Electron beam X-Y deflection system Final report

Design and fabrication of electron beam X-Y deflection system for retrofit on welding gun

Quantum data processing and error correction

This paper investigates properties of noisy quantum information channels. We define a new quantity called {\em coherent information} which measures the amount of quantum information conveyed in the noisy channel. This quantity can never be increased by quantum information processing, and it yields a simple necessary and sufficient condition for the existence of perfect quantum error correction.Comment: LaTeX, 20 page

Inequalities for quantum channels assisted by limited resources

The information capacities and ``distillability'' of a quantum channel are studied in the presence of auxiliary resources. These include prior entanglement shared between the sender and receiver and free classical bits of forward and backward communication. Inequalities and trade-off curves are derived. In particular an alternative proof is given that in the absence of feedback and shared entanglement, forward classical communication does not increase the quantum capacity of a channel.Comment: 8 pages, 4 figures (references updated, minor changes

Robust single-parameter quantized charge pumping

This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs-GaAs gated nanowire. We find a remarkable robustness of the quantized regime against variations in the driving signal, which increases with applied rf power. This feature together with its simple configuration makes this device a potential module for a scalable source of quantized current.Comment: Submitted to Appl. Phys. Let

Reversible quantum operations and their application to teleportation

Quantum operations provide a general description of the state changes allowed by quantum mechanics. Simple necessary and sufficient conditions for an ideal quantum operation to be reversible by a unitary operation are derived in this paper. These results generalize recent work on reversible measurements by Mabuchi and Zoller [Phys. Rev. Lett. {\bf 76}, 3108 (1996)]. Quantum teleportation can be understood as a special case of the problem of reversing quantum operations. We characterize completely teleportation schemes of the type proposed by Bennett {\it et al.} [Phys. Rev. Lett. {\bf 70}, 1895 (1993)].Comment: 10 pages, Revte

Population inversion in optically pumped asymmetric quantum well terahertz lasers

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics