The derivation of Casimir forces between dielectrics can be simplified by ignoring absorption, calculating energy changes due to displacements of the dielectrics, and only then admitting absorption by allowing permittivities to be complex. As a first step toward a better understanding of this situation we consider in this article the model of a dielectric as a collection of oscillators, each of which is coupled to a reservoir giving rise to damping and Langevin forces on the oscillators and a noise polarization acting as a source of a fluctuating electromagnetic field in the dielectric. The model leads naturally to expressions for the quantized electric and magnetic fields that are consistent with those obtained in approaches that diagonalize the coupled system of oscillators for the dielectric medium, the reservoir, and the electromagnetic field. It also results in a fluctuation-dissipation relation between the noise polarization and the imaginary part of the permittivity; comparison with the Rytov fluctuation-dissipation relation employed in the well-known Lifshitz theory for the van der Waals (or Casimir) force shows that the Lifshitz theory is actually a classical stochastic electrodynamical theory. The approximate classical expression for the energy density in a band of frequencies at which absorption in a dielectric is negligible is shown to be exact as a spectral thermal equilibrium expectation value in quantum electrodynamic theory. Our main result is the derivation of an expression for the QED energy density of a uniform dispersive, absorbing media in thermal equilibrium. The spectral density of the energy is found to have the same form with or without absorption. We also show how the fluctuation-dissipation theorem ensures a detailed balance of energy exchange between the (absorbing) medium, the reservoir, and the electromagnetic field in thermal equilibrium.

The task of changing the overlap between two quantum states cannot be performed by making use of unitary evolution only. However, by means of a unitary-reduction process, it could be modified. Here we study in detail the problem of mapping two known pure states onto two other states in such a way that the overlap between the outcome states is different from the one of the initial states. We show that the modulus of the overlap can be reduced only probabilistically, whereas it can be increased deterministically. Our analysis shows that the phases of the involved overlaps play an important role in the increase of the success probability of the desired process.

In this Brief Report, we propose a potential scheme to implement one-way quantum computation with circuit quantum electrodynamics (QED). Large cluster states of charge qubits can be generated in just one step with a superconducting transmission line resonator (TLR) playing the role of a dispersive coupler. A single-qubit measurement in the arbitrary basis can be implemented using a single electron transistor with the help of one-qubit gates. By examining the main decoherence sources, we show that circuit QED is a promising architecture for one-way quantum computation.

We propose a selective, efficient, and robust way to realize control of coherent population transfer in a $\Lambda$-type four-level system with a closely spaced doublet in the final state with time-separated chirped pump pulse and Stokes pulse pair by merging stimulated Raman adiabatic passage, temporal coherent control, and chirped adiabatic passage techniques. Moreover, an arbitrary coherent superposition between the final doublet, or between the intermediate state and either of the doublets can be created. This method holds the ability to “control with control” and has potential applications in coherent control of chemical reactions and quantum information processing.

We report on strong interference effects for the dominant, highly correlated, broad, and asymmetric $3p^{5}3d^2({}^2{F}_{5/2,7/2}^o)$ giant resonances in the photorecombination of ${\mathrm{Sc}}^{3+}$. Using a nonorthogonal perturbative multiconfiguration Breit-Pauli approach, we present theoretical photorecombination cross sections that are in line with the Test Storage Ring measurements of Schippers et al. In order to reproduce the observed asymmetric resonance profiles near threshold, it was necessary to include resonance-continuum interference. Also, we present ${\mathrm{Sc}}^{2+}$ photoionization cross sections that agree with the Advance Light Source measurements of Schippers et al. This perturbative method is based on analytical expressions for the cross sections in terms of computed energies and transition rates, thereby directly determining resonance strengths and Fano asymmetry parameters. Of particular note, our reported absolute cross sections are in excellent agreement with experimental results, in contrast to all previous theoretical calculations. Furthermore, the apparent violation of the sum rule prediction, determined both from our integrated photoionization cross sections and from experimental results, is found to be due to radiative damping of narrow resonances.

It has become common practice to model large spin ensembles as an effective pseudospin with total angular momentum $J=\mathit{Nj}$, where $j$ is the spin per particle. Such approaches (at least implicitly) restrict the quantum state of the ensemble to the so-called symmetric Hilbert space. Here, we argue that symmetric states are not generally well preserved under the type of decoherence typical of experiments involving large clouds of atoms or ions. In particular, symmetric states are rapidly degraded under models of decoherence that act identically but locally on the different members of the ensemble. Using an approach [Phys. Rev. A 78, 052101 (2008)] that is not limited to the symmetric Hilbert space, we explore potential pitfalls in the design and interpretation of experiments on spin-squeezing and collective atomic phenomena when the properties of the symmetric states are extended to systems where they do not apply.

Franson-like setups are inadequate for multiparty Bell experiments with energy-time entanglement because postselected events can depend on the local settings, and local models can exploit this feature to reproduce the quantum predictions, even in the case of ideal devices. We extend a previously introduced interferometric scheme [A. Cabello et al., Phys. Rev. Lett. 102, 040401 (2009)] to solve this problem in the $N$-qubit and $N$-qu$N$it cases. In addition, the proposed setups allow us to prepare and test $N$-qubit Greenberger-Horne-Zeilinger and $({\sum }_{i=1}^N|i\dots i\rangle )/\sqrt{N}$ energy-time entangled states.

A potential quantum-information processor is proposed using an array of the endohedral fullerenes ${}^{15}\mathrm{N}@{\mathrm{C}}_{60}$ or ${}^{31}\mathrm{P}@{\mathrm{C}}_{60}$ contained in a single walled carbon nanotube (SWCNT). The qubits are encoded in the nuclear spins of the doped atoms, while the electronic spins are used for initialization and readout, as well as for two-qubit operations.

We compute the multipartite entanglement measures such as the global entanglement of various one- and two-dimensional quantum systems to probe the quantum criticality based on the matrix and tensor product states (MPSs and TPSs). We use the infinite time-evolving block decimation (iTEBD) method to find the ground states numerically in the form of MPSs and TPSs, and then evaluate their entanglement measures by the method of tensor renormalization group (TRG). We find that these entanglement measures can characterize the quantum phase transitions by their derivative discontinuity right at the critical points in all models considered here. We also comment on the scaling behaviors of the entanglement measures by the ideas of quantum-state renormalization group transformations.

The final-state spectrum of $\beta$ decaying tritium anions ${\mathrm{T}}^{-}$ was calculated. The wave functions describing the initial ${\mathrm{T}}^{-}$ ground state and the final ${}^3\mathrm{He}$ states were obtained by the full configuration-interaction method. The transition probability was calculated within the sudden approximation. The transition probability into the electronic continuum was extracted from the complex-scaled resolvent and shown to converge for very high energies to an approximate analytical model probability distribution.

In this article, we derive the formula for the Casimir force acting on a piston made of real material moving inside a perfectly conducting rectangular box. It is shown that by taking suitable limits, one recovers the formula for the Casimir force acting on a perfectly conducting piston or an infinitely permeable piston. The Lifshitz formula for finite temperature Casimir force acting on parallel plates made of real materials is re-derived by considering the five-layer model in the context of the piston approach. It is observed that the divergences of the Casimir force will only cancel under certain conditions, for example, when the regions separated by the plates are filled with media of the same refractive index.

Relativistic configuration-interaction calculations have been performed for all possible $E1$, $M1$, and $E2$ transitions between bound anion states of ${\mathrm{La}}^{-}$ and ${\mathrm{Os}}^{-}$. We pay particular attention to $E1$ transitions in each case that may be of use in laser cooling of these anions. Although the ${\mathrm{La}}^{-}$ transition energy is approximately one-third of the ${\mathrm{Os}}^{-}$ transition, our results indicate that the Einstein $A$ coefficient is nearly two orders of magnitude larger, which would lead to more efficient laser cooling. We have also explored long-lived opposite-parity excited states in ${\mathrm{Lu}}^{-}$ and ${\mathrm{Lr}}^{-}$ which are restricted to $M2$ decay by selection rules. Finally, in ${\mathrm{Pr}}^{-}$, we find sufficient mixing between a weakly bound excited $4f^{2}5d^{2}6s^2$ state with a nearby $4f^{3}6s^{2}6p$ resonance to result in a lifetime similar to that of the other excited anion states, despite the fact that the dominant configurations of these $M1$ and $E2$ transitions differ by two electrons.

We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein condensate by a temporal modulation of spin exchange interaction, which is tunable with optical Feshbach resonance. Adopting techniques from coherent control, we demonstrate the localization and freezing of spin mixing dynamics, and the suppression of the intrinsic dynamic instability and spontaneous spin domain formation in a ferromagnetically interacting condensate of ${}^{87}\mathrm{Rb}$ atoms. This work points to a promising scheme for investigating the weak magnetic spin dipole interaction, which is usually masked by the more dominant spin exchange interaction.

We study the efficiency of the atomic frequency comb storage protocol. We show that for a given optical depth, the preparation procedure can be optimize to significantly improve the retrieval. Our prediction is well supported by the experimental implementation of the protocol in a ${\mathrm{Tm}}^{3+}$:YAG crystal. We observe a net gain in efficiency from 10 to $17\%$ by applying the optimized preparation procedure. In the perspective of high bandwidth storage, we investigate the protocol under different magnetic fields. We analyze the effect of the Zeeman and superhyperfine interaction.

We describe a white-light cavity scheme based on a cavity quantum electrodynamics system that consists of multiple three-level atoms confined in an optical cavity and coherently driven by a free-space, circularly polarized field. A linearly polarized field is coupled into the cavity mode and its two circular components induce coherent Raman transitions through the normal modes of the coupled atom-cavity system. One circular component of the cavity field experiences anomalous dispersion which enables broadband light transmission through the cavity. We present the experimental demonstration of the broadband light transmission through an optical cavity coupled to cold Rb atoms.

In order to optimize quantum information processing in individual traps such as optical lattices, we propose a combined atom-molecule system. In particular, gates, initialization, and readout are suggested, using two atoms of different species—one atom carrying the qubit and the other enabling interaction. We describe in some detail the implementation of a two-qubit phase gate in which a pair of atoms is transferred into the ground rovibrational state of a polar molecule with a large dipole moment, thus allowing molecules in adjacent sites to interact via their dipole-dipole interaction. We also discuss how the reverse process could be used as a nondestructive readout tool.

We propose an ion trap configuration that, by symmetry, is three-dimensionally frequency degenerate. This fundamental trap configuration can be stacked together in a three-dimensional simple cubic arrangement. The isolated trap, as well as the extended array of ion traps, is characterized for different locations in the lattice, illustrating the robustness of the lattice of traps concept. The ease of addressing the ions at each lattice site, individually or simultaneously, makes this system naturally suitable for a number of experiments. Application of this trap to precision spectroscopy, quantum information processing, and the study of few-particle interacting systems are discussed.

We extend the standard Bose-Hubbard model to capture arbitrarily strong on-site correlations. In addition to being important for quantitatively modeling experiments, for example, with rubidium atoms, these correlations must be included to describe more exotic situations. Two such examples are when the interactions are made large via a Feshbach resonance and when each site rotates rapidly, making a coupled array of quantum Hall puddles. Remarkably, even the mean field approximation to our model includes all on-site correlations. We describe how these on-site correlations manifest themselves in the system’s global properties: modifying the phase diagram and depleting the condensate.

Recently, the principle of nonviolation of information causality [Nature 461, 1101 (2009)] has been proposed as one of the foundational properties of nature. We explore the Hardy’s nonlocality theorem for two-qubit systems, in the context of generalized probability theory, restricted by the principle of nonviolation of information causality. Applying a sufficient condition for information causality violation, we derive an upper bound on the maximum success probability of Hardy’s nonlocality argument. We find that the bound achieved here is higher than that allowed by quantum mechanics but still much less than what the no-signaling condition permits. We also study the Cabello type nonlocality argument (a generalization of Hardy’s argument) in this context.