We theoretically investigate the possibility of performing high precision estimation of an externally imposed acceleration using scalar bosons in a single-well trap. We work at the level of a two-mode truncation, valid for weak to intermediate two-body interaction couplings. The splitting process into two modes is in our model entirely caused by the interaction between the constituent bosons and is hence neither due to an externally imposed double-well potential nor due to populating a spinor degree of freedom. The precision enhancement gained by using various initial quantum states using a two-mode bosonic system is well established. Here we therefore instead focus on the effect of the intrinsic dynamics on the precision, where, in a single well, the Hamiltonian assumes a form different from that of the typical double-well case. We demonstrate how interactions can significantly increase the quantum Fisher information maximized over initial states as well as the quantum Fisher information for a fragmented or a coherent state, the two many-body states that can commonly represent the ground state of our system.

In this paper, we consider the generation of mechanical squeezed states and single-phonon Fock states, respectively, by homodyne detection and photon subtraction in a dissipative or dispersive optomechanical system under the situation that the cavity linewidth ${\kappa }_c$ is much larger than the mechanical frequency ${\omega }_m$. We at first show that strong mechanical squeezing beyond the 3-dB limit can be achieved by homodyning the filtered cavity output field in a purely dispersive or purely dissipative optomechanical system for ${\kappa }_c\gg {\omega }_m$, while the combination of the two kinds of coupling can also effectively enhance the mechanical squeezing. We next show that in these optomechanical systems, mechanical single-phonon states with high fidelity can be generated via photon subtraction on the filtered cavity output field in the regimes of weak optomechanical entanglement and ${\kappa }_c\gg {\omega }_m$. It is found that the single-phonon Fock state via purely dissipative optomechanical coupling is attainable in the blue-detuned regime, whereas it is present in the red-detuned regime by purely dispersive optomechanical coupling. In addition, the effects of thermal fluctuations on the mechanical squeezing and the negativity of the Wigner function of the mechanical single-phonon states are also studied. It is shown that the Gaussian squeezing is much more robust against decohering thermal fluctuations than the non-Gaussian nonclassicality.

We use astigmatic transformations to characterize two-dimensional superpositions of orbital-angular-momentum states in laser beams. We propose two methods for doing this, both relying only on astigmatic transformations, viewed as rotations on the Poincaré sphere, followed by imaging. These methods can be used as a tomographic tool for communication protocols based on optical vortices.

We propose a scheme to realize slow-light soliton beam splitters by using a tripod-type four-level atomic system. We show that optical solitons, which have ultraslow propagation velocity and ultralow generation power, can be generated in the system via electromagnetically induced transparency and can be stored and retrieved with high efficiency and fidelity. In particular, a nonlinear beam splitter that splits one optical soliton into two or more ones can be obtained by switching on and off of two or more control laser fields subsequently. The results reported here open a route not only for active manipulation of nonlinear optical pulses in multistate quantum systems but also for promising applications in optical information processing and transmission.

We analyze the performance of photon-number-resolving (PNR) detectors and introduce a figure of merit for the accuracy of such detectors. This figure of merit is the (worst-case) probability that the photon-number-resolving detector correctly predicts the input photon number. Simulations of various PNR detectors based on multiplexed single-photon “click detectors” is performed. We conclude that the required quantum efficiency is very high in order to achieve even moderate (up to a handful) photon resolution, we derive the required quantum efficiency as a function of the the maximal photon number one wants to resolve, and we show that the number of click detectors required grows quadratically with the maximal number of photons resolvable.

Magnetic-field uniformity is of the utmost importance in experiments to measure the electric dipole moment of the neutron. A general parametrization of the magnetic field in terms of harmonic polynomial modes is proposed, going beyond the linear-gradients approximation. We review the main undesirable effects of nonuniformities: depolarization of ultracold neutrons and Larmor frequency shifts of neutrons and mercury atoms. The theoretical predictions for these effects were verified by dedicated measurements with the single-chamber neutron electric-dipole-moment apparatus installed at the Paul Scherrer Institute.

Quantum resource theories offer a powerful framework for studying various phenomena in quantum physics. Although considerable effort has been devoted to developing a unified framework of resource theories, there are few common properties that hold for all quantum resources. In this paper, we fill this gap by introducing the flag additivity based on the tensor product structure and the flag basis for the general quantum resources. To illustrate the usefulness of flag additivity, we show that flag additivity can be used to derive other nontrivial properties in quantum resource theories, e.g., strong monotonicity, convexity, and full additivity.

In quantum lattice models, in the large-$N$ limit, boundary conditions have little effect upon local observables for sites in the centers of the lattices. In this paper, we will study the boundary effects upon multipartite nonlocality (a kind of multipartite quantum correlation associated with Bell-type inequalities) in one-dimensional finite-size spin chains, both for zero temperature and for finite temperatures. We define a quantity $\frac{\delta \mathcal{S}}{\mathcal{S}}$ to characterize the boundary effects, where $\mathcal{S}$ is a measure of global multipartite nonlocality of the entire lattice, and $\delta \mathcal{S}$ is the difference of the measure induced by changing the boundary conditions. We find $\frac{\delta \mathcal{S}}{\mathcal{S}}$ does not vanish in the large-$N$ limit. Instead, at zero temperature, with the increase of $N$, $\frac{\delta \mathcal{S}}{\mathcal{S}}$ would increase steadily in the vicinity of the quantum phase transition point of the models, and converge to a nonzero constant in noncritical regions. It shows clearly that boundary effects generally exist, in the form of multipartite correlations, in long chains. The boundary effects are explained by the competition between the two orders of the models. In addition, based on these numerical results, we construct a Bell inequality, which is violated by chains with periodic (closed) boundary conditions and not violated by chains with open boundary conditions. Furthermore, we study $\frac{\delta {\mathcal{S}}_T}{{\mathcal{S}}_T}$ of finite-size chains at finite temperatures, and show that boundary effects survive in finite temperature regions.

Using a microwave and radio frequency resonance approach we observe the transitions of ytterbium from the $6s(n+3)d$ states to the $6sn\ell$ states for $4\le \ell \le 6$ and $28\le n\le 33$. The energies of the $6sn\ell$ states of $\ell \ge 4$ are determined from the observed intervals and the known values of the $6snd$ energies. We use a nonadiabatic core polarization model to analyze the energy levels to determine the dipole $\left({\alpha }_d\right)$ and quadrupole $\left({\alpha }_q\right)$ polarizabilities of the ground state of ${\mathrm{Yb}}^{+}$. We find the values ${\alpha }_d=60.51\left(10\right)a_0^3$ and ${\alpha }_q=672\left(28\right)a_0^5$.

The high-order harmonic spectrum generated in a two-color intense laser field under certain conditions has a pronounced maximum caused by the so-called spectral caustic. Using a numerical solution of the three-dimensional time-dependent Schrödinger equation we study the width of the maximum and the degree of the generation enhancement due to the caustic as a function of the fundamental intensity, wavelength, and atomic ionization potential. It is shown that the degree of this enhancement can be quantitatively characterized well by a single parameter: the ratio of the radius of the free electronic oscillation in the laser field to the atomic size. This behavior can be explained by the Coulomb attraction of the photoelectron to the parent ion, whereas the effect of this attraction on the width of the maximum is negligible. Choosing the field parameters providing a pronounced enhancement, we calculate the high-order harmonic macroscopic response taking into account the transient phase-matching. We show that the caustic feature can be used to provide a quasimonochromatic XUV source with an almost linear frequency vs time dependence. Such source can be used, in particular, for time-resolved single-shot XUV imaging.

We have conducted an experimental study on the photo double ionization (PDI) of carbon-dioxide dimers at photon energies of 37 and 55 eV and oxygen dimers at photon energies of 38, 41.5, and 46 eV, while focusing on the dissociation dynamics upon single-photon absorption. The investigation was performed by applying the cold-target recoil-ion momentum spectroscopy method in order to collect and record the three-dimensional momenta of the ionic fragments and emitted electrons from the dissociating dimer in coincidence. The kinetic-energy release upon fragmentation and the electron angular distributions in the laboratory and body-fixed frames, as well as the relative electron-electron emission angle, show unambiguous experimental evidence of intermolecular Coulombic decay (ICD) in carbon-dioxide dimers upon photoionization below and above the double-ionization threshold of ${\mathrm{CO}}_2$ monomers. The PDI of oxygen dimers is less conclusive and shows contributions from ICD and knock-off ionization mechanisms. As for atomic dimers, the present results reveal that ICD in ${\mathrm{CO}}_2$ dimers after valence PDI can also serve as a source for low-energy electrons, known to be very relevant in biological systems, cells, and tissues.

We present a variational model suitable for rapid preliminary design of atom interferometers in a microgravity environment. The model approximates the solution of the three-dimensional rotating-frame Gross-Pitaevskii equation as the sum of $N_c$ Gaussian clouds. Each Gaussian cloud is assumed to have time-dependent center positions, widths, and linear and quadratic phase parameters. We applied the Lagrangian variational method (LVM) with this trial wave function to derive equations of motion for these parameters that can be adapted to any external potential. We also present a one-dimensional (1D) version of this variational model. As an example we apply the model to a 1D atom interferometry scheme for measuring Newton's gravitational constant, $G$, in a microgravity environment. We show how the LVM model can (1) constrain the experimental parameter space size, (2) show how the value of $G$ can be obtained from the experimental conditions and interference pattern characteristics, and (3) show how to improve the sensitivity of the measurement and construct a preliminary error budget.

The self-trapped optical beams possessing both chaotic and solitonlike properties, which are termed as chaoticons, were predicted by us [Sci. Rep. 7, 41438 (2017)] in the strongly nonlocal nonlinear media. We reveal that any random input beam, which has random initial transverse distribution and arbitrary input power, propagating in the strongly nonlocal nonlinear media with the exponential-decay response, will evolve into a chaoticon. The chaotic properties are signified by the positive Lyapunov exponents and spatial decoherence, while the solitonlike properties are demonstrated by the invariance of the beam width and the interaction of quasielastic collisions. Distinctively, the propagations of random inputs are always periodic in the strongly nonlocal media with the Gaussian response.

In this paper, we investigate the optomechanically induced transparency (OMIT) phenomenon in the Laguerre-Gaussian (L-G) rotational-cavity optomechanical system, which can be regarded as an analog of the OMIT in a cavity optomechanical system with a vibrational mirror. We find that the window width of OMIT is dependent on the orbital angular momentum of the L-G light, which can be used to detect the orbital angular momentum of L-G light. We then accordingly propose a scheme to measure the orbital angular momentum of L-G light with OMIT, and its feasibility is justified by numerical simulation.

We study the effects of parity-time ($\mathcal{PT}$) symmetry on the photon blockade and distinguish the different blockade mechanisms in a double-cavity optomechanical system. By studying the light statistics of the system, we find the completely different photon blockade behaviors when the $\mathcal{PT}$ symmetry is broken or unbroken, which is related to the $\mathcal{PT}$ phase transition. Furthermore, an interesting phenomenon that the two cavities are blocked at the same time is found with the appropriate system parameters. Those statistical phenomena are all analyzed in detail and demonstrated by analytically solving the Schrödinger equation and numerically simulating the master equation, respectively. Finally, we also consider the non-$\mathcal{PT}$-symmetric situations which further reveal the physical essence of the photon blockade by comparing those results. Different from the usual photon blockade, our proposal is feasible even with weak parameter mechanism, i.e., the proposal neither requires the strong optomechanical coupling nor the large tunneling coupling between cavities.

Comparison of high-accuracy calculations with precision measurement of the 413-nm tune-out wavelength of the $\mathrm{He}\left(2{}^3{S}_1\right)$ state provides a unique test of quantum electrodynamics (QED). We perform large-scale relativistic-configuration-interaction (RCI) calculations of the tune-out wavelength that include the mass-shift operator and fully account for leading relativistic nuclear recoil terms in the Dirac-Coulomb-Breit (DCB) Hamiltonian. We obtain the QED correction to the tune-out wavelength using perturbation theory, and the effect of finite nuclear size is also evaluated. The resulting tune-out wavelengths for the $2{}^3{S}_1(M_J=0)$ and $2{}^3{S}_1(M_J=\pm 1)$ states are 413.084 26(4) nm and 413.090 15(4) nm, respectively. When we incorporate the retardation correction of 0.000 560 0236 nm obtained by Drake et al. [Hyperfine Interact 240, 31 (2019)] to compare results with the only current experimental value of $413.0938\left(9_{\text{stat}}\right)\left({20}_{\text{syst}}\right)$ nm for the $2{}^3{S}_1(M_J=\pm 1)$ state, there is $1.4\sigma$ discrepancy between theory and experiment, which stimulates further theoretical and higher precision experimental investigations on the 413-nm tune-out wavelength. In addition, we also determine the QED correction for the static dipole polarizability of the $\mathrm{He}\left(2{}^3{S}_1\right)$ state to be 22.5 ppm, which may enable a new test of QED in the future.

Quantum state tomography is of crucial importance in assessing the quality of quantum information processing devices. Tomography fundamentally requires both experiments and data processing resources, which increase exponentially with the size of qubits. We propose using phase lift to precisely characterize an unknown quantum state using only a small part of the data. We numerically reconstruct the density matrix of multiqubit pure states including the Greenberger-Horne-Zeilinger (GHZ) state, W-class state, cluster state, and random states. The Nesterov algorithm shows high accuracy and high speed for pure states especially for the specific entangled states with a large number of qubits. It shows the highest accuracy among the several specific algorithms, specially for larger number of qubits.

Highly accurate measurements of the $g$ factor of boronlike Ar are currently implemented within the ARTEMIS experiment at GSI (Darmstadt, Germany) and within the ALPHATRAP experiment at the MPIK (Heidelberg, Germany). A comparison with the corresponding theoretical predictions will allow one to test the modern methods of bound-state QED. However, at least three different theoretical values of the $g$ factor have been published up to date. The systematic study of the $g$-factor value of ${}^{40}\mathrm{Ar}^{13+}$ in the ground $\left[{\left(1s\right)}^2{\left(2s\right)}^{2}2p^1\right]{}^{2}P_{1/2}$ and the first excited $\left[{\left(1s\right)}^2{\left(2s\right)}^{2}2p^1\right]{}^{2}P_{3/2}$ states is performed within the high-order coupled cluster and configuration interaction theories up to the full configuration interaction treatment. Correlation contributions are discussed and results are compared with previous studies.

A zero-area four-blade perfect crystal neutron interferometer (NI) possess a decoherence-free subspace (DFS) for low-frequency mechanical vibrations and thus is easier to site. However, unlike the standard three-blade Mach-Zehnder NI the ideal contrast of this four-blade NI geometry is less than 1. By applying a recently introduced quantum information model for dynamical diffraction we show that the contrast for the four-blade DFS NI can be increased by offsetting the focusing condition. The contrast optimization leads to an NI geometry where the distances between the centers of the blades are equidistant. An experiment is proposed to verify the increase in contrast.

In the context of phase estimation with Gaussian states, we introduce a quantifiable definition of metrological advantage that takes into account thermal noise in the preparation procedure. For a broad set of states—isotropic nonpure Gaussian states—we show that squeezing is not only necessary but sufficient to achieve metrological advantage. We interpret our results in the framework of resource theory and discuss possible sources of advantage other than squeezing. Our work is a step towards using phase estimation with pure and mixed states to define and quantify nonclassicality. This work is complementary with studies that defines nonclassicality using quadrature displacement estimation.