We have investigated experimentally and by computer simulations the energy-loss distributions of low-energy ($E<10$ keV) protons and deuterons transmitted through polycrystalline palladium thin films. In contrast to previous experiments on various transition metals we find that the stopping power of Pd is proportional to the ion velocity. Data of protons and deuterons are coincident within the experimental uncertainties, showing the absence of an isotopic effect on the stopping power of Pd in this energy range. The experimental results were analyzed and compared with Monte Carlo computer simulations and previous theoretical models. The difference in the velocity dependence of the energy loss of hydrogen ions in Pd with respect to other transition metals (Cu, Ag, and Au) is explained by a theoretical analysis based on the properties of the $d$-electron bands of those elements.

We experimentally demonstrated a fast manipulation of two orthogonal spin-wave excitations in an ensemble of cold ${}^{87}$Rb atoms. The spin-wave manipulation is realized by transferring the excitations between two collective states, and a π rotation between the two spin waves is accomplished on a time scale of ∼100 ns. The multiple π rotations are completed based on the single π rotation. The results show that the retrieval optical signal from the manipulated spin waves gradually decreases along with the increasing of π-rotation numbers. The loss mechanism of spin waves caused by a Raman π rotation is simply analyzed, and the possible methods to mitigate the loss are discussed. Using multiple π rotations, one can implement the dynamical decoupling to protect the qubit memory in an atom ensemble from the influence of environmental noise.

We theoretically demonstrate the dynamics of field-free molecular orientation under the radiation of a femtosecond dual-color field and a delayed single-cycle terahertz (THz) field, with CO and LiH as the prototype molecules. The results show that the impulsive Raman processes of dual-color field and the resonant effect of the THz field exhibit higher excitation efficiency in a combined way and give rise to a significant enhancement of orientation degree when the THz field is introduced around the full revival time of molecules. It also shows that the dual-color field has an advantage over the single-color field when they combine with the THz field in creating field-free orientation.

We study the localization properties of a test dipole feeling the disordered potential induced by dipolar impurities trapped at random positions in an optical lattice. This random potential is marked by correlations which are a convolution of short-range and long-range ones. We show that when short-range correlations are dominant, extended states can appear in the spectrum. Introducing long-range correlations, the extended states, if any, are wiped out and localization is restored over the whole spectrum. Moreover, long-range correlations can either increase or decrease the localization length at the center of the band, which indicates a richer behavior than previously predicted.

We investigate a dilute Fermi gas of polar molecules confined into a bilayer setup with dipole moments polarized perpendicular to the layers. In particular, we consider the extreme case of population imbalance, where we have only one particle in one layer and many particles in the other one. The single molecule is attracted by the dilute Fermi gas through the interlayer dipole-dipole force, presenting an interesting impurity problem with long-range anisotropic interaction. We characterize the quasiparticle, calculating its chemical potential with a Brueckner-Hartree-Fock approach. Moreover, we determine the momentum relaxation rate for finite momentum and temperature. The latter is reminiscent of Coulomb drag in bilayer electronic systems. For a confined system we relate the results for the chemical potential with the measurement of the oscillation frequency of the impurity. The momentum relaxation rate provides instead an estimate on how quickly the oscillations are damped.

We consider a recently proposed four-level quantum heat engine (QHE) model to analyze the role of quantum coherences in determining the thermodynamic properties of the engine, such as flux, output power, and efficiency. A quantitative analysis of the relative effects of the coherences induced by the two thermal baths is brought out. By taking account of the dissipation in the cavity mode, we define useful work obtained from the QHE and present some analytical results for the optimal values of relative coherences that maximizes flux (hence output power) through the engine. We also analyze the role of quantum effects in inducing population inversion (lasing) between the states coupled to the cavity mode. The universal behavior of the efficiency at maximum power ($\mathrm{EMP}$) is examined. In accordance with earlier theoretical predictions, to leading order, we find that $\mathrm{EMP}\sim {\eta }_c/2$, where ${\eta }_c$ is Carnot efficiency. However, the next higher order coefficient is system dependent and hence nonuniversal.

Using two equivalent methods, the Heisenberg-Langevin and the master equation, we investigate the properties of a single-emitter nanolaser: an incoherently pumped single two-level system interacting with a single cavity mode of finite finesse. We are interested in a stationary generation regime when the mean number of photons inside the laser cavity is much larger than unity. In this case we linearize the Heisenberg-Langevin equations around the stationary classical solution and obtain analytical results for the linewidth, the quadrature fluctuation spectra, and the intracavity Mandel $Q$ parameter. As the second method we use the master equation for the density operator of the laser field. Using the coherent-state representation of the density matrix we obtain the stationary solution for the Glauber $P$ function of the laser mode and investigate the quantum statistics of the laser field and its threshold behavior. We compare the results of both methods with numerical simulations and find very good agreement. In the end we use our theoretical results for analyzing experiment with single-ion nanolasers.

Heavy diatomic molecules have been identified as good candidates for use in electron electric dipole moment (eEDM) searches. Suitable molecular species can be produced in pulsed beams, but with a total flux and/or temporal evolution that varies significantly from pulse to pulse. These variations can degrade the experimental sensitivity to changes in the spin precession phase of an electrically polarized state, which is the observable of interest for an eEDM measurement. We present two methods for measurement of the phase that provide immunity to beam temporal variations, and make it possible to reach shot-noise-limited sensitivity. Each method employs rapid projection of the spin state onto both components of an orthonormal basis. We demonstrate both methods using the eEDM-sensitive $H{}^3{\Delta }_1$ state of thorium monoxide, and use one of them to measure the magnetic moment of this state with increased accuracy relative to previous determinations.

We show here that due to nonadiabatic couplings in decaying systems, applying the same time-dependent protocol in the forward and reverse direction to the same mixed initial state leads to different final pure states. In particular, in laser-driven molecular systems, applying a specifically chosen positively chirped laser pulse or an equivalent negatively chirped laser pulse yields entirely different final vibrational states. This phenomenon occurs when the laser frequency and intensity are slowly varied around an exceptional point (EP) in the laser intensity and frequency parameter space where the non-Hermitian spectrum of the problem is degenerate. The protocol implies that a positively chirped laser pulse traces a loop in time in the laser parameters’ space whereas a negatively chirped pulse follows the same loop in the opposite direction. According to this protocol one can choose the final pure state from any initial state. The obtained results imply the intrinsic nonadiabaticity of quantum transport around an EP, and offer a way to observe the EP experimentally in time-dependent quantum systems.

We explore the quantum correlation distribution in multipartite quantum states based on the square of quantum discord (SQD). For tripartite quantum systems, we derive the necessary and sufficient condition for the SQD to satisfy the monogamy relation. Particularly, we prove that the SQD is monogamous for three-qubit pure states, based on which a genuine tripartite quantum correlation measure is introduced. In addition, we also address the quantum correlation distributions in four-qubit pure states. As an example, we investigate multipartite quantum correlations in the dynamical evolution of multipartite cavity-reservoir systems.

The quantum jump approach allows to characterize the stochastic dynamics associated with an open quantum system submitted to a continuous measurement action. In this paper we show that this formalism can consistently be extended to non-Markovian system dynamics. The results rely on studying a measurement process performed on a bipartite arrangement characterized by a Markovian Lindblad evolution. Both renewal and nonrenewal extensions are found. The general structure of nonlocal master equations that admit an unraveling in terms of the corresponding non-Markovian trajectories is also found. By studying a two-level system dynamics, it is demonstrated that non-Markovian effects such as an environment-to-system flow of information may be present in the ensemble dynamics.

We systematically derive a linear quantum collision operator for the spinorial Wigner transport equation from the dynamics of a composite quantum system. For suitable two-particle interaction potentials, the particular matrix form of the collision operator describes spin decoherence or even spin depolarization as well as relaxation towards a certain momentum distribution in the long time limit. It is demonstrated that in the semiclassical limit the spinorial Wigner equation gives rise to several semiclassical spin-transport models. As an example, we derive the Bloch equations as well as the spinorial Boltzmann equation, which in turn gives rise to spin-drift-diffusion models, which are increasingly used to describe spin-polarized transport in spintronic devices. The presented derivation allows to systematically incorporate Born-Markov as well as quantum corrections into these models.

The properties of the electronic ground state of the polar and paramagnetic chromium–closed-shell-atom molecules have been investigated. State-of-the-art ab initio techniques have been applied to compute the potential energy curves for the chromium–alkaline-earth-metal-atom, Cr$X$ ($X=\mathrm{Be}$, Mg, Ca, Sr, Ba), and chromium–ytterbium, CrYb, molecules in the Born-Oppenheimer approximation for the high-spin $X^7{\Sigma }^{+}$ electronic ground state. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), was employed and the scalar relativistic effects within the Douglas-Kroll-Hess Hamiltonian or energy-consistent pseudopotentials were included. The permanent electric dipole moments and static electric dipole polarizabilities were computed. The leading long-range coefficients describing the dispersion interaction between the atoms at large interatomic distances $C_6$ are also reported. The molecules under investigation are examples of species possessing both large magnetic and electric dipole moments making them potentially interesting candidates for ultracold many-body physics studies.

We develop the recently proposed analytical $R$-matrix (ARM) method to encompass strong-field ionization by circularly polarized fields, for atoms with arbitrary binding potentials. Through the ARM method, the effect of the core potential can now be included consistently both during and after ionization. We find that Coulomb effects modify the ionization dynamics in several ways, including modification of (i) the ionization times, (ii) the initial conditions for the electron continuum dynamics, (iii) the “tunneling angle” at which the electron “enters” the barrier, and (iv) the electron drift momentum. We derive analytical expressions for the Coulomb-corrected ionization times, initial velocities, momentum shifts, and ionization rates in circularly polarized fields, for arbitrary angular momentum of the initial state. We also analyze how nonadiabatic Coulomb effects modify (i) the calibration of the attoclock in the angular streaking method and (ii) the ratio of ionization rates from $p^{-}$ and $p^{+}$ orbitals, predicted by Barth and Smirnova [Phys. Rev. A 84, 063415 (2011)] for short-range potentials.

We simultaneously probe the molecular structure and the symmetry of valence electronic orbital of an anisotropic atomic-molecular complex of ArCO by tracing its three-body Coulomb breakup following triple ionization in a phase-controlled elliptically polarized two-color pulse. The geometry of ArCO is found to be tilted T shaped, where the angle between the covalent and van der Waals bonds is 65° with oxygen pointing towards argon. The asymmetric profiles of the outmost orbitals from the CO site are probed by directional dissociation of the contained CO subunit as a function of the laser phase. Our results clearly image the asymmetric geometry of ArCO and thus reveal the anisotropic interaction between a rare-gas atom and a heteronuclear diatomic molecule.

We study the interplay between the Zeeman field and spin-orbit coupling (SOC) in harmonically trapped Fermi gases loaded into a two-dimensional single-band tight-binding optical lattice. Using the Bogoliubov-de Gennes theory, we find that the Zeeman field combined with a Rashba SOC gives rise to (i) Fulde-Ferrell-like superfluidity and (ii) skyrmionlike polarization textures near the edges of the system. We also discuss the effects of interaction, temperature, SOC anisotropy, and Zeeman field anisotropy on the superfluid ground-state and polarization textures.

It is shown that light transfer between two evanescently coupled optical waveguides can be interrupted when strong interaction with a third waveguide is induced. In the strong-interaction regime the transfer can be reactivated upon proper detuning of the waveguide propagation constants. These phenomena can be easily understood using the analog of Autler-Townes splitting and electromagnetically induced transparency from atomic physics. Experimental demonstration is provided using photoinduced reconfigurable waveguides.

We study optical wave deflection in a three-level active Raman gain medium using a spatially inhomogeneous pump field. Using the eikonal approximation, we derive an analytical expression for the deflection angle and demonstrate more than an order of magnitude increase in deflection when compared to the electromagnetically induced transparency method. Numerical simulations have shown excellent agreement with semi-classical theoretical predictions. We further discuss the concept of light-beam-deflection-based wavelength division multiplexing which may have important applications in integrated circuits for optical telecommunications.

We present schemes for geometric phase compensation in an adiabatic passage which can be used for the implementation of quantum logic gates with atomic ensembles consisting of an arbitrary number of strongly interacting atoms. Protocols using double sequences of stimulated Raman adiabatic passage (STIRAP) or adiabatic rapid passage (ARP) pulses are analyzed. Switching the sign of the detuning between two STIRAP sequences, or inverting the phase between two ARP pulses, provides state transfer with well-defined amplitude and phase independent of atom number in the Rydberg blockade regime. Using these pulse sequences we present protocols for universal single-qubit and two-qubit operations in atomic ensembles containing an unknown number of atoms.