpha \right)$ Uehling contribution to the renormalized vacuum polarization is reported in a form that is convenient for implementation in computational studies of the relativistic electronic structures of molecules. Benchmark calculations based on these methods are reported that include the leading-order vacuum polarization effects within relativistic mean-field methods for the $\mathrm{E}{119}^{+}$ ion and the closed-shell diatomic species E119F.

We outline a general formalism for treating vacuum polarization phenomena within an effective field expansion. The coupling between source charges and virtual fields is examined from the perspectives of electrostatic potentials, induced charge densities, and form factors in momentum space. A strategy for the efficient calculation of vacuum polarization potentials is outlined, implemented, and applied towards the construction of fitting potentials that are suitable for molecular electronic structure calculations, which enclose no overall charge by construction. The order-$\alpha \left(Z\alpha \right)$, -$\alpha {\left(Z\alpha \right)}^3$, and -${\alpha }^2\left(Z\alpha \right)$ effects of a Gaussian nuclear charge on the electron-positron field are applied variationally towards the E119F molecule, as well as the order-$\alpha \left(Z\alpha \right)$ effects arising from the virtual muon and charged pion fields.

A fairly large number of optical frequency comb (OFC) generation methods have been proposed and practically implemented to date. All of them have their own advantages and disadvantages. For example, the application of bulk whispering gallery modes or on-chip optical ring microresonators allows one to obtain soliton Kerr combs in the spectral band achieving tens of nm and containing hundreds of lines. However, the spectral spacing between these lines will be determined by the dimensions of the microresonator and, as a rule, ranges from tens to hundreds of GHz. On the other hand, the application of frequency-shifting loop (FSL) systems with an acousto-optic (AO) device as the frequency shifter allows one to obtain OFCs with a frequency spacing of tens of MHz, but the spectral band of the AO FSL OFCs containing several thousand lines will hardly exceed 0.5 nm. In this paper, we propose a method to expand the AO FSL OFCs' spectral band applying multifrequency optical seeding. As a source of such seeding we propose to use lines of a soliton comb spectrum generated with an optical microresonator. This approach can also be considered as a method for enriching the optical spectrum of the microresonator OFC by adding spectral components generated in AO FSLs with a frequency spacing that is a multiple of the seeding soliton microcomb lines' frequency spacing. The paper presents the results of an experiment that confirms the possibility of implementation of such a concept.

Asymmetrical interactions are ubiquitous in nature, and in physics their study becomes fundamental. Despite the prevalence of evanescent coupling in physics, little attention has been paid to wave function profiles, with symmetrical reciprocal interactions often assumed for practical reasons. This work challenges that assumption by analytically demonstrating the origin of nonsymmetrical coupling in a photonic platform, focusing on the behavior of evanescent tails from adjacent waveguides. We experimentally validate an asymmetrical dynamics by studying detuned photonic directional couplers, fabricated via femtosecond laser writing, and corroborate our findings through continuous numerical simulations.

Spin ensembles play a pivotal role in various quantum applications such as metrology and simulations of many-body physics. Recent research has proposed utilizing spin cat states to encode logical quantum information, with logical lifetimes potentially on the order of seconds, achieved via enhanced collective interactions that scale with system size. We investigate the dynamics of spin cat states under inhomogeneous broadening, revealing a phenomenon termed “parity-sensitive inhomogeneous dephasing”: For small amplitudes, odd cat states are significantly more susceptible to inhomogeneous dephasing than even cat states due to the difference in parity symmetry. This discrepancy between even and odd cat states vanishes at large amplitudes and behaves similarly to a spin coherent state with the same amplitude. To analyze the stability of the spin coherent state, we perform a mean-field analysis of the driven-dissipative dynamics, from which we identify a synchronization phase transition wherein the ensemble becomes completely dephased beyond a critical inhomogeneous linewidth. The mean-field analysis suggests that the dissipative stabilization can suppress the decoherence effects from inhomogeneous broadening. We argue that the stability of the mean-field model provides a reasonable estimate for that of spin cat states with a large amplitude in the full quantum model. Our findings shed light on the stability of collective spin states, which is important for advancing quantum technologies.

Open quantum systems are governed by both unitary and nonunitary dynamics, with dissipation arising from the latter. Traditional quantum divergence measures, such as quantum relative entropy, fail to account for the nonunitary oriented dissipation as the divergence is positive even between unitarily connected states. We introduce a framework for quantifying the dissipation by isolating the nonunitary components of quantum dynamics. We define equivalence relations among Hermitian operators through unitary transformations and characterize the resulting quotient set. By establishing an isomorphism between this quotient set and a set of real vectors with ordered components, we induce divergence measures that are invariant under unitary evolution, which we refer to as the unitarily residual measures. These unitarily residual measures inherit properties such as monotonicity and convexity and, in certain cases, correspond to classical information divergences between sorted eigenvalue distributions. Our results provide a powerful tool for quantifying dissipation in open quantum systems, advancing the understanding of quantum thermodynamics.

We investigate the effect of counter-rotating-wave terms on nonlocality and entanglement for three qubits coupled to a common bath for strong- and ultrastrong-coupling regimes beyond the traditional treatment of Born-Markovian, perturbative, and rotating-wave approximations by employing the numerical hierarchical equations-of-motion approach. Our findings are as follows: (1) In the strong-coupling regime, the counter-rotating terms accelerate the decay of genuine three-party correlations, and the obvious sudden birth of Bell nonlocality is found. (2) In the ultrastrong-coupling regime, we observe a phenomenon in which nonlocality is consistently transferred between a three-qubit system and its subsystem. In addition, the inclusion of counter-rotating wave terms obviously enhances genuine tripartite nonlocality. (3) These counter-rotating terms cannot effectively generate genuine three-party correlations in zero-excitation cases, which differs from previous studies involving only two qubits. (4) A significant reduction in steady-state correlations for three- and two-party systems due to counter-rotating-wave terms is observed, which is not detectable under the rotating-wave approximation.

We study the deep multiscale entanglement renormalization Ansatz (DMERA) on quantum hardware and the causal cone of a subset of the qubits, which make up the Ansatz. This causal cone spans $O(M+logN)$ physical qubits on a quantum device, where $M$ and $N$ are the subset size and the total number qubits in the Ansatz, respectively. This allows for the determination of the von Neumann entanglement entropy of the $N$-qubit wave function using $O(M+logN)$ qubits by diagonalization of the reduced density matrix (RDM). We show this by randomly initializing a 16-qubit DMERA and diagonalizing the resulting RDM of the $M$-qubit subsystem using density-matrix simulation. As an example of practical interest, we also encode the variational ground state of the long-range transverse field Ising model (LRTIM) on eight spins using DMERA. We perform density-matrix simulation with and without noise to obtain entanglement entropies in separate experiments using only four qubits. Finally, we repeat the experiment on the IBM Kyoto back end reproducing simulation results.

Entanglement is a resource to improve the sensitivity of quantum sensors. In an ideal case, using an entangled state as a probe to detect target fields, we can beat the standard quantum limit by which all classical sensors are bounded. However, since entanglement is fragile against decoherence, it is unclear whether entanglement-enhanced metrology is useful in a noisy environment. Its benefit is indeed limited when estimating the amplitude of dc magnetic fields under the effect of parallel Markovian decoherence, where the noise operator is parallel to the target field. In this paper, on the contrary, we show an advantage to using an entanglement over the classical strategy under the effect of parallel Markovian decoherence when we try to detect ac magnetic fields. We consider a scenario to induce a Rabi oscillation of the qubits with the target ac magnetic fields. Although we can, in principle, estimate the amplitude of the ac magnetic fields from the Rabi oscillation, the signal becomes weak if the qubit frequency is significantly detuned from the frequency of the ac magnetic field. We show that, by using the Greenberger-Horne-Zeilinger (GHZ) states, we can significantly enhance the signal of the detuned Rabi oscillation even under the effect of parallel Markovian decoherence. Our method is based on the fact that the interaction time between the GHZ states and ac magnetic fields scales as $1/L$ to mitigate the decoherence effect, where $L$ is the number of qubits, which contributes to improving the bandwidth of the detectable frequencies of the ac magnetic fields. Our results pave the way for new applications of entanglement-enhanced ac magnetometry.

We present a method to prepare nonclassical states of the electromagnetic field in a microwave resonator. It is based on a controlled gate that applies a squeezing operation on a SQUID-terminated resonator conditioned on the state of a dispersively coupled qubit. This controlled-squeeze gate, when combined with Gaussian operations on the resonator, is universal. We explore the use of this tool to map an arbitrary qubit state into a superposition of squeezed states. In particular, we target a bosonic code with well-defined superparity which makes photon losses detectable by nondemolition parity measurements. We analyze the possibility of implementing this using state-of-the-art circuit QED tools and conclude that it is within reach of current technologies.

A methodology based on configuration-state-function generators (CSFGs) has recently been implemented in the General-Purpose Relativistic Atomic Structure Package (grasp) to reduce the computational load of configuration-interaction (CI) calculations Y. T. Li et al., Comput. Phys. Commun. 283, 108562 (2023). Large CI calculations can be performed if part of the interaction is treated perturbatively. Here, we present enhancements to the perturbative estimates by implementing blockwise methods, where the blocks are given by configuration-state-functions spanned by CSFGs. We compute excitation energies for $4s^{2}4p^{6}4d, 4s^{2}4p^{6}4f$, and $4s^{2}4p^{5}4d^2$ states in Rb-like ${\mathrm{W}}^{37+}$ and corresponding transition wavelengths and rates to evaluate the methods. The final relative difference between calculated and experimental wavelengths is 0.01%. Thus, the calculations provide highly accurate values for ${\mathrm{W}}^{37+}$ properties useful for a variety of applications, including fusion applications.

We propose a scheme for quantum-logic spectroscopy of an electron or positron in a Penning trap. An electron or positron in a spectroscopy trap is coupled to a remote logic electron or positron via a wire to achieve motional entanglement. By separating the two traps, one can significantly improve magnetic field homogeneity, microwave characteristics, and detection sensitivity. The proposed scheme will improve the measurement precision of the electron's and positron's magnetic moments and charge-to-mass ratios, enabling precise tests of the standard model of particle physics.

We carry out first-principle calculations of scalar and tensor components of the static electric dipole polarizabilities of six low-lying states of lithium (Li), sodium (Na) and potassium (K) alkali-metal atoms in the linear-response approach. Results are compared from the Dirac-Hartree-Fock (DHF) method, third-order many-body perturbation theory [MBPT(3) method], random-phase approximation (RPA) and singles and doubles approximated relativistic coupled-cluster theory (RCCSD method). We find the DHF and RPA results are close to each other, while the MBPT(3) and RCCSD results are close to each other. This suggests that pair-correlation effects play significant roles over core-polarization effects to determine these quantities accurately in the above alkali-metal atoms. We also compare contributions arising through the core, core-valence, and valence correlations through all the methods in Li, Na, and K, which show that the core-valence contributions are negligibly small in all the methods and there is no particular trends of the core and valence correlation contributions with the size of the atom. Uncertainties to the RCCSD results are estimated to quote the final values, and they are compared with the previous calculations and experimental results.

One long-term goal of attophysics is to deepen our knowledge on the ultrafast dynamics of quantum systems with the prospect of stirring electrons in their natural time and space scales. Two-photon processes are the lowest-order methods able to provide such information. Despite the long history backing two-photon studies and the success of many different exact and approximate methods, there are still some details to be unraveled. We use the Dalgarno-Lewis method to obtain both numerically exact results and accurate analytic expressions for short- and long-range contributions to the wave packets condensing information from the initial state and its coupling with the infinitely many virtual intermediate states in these two-photon processes. We identify some specific conditions under which short- and long-range terms adding up into the intermediate state induce radial matrix elements to hold competing coherent contributions for both single- and two-color cases. In the first case, interference structures marking a regime change may appear. On the second, short-range contributions may mask the compliance with propensity rules.

Molecular cavity optomechanics (COM), characterized by remarkably efficient optomechanical coupling enabled by a highly localized light field and ultrasmall effective mode volume, holds significant promise for advancing applications in quantum science and technology. Here, we study optomechanically induced transparency and the associated group delay in a hybrid molecular COM system. We find that even with an extremely low optical quality factor an obvious transparency window can appear, which is otherwise unattainable in a conventional COM system. Furthermore, by varying the ports of the probe light, the optomechanically induced transparency or absorption can be achieved, along with corresponding slowing or advancing of optical signals. These results indicate that our scheme provides an alternative method for adjusting the storage and retrieval of optical signals in such a molecular COM device.