Back to basics on quantum theory

GU Guo-tai

This paper first introduces the concept of quantum computer and some basic applications,then looks back the general research situation of quantum computer theory,explaining the basic quantum computer theory,the differences between quantum computer and classic computer,and at last points out the situations to realize quantum computer and the present difficulties.

Aashish A. Clerk

After a quick review of the basic theory of quantum optomechanical systems, based largely on linearized Heisenberg–Langevin equations, this chapter focuses on selected topics related to quantum measurement and quantum optomechanics. Included are: a comprehensive discussion of the quantum limit on the added noise of a continuous position detector, following the quantum linear response approach; a detailed discussion of the role of noise correlations, and how these can be achieved in an optomechanical cavity (by using squeezed input light, or by modifying the choice of measured output quadrature); and a discussion of back-action evading measurements of a mechanical quadrature, discussing how this can be achieved in a two-tone driven cavity system. The chapter ends with a quick introduction to the theory of conditional continuous quantum measurement, and a discussion on how a back-action evading measurement can be used to produce conditional mechanical squeezed states.

Michael Springborg, Meijuan Zhou

E. T. Jaynes

One of the most successful physicists of the generation immediately before Hugh Everett III, E. T. Jaynes shared both Everett's interest in applications of information theory to physics and his foundational orientation. But whereas Everett focused on quantum mechanics, much of Jaynes' work concerned how to use information theory in thermodynamics. This document is a single page from Jaynes' paper "Information Theory and Statistical Mechanics," Physical Review, 106, 620-630 (1957). Based on the basic content of his penciled observations, Everett wrote to Jaynes with an analysis of the flaws in Jaynes paper. He enclosed a copy of his own relative states preprint. Jaynes wrote back at great length.