Schrödinger's cat and her laboratory cousins

Somshubhro Bandyopadhyay

James D. Stein

A. J. Leggett

In this paper I first briefly review the apparently bizarre consequences of attempting to apply quantum mechanics consistently to macroscopic bodies in certain kinds of situations (the ‘Schrödinger's Cat’ paradox). The paradox results from the assumption that the linear superpositions of macroscopically distinct states, which are unambiguously predicted by the formalism, do indeed exist in nature. Until recently, this assumption was experimentally untested. However, recent advances in techniques of microfabrication, cryogenics and noise control have opened up the possibility of indirect and possibly even direct tests, in particular in superconducting systems incorporating Josephson devices. I describe some of these tests, review the current experimental and theoretical situation and discuss the implications of various possible outcomes to the experiments.

Peter John Bussey

Anthony J. Leggett

In a famous 1935 paper, Erwin Schroedinger pointed out the apparently bizarre consequences which flow from the assumption that the formalism of quantum mechanics can be extrapolated from the world of electrons and atoms to the level of our own direct consciousness (the “Cat” paradox). In this paper I first discuss some alleged resolutions of the paradox, then point out that the premise is not self-evident, and define a class of alternative (“macrorealistic”) scenarios. I then review the extent to which the experimental predictions of quantum mechanics are currently tested in the direction of the everyday world, and explain a crucial test, yet to be performed, of these predictions vis-a-vis those of macrorealism.

Philip Yam