The three-body Schrödinger equation of the system composed of an $\alpha$ particle ${\mathrm{He}}^{2+}$, a negatively charged pion ${\pi }^{-}$, and an electron interacting through Coulomb forces is solved in perimetric coordinates with the Lagrange-mesh method. The ground state, quasibound states, and resonances are obtained for total orbital momenta $L=0-20$. Mean distances between the particles allow for identifying the structure of these states. The widths of resonances broader than ${10}^{-5}$ atomic units are derived with the complex scaling method. A transition from atomic to molecular structure occurs between $L=10$ and $L=13$. Excited levels obtained for $L=0-5$ display hydrogenlike properties for both the $\alpha$-pion system and the electron excitations. Excited levels with $L\ge 14$ correspond to a vibrational excitation of the relative motion of the heavy particles. The validity of the Born-Oppenheimer approximation is found to be fair over the whole range of total orbital momenta.

We demonstrate photoassociation (PA) of ultracold fermionic ${}^{87}\mathrm{Sr}$ atoms. The binding energies of a series of molecular states on the ${}^1\mathrm{\Sigma }_u^{+}5s^2{}^{1}S_0+5s5p{}^{1}P_1$ molecular potential are fit with the semiclassical LeRoy-Bernstein model, and PA resonance strengths are compared to predictions based on the known ${}^{1}S_0+{}^{1}S_0$ ground-state potential. Similar measurements and analysis were performed for the bosonic isotopes ${}^{84}\mathrm{Sr}$ and ${}^{86}\mathrm{Sr}$, allowing a combined analysis of the long-range portion of the excited-state potential and determination of the $5s5p{}^{1}P_1$ atomic state lifetime of $5.20\pm 0.02\mathrm{ns}$. The results enable prediction of PA rates across a wide range of experimental conditions.

We demonstrate a technique for the accurate measurement of diffusion coefficients for alkali vapor in an inert buffer gas. The measurement was performed by establishing a spatially periodic density grating in isotopically pure ${}^{87}\mathrm{Rb}$ vapor and observing the decaying coherent emission from the grating due to the diffusive motion of the vapor through ${\mathrm{N}}_2$ buffer gas. We obtain a diffusion coefficient of $0.245\pm 0.002{\text{cm}}^2/\text{s}$ at $50{}^{\circ }\mathrm{C}$ and 564 Torr. Scaling to atmospheric pressure, we obtain $D_0=0.1819\pm 0.0024{\text{cm}}^2/\text{s}$. To the best of our knowledge, this represents the most accurate determination of the $\mathrm{Rb}\text{−}{\mathrm{N}}_2$ diffusion coefficient to date. Our measurements can be extended to different buffer gases and alkali vapors used for magnetometry and can be used to constrain theoretical diffusion models for these systems.

We report a Mach-Zehnder-type dual-atom-interferometer gyroscope with an interrogation arm of 40-cm length and the interference area up to $1.2{\mathrm{cm}}^2$. The precise angular alignment of the large-scale separated Raman lasers is demonstrated by seeking the phase intersection of Ramsey-$\mathrm{Bord}\acute{\mathrm{e}}$ interferometers after the gravity effect is compensated and by decoupling the velocity dependent cross-talk phase shifts, and applied to build the Mach-Zehnder atom interferometer. Then a compact inertial rotation sensor is realized based on dual large-area Mach-Zehnder atom interferometers by precisely aligning the large-scale separated Raman lasers, in which the coherence is well preserved and the common noise is differentially suppressed. The sensor presents a sensitivity of $1.5\times {10}^{-7}$ $\mathrm{rad}/\mathrm{s}/{\mathrm{Hz}}^{1/2}$, and a stability of $9.5\times {10}^{-10}\mathrm{rad}/\mathrm{s}$ at 23000 s. The absolute rotation measurement is carried out by adjusting the atomic velocity which corresponds to modulating the scale factor.

Atoms can form molecules if they attract each other. Here, we show that atoms are also able to form bound states not due to the attractive interaction but because of destructive interference. If the interaction potential changes in a disordered way with a change of the distance between two atoms, Anderson localization can lead to the formation of exponentially localized bound states. While disordered interaction potentials do not exist in nature, we show that they can be created in the laboratory by means of random modulation in time of the strength of the original interaction potential between atoms and objects that we dub Anderson complexes can be realized.

Kerr comb generation is usually based on the nonlinear dynamics of the intracavity field in a whispering-gallery-mode resonator pumped by a continuous-wave laser. However, using a pulsed instead of a continuous-wave pump opens an alternative research avenue from both the theoretical and experimental viewpoints, as it permits us to tailor the spectral properties of ultrashort pulse trains with a single passive nonlinear element. In this article we study the dynamics of Kerr optical frequency combs when the whispering-gallery-mode resonator is pumped by a synchronous pulse train. We propose a model that is based on an extension of the Lugiato-Lefever equation, which accounts for both the pulsed nature of the pump and the mismatch between the free-spectral range of the resonator and the repetition rate of the pulse train. We lay a particular emphasis on the effect of pump-cavity desynchronization on the spectral shape of the output combs. The numerical simulations are successfully compared with experimental measurements where the optical pulses are generated via time-lens soliton compression, and the resonator is a millimeter-size magnesium fluoride resonator with a billion quality factor at the pump wavelength.

We show how the Jaynes-Cummings-Rabi model of cavity quantum electrodynamics can be realized via an isomorphism to the Hamiltonian of a qubit inside a parametric amplifier cavity. This realization clears the way to observe the full spectrum of the Rabi model via a probe applied to a parametric amplifier cavity containing a qubit and a parametric oscillator operating below threshold. An important outcome of the isomorphism is that the actual frequencies are replaced by detunings which make it feasible to reach the ultrastrong coupling regime. We find that inside this regime the probed spectrum displays a narrow resonance peak that is traced back to the transition between ground and first excited states. The exact form of these states is given at an energy crossing and then extended numerically. At the crossing, the eigenstates are entangled states of field and atom where the field is found inside squeezed cat states.

Bohr's complementarity principle is of fundamental historic and conceptual importance for quantum mechanics (QM), and states that, with a given experimental apparatus configuration, one can observe either the wave-like or the particle-like character of a quantum system, but not both. However, it was eventually realized that these dual behaviors can both manifest partially in the same experimental setup, and, using ad hoc proposed measures for the wave and particle aspects of the quanton, complementarity relations were proposed limiting how strong these manifestations can be. Recently, a formalism was developed and quantifiers for the particleness and waveness of a quantum system were derived from the mathematical structure of QM entailed in the density matrix's basic properties ($\rho \ge 0, \mathrm{Tr}\rho =1$). In this article, using IBM Quantum Experience quantum computers, we perform experimental tests of these complementarity relations applied to a particular class of one-qubit quantum states and also for random quantum states of one, two, and three qubits.

We study the question of how to decompose Hilbert space into a preferred tensor-product factorization without any preexisting structure other than a Hamiltonian operator, in particular the case of a bipartite decomposition into “system” and “environment.” Such a decomposition can be defined by looking for subsystems that exhibit quasiclassical behavior. The correct decomposition is one in which pointer states of the system are relatively robust against environmental monitoring (their entanglement with the environment does not continually and dramatically increase) and remain localized around approximately classical trajectories. We present an in-principle algorithm for finding such a decomposition by minimizing a combination of entanglement growth and internal spreading of the system. Both of these properties are related to locality in different ways. This formalism is relevant to questions in the foundations of quantum mechanics and the emergence of spacetime from quantum entanglement.

One of the fundamental features of quantum mechanics is the superposition principle, a manifestation of which is embodied in quantum coherence. Coherence of a quantum state is invariably defined with respect to a preferred set of pointer states, and there exist quantum coherence measures with respect to deterministically as well as probabilistically distinguishable sets of quantum state vectors. Here we study the resource theory of quantum coherence with respect to an arbitrary set of quantum state vectors, that may not even be probabilistically distinguishable. Geometrically, a probabilistically indistinguishable set of quantum state vectors forms a linearly dependent set. In quantum optics, the coherent states form an “overcomplete basis” of linearly dependent states and are useful in dealing with states that can be prepared in optical systems. Also, the resource theory of magic can be looked upon as a resource theory of quantum coherence with respect to a set of basis vectors that are probabilistically indistinguishable. These motivate us to consider a resource theory of coherence with respect to probabilistically indistinguishable pointers. We find the free states of the resource theory, and analyze the corresponding free operations, obtaining a necessary condition for an arbitrary quantum operation to be free. We identify a class of measures of the quantum coherence and, in particular, establish the monotonicity property of the measures. We find a connection of an arbitrary set of quantum state vectors with positive operator-valued measurements with respect to the resource theory being considered, which paves the way for an alternate definition of the free states. We subsequently examine the wave-particle duality in a double-slit setup in which superposition of probabilistically indistinguishable quantum state vectors is possible. Specifically, we report a complementary relation between quantum coherence and path distinguishability in such a setup.

We demonstrate a method of light phase shift measurement using a high-finesse optical ring cavity which exhibits reduced phase noise due to cavity length fluctuations. Two laser beams with a frequency difference of one cavity free spectral range are simultaneously resonant with the cavity, demonstrating noise correlations in the error signals due to the common-mode cavity length fluctuations. The differential error signal shows a 30 dB reduction in cavity noise down to the noise floor in a frequency range up to half the cavity linewidth ($\delta \nu /2\simeq 30$ kHz). Various noise sources are analyzed and their contributions to the noise floor are evaluated. Additionally, we apply this noise-reduced phase shift measurement scheme in a simulated spin-squeezing experiment where we have achieved a factor of 40 improvement in phase sensitivity with a phase resolution of 0.7 mrad, which may remove one important barrier against attaining highly spin-squeezed states. The demonstrated method provides a flexible situation by using an optical ring cavity and two independent beams. This method can find direct application to nondestructive measurements in quantum systems, such as for the generation of spin-squeezed states in atom interferometers and atomic clocks.

We conduct a systematic theoretical study of strong field tunneling ionization of noble-gas atoms, from He to Kr, by elliptically polarized laser pulses in the so-called attoclock setup. Our theoretical model is based on a numerical solution of the time-dependent Schrödinger equation in the single active electron approximation. We simulate laboratory measurements utilizing few optical cycle pulses to benchmark our calculations against experiment. We further conduct “numerical attoclock” simulations with short, nearly single-cycle pulses to test various tunneling ionization models. We examine the attoclock offset angles as affected by the target orbital structure and the laser pulse intensity. Finally, we exclude a finite tunneling time scenario and attribute the attoclock offset angle entirely to the Coulomb field of the ion remainder as was recently demonstrated for the hydrogen atom [U. S. Sainadh et al., Nature (London) 568, 75 (2019)].

We theoretically investigate estimation of the control parameter in a ferromagnetic Bose-Einstein condensate near second-order quantum phase transitions. We quantify sensitivity by quantum and classical Fisher information and use the error-propagation formula. For these different metrics, we find the same beyond standard quantum limit (SQL) scaling with atom number near critical points and SQL scaling away from critical points. We find that both depletion of the $m_f=0$ Zeeman sublevel and transverse magnetization provide signals of sufficient quality to saturate the sensitivity scaling. To explore the effect of experimental imperfections, we study the scaling around criticality at nonzero temperature and with nonzero detection noise. Our results suggest the feasibility of sub-SQL sensing in ferromagnetic condensates with current experimental capabilities.

We theoretically investigate the use of quantum nondemolition measurement to enhance the sensitivity of atom interferometry with Bose-condensed atoms. In particular, we are concerned with enhancing existing high-precision atom interferometry apparatuses, and so restrict ourselves to dilute atomic samples and the use of free-propagating light or optical cavities in the weak-coupling regime. We find the optimum parameter regime that balances between spin squeezing and atomic loss and find that significant improvements in sensitivity are possible. Finally, we consider the use of squeezed light and show that this can provide further boosts to sensitivity.

Using full-wave numerical simulations and analytical multipole expansions, we investigated the properties of real-space polarization singularities that emerge in light scattering by subwavelength particles. We considered spherical and torus particles under the excitation of a linearly polarized plane wave. We determined the topological indices and the trajectories of electric-field polarization singularities in both the near-field and far-field regions. In the far-field region, a total of four singularities are identified, and the sum of their polarization topological indices is two, independent of the particle's geometric shape. In the near-field region, the polarization singularities strongly depend on the particle's shape and the polarization of incident light, and their index sum is not governed by the Poincaré-Hopf theorem anymore due to the nontransverse nature of the fields. From near field to far field, a flipping of sign can happen to the polarization topological indices of the C lines. The far-field properties of the singularities can be well explained by the interference of the excited multipoles, but their near-field properties can be strongly affected by the evanescent fields that are not captured by the multipole expansions. Our work uncovers the important relationship between particles' geometric properties and the polarization singularities of their scattering field. The results can be applied to manipulate polarization singularities in nanophotonic systems, and they could generate novel applications in optical sensing.

After propagating through a random amplifying medium, a squeezed state commonly shows excess noise above the shot-noise level. Since large noise can significantly reduce the signal-to-noise ratio, it is detrimental for precision measurement. To circumvent this problem, we propose a noise-reduction scheme using wave-front shaping. It is demonstrated that the average output quantum noise can be effectively suppressed even beyond the shot-noise limit. Both the decrease of amplification strength and the increase of input squeezing strength can give rise to a decrease in the suppressed average quantum noise. Our results not only show the feasibility of manipulating the output quantum noise of random amplifying media but also indicate potential applications in quantum information processing in complex environments, such as quantum imaging, quantum communication, and quantum key distribution.

We introduce action quantum speed limits (QSLs) as a family of bounds on the minimal time to connect two states that, unlike the usual geometric approach, crucially depend on how the path is traversed, i.e., on the instantaneous speed. The two approaches provide consistent bounds when the instantaneous speed is optimized along a fixed path and we demonstrate this explicitly for the case of a thermalizing qubit employing techniques from optimal control theory. In addition, we critically analyze the interpretation of QSLs based on different choices of metric establishing that, in general, these open-system QSL times provide an indication of optimality with respect to the geodesic path, rather than necessarily being indicative of an achievable minimal time.

The conspiracy of ontic states responding to measurements contextually to comply with noncontextual quantum mechanical probabilities is analyzed for general ontological models. A general physical picture of ontological space structure and how ontic states are disturbed by measurement contexts is presented. A common assumption in ontological models called $\lambda$ sufficiency is analyzed and argued to be inconsistent with measurement contextuality for ontological models with certain symmetry in ontic space with respect to quantum states and measurements.