Relativistic electron vortices

The desire to push recent experiments on electron vortices to higher energies has led to some theoretical difficulties. In particular the simple and very successful picture of phase vortices of vortex charge $\ell$ associated with $\ell\hbar$ units of orbital angular momentum per electron has been challenged by the facts that: (i) the spin and orbital angular momentum are not separately conserved for a Dirac electron, which suggests that the existence of a spin-orbit coupling will complicate matters and (ii) that the velocity of a Dirac electron is not simply the gradient of a phase as it is in the Schr\"{o}dinger theory suggesting that, perhaps, electron vortices might not exist at a fundamental level. We resolve these difficulties by showing that electron vortices do indeed exist in the relativistic theory and show that the charge of such a vortex is simply related to a conserved orbital part of the total angular momentum, closely related to the familiar situation for the orbital angular momentum of a photon

Furlable antenna

An improved furlable antenna particularly suited for use in a celestial space environment is described. The antenna is characterized by an actuator comprising an elastomeric member of an annular configuration, an annular array of uniformly spaced antenna ribs rigidly affixed at the base ends to an actuator which enables it to be supported for pivotal displacement from a deployed configuration. The ribs are radially extended from the actuator to a furled configuration. The ribs are extended parallel to the axis of the actuator with flexible reflecting web affixed to the ribs, with angularly spaced bearing blocks

Comment on "Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation"

This editorial discusses "Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation"

Quantum state comparison and the universal-NOT operation

We show that the form of the optimal universal-NOT operation for a single qubit can be determined by considering quantum-limited state comparison. Similarly, optimal state comparison can be derived from the properties of the universal-NOT. This points to the possibility of a fundamental link between these processes

On the recoil and Doppler shifts

The recoil shift due to the finite mass of an absorbing atom is, when viewed in the right way, simply part of the total Doppler shift. This is true both in the low speed and relativistic limits and also for the reflection of light from a low-mass mirror

Eating Disorders: Anorexia and Bulimia as Developmental Crises

Eating disorders are classified as developmental crises and typically develop during the adolescent years when youths face the identity versus role confusion psychosocial stage of development. Individuals struggling with anorexia nervosa or bulimia nervosa share characteristics similar to those found in a drug addiction. Social comparison theory may be used to explain the way individuals look to culture and media to examine whether their body images are acceptable. This body image comparison may result in an eating disorder, as can an environment where family dynamics are dysfunctional and therefore cannot cultivate healthy life stage development. Both anorexia nervosa and bulimia nervosa are best treated with an intervention process that involves the family

Asynchronous quantum key distribution on a relay network

We show how quantum key distribution on a multi-user, multi-path, network can be used to establish a key between any two end-users in an asynchronous fashion using the technique of bit-transport. By a suitable adaptation of our previous secret-sharing scheme we show that an attacker has to compromise all of the intermediate relays on the network in order to obtain the key. Thus, two end-users can establish a secret key provided they trust at least one of the network relays

Retrodiction with two-level atoms: atomic previvals

In the Jaynes-Cummings model a two-level atom interacts with a single-mode electromagnetic field. Quantum mechanics predicts collapses and revivals in the probability that a measurement will show the atom to be excited at various times after the initial preparation of the atom and field. In retrodictive quantum mechanics we seek the probability that the atom was prepared in a particular state given the initial state of the field and the outcome of a later measurement on the atom. Although this is not simply the time reverse of the usual predictive problem, we demonstrate in this paper that retrodictive collapses and revivals also exist. We highlight the differences between predictive and retrodictive evolutions and describe an interesting situation where the prepared state is essentially unretrodictable.Comment: 15 pages, 3 (5) figure

Mutually unbiased measurements for high-dimensional time-bin based photonic states

The task of measuring in two mutually unbiased bases is central to many quantum information protocols, as well as being of fundamental interest. Increasingly, there is an experimental focus on generating and controlling high-dimensional photonic states. One approach is to use the arrival time of a photon, which can be split into discrete time bins. An important problem associated with such states is the difficulty in experimentally realizing a measurement that is mutually unbiased with respect to the time-of-arrival. We propose a simple and compact scheme to measure in both the time of arrival basis and a basis that is approximately mutually unbiased with respect to the arrival time.Comment: Accepted in EPL, 4.1 pages and 2 figure

Analytic stochastic treatment of a nonlinear quantum model with negative diffusion

We apply a proposal of Yuen and Tombesi, for treating stochastic problems with negative diffusion, to the analytically soluble problem of the single-mode anharmonic oscillator. We find that the associated stochastic realizations include divergent trajectories. It is possible, however, to solve the stochastic problem exactly, but the averaging must be performed with great care.Comment: Phys.Rev.