Equivalence of the perturbation theories of Hori and Deprit

Equivalence of perturbation theories of Hori and Deprit, based on Poisson brackets, and computer calculations through sixth orde

Frequency stabilization of an external-cavity diode laser

Using a hybrid optical/electronic technique, an external-cavity diode laser was frequency stabilized with respect to the sub-Doppler spectrum of cesium vapor. Laser linewidths of 65 kHz and frequency stabilities of ±10 kHz were obtained

Teleporting bipartite entanglement using maximally entangled mixed channels

The ability to teleport entanglement through maximally entangled mixed states as defined by concurrence and linear entropy is studied. We show how the teleported entanglement depends on the quality of the quantum channel used, as defined through its entanglement and mixedness, as well as the form of the target state to be teleported. We present new results based on the fidelity of the teleported state as well as an experimental set-up that is immediately implementable with currently available technology.Comment: 8 pages, 7 figures, RevTeX4, Accepted for publication in the IJQI special issue on Distributed Quantum Information Processin

Transfer of BECs through discrete breathers in an optical lattice

We study the stability of a stationary discrete breather (DB) on a nonlinear trimer in the framework of the discrete nonlinear Schr\"odinger equation (DNLS). In previous theoretical investigations of the dynamics of Bose-Einstein condensates in leaking optical lattices, collisions between a DB and a lattice excitation, e.g. a moving breather (MB) or phonon, were studied. These collisions lead to the transmission of a fraction of the incident (atomic) norm of the MB through the DB, while the DB can be shifted in the direction of the incident lattice excitation. Here we show that there exists a total energy threshold of the trimer, above which the lattice excitation can trigger the destabilization of the DB and that this is the mechanism leading to the movement of the DB. Furthermore, we give an analytic estimate of upper bound to the norm that is transmitted through the DB. Our analysis explains the results of the earlier numerical studies and may help to clarify functional operations with BECs in optical lattices such as blocking and filtering coherent (atomic) beams.Comment: 8 pages, 5 figure

Pathology and treatment of Meniere's disease

Many patients with Meniere's disease are subject to anxiety and nervous tension. The patient who has just had an attack of vertigo, possibly with accompanying nausea and vomiting, is an anxious and worried person. Therefore the pyhsician's approach to the case is important, and he must be prepared to spend time and patience. This may prove difficult, since these cases, like neurotics, are not easily reassured and often have many symptoms to describe.The doctor must be prepared to discuss and explain what is happening to the patient, that several kinds of treatment are available and effective in many cases, and that the disease is not due to any irreparable intracranial condition. The first essential in re- establishing the patient's confidence is a complete and careful physical examination.At the same time it is a mistake not to point out that there is no quick cure, that the course of treatment is liable to be prolonged and that relapses do occur in certain cases. Most patients are prepared to accept the liklihood of a lengthy period of treatment and at least some restriction of their activities.Most authorities agree that ¡0;g - 31015 of cases of tree Meniere's disease are benefited by medical treatment. It is difficult to estimate the efficacy of any treatment because of the characteristic natural remissions of the condition.About 20' - 30' of cases are severe enough to call for surgical intervention. In general, destructive surgery is reserved for severe cases with gross incapacity due to unilateral disease. The factors which must be considered in the decision to operate or not are: -1. The presence of bilateral disease. 2. The age and physical condition of the patient. 3. The amount of hearing retained in the affected ear, and the presence of good or bad hearing in the other ear. not 4. The status of the patient, e.g. a labourer may not be prepared to bear the financial burden of at least two months and possibly longer off work.In unilateral cases, destructive labyrinthectomy is probably the operation of choice, and here Cawthorne's method would appear to be the safest.It would appear also that in such cases, with good hearing in the affected ear, there is a place for hemisection of the VIIIth cranial nerve, or ultrasonic therapy, preferably the latter in view of the mortality associated with hemisection.The difficulty in choice of procedure arises in bilateral cases. Bilateral sympathectomy may be the answer here. On the other hand ultrasonic therapy to both ears may prove the only surgical alternative. Only time will tell

Magnetic order in a spin-1/2 interpolating kagome-square Heisenberg antiferromagnet

The coupled cluster method is applied to a spin-half model at zero temperature ($T=0$), which interpolates between Heisenberg antiferromagnets (HAF's) on a kagome and a square lattice. With respect to an underlying triangular lattice the strengths of the Heisenberg bonds joining the nearest-neighbor (NN) kagome sites are $J_{1} \geq 0$ along two of the equivalent directions and $J_{2} \geq 0$ along the third. Sites connected by $J_{2}$ bonds are themselves connected to the missing NN non-kagome sites of the triangular lattice by bonds of strength $J_{1}' \geq 0$. When $J_{1}'=J_{1}$ and $J_{2}=0$ the model reduces to the square-lattice HAF. The magnetic ordering of the system is investigated and its $T=0$ phase diagram discussed. Results for the kagome HAF limit are among the best available.Comment: 21 pages, 8 figure

Reinventing spacetime on a dynamical hypersurface

In braneworld models, Space-Time-Matter and other Kaluza-Klein theories, our spacetime is devised as a four-dimensional hypersurface {\it orthogonal} to the extra dimension in a five-dimensional bulk. We show that the FRW line element can be "reinvented" on a dynamical four-dimensional hypersurface, which is {\it not} orthogonal to the extra dimension, without any internal contradiction. This hypersurface is selected by the requirement of continuity of the metric and depends explicitly on the evolution of the extra dimension. The main difference between the "conventional" FRW, on an orthogonal hypersurface, and the new one is that the later contains higher-dimensional modifications to the regular matter density and pressure in 4D. We compare the evolution of the spacetime in these two interpretations. We find that a wealth of "new" physics can be derived from a five-dimensional metric if it is interpreted on a dynamical (non-orthogonal) 4D hypersurface. In particular, in the context of a well-known cosmological metric in $5D$, we construct a FRW model which is consistent with the late accelerated expansion of the universe, while fitting simultaneously the observational data for the deceleration parameter. The model predicts an effective equation of state for the universe, which is consistent with observations.Comment: References added to the Introduction, and Abstract modified. Accepted for publication in Mod. Phys. Lett.

The frustrated Heisenberg antiferromagnet on the honeycomb lattice: J1J_{1}--J2J_{2} model

We study the ground-state (gs) phase diagram of the frustrated spin-1/2 $J_{1}$--$J_{2}$ antiferromagnet with $J_{2}=\kappa J_1>0$ ($J_{1}>0$) on the honeycomb lattice, using the coupled-cluster method. We present results for the ground-state energy, magnetic order parameter and plaquette valence-bond crystal (PVBC) susceptibility. We find a paramagnetic PVBC phase for $\kappa_{c_1}<\kappa<\kappa_{c_2}$, where $\kappa_{c_1} \approx 0.207 \pm 0.003$ and $\kappa_{c_2} \approx 0.385 \pm 0.010$. The transition at $\kappa_{c_1}$ to the N\'{e}el phase seems to be a continuous deconfined transition (although we cannot exclude a very narrow intermediate phase in the range $0.21 \lesssim \kappa \lesssim 0.24$), while that at $\kappa_{c_2}$ is of first-order type to another quasiclassical antiferromagnetic phase that occurs in the classical version of the model only at the isolated and highly degenerate critical point $\kappa = 1/2$. The spiral phases that are present classically for all values $\kappa > 1/6$ are absent for all $\kappa \lesssim 1$.Comment: 6 pages, 5 figure

The frustrated Heisenberg antiferromagnet on the honeycomb lattice: A candidate for deconfined quantum criticality

We study the ground-state (gs) phase diagram of the frustrated spin-1/2 $J_{1}$-$J_{2}$-$J_{3}$ antiferromagnet with $J_{2} = J_{3} =\kappa J_1$ on the honeycomb lattice, using coupled-cluster theory and exact diagonalization methods. We present results for the gs energy, magnetic order parameter, spin-spin correlation function, and plaquette valence-bond crystal (PVBC) susceptibility. We find a N\'eel antiferromagnetic (AFM) phase for $\kappa < \kappa_{c_{1}} \approx 0.47$, a collinear striped AFM phase for $\kappa > \kappa_{c_{2}} \approx 0.60$, and a paramagnetic PVBC phase for $\kappa_{c_{1}} \lesssim \kappa \lesssim \kappa_{c_{2}}$. The transition at $\kappa_{c_{2}}$ appears to be of first-order type, while that at $\kappa_{c_{1}}$ is continuous. Since the N\'eel and PVBC phases break different symmetries our results favor the deconfinement scenario for the transition at $\kappa_{c_{1}}$