A model of two Calogero-Sutherland Bose gases $A$ and $B$ with strong odd-wave $\mathit{AB}$ attractions induced by a $p$-wave $\mathit{AB}$ Feshbach resonance is studied. The ground-state wave function is found analytically by a Bose-Bose duality mapping, which permits one to accurately determine static physical properties by a Monte Carlo method. The condensation of particles or particle pairs (molecules) is tested by analyzing the presence of the off-diagonal long-range order in one- or two- body density matrices. The $p$-wave symmetry of $\mathit{AB}$ interaction makes possible quasicondensation of type $A$ particles at the Fermi momentum of the $B$ component. The zero-temperature phase diagram is drawn in terms of densities and interaction strengths.

We present protocols for creating entangled states of two modes of the electromagnetic field by using a beam of atoms crossing microwave resonators. The atoms are driven by a transverse, classical field and pump correlated photons into (i) two modes of a cavity and (ii) the modes of two distant cavities. The protocols are based on a stochastic dynamics, characterized by random arrival times of the atoms and by random interaction times between atoms and cavity modes. The resulting effective model yields a master equation, whose steady state is an entangled state of the cavity modes. In this respect, the atoms act like a quantum reservoir, pulling the cavity modes into an entangled, Einstein-Podolski-Rosen state, whose degree of entanglement is controlled by the intensity and the frequency of the transverse field. This scheme is robust against stochastic fluctuations in the atomic beam, and it does not require atomic detection nor velocity selection.

Joint measurements of multiple qubits open new possibilities for quantum information processing. Here we present an approach based on homodyne detection to realize such measurements in the dispersive regime of cavity or circuit QED. By changing details of the measurement, the readout can be tuned from extracting only single-qubit to extracting only multiqubit properties. We obtain a reduced stochastic master equation describing this measurement and its effect on the qubits. As an example, we present results showing parity measurements of two qubits. In this situation, measurement of an initially unentangled state can yield, with near unit probability, a state of significant concurrence.

We study excitations of the local field (locsitons) in nanoscale two-dimensional (2D) lattices of strongly interacting resonant atoms and various unusual effects associated with them. Locsitons in low-dimensional systems and the resulting spatial strata and more complex patterns on a scale of just a few atoms were predicted by us earlier [A. E. Kaplan and S. N. Volkov, Phys. Rev. Lett. 101, 133902 (2008)]. These effects present a radical departure from the classical Lorentz-Lorenz theory of the local field (LF), which assumes that the LF is virtually uniform on this scale. We demonstrate that the strata and patterns in the 2D lattices may be described as an interference of plane-wave locsitons, build an analytic model for such unbounded locsitons, and derive and analyze dispersion relations for the locsitons in an equilateral triangular lattice. We draw useful analogies between 1D and 2D locsitons but also show that the 2D case enables locsitons with the most diverse and unusual properties. Using the nearest-neighbor approximation, we find the locsiton frequency band for different mutual orientations of the lattice and the incident field. We demonstrate a formation of distinct vector locsiton patterns consisting of multiple vortices in the LF distribution and suggest a way to design finite 2D lattices that exhibit such patterns at certain frequencies. We illustrate the role of lattice defects in supporting localized locsitons and also demonstrate the existence of “magic shapes,” for which the LF suppression at the exact atomic resonance is canceled.

We investigate how quantum correlations [quantum discord (QD)] of a two-qubit one-dimensional $\mathit{XYZ}$ Heisenberg chain in thermal equilibrium depend on the temperature $T$ of the bath and also on an external magnetic field $B$. We show that the behavior of thermal QD differs in many unexpected ways from thermal entanglement. For example, we show situations where QD increases with $T$ when entanglement decreases, cases where QD increases with $T$ even in regions with zero entanglement, and that QD signals a quantum phase transition even at finite $T$. We also show that by properly tuning $B$ or the interaction between the qubits we get nonzero QD for any $T$ and we present an effect not seen for entanglement, the “regrowth” of thermal QD.

A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser and a vacuum UV free-electron laser is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed in the time profiles of photoioinzation intensity and time-dependent photoelectron images.

We investigate the dynamics of the eigenstate of an infinite well under an abrupt shift of the well’s wall. It is shown that when the shift is small compared to the initial well’s dimensions, the short-time behavior changes from the well-known $t^{3/2}$ behavior to $t^{1/2}$. It is also shown that the complete dynamical picture converges to a universal function, which has fractal structure with dimensionality $D=1.25$.

We study the possibility of performing quantum state reconstruction from a measurement record that is obtained as a sequence of expectation values of a Hermitian operator evolving under repeated application of a single random unitary map, $U_0$. We show that while this single-parameter orbit in operator space is not informationally complete, it can be used to yield surprisingly high-fidelity reconstruction. For a $d$-dimensional Hilbert space with the initial observable in $\mathfrak{su}(d)$, the measurement record lacks information about a matrix subspace of dimension $⩾d-2$ out of the total dimension $d^2-1$. We determine the conditions on $U_0$ such that the bound is saturated, and show they are achieved by almost all pseudorandom unitary matrices. When we further impose the constraint that the physical density matrix must be positive, we obtain even higher fidelity than that predicted from the missing subspace. With prior knowledge that the state is pure, the reconstruction will be perfect (in the limit of vanishing noise) and for arbitrary mixed states, the fidelity is over $0.96$, even for small $d$, and reaching $\mathcal{F}>0.99$ for $d>9$. We also study the implementation of this protocol based on the relationship between random matrices and quantum chaos. We show that the Floquet operator of the quantum kicked top provides a means of generating the required type of measurement record, with implications on the relationship between quantum chaos and information gain.

We investigate the effect of the Dzyaloshinskii-Moriya (DM) interaction on the fidelity of the $1\to M$ phase-covariant cloning machine (PCCM) in a spin star network. The results of numerical calculation show that the DM interaction can further improve the cloning fidelity to reach the optimal value. Furthermore, the physical mechanism is investigated by analyzing the effect of the DM interaction on the populations of the qubits. It is shown that the DM interaction leads to the populations of states $|1\rangle |S(M,k+1)\rangle$ and $|1\rangle |S(M,k)\rangle$ [or $|0\rangle |S(M,k)\rangle$ and $|0\rangle |S(M,k-1)\rangle$] simultaneously reaching the maximum or minimum value periodically, where the first ket $|i\rangle$ $(i\in 0,1)$ in $|i\rangle |S(M,k)\rangle$ denotes the state of central spin with $|0\rangle$ and $|1\rangle$ representing the spin-up and spin-down states, respectively, while the second ket $|S(M,k)\rangle$ denotes the state of outer spins with $M$ being the total number of outer spins and $k$ the number of up spins. At these extreme overlapping points of two states, the fidelity of quantum cloning can reach optimal value. Finally the forms of these two different $1\to M$ optimal cloning transformations are presented.

We provide a simple example that illustrates the advantage of adaptive over nonadaptive strategies for quantum channel discrimination. In particular, we give a pair of entanglement-breaking channels that can be perfectly discriminated by means of an adaptive strategy that requires just two channel evaluations, but for which no nonadaptive strategy can give a perfect discrimination using any finite number of channel evaluations.

Precise knowledge of the Hamiltonian of a system is a key to many of its applications. Tasks such as the state transfer or quantum computation have been well studied with a linear chain, but rarely with systems, which do not possess a linear structure. While this difference does not disturb the end-to-end dynamics of a single excitation, the evolution is significantly changed in other subspaces. Here we quantify the difference between a linear chain and a pseudochain, which have more than one spin at some site (in such a case we will call the site a block). We show how to estimate a number of all spins in the system and the intrablock coupling constants. We also suggest how it is possible to eliminate excitations trapped in such blocks, which may disturb the state transfer. Importantly, one uses only at-ends data and needs to be able to put the system to either the maximally magnetized or the maximally mixed state. This can obtained by controlling a global decoherence parameter, such as temperature.

We report studies of photon-stimulated desorption, also known as light-induced atomic desorption, of sodium atoms from a vacuum-cell glass surface used for loading a magneto-optical trap (MOT). Fluorescence detection was used to record the trapped atom number and the desorption rate. We observed a steep wavelength dependence of the desorption process above $2.6\hspace{0.5em}\mathrm{eV}$ photon energy, a result significant for estimations of sodium vapor density in the lunar atmosphere. Our data fit well to a simple model for the loading of the MOT dependent only on the sodium desorption rate and residual gas density. Up to $3.7\times {10}^7$ Na atoms were confined under ultrahigh-vacuum conditions, creating promising loading conditions for a vapor-cell-based atomic Bose-Einstein condensate of sodium.

Thanks to the high peak intensities of ultrashort pulse trains that make up an optical frequency comb, conversion to much shorter wavelengths is readily available. Therefore direct frequency comb spectroscopy may offer the possibility of extending high-resolution spectroscopy to spectral regions that are unexplored so far. In this work, we investigate the impact of a chirp, i.e., a varying frequency across the pulses, on the excitation rate obtainable with two-photon direct frequency comb spectroscopy. Using the cesium $6\hspace{0.5em}{}^2{S}_{1/2}$-$8\hspace{0.5em}{}^2{S}_{1/2}$ two-photon transition at $822$ nm, we show that destructive interference of various quantum paths reduces the excitation rate with the inverse of the time bandwidth product of the exciting pulses.

A theoretical investigation is presented that uses a strong two-color laser field composed of a linearly chirped fundamental ($900$ nm) and its subharmonic ($1800$-nm) laser pulses to control coherently the broadband isolated attosecond pulses in high-order harmonic generations. After the subharmonic field is added, the intrinsic chirp of harmonic emission can be reduced significantly, and consequently, the temporal synchronization of harmonic emission with different photon energies at the level of the single-atom response can be realized. In addition, the scheme is robust against the carrier envelope phase variation to produce a twin pulse of stable sub-$100$-as duration, and the relative intensity of the twin pulses can be changed just by adjusting the relative time delay of the two driving pulses, which is of benefit in general pump-probe experiments.

Measurements of the photoelectron angular distributions in the body-fixed frame (MFPAD) have been carried out for $290$- to $320$-eV photons (just above the carbon $K$-shell ionization threshold) on ${\mathrm{C}}_2$H${}_4$ using an approach based on cold-target recoil-ion momentum spectroscopy (COLTRIMS). The results are compared with a theoretical calculation and excellent agreement is found. A direct verification of the “$f$-wave shape resonance” is accomplished by obtaining the complex amplitude of the $l=3$ partial wave, which shows a peak in its absolute value and a relative phase change of $\pi$ as the energy is scanned across the resonance.

We study the splitting of multiply quantized vortices with large quantum numbers in dilute nonrotated Bose-Einstein condensates in the zero-temperature limit. The splitting is observed to result in vortex-free condensate fragments which are separated by vortex sheets. The number of these fragments is found to be equal to the angular-momentum quantum number of the Bogoliubov excitation mode responsible for the splitting, although the formulation of the fragments cannot be described by small-amplitude excitations. Thus, the realization of an isolated giant vortex and the observation of its splitting would provide a means to directly relate the experimental data to discrete theoretical quantities.

We study the three-fermion problem within a 1D model of a Feshbach resonance in order to gain insight into how the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state at small negative scattering lengths evolves into a Bose-Fermi mixture at small positive scattering lengths. The FFLO state possesses an oscillating superfluid correlation function, while in a Bose-Fermi mixture correlations are monotonic. We find that this behavior is already present at the three-body level. We present an exact study of the three-body problem and gain extra insights by considering world lines of a path-integral Monte Carlo calculation.

We consider quantized vortices in two-component Bose-Einstein condensates and three-component Fermi gases with attractive interactions. In these systems, the vortex core can be either empty (normal in the fermion case) or filled with another superfluid. We determine critical values of the parameters—chemical potentials, scattering lengths, and, for Fermi gases, temperature—at which the transition between the two types of vortices occurs. Population imbalance can lead to superfluid core (coreless) vorticity in multicomponent superfluids which otherwise support only usual vortices. For multicomponent Fermi gases, we construct the phase diagram, including regions of coreless vorticity. We extend our results to trapped bosons and fermions using an appropriate local approximation, which goes beyond the usual Thomas-Fermi approximation for trapped bosons.

By developing a quantum virial expansion theory, we quantitatively calculate the dynamic density response function of a trapped strongly interacting Fermi gas at high temperatures near unitarity. A clear transition from atomic to molecular responses is identified in the spectra when crossing from the BCS to BEC regimes, in qualitative agreement with recent Bragg spectroscopy observations. Our virial expansion method provides a promising way to solve the challenging strong-coupling problems and is applicable to other dynamical properties of strongly correlated Fermi gases.

Recent theoretical investigations have demonstrated that the stability of mode-locked solutions of multiple frequency channels depends on the degree of inhomogeneity in gain saturation. In this article, these results are generalized to determine conditions on each of the system parameters necessary for both the stability and the existence of mode-locked pulse solutions for an arbitrary number of frequency channels. In particular, we find that the parameters governing saturable intensity discrimination and gain inhomogeneity in the laser cavity also determine the position of bifurcations of solution types. These bifurcations are completely characterized in terms of these parameters. In addition to influencing the stability of mode-locked solutions, we determine a balance between cubic gain and quintic loss, which is necessary for the existence of solutions as well. Furthermore, we determine the critical degree of inhomogeneous gain broadening required to support pulses in multiple-frequency channels.