The simulation of spontaneous (RIXS) and stimulated x-ray Raman scattering (SXRS) signals in isotropic samples requires rotational averaging of a fourth-rank tensor product of two polarizabilities. Attosecond stimulated x-ray Raman spectroscopy excites multiple valence transitions covered by the pulse bandwidths. These excitations depend on the orientation of the molecule with respect to the pulse polarizations in the laboratory frame, making the response a high-rank tensor operator. Many contributions to the response coming from different tensor components complicate the analysis and interpretation of these measurements. By using the magic angle between the excitation and detection fields these signals may be expressed as correlation functions of the scalar isotropic polarizabilities, which greatly simplifies their interpretation. We show that a similar simplification of three-pulse two-dimensional stimulated x-ray Raman scattering (2D-SXRS), which depends on a rotationally averaged sixth-rank tensor, is possible by a super magic angle (SMA) combination of two measurements with specific pulse polarization configurations. Calculated SMA 2D-SXRS signals for trans-$N$-methylacetamide (NMA) at the nitrogen $K$ edge reveal different features compared with the all-parallel polarization configuration.

We solve the problem of quantum state discrimination with “general (symmetric) figures of merit” for an even number of symmetric quantum bits with use of the no-signaling principle. It turns out that conditional probability has the same form for any figure of merit. Optimal measurement and corresponding conditional probability are the same for any monotonous figure of merit.

We show that nonorthogonal states achieve a higher level of entanglement when one party undergoes uniform acceleration. We also show that in this regime nonorthogonal states achieve a higher fidelity for teleportation. A quantum field as observed by an observer confined to a Rindler wedge acts as an open system. When one traces over the field modes in the causally disconnected region of space time, one finds that, for a qubit derived from the modes of a scalar field, the effective state space of a qubit is deformed. In order to show this we numerically calculate the Bures angle between states as seen by an accelerating observer. We also derive the Bures metric of an effective qubit in the limit of low accelerations. In order to show that the deformation is not just a coordinate transform, we calculate the scalar curvature of the effective Bures metric. We see that the effective Bures metric loses its isotropic nature. Despite taking the limit of low accelerations, our results are also relevant to large gravitational fields.

We extend the classification of mixed states of quantum systems composed of arbitrary numbers of subsystems of arbitrary dimensions. This extended classification is complete in the sense of partial separability and gives $1+18+1$ partial separability classes in the tripartite case contrary to a former $1+8+1$. Then we give necessary and sufficient criteria for these classes, which make it possible to determine to which class a mixed state belongs. These criteria are given by convex roof extensions of functions defined on pure states. In the special case of three-qubit systems, we define a different set of such functions with the help of the Freudenthal triple system approach of three-qubit entanglement.

A generalization of homogeneous coordinate scaling for wave functions [${\phi }_{\alpha \beta mp}^{\left(i\right)}\left(\mathbf{r}\right)={\alpha }^{m/2}{\phi }_i\left({\beta }^p\mathbf{r}\right),(\alpha ,\beta )\in {\mathbb{R}}^{+},(m,p)\in \mathbb{R}$] and electron densities [$n_{\alpha \beta mp}\left(\mathbf{r}\right)={\alpha }^{m}n\left({\beta }^p\mathbf{r}\right)$] is introduced. It is shown that, under such a scaling, the Kohn-Sham (KS) noninteracting kinetic energy $T_s\left[n\right]$ scales as $T_s\left[n_{\alpha \beta mp}\right]={\alpha }^m{T}_s\left[n\right]/{\beta }^p$, which leads to the integral, or generalized virial, expression $T_s\left[n\right]=1/\left(m-p\right)\int \delta T_s\left[n\right]/\delta n\left(\mathbf{r}\right)[mn\left(\mathbf{r}\right)+p\mathbf{r}·\nabla n\left(\mathbf{r}\right)]d^{3}r.$ For $m=3$ and $p=2$ the general expression yields the well-known relation $T_s\left[n\right]=1/2\int \delta T_s\left[n\right]/\delta n\left(\mathbf{r}\right)[3n\left(\mathbf{r}\right)+\mathbf{r}·\nabla n\left(\mathbf{r}\right)]d^{3}r$. The general virial also reduces to the new integral expression $T_s\left[n\right]=-\int \delta T_s\left[n\right]/\delta n\left(\mathbf{r}\right)\mathbf{r}·\nabla n\left(\mathbf{r}\right)d^{3}r,$ as well as to the controversial one, $T_s\left[n\right]=-\int \delta T_s\left[n\right]/\delta n\left(\mathbf{r}\right)n\left(\mathbf{r}\right)d^{3}r,$ due to the scaling of $T_s\left[n\right]$ under $n_{\alpha mp}\left(\mathbf{r}\right)={\alpha }^{m}n\left({\alpha }^p\mathbf{r}\right)$ and its invariance for $m=p$. The validity of the controversial expression is further discussed and the first-degree homogeneous character of $T_s\left[n\right]$ under density scaling established. The scaling properties of the KS potential and eigenvalues are also analyzed. Examples of numerical tests that confirmed all the integral expressions for $T_s\left[n\right]$ and its scaling properties, as well as the scaling of the KS potential and eigenvalues, are provided.

We report experimental and theoretical results for associative detachment (AD) of ${\mathrm{D}}^{-}+\mathrm{D}\to {\mathrm{D}}_2+e^{-}$. We compare these data to our previously published results for ${\mathrm{H}}^{-}+\mathrm{H}\to {\mathrm{H}}_2+e^{-}$. The measurements show no significant isotope effect in the total cross section. This is to be contrasted with previously published experimental and theoretical work which has found a significant isotope effect in diatomic systems for partial AD cross sections, i.e., as a function of the rotational and vibrational levels of the final molecule formed. Our work implies that though the rovibrational distribution of flux is different for AD of H${}^{-}$ $+$ H and D${}^{-}$ $+$ D, the total flux for these two systems is essentially the same when summed over all possible final channels.

The photoinduced ejection of atoms from superfluid helium nanodroplets is exploited to populate metastable atomic states which cannot easily be reached from the ground state. We demonstrate this method with chromium (Cr) atoms which are located inside the droplet. The ejection is triggered by the $y{}^7{P}_{2,3,4}^o\leftarrow a{}^7{S}_3$ excitation. Due to relaxation during ejection we obtain bare, excited Cr${}^{*}$ atoms in the $z{}^5{P}_{1,2,3}^o$ states. The Cr${}^{*}$ atoms are photoionized into a region close above the threshold of the $a{}^{6}S$ continuum of Cr ii. Discrete autoionizing states ($g{}^5{D}_{2,3,4}$ and $e{}^3{D}_{1,2,3}$) embedded into the continuum are observed as sharp lines with characteristic, asymmetric line profiles. These Fano profiles provide information about the coupling of the autoionizing states to the continuum (autoionization rates) and cross sections for photoionization and resonant excitation. The $g{}^5{D}_{2,3,4}\leftarrow z{}^5{P}_{1,2,3}^o$ line strengths provide insight into the relaxation process, and we find that energetically lower $J$ components of $z{}^5{P}_{1,2,3}^o$ are significantly more strongly populated.

We investigate experimentally the role of spatial coherence on optical beam shifts. This topic has been the subject of recent theoretical debate. We consider Gaussian Schell-model beams, with different spatial degrees of coherence, reflected at an air-glass interface. We prove that the angular Goos-Hänchen and the angular Imbert-Fedorov effects are affected by the spatial degree of coherence of the incident beam, whereas, the spatial Goos-Hänchen effect does not depend on incoherence. Our data unambiguously resolve the theoretical debate in favor of one specific theory.

General statistical ensembles in the Hamiltonian formulation of hybrid quantum-classical systems are analyzed. It is argued that arbitrary probability densities on the hybrid phase space must be considered as the class of possible physically distinguishable statistical ensembles of hybrid systems. Nevertheless, statistical operators associated with the hybrid system and with the quantum subsystem can be consistently defined. Dynamical equations for the statistical operators representing the mixed states of the hybrid system and its quantum subsystem are derived and analyzed. In particular, these equations irreducibly depend on the total probability density on the hybrid phase space.

A consensus that questions the perfunctory use of the quantum adiabatic theorem has emerged since Marzlin and Sanders [Phys. Rev. Lett. 93, 160408 (2004)] showed the existence of an inconsistency in the applicability of the theorem. Further analysis proved that the inconsistency may arise from the existence of resonant terms in the Hamiltonian, but recent work indicates that the debate about the full extent of the problem remains open. Here, we first show that key premises required in the standard demonstration of the theorem do not hold for a dual Hamiltonian involved in the Marzlin-Sanders inconsistency. Also, we show that two simple conditions can identify systems for which the adiabatic approximation fails, in spite of satisfying traditional quantitative conditions that were believed to guarantee its validity. Finally, we prove that the inconsistency only arises for Hamiltonians that contain resonant terms whose amplitudes go asymptotically to zero.

It was recently shown that entanglement in quantum systems being in a nonequilibrium state can appear at much higher temperatures than in an equilibrium state. However, any system is subject to the natural relaxation process establishing equilibrium. The work deals with the numerical study of entanglement dynamics in a dipolar coupled spin-1/2 system under the transition from a nonequilibrium state to an equilibrium state. The spin system is characterized by a two-temperature density matrix, and the process of the establishment of equilibrium is in the equalization of these temperatures. The method of the nonequilibrium statistical operator is used to describe the evolution of the system. The process of establishing an equilibrium state in the homonuclear spin systems at low temperature was first considered. It was shown that the time dependencies of the inverse temperatures of the spin subsystems are given by a solution of nonlinear equations in contrast to the linear equations in the well-known high-temperature approximation. We have first studied the entanglement dynamics during the equilibrium state establishment and have found that the concurrence changes nonmonotonically with time and temperatures while equilibrium is being established. Entanglement fades long before equilibrium is established in the system. It was shown that the entanglement dynamics depends strongly on the ratio of the Zeeman energy to the dipolar energy. At a high ratio, the concurrence in the system decreases quickly for a time of about 100 $\mu \text{s}$ whereas, at a low ratio, establishment of equilibrium and fading entanglement takes a prolonged time up to 1 $\text{ms}$.

We show that, in analogy to light fields, effective bosonic modes of atomic ensembles in the Holstein-Primakoff representation can be prepared in multimode squeezed states, and multipartite continuous-variable cluster and Greenberger-Horne-Zeilinger (GHZ) entangled states. Our scheme uses a cascade of optical cavities, in each of which one atomic ensemble is placed. Through Raman transitions between stable atomic ground states, the atomic ensembles are in the interactions with the cavity and laser fields. Because of the long-lived ground states, the atomic ensembles act as quantum network nodes, whose cluster entangled states are applicable in the one-way quantum computer, and whose GHZ entangled states have potential for quantum communication.

We relate the principle of quantum-memory-assisted entropic uncertainty to quantum teleportation and show geometrically that any two-qubit state which lowers the upper bound of this uncertainty relation is useful for teleportation. We also explore the efficiency of this entropic uncertainty principle on witnessing entanglement in a general class of bosonic structured reservoirs. The entanglement regions witnessed by different estimates are determined, which may have no relation with the explicit form of the spectral density of the reservoir for certain special chosen sets of the initial states.

The effects of an electric field on the magnetically induced ${}^6$Li-${}^{40}$K Feshbach resonances are investigated theoretically by using the asymptotic bound-state model. We calculate the positions and widths of the Feshbach resonances observed in the experiments in the presence of an electric field and give a detailed analysis. An electric field can change the relative magnetic moment and the coupling strength to a different extent. The variation of resonant width caused by a strong electric field mainly depends on the coupling strength, and the $s$-wave scattering cross section in an electric field is sensitive to the temperature of the colliding system and the magnetic-field intensity. The maximum of the thermal average scattering rate constant can be changed by several factors by applying an electric field.

We develop a symmetry classification scheme to find ground states of pseudo-spin-$\frac{1}{2}$, spin-1, and spin-2 spin-orbit-coupled spinor Bose-Einstein condensates and show that as the SO(2) symmetry of simultaneous spin and space rotations is broken into discrete cyclic groups, various types of lattice structures emerge in the absence of a lattice potential. Examples include two different kagome lattices for pseudo-spin-$\frac{1}{2}$ condensates and a nematic vortex lattice in which uniaxial and biaxial spin textures align alternatively for spin-2 condensates. For the pseudo-spin-$\frac{1}{2}$ system, although mean-field states always break time-reversal symmetry, there exists a time-reversal invariant many-body ground state, which is fragmented and expected to be observed in a microcondensate.

We study the generation of entanglement for interacting cold atoms in a three-site ring. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current. A proposal for an experimental setup is discussed.

We study small systems of strongly interacting ultracold atoms under the influence of gauge potentials and spin-orbit couplings. We use second-order perturbation theory in tunneling, derive an effective theory for the strongly correlated insulating states with one atom per site, and solve it exactly. We find dramatic changes in the level structure and in the amount of degeneracies expected. We also demonstrate the dynamical behavior as the barriers between plaquettes are gradually removed and find potentially high overlap with the resonating valence bond (RVB) state of the larger system.

We study the spontaneous excitation of a uniformly accelerated two-level atom nonlinearly coupled to vacuum Dirac field fluctuations using the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji and generalized by us to the present case in the current paper. We find that a cross term involving both vacuum fluctuations and radiation reaction appears, which is absent in the linear coupling cases such as an atom interacting with vacuum scalar or electromagnetic fluctuations. Furthermore, the contribution of this term actually dominates over that of radiation reaction. Thus, the mean rate of change of the atomic energy can no longer be distinctively separated into only the contributions of vacuum fluctuations and radiation reaction as in the scalar and electromagnetic cases where the coupling is linear. Our result shows that a uniformly accelerated atom interacting with vacuum Dirac fluctuations would spontaneously excite and a unique feature in sharp contrast to the scalar and electromagnetic cases is the appearance of a term in the excitation rate, which is proportional to the quartic acceleration.

Wigner gave a well-known proof of Kramers degeneracy for time reversal invariant systems containing an odd number of half-integer spin particles. But Wigner's proof relies on the assumption that the Hamiltonian has an eigenvector, and thus does not apply to many quantum systems of physical interest. This Brief Report illustrates an algebraic way to talk about Kramers degeneracy that does not appeal to eigenvectors and provides a derivation of Kramers degeneracy in this more general context.