Quantum interference at corners

We show that a radiating atom, or molecule, localised at sub-wavelength distances from a corner arising from the intersection of three planar material surfaces, exhibits novel quantum interference effects. The simplest case arises for a corner formed by the intersection of three perfect conductors, all at right angles. This situation is shown here to give rise to super-radiance and sub-radiance effects that are highly sensitive to the dipole moment orientation and position of the radiating atom or molecule in the vicinity of the corner.     

Conditional Generation of Multiparticle Entanglement via Cavity QED

We propose a simple scheme to not only generate GHZ states and W states of the multiparticle but also form a new category of multiparticle entangled states by letting the A-type three-level atoms simultaneously interacting with a coherent cavity field followed by the selective measurements on the cavity mode. We investigate the influence of the cavity dissipation on the generated entangled state and discuss the experimental feasibility of our scheme. It is shown that the intensity of the coherent cavity field plays an instructive role in contribution to state preparation process while the cavity decay and the detuning between the atoms and cavity mode result in the deterioration of the generated entangled state.     

Infinite horizon asymptotic average optimality for large-scale parallel server networks

We study infinite-horizon asymptotic average optimality for parallel server networks with multiple classes of jobs and multiple server pools in the Halfin–Whitt regime. Three control formulations are considered: (1) minimizing the queueing and idleness cost, (2) minimizing the queueing cost under constraints on idleness at each server pool, and (3) fairly allocating the idle servers among different server pools. For the third problem, we consider a class of bounded-queue, bounded-state (BQBS) stable networks, in which any moment of the state is bounded by that of the queue only (for both the limiting diffusion and diffusion-scaled state processes). We show that the optimal values for the diffusion-scaled state processes converge to the corresponding values of the ergodic control problems for the limiting diffusion. We present a family of state-dependent Markov balanced saturation policies (BSPs) that stabilize the controlled diffusion-scaled state processes. It is shown that under these policies, the diffusion-scaled state process is exponentially ergodic, provided that at least one class of jobs has a positive abandonment rate. We also establish useful moment bounds, and study the ergodic properties of the diffusion-scaled state processes, which play a crucial role in proving the asymptotic optimality.     

DNA: beyond the double helix

Reciprocal exchange can be used to produce DNA motifs based on branching at the level of secondary structure. These motifs can be combined by sticky-ended cohesion to produce a variety of structures. Stick polyhedra and nanomechanical devices have been produced by self-assembly from motifs based on branched DNA. Periodic arrays with tunable surface features has also been produced; aperiodic arrangements have been used for DNA-based computation.     

Negative energy correction for nuclear polarization in muonic atoms

Negative energy corrections to the conventional calculations of nuclear polarization effects in muonic atoms are calculated. It is shown that the corrections are negligible as far as the NP effects due to low lying nuclear states and states in the giant resonance regions are concerned. However, the formula used for the muonic NP calculations breaks down if nuclear excitations with larger energies than the muonic mass are considered. This means that the method cannot be used for calculations of NP effects in electronic atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Generation of Maximally Entangled States of Two Nonidentical Atoms in Cavity QED

We have discussed the system which consists of two nonidentical two-level atoms trapped simultaneously in a large-detuned single-mode cavity field in this paper. The results show that it is possible to generate maximally entangled states for two nonidentical two-level atoms only if the cavity frequency and difference of two nonidentical atoms transition frequency are selected and the cavity-atom interacation time is controlled.