We provide several general upper bounds on the rate of a key secure against a quantum adversary in the device-independent conference key agreement (DI-CKA) scenario. They include bounds by reduced entanglement measures and those based on multipartite secrecy monotones such as a multipartite squashed entanglement-based measure, which we refer to as reduced c-squashed entanglement. We compare the latter bound with the known lower bound for the protocol of conference key distillation based on the parity Clauser-Horne-Shimony-Holt game. We also show that the gap between the DI-CKA rate and the device-dependent rate is inherited from the bipartite gap between device-independent and device-dependent key rates, giving examples that exhibit the strict gap.

Atom interferometry offers new perspectives for geophysics and inertial sensing. We present the industrial prototype of a quantum-based instrument: a compact, transportable, differential quantum gravimeter capable of measuring simultaneously the absolute values of both gravitational acceleration $g$ and its vertical gradient ${\mathrm{\Gamma }}_{zz}$. While the sensitivity to $g$ is competitive with the best industrial gravimeters, the sensitivity on ${\mathrm{\Gamma }}_{zz}$ reaches the limit set by quantum projection noise—leading to a long-term stability of $0.1\mathrm{E}$ ($1\mathrm{E}=1\times {10}^{-9}{\mathrm{s}}^{-2}$). This dual-purpose instrument constitutes the industrial integration of cold atom sensors for practical applications. It paves the way for different applications in geophysics, civil engineering, and gravity-aided navigation, where accurate mapping of the gravitational field plays an important role.

We develop the nonretarded limit of the Lifshitz theory of van der Waals forces in a wedge of a dielectric material. The nonplanar geometry of the problem requires determining the pointwise distribution of stresses. The findings are relevant to a wide range of phenomena from crack propagation to contact-line motion. First, the stresses prove to be anisotropic as opposed to the classical fluid-mechanics treatment of the contact-line problem. Second, the wedge configuration is always unstable, with its angle tending either to collapse or to unfold. The presented theory unequivocally demonstrates the quantum nature of the forces dictating the wedge behavior, which cannot be accounted for with classical methods.

We formulate a parity-mixed coupled-cluster (PM-CC) approach for high-precision calculations of parity-nonconserving amplitudes in monovalent atoms. Compared to the conventional formalism which uses parity-proper (PP) one-electron orbitals, the PM-CC method is built using parity-mixed (PM) orbitals. The PM orbitals are obtained by solving the Dirac-Hartree-Fock equation with the electron-nucleus electroweak interaction included (PM-DHF). There are several advantages to such a PM-CC formulation: (i) reduced role of correlations, as for the most experimentally accurate to date ${}^{133}\mathrm{Cs} 6S_{1/2}\text{−}7S_{1/2}$ transition, the PM-DHF result is only 3% away from the accurate many-body value, while the conventional DHF result is off by 18%; (ii) avoidance of directly summing over intermediate states in expressions for parity-nonconserving amplitudes which reduces theoretical uncertainties associated with highly excited and core-excited intermediate states, and (iii) relatively straightforward upgrade of existing and well-tested large-scale PP-CC codes. We reformulate the CC method in terms of the PM-DHF basis and demonstrate that the cluster amplitudes are complex numbers with opposite-parity real and imaginary parts. We then use this fact to map out a strategy through which the new PM-CC scheme may be implemented.

We explore features of stabilization in the angle-resolved spectra of photoelectrons when ground-state atomic hydrogen is exposed to an intense ($\sim {10}^{18} \mathrm{W}/{\mathrm{cm}}^2$) linearly polarized ultrashort XUV pulse. In this regime, atomic stabilization can be traced to the temporal destructive interference between wave packets released by the intense field at different instants of time. By a comparison between the numerical solution of the time-dependent Schrödinger equation and a semianalytical model, we can identify the observed oscillations in the momentum distribution and the suppression of photoemission into the laser polarization direction as a direct result of stabilization. We also explore the effect of nondipole corrections on the angular distribution.

We have investigated magnetically tunable Feshbach resonances in ultracold collisions of Rb with Yb in its metastable ${}^3{P}_2$ and ${}^3{P}_0$ states, using coupled-channel scattering and bound-state calculations. For the ${}^3{P}_2$ state, we find sharp resonances when both atoms are in their lowest Zeeman sublevels. However, these resonances are decayed by inelastic processes that produce Yb atoms in ${}^3{P}_1$ and ${}^3{P}_0$ states. The molecules that might be produced by magnetoassociation at the ${}^3{P}_2$ thresholds can decay by similar pathways and would have lifetimes no more than a few microseconds. For the ${}^3{P}_0$ state, by contrast, there are resonances that are promising for magnetoassociation. There are resonances due to both rotating and nonrotating molecular states that are significantly stronger than the analogous resonances for $\mathrm{Yb}{(}^{1}S$). The ones due to rotating states are denser in magnetic field; in contrast to $\mathrm{Yb}{(}^{1}S$), they exist even for bosonic isotopes of $\mathrm{Yb}{(}^3{P}_0$).

We present a study of superfluid vortex dynamics on general axisymmetric compact surfaces with no holes. Specifically, we develop a general method to transform conformally from the axisymmetric surface to a plane, where we use familiar methods based on the hydrodynamic stream function. Our approach shows that vortices constitute a Hamiltonian dynamical system, with their angular positions on the surface as canonical variables. The dynamical motion conserves both the total energy and the angular momentum, and it features a marked anticorrelation between the vortex speed and the local curvature of the surface.

In this paper we develop a theory for an infinitely long droplet state of a zero-temperature dipolar bosonic gas. The infinite droplet theory yields simpler equations to solve for the droplet state and its collective excitations. We explore the behavior of infinite droplets using numerical and variational solutions, and we demonstrate that it can provide a quantitative description of large finite droplets of the type produced in experiments. We also consider the axial speed of sound and the thermodynamic limit of a dipolar droplet.

The remarkable single-particle control of individual ions combined with the versatility of ultracold atomic gases makes hybrid ion-atom systems an exciting new platform for quantum simulation of few- and many-body quantum physics. Here, we study theoretically the properties of a mobile ion immersed in a quantum degenerate gas of fermionic atoms. Using an effective low-energy atom-ion interaction together with a well-established approach that includes exactly two-body correlations, we calculate the full spectral response of the ion and demonstrate the existence of several quasiparticle branches, which are charged analogs of the Fermi polaron observed in neutral atomic gases. Due to the long-range nature of the atom-ion interaction, these ionic Fermi polarons have several properties distinct from their neutral counterparts such as the simultaneous presence of several stable states and smooth transitions from repulsive to attractive polarons with increasing interaction strength. Surprisingly, the residue of the ionic polaron is shown to increase with the Fermi density for fixed interaction strength, which is in marked contrast with the neutral polaron. The properties of the ionic polaron approach that of the neutral polaron only in the low-density limit where the average interparticle spacing is larger than the characteristic length of the atom-ion interaction. We finally analyze the effects of the Fermi gas on the molecular ions, which are bound atom-dimer states.

Motivated by recent experiments, we model the dynamics of a condensed Bose gas in a rotating anisotropic trap, where the equations of motion are analogous to those of charged particles in a magnetic field. As the rotation rate is ramped from zero to the trapping frequency, the condensate stretches along one direction and is squeezed along another, becoming long and thin. When the trap anisotropy is slowly switched off on a particular timescale, the condensate is left in the lowest Landau level. We use a time-dependent variational approach to quantify these dynamics and give intuitive arguments about the structure of the condensate wave function. This preparation of a lowest Landau level condensate can be an important first step in realizing bosonic analogs of quantum Hall states.

Ground-state cooling of mechanical resonators is an important task in quantum optomechanics because it is a necessary prerequisite for the creation, manipulation, and application of macroscopic mechanical coherence. Here, we propose a transient-state scheme to accelerate ground-state cooling of a mechanical resonator in a three-mode loop-coupled optomechanical system via shortcuts to adiabaticity (STA). We consider four kinds of coupling protocols and calculate the evolution of the mean phonon number of the mechanical resonator in both the adiabatic and STA cases. We verify that the ground-state cooling of the mechanical resonator can be achieved with the STA method in a much shorter period. The STA method can be generalized to accelerate other adiabatic processes in cavity optomechanics, and hence this work will open up a realm of fast optomechanical manipulations.

Three-dimensional (3D) microscopic imaging is fundamentally important for microscale observations and manipulations. Here, we show that single-pixel imaging (SPI) is available for realizing superior 3D microscopic imaging, which relies on the near-field illumination with chaotic light. Like considering a two-point object to investigate two-dimensional microscopic imaging, we theoretically and experimentally studied the image formation process for a 3D object with two slices, demonstrating the excellent capability of the SPI for 3D microscopic imaging. The proposed 3D microscopic imaging via SPI would be useful for applications such as biological imaging and micromanipulations.

Channel-position finding is the task of determining the location of a single target channel among an ensemble of background channels. It has many potential applications, including quantum sensing, quantum reading, and quantum spectroscopy. In particular, it could allow for simple detection protocols to be extended to ones of measurement, for example, target ranging with quantum illumination. The use of quantum states and entanglement in such protocols has shown to yield quantum advantages over their optimal classical counterparts. Here we consider quantum channel-position finding using sources specified by at most one single photon on average per mode, using the discrete-variable formalism. By considering various quantum sources, it is shown through the derivation of performance bounds that a quantum enhancement may be realized.

We report on the observation of laser oscillation using the magnetically assisted gain in an ensemble of coherently prepared cold cesium atoms. This gain mechanism was recently demonstrated and is based on the modification of the Zeeman populations and coherences induced by a coupling and a probe beams by the presence of a transverse magnetic field. We have also investigated the enhancement of the gain due to the presence of a resonant ring cavity having different finesses. In the case of a low-finesse cavity operating below threshold, a 14-fold gain enhancement, in comparison with the single-pass gain, was measured and, finally, the system showed laser oscillation when a higher-finesse cavity was used. The present demonstration of laser oscillation constitutes an unconventional kind of lasing without inversion which is based on the manipulation of the dark state by an external magnetic field.

Applying the semiclassical model, we identify two connected effects in intraband high-order harmonic generation (HHG): (1) propagation time from the point of emission at the source to the point of detection, and (2) beyond-electric-dipole corrections to the light-matter interaction. These effects inherit information regarding the dispersion and cause specific features in the spectra including even-ordered harmonics in systems with space- and time-inversion symmetry. They can for certain experimental geometries be measured free of the dipole background.

We use a convolutional neural network to retrieve the internuclear distance in the two-dimensional ${\mathrm{H}}_2^{+}$ molecule ionized by a strong few-cycle laser pulse based on the photoelectron momentum distribution. We show that a neural network trained on a relatively small dataset consisting of a few thousand images can predict the internuclear distance with an absolute error less than $0.1$ a.u. Deep learning allows us to retrieve more than one parameter from a given momentum distribution. Specifically, we used a convolutional neural network to retrieve both the internuclear distance and the laser intensity. We study the effect of focal averaging, and we find that the convolutional neural network trained using the focal averaged electron momentum distributions also shows a good performance in reconstructing the internuclear distance.

Fano profiles usually refer to the line profiles due to the total photon absorption cross sections. In this work, we measured the angle-resolved line profiles of the $\mathrm{D}(2s,2p)$ fragments from the predissociation of ${\mathrm{D}}_2$ near the second threshold using the D-atom Rydberg tagging time-of-flight method. The line profiles of the fragments recoiling at the parallel and perpendicular directions to the polarization direction of the excitation laser were found to be significantly different from each other, as well as with the Fano profiles of total absorption cross sections. Based on the previous theoretical results, we found that the angle-resolved line profiles can be expressed as a summation of Fano and Lorentzian profiles. Using the formula and the previously determined parameters from the so-called β profiles, we calculated the angle-resolved line profiles, which are in good agreement with the experimental data. Anisotropy parameters arising from the interferences between the continuum and discrete states were found to play a role in the angle-resolved line profiles.

A time-dependent equation-of-motion coupled-cluster singles and doubles (TD-EOM-CCSD) method is implemented, which uses a reduced basis calculated with the asymmetric band Lanczos algorithm. The approach is used to study weak-field processes in small molecules induced by ultrashort valence pump and core probe pulses. We assess the reliability of the procedure by comparing TD-EOM-CCSD absorption spectra to spectra obtained from the time-dependent coupled-cluster singles and doubles method, and observe that spectral features can be reproduced for several molecules, at much lower computational times. We discuss how multiphoton absorption and symmetry can be handled in the method, and general features of the core-valence separation projection technique. We also model the transient absorption of an attosecond x-ray probe pulse by the glycine molecule.

The generation of dissipative optical solitons is explored in doped fibers with correction effects under the activation of modulational instability (MI). The model, described by the cubic-quintic-septic complex Ginzburg-Landau equation, includes higher-order dispersion and nonlinear gradient terms. The Lange-Newell's criterion for MI of Stokes wave, boundary domains of MI, and integrated gain of MI are obtained via the linear stability analysis. Particular attention is given to the physical effect on the critical frequency detuning, especially in the normal regime, when varying the values of odd dispersion coefficients. Numerical simulations are undertaken and confronted with analytical predictions. Beyond the agreement between the linear stability analysis and trains of soliton generation, the soliton map induced by MI, along with the subsequent physical effects, is debated via bifurcation diagrams. This allows accurate prediction of transitions between various types of localized modes and well-calibrated generation of a wide variety of solitons with different energies. It is argued that knowing the center of mass and the energy of the generated structures can better characterize the long-time evolution of MI and, eventually, its nonlinear manifestations.