The fields produced by a classical point electric dipole are investigated. The dipole is turned on smoothly at $t=0$ and the classical dipole moment is assumed to correspond to either a linearly polarized damped oscillator, a static dipole, or a rotating dipole. It is shown that Poynting's theorem can be violated if it is assumed the dipole is turned on suddenly and derivatives of the step function associated with the sudden turn on are not properly accounted for. For the rotating dipole, it is shown that the angular momentum in the field need not be equal to the sum of its spin and orbital components. Moreover, the total angular momentum that is radiated by the rotating dipole is not equal to the original mechanical angular momentum of the dipole.

Non-Hermitian Hamiltonians play a crucial role in describing open quantum systems and nonequilibrium dynamics. In this paper, we derive trade-off relations for systems governed by non-Hermitian Hamiltonians, focusing on the Margolus-Levitin-type and Mandelstam-Tamm-type bounds, which are originally derived as quantum speed limits in isolated quantum dynamics. While the quantum speed limit for the Mandelstam-Tamm bound in general non-Hermitian systems was derived in the literature, we obtain a Mandelstam-Tamm quantum speed limit for continuous measurement using the continuous matrix product state formalism. Moreover, we derive a Margolus-Levitin quantum speed limit in the non-Hermitian setting. We derive additional bounds on the ratio of the standard deviation to the mean of an observable, which take the same form as the thermodynamic uncertainty relation. As an example, we apply these bounds to the continuous measurement formalism in open quantum dynamics, where the dynamics is described by discontinuous jumps and smooth evolution induced by the non-Hermitian Hamiltonian. Our work provides a unified perspective on the quantum speed limit and thermodynamic uncertainty relations in open quantum dynamics from the viewpoint of the non-Hermitian Hamiltonian, extending the results of previous studies.

One of the main bottlenecks in solving combinatorial optimization problems with quantum annealers is the qubit connectivity in the hardware. A possible solution for larger connectivity is minor embedding. This technique makes the geometrical properties of the combinatorial optimization problem, encoded as a Hamiltonian, match the properties of the quantum annealing hardware. The embedding itself is a hard computational problem, and therefore heuristic algorithms are required. In this work we present fixed, modular, and scalable embeddings that can be used to embed any combinatorial optimization problem described as an Ising Hamiltonian. These embeddings are the result of an extension of the well-known parity mapping, which has been used in the past to map higher-order Ising Hamiltonians to quadratic Hamiltonians, which are suitable for existing quantum hardware. We show how our new embeddings can be mapped to existing quantum annealers and that the embedded Hamiltonian physical properties match the original Hamiltonian properties.

Quantum networks consist of various quantum technologies, spread across vast distances, and involve various users at the same time. Certifying the functioning and efficiency of the individual components is a task that is well studied and widely used. However, the power of quantum networks can only be realized by integrating all the required quantum technologies and platforms across a large number of users. In this work, we demonstrate how to certify the distillable entanglement available in multipartite states produced by quantum networks, without relying on the physical realization of its constituent components. We do so by using the paradigm of device independence.

One promising application of near-term quantum devices is to prepare trial wave functions using short circuits for solving different problems via variational algorithms. For this purpose, we introduce a circuit design that combines graph-based diagonalization circuits with arbitrary single-qubit rotation gates to get a Hamiltonian-based graph states ansatz. We test the accuracy of the proposed ansatz in estimating ground-state energies of various molecules of size up to 12 qubits. Additionally, we compare the gate count and parameter number complexity of the proposed ansatz against previously proposed schemes and find an order magnitude reduction in gate count complexity with a slight increase in the number of parameters. Our work represents a significant step towards constructing compact quantum circuits with good trainability and convergence properties and applications in solving chemistry and physics problems.

Molecular frame photoelectron angular distributions (MFPADs) provide the full available detail of the photoionization process. Careful analysis of the evolving photoelectron angular distribution during the coherent rotation of a nonadiabatically aligned sample of molecules allows the detail which is smoothed out by orientational averaging in the laboratory frame to be resolved. Here we exploit a high flux monochromated HHG lightsource to provide single-photon photoelectron angular distributions of field-free aligned molecules. Our measurements are sensitive to alignment frame variations in even ${\beta }_n$ parameters up to $n=6$ in the PADs of the first four ionization channels of OCS, allowing for rigorous benchmarking of the cutting edge theoretical methods used for simulation of MFPADs. We demonstrate that experimentally derived molecular alignment distributions may be combined with theoretical MFPADs to generate theoretical alignment-frame PADs which provide a quantitative comparison to the experimental ${\beta }_n$ parameters. The experimental data and ePSproc simulated PADs show quantitative agreement and sensitivity to picometer-scale changes in the molecular geometry. This combined methodology therefore provides a versatile way of studying geometry-sensitive continuum structural features for nondissociative ionization processes which may not be studied in the recoil frame. These measurements therefore provide a strict test of the theoretical descriptions and will stand as benchmark measurements for future comparisons to higher-level theory.

We experimentally and theoretically investigate the nondipole shift of the electron momentum distribution in the light-propagation direction in strong-field ionization of Ar atoms using counterrotating circularly polarized two-color laser fields. We observe that the electron mean momentum in the laser propagation direction in bicircular fields is strongly dependent on both the emission angle $\theta$ and the radial momentum $p_r$ of the electron. In low-energy electrons, the mean momentum follows the relation $p_r^2/2c+I_p/3c$ ($c$ is the velocity of light and $I_p$ is the ionization potential), while for high-energy electrons it is significantly suppressed and deviates from the predicted values. Using nondipole-corrected classical trajectory Monte Carlo simulations, we identify that the nondipole shift is significantly influenced by the electron scattering process. The dominance of scattered electrons in the high-energy region leads to the reduction of the mean momentum shift. By extracting the angle- and momentum-resolved mean momentum spectrum, we show that the scattered and nonscattered electrons are emitted at different angles in counterrotating circularly polarized fields due to the nondipole shift. The sensitivity of the nondipole effect to the scattering process serves as a promising tool for probing strong-field-driven electron dynamics.

Using radio-frequency (rf) spectroscopy, we measure the $p$-wave contacts in a Fermi gas of ${}^6\mathrm{Li}$ atoms near the $p$-wave Feshbach resonance. The rf spectrum exhibits clear asymptotic behavior, characterized by ${\tilde{\omega }}^{-1/2}$ and ${\tilde{\omega }}^{-3/2}$ dependencies. The magnetic-field dependence of the $p$-wave contacts agrees reasonably well with the virial expansion theory in a detuned magnetic-field range, validating the theory near half of the Fermi temperature. The $p$-wave contacts measured in this article constitute a second data set, complementing the data obtained from the ${}^{40}\mathrm{K}$ system and contributing valuable insights into $p$-wave interactions in ultracold Fermi gases.

We investigate the dynamics of one-dimensional interacting bosons in an optical lattice after a sudden quench in the weakly interacting (Bose-Hubbard) and strongly interacting (sine-Gordon) regimes. While in a higher dimension, the Mott-superfluid phase transition is observed for weakly interacting bosons in deep lattices, in one dimension an instability is generated also for shallow lattices with a commensurate periodic potential pinning the atoms to the Mott state through a transition described by the sine-Gordon model. The present work aims at identifying the quench dynamics in both the Bose-Hubbard and sine-Gordon interaction regimes. We numerically exactly solve the time-dependent Schrödinger equation for a small number of atoms and obtain dynamical measures of several key quantities. We investigate the correlation dynamics of first and second order; both exhibit rich many-body features in the dynamics. We conclude that in both cases, dynamics exhibits collapse-revival phenomena, though with different timescales. We argue that the dynamical fragmentation is a convenient quantity to distinguish the dynamics especially near the pinning zone. To understand the relaxation process we measure the many-body information entropy. Bose-Hubbard dynamics clearly establishes the possible relaxation to the maximum entropy state. In contrast, the sine-Gordon dynamics is so fast that it does not exhibit any signature of relaxation in the present timescale of computation.

Optomechanics with semi-transparent membrane multioscillators in a high-finesse cavity is an established solution for designing the dispersive interaction, and reaching many achievements, such as the study of nonlinear dynamics, heat transfer, and so on. The multioscillators are dielectric slabs, usually with low reflectivity, constituting an etalon. Here we propose the theoretical and experimental investigation of a low-finesse optical cavity formed by two (nominally identical) parallel semi-transparent membranes. The experiment consists in laser-driving the cavity, detecting interferometrically the field reflected by the etalon, and measuring the intensity of the transmitted field, for different distances within the two membranes. A complete characterization of the membrane sandwich is provided. Moreover, we develop an analytical model to describe the fields, which reproduces all the experimental results, under specific approximations. As expected, the model reproduces the known results when high-reflectivity, and/or fixed mirrors conditions are restored. This work paves the way for a complete and analytical model to describe multi-oscillators “membrane-in-the-middle” optomechanics.

Ruling a wide range of phenomena, dipole-dipole interactions (DDI) are typically constrained to the short range due to their rapid decay with increasing dipole separations, limiting performance in long-range applications. By judiciously designing the photonic structures that control the two-point Green's functions of the electromagnetic environment, the spontaneous emission of quantum emitters (luminescence) and their interactions (e.g., Förster energy transfer) can be conveniently tuned. In this paper, we design a matched nanoparticle-on-mirror antenna pair with enhanced DDI guided by surface plasmon polaritons confined to the metal substrate, which ensures concentrated and enhanced interaction over long ranges of tens of wavelengths. The long-range ($\sim 10\lambda$) DDI between donor-acceptor emitters is enhanced by $6\times {10}^3$ times respective to bare gold film, and $4.4\times {10}^4$ times respective to a vacuum. Our result provides a promising testbed for investigating long-range DDI phenomena on the nanoscale.

In the work by Balybin et al. [Phys. Rev. A 108, 053708 (2023)], the scheme of quantum nondemolition measurement of optical quanta that uses a resonantly enhanced Kerr nonlinearity in the optical microresonator, presqueezing of the probe beam, and its parametric amplification before the detection was analyzed theoretically. It was shown that the main factor that limits the sensitivity of the considered scheme is the interplay of optical losses and the nonlinear self-phase modulation (SPM) effect. Here we show that using the intracavity squeezing of the probe beam in this scheme, it is possible to cancel out the SPM effect. In this case, the sensitivity will be limited only by the available power in the pump beam and by the input/output losses in the signal beam. Our estimates show that using the best optical microresonators currently available, the sensitivity for the intracavity photon number approaching the single-photon one can be achieved. Therefore, this scheme could be of interest for optical quantum information processing tasks.

Circuit knitting, a method for connecting quantum circuits across multiple processors to simulate nonlocal quantum operations, is a promising approach for distributed quantum computing. While various techniques have been developed for circuit knitting, we uncover fundamental limitations to the scalability of this technology. We prove that the sampling overhead of circuit knitting is exponentially lower bounded by the exact entanglement cost of the target bipartite dynamic, even with the asymptotic amount of resources using the parallel cut strategy. Specifically, we prove that the regularized sampling overhead assisted with local operations and classical communication of any bipartite quantum channel is lower bounded by the exponential of its exact entanglement cost under separable preserving operations. Furthermore, we develop the faithful lower bounds for the regularized sampling overhead based on channels' $\kappa$ entanglement and max-Rains information, providing efficiently computable benchmarks. Our work reveals a profound connection between virtual quantum information processing via quasiprobability decomposition and quantum Shannon theory, highlighting the critical role of entanglement in distributed quantum computing.

Coherent manipulation of three-level systems is of critical significance to quantum information processing. Here, we propose a scheme to achieve quantum state engineering in arbitrary three-level systems, in which the controlling Hamiltonian can be inversely engineered based on Lewis-Riesenfeld invariants and a gauge transformation. With well-designed control pulses, the three-level system continually evolves from the initial state to a desired final state in one step. The proposed scheme allows diverse optimizations, which gives it a significant advantage in robustness and fidelity over the commonly used resonant-pulse multistep method. The scheme can also be extended to produce multiqubit entangled states provided with a similar state subspace. In a particular application, we demonstrate numerically that our protocol can reliably and robustly prepare qutrit states as well as three-qubit entangled $W$ states within superconducting circuits.

In the field of chemistry, where nuclear motion has traditionally been a focal point, we now explore the ultrarapid electronic motion spanning attoseconds to femtoseconds, demonstrating that it is equally integral and relevant to the discipline. The advent of ultrashort attosecond pulse technology has revolutionized our ability to directly observe electronic rearrangements in atoms and molecules, offering a time-resolved insight into these swift processes. Prominent examples include Auger-Meitner decay and interparticle Coulombic decay. However, the real challenge lies in interpreting these observations, where theoretical models are indispensable. Building upon the analytical framework introduced by Fasshauer and Madsen [Phys. Rev. A 101, 043414 (2020)], which analyzed the spectra of electrons emitted during electronic decay processes from a purely electronic perspective, we extend this theoretical base to include nuclear dynamics, utilizing the Born-Oppenheimer approximation to deepen our understanding of the intricate interaction between electronic and nuclear motion in these processes. We illustrate the impact of incorporating nuclear degrees of freedom in several theoretical cases characterized by different numbers of vibrational bound states in both the electronic resonance and the electronic final state. This approach not only clarifies complex spectral features and unusual peak shapes but also demonstrates a method for extracting the energy differences between multiple vibrational resonance states through their distinctive interference patterns.

The quantum optical description of high-order harmonic generation where both the electrons of the generating medium and the driving and generated light fields are described quantum mechanically has been of significant interest in the past years. The quantum optical formulation leads to equations of motion for the generated light field in which the quantum optical field couples to the time-dependent current of the electronic medium irrespectively of the specifics of the electronic system being an atom, molecule, or solid. These equations of motion are not solvable for any realistic system and accurate and verified approximations are hence needed. In this paper, we present a hierarchy of approximations for the equations of motion for the photonic state. At each level in this hierarchy, we compare it to the previous level justifying the validity using the Fermi-Hubbard model as an example of an electronic system with correlations. This model allows us to perform an accurate simulation of the electron motion of all the required states. We find that for the typical experimental situation of weak quantized-light-matter-coupling constant and at intensities well below the damage threshold, an explicit expression for the generated quantum light, referred to as the Markov-state approximation, captures the high-harmonic spectrum quantitatively and describes the single-mode quantum properties of the generated light as characterized by the Mandel-$Q$ parameter and the degree of squeezing qualitatively.

We theoretically investigate the possibility of the formation of subcycle dissipative solitons propagating in a multilevel resonant medium. We examine the case when the duration of light pulses is significantly smaller than the periods of resonant transitions in the medium. Within such an approximation, a nonlinear integro-differential equation describing the spatiotemporal evolution of the electric field was derived. We demonstrate that in the case of a preexcited medium, this equation has solutions in the form of stable half-cycle unipolar dissipative solitons with the parameters determined by the medium properties. The obtained results can provide an important step towards the efficient transmission of subcycle pulses through optical media.

We present results on the second-harmonic generation using nondiffracting speckle fields in the fundamental frequency to pump a nonlinear medium to obtain the sum-frequency generation. Our findings reveal a significant enhancement in the spatial coherence within the central region of the far-field diffraction pattern of the second-harmonic field when using nondiffracting speckles, compared to a diffracting speckle field of the same coherence length before the nonlinear medium. Our findings may contribute to the design of systems for free-space optical communication or the implementation of imaging and sensing systems using nondiffracting speckles fields.

We theoretically investigate the steady-state bipartite entanglements, mechanical ground-state cooling, and mechanical quadrature squeezing in a hybrid electro-optomechanical system where a moving membrane is linearly coupled to the microwave field mode of an LC circuit, while it simultaneously interacts both linearly and quadratically with the radiation pressure of a single-mode optical cavity. We show that by choosing a suitable sign and amplitude for the quadratic optomechanical coupling (QOC), one can achieve enhanced and thermally robust stationary bipartite entanglement between the subsystems, improved mechanical ground-state cooling, and $Q$-quadrature squeezing of the mechanical mode beyond the 3-dB limit of squeezing. In particular, we find that in the presence of QOC with negative sign and in the resolved sideband regime the bipartite optical-mechanical entanglement can be increased by about 2 orders of magnitude around the temperature of 1 mK, and it can be preserved against thermal noise up to the ambient temperature of 0.1 K. Furthermore, the QOC with positive sign can give rise to the enhancement of the mechanical ground-state cooling by about 1 order of magnitude in the optical and microwave red-detuned regime. We also find that for the positive sign of QOC and near the microwave resonance frequency the squeezing degree of the $Q$ quadrature of the mechanical mode can be amplified up to 15 dB. Such a hybrid electro-optomechanical system can serve as a promising platform to engineer an improved entangled source for quantum sensing as well as quantum information processing.