We theoretically study an interacting few-body system of Rashba spin-orbit-coupled two-component Bose gases confined in a harmonic trapping potential. We solve the interacting Hamiltonian at large Rashba coupling strengths using an exact-diagonalization scheme, and obtain the ground-state phase diagram for a range of interatomic interactions and particle numbers. At small particle numbers, we observe that the bosons condense to an array of topological states with $n+1/2$ quantum angular momentum vortex configurations, where $n=0,1,2,3,...$. At large particle numbers, we observe two distinct regimes: at weaker-interaction strengths, we obtain ground states with topological and symmetry properties that are consistent with mean-field theory computations; at stronger-interaction strengths, we report the emergence of strongly correlated ground states.

We laser cool rubidium atoms to form a magneto-optical trap, within a Fabry-Perot cavity, and demonstrate strong coupling of the cold atoms to the cavity. The coupling strength is measured using the vacuum Rabi frequency splitting (VRS) of transmitted, cavity-coupled light on atomic resonance. The VRS is measured for two- and three-level atomic systems and the atom-cavity-coupling strength for each system is determined. By allowing the laser-cooled atoms to expand for different times and measuring the corresponding VRS, we determine the number of atoms overlapped with the cavity mode as a function of time. This time-of-flight of atoms from the cavity permits the measurement of the temperature of the laser-cooled atoms. Finally, the need for this technique and its utility is discussed.

We study the role of geometry-dependent phase shifts of the optical electric field in stimulated coherent spectroscopy, a special class of heterodyne optical spectroscopy techniques. We generalize the theoretical description of stimulated spectroscopy to include spatial phase effects, and study the measured material response for several representative excitation and detection configurations. Using stimulated Raman scattering microscopy as an example, we show that different components of the material response are measured by varying the position of the object in focus. We discuss the implications of the position-dependent phase in stimulated coherent microscopy and point out a detection configuration in which its effects are minimized.

Monogamy of bipartite correlations leads, for arbitrary pure multiqubit states, to simple conditions able to indicate various types of multipartite entanglement by being capable of excluding the possibility of $k$ separability.

Intense-field molecular photodissociation offers the possibility to define resonances of zero width for particular intensities at given wavelengths. We show how a laser pulse can be shaped to fulfill, at all times, the conditions leading to a zero width for a particular resonance originating from a field-free vibrational state. The solution of the time-dependent Schrödinger equation confirms that only this state survives after the pulse is off. This is the basis for a purification procedure leading to population left only in a single state chosen at will. The illustrative example is ${{\mathrm{H}}_2}^{+}$.

The recent realization of mixed-dimensional systems of cold atoms has attracted much attention from both experimentalists and theorists. In this article we investigate a two-species Fermi atom mixture: one species of atom exists in two hyperfine states and is confined to move in a two-leg ladder, interacting with an on-site interaction, and the other moves freely in a two-dimensional square lattice that contains the two-leg ladder. The two species of atoms interact via an on-site interaction on the ladder. In the limit of weak interspecies interactions, the two-dimensional gas can be integrated out, leading to an effective long-range mediated interaction in the ladder, generated by the on-site interspecies interaction. We show that the form of the mediated interaction can be controlled by the density of the two-dimensional gas and that it enhances the charge-density wave instability in the two-leg ladder after the renormalization-group transformation. Parametrizing the phase diagram with various experimentally controllable quantities, we discuss the possible tuning of the macroscopic quantum many-body phases of the two-leg ladder in this mixed-dimensional fermionic cold atom system.

We show that spin-orbit coupling (SOC) significantly enhances the depletion of a homogeneous Bose-Einstein condensate in three dimensions. With decreasing anisotropy of the SOC, both the quantum and thermal depletion increase. In particular, different types of SOC give rise to qualitatively different dependences of the condensate depletion on microscopic variables including the scattering length, the strength of the SOC, and the temperature, which can be directly observed once these types of SOC are realized in experiments. Moreover, we point out that thermal depletion in three dimensions becomes logarithmically divergent at any given finite temperature when both the SOC and the interaction approach the isotropic limit.

We review the introduction of likelihood functions and Fisher information in classical estimation theory, and we show how they can be defined in a very similar manner within quantum measurement theory. We show that the stochastic master equations describing the dynamics of a quantum system subject to a definite set of measurements provides likelihood functions for unknown parameters in the system dynamics, and we show that the estimation error, given by the Fisher information, can be identified by stochastic master equation simulations. For large parameter spaces we describe and illustrate the efficient use of Markov chain Monte Carlo sampling of the likelihood function.

High-fidelity quantum operations are a key requirement for fault-tolerant quantum information processing. Manipulation of electron spins is usually achieved with time-dependent microwave fields. In contrast to the conventional dynamic approach, adiabatic geometric phase operations are expected to be less sensitive to certain kinds of noise and field inhomogeneities. Here, we introduce an adiabatic geometric phase gate for the electron spin. Benchmarking it against existing dynamic and nonadiabatic geometric gates through simulations and experiments, we show that it is indeed inherently robust against inhomogeneity in the applied microwave field strength. While only little advantage is offered over error-correcting composite pulses for modest inhomogeneities $\lesssim 10\%$, the adiabatic approach reveals its potential for situations where field inhomogeneities are unavoidably large.

A composite system of Majorana-hosted semiconductor nanowire and superconducting flux qubits, named top-flux-flux, is presented to process quantum information. We can electrically control the coupling between the Majorana-based topological qubit and the readout flux qubit, supplying a convenient method to implement a $\pi /8$ phase gate of the topological qubit. In addition, we design a scheme to transfer quantum information back and forth between the topological qubit and the flux qubit by employing the Landau-Zener transition. With the demonstration of the entanglement of two topological qubits, it is very promising to use this hybrid system for quantum-information processing.

We derive an adiabatic technique that implements the most general SU($d$) transformation in a quantum system of $d$ degenerate states, featuring a qudit. This technique is based on the factorization of the SU($d$) transformation into $d$ generalized quantum Householder reflections, each of which is implemented by a two-shot stimulated Raman adiabatic passage with appropriate static phases. The energy of the lasers needed to synthesize a single Householder reflection is shown to be remarkably constant as a function of $d$. This technique is directly applicable to a linear trapped ion system with $d+1$ ions. We implement the quantum Fourier transform numerically in a qudit with $d=4$ (defined as a quartit) as an example.

Several entanglement measures are used to define equivalence classes in the set of hypergraph states of three qubits. Our classifications reveal that (i) under local unitary transformations, hypergraph states of three qubits are split into six classes and only one of them is not equivalent to any graph state; (ii) under stochastic local operations with classical communication, for the single-copy case hypergraph states of three qubits, partitioned into five classes which cannot be converted into a $W$ state, are equivalent to graph states; and (iii) when bipartite entanglement in three qubits is considered, hypergraph states of three qubits are split into five classes and only one of them has the same entangled graph as the $W$ state.

The monogamy of entanglement is generally discussed using a bipartite entanglement measure as an upper bound. Here we discuss a new kind of monogamous relation where the upper bound is given by a multipartite measure of entanglement, the generalized concurrence. We show a monogamous equality involving the multipartite concurrence, all the bipartite concurrences, and the genuine tripartite entanglement for pure three-qubit systems. The result extends to mixed states in an inequality involving the generalized concurrence and all the bipartite concurrences. We provide a counterexample showing that the result cannot be extended for systems with more than three qubits.

Integrating a single Fredkin (controlled swap) gate to the previously introduced $W$ state fusion mechanism [Ozdemir et al.,  New J. Phys. 13, 103003 (2011)] and using an ancillary photon, we increase the size of the fused $W$ states and essentially, we improve the success probability of the fusion process in a promising way for a possible deterministic $W$-state fusion mechanism. Besides fusing arbitrary size $W$ states, our setup can also fuse Bell states to create $W$ states with a success probability $3/4$ which is much higher than the previous works. Therefore using only this setup, it is now possible to start with Bell pairs to create and expand arbitrary size $W$ states. Since a higher probability of success implies a lower cost of resource in terms of the number of the states spent to achieve a target size, our setup gives rise to more cost-efficient scenarios.

We report the results of a study of the pressure broadening and resonant frequency shift of the absorption profiles of the $D_1$ and $D_2$ lines of Rb and K in the presence of ${}^3$He and N${}_2$ gases over a range of number densities. We have also examined the temperature dependence of the broadening and shift over a range of approximately 340 to 400 K. We compare our results for the broadening and shift coefficients for Rb $D_1$ and $D_2$ to current values and present coefficients for K $D_1$ and $D_2$.

We explore the scattering properties of ultracold ground-state Cs atoms at magnetic fields between 450 G (45 mT) and 1000 G. We identify 17 previously unreported Feshbach resonances, including two very broad ones near 549 and 787 G. We measure the binding energies of several different dimer states by magnetic field modulation spectroscopy. We use least-squares fitting to these experimental results, together with previous measurements at lower field, to determine a six-parameter model of the long-range interaction potential, designated M2012. Coupled-channels calculations using M2012 provide an accurate mapping between the $s$-wave scattering length and the magnetic field over the entire range of fields considered. This mapping is crucial for experiments that rely on precise tuning of the scattering length, such as those on Efimov physics.

We present kinematically complete theoretical calculations and experiments for transfer ionization in H${}^{+}+$He collisions at 630 keV/u. Experiment and theory are compared on the most detailed level of fully differential cross sections in the momentum space. This allows us to unambiguously identify contributions from the shake-off and binary encounter mechanisms of the reaction. It is shown that the simultaneous electron transfer and ionization is highly sensitive to the quality of a trial initial-state wave function.

We report the energy and angular distribution of the electron emission from an RNA base molecule uracil in collisions with 3.5-MeV/u bare C ions. The absolute double differential cross sections (DDCS) are measured for emission energy between a few to 600 eV. The angular distributions are compared to those obtained for the O${}_2$ molecule in the same experiment. The single differential cross sections (SDCS) are also deduced. The energy and angular distributions of the DDCS and SDCS are compared with the state-of-the-art quantum-mechanical models based on continuum distorted wave-eikonal initial state (CDW-EIS) and correct boundary first Born (CB1) approximations which use a suitable molecular wave function for uracil. The models, however, give substantial deviations from the observed energy and angular distributions of the DDCS as well as SDCS. The CDW-EIS calculations are closer to the data compared to the CB1. In the case of uracil a large difference in the forward-backward emission of electrons was observed in comparison to that in collisions with an oxygen molecule.

We report a theoretical study on electron scattering by two strongly polar molecules, namely, formaldehyde (CH${}_2$O) and pyrimidine (C${}_4$H${}_4$N${}_2$), in the low- and intermediate-energy ranges. Calculated elastic differential, integral, and momentum-transfer cross sections, as well as total (elastic $+$ inelastic) and total absorption cross sections, are reported for impact energies ranging from 0.2 to 500 eV. A complex optical potential is used to represent the electron-molecule interaction dynamics, whereas a single-center-expansion method associated with the Padé approximant technique is used to solve the scattering equations. Our calculated results are compared with experimental results and other theoretical data available in the literature. Generally good agreement is seen in these comparisons.