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International Journal of Modern Physics B

Generation and Detection of Linear Superpositions of Classically Distinguishable States of a Radiation Mode

David Vitali, P. Tombesi

Published Jul 20, 1997• 3 citations
Publisher

Abstract

A full comprehension of the fuzzy boundary between the classical and the quantum world is still lacking. A deeper understanding of the problem can be obtained form the study of the so-called "Schrödinger cat states", i.e. the paradoxical states arising when the superposition principle of quantum mechanics is extended to the macroscopic world. Quantum optics is, up to now, the most studied field for the experimental realization of these states. A survey of all the proposals made for generating and detecting linear superpositions of classically distinguishable states in quantum optical systems is presented. Then, one of the most recent proposals [P. Tombesi and D. Vitali, Phys. Rev. Lett.77, 411 (1996)] is presented in detail and its experimental feasibility discussed.

DOI
10.1142/s021797929700109x

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A full comprehension of the fuzzy boundary between the classical and the quantum world is still lacking. A deeper understanding of the problem can be obtained form the study of the so-called "Schrödinger cat states", i.e. the paradoxical states arising when the superposition principle of quantum mechanics is extended to the macroscopic world. Quantum optics is, up to now, the most studied field for the experimental realization of these states. A survey of all the proposals made for generating and detecting linear superpositions of classically distinguishable states in quantum optical systems is presented. Then, one of the most recent proposals [P. Tombesi and D. Vitali, Phys. Rev. Lett.77, 411 (1996)] is presented in detail and its experimental feasibility discussed.
We describe the properties of a quantum system prepared in superpositions of classically distinguishable states. These states, often called Schrödinger cat states, are of great interest at present. We discuss how they may be realized in quantum optics using nonlinear interactions and cavity quantum electrodynamics. We first describe the quantum properties of field states in a cavity, and demonstrate the interference properties which characterize superposition states and discuss how fragile they are in dissipative environments. Finally, we review current experimental approaches which may realize these states.
Parallel worlds are imaginative ideas in quantum mechanics and cosmology. The superpositions of parallel worlds are novel states of quantum gravity and have no classical correspondences generally. In this letter, we investigate the superposition or the Schrödinger's cat state of optical parallel worlds, which could be realized in laboratory and may shed some light on the detection of parallel universes in a real world. We propose two realizable experimental schemes, which enable to explore the mysterious `parallel universes' by a Mach-Zehnder interferometer. The first one is based on an atomic ensemble in a superposition state, which is a fat Schrödinger's cat state. The second one is to prepare a photon in a superposition of different paths, where each path lies in an optical parallel universe.
. It is pointed out that the conclusions drawn from a recent quantum interference experiment with light suggest an operational resolution of the Schrödinger cat paradox. On this occasion in honor of Prof. E.T. Jaynes, we recall that he devoted some of his research efforts to the interpretation of quantum mechanics, which led him to propose several experimental tests. Although the ‘neoclassical’ theory he developed was found not to be confirmed by experiment, it nevertheless played a role in encouraging us to think critically about quantum mechanics and to carry out new experiments. This short contribution is concerned with a well-known quantum problem of interpretation. The quantum paradox known as Schrödinger's cat, in which the cat is cast in a linear superposition of the state of being alive and the state of being dead, has been debated since the beginnings of quantum mechanics. Whereas most physicists are ready to concede the existence of superposition states for a microscopic quantum system like an atom, such states appear to be ruled out for a macroscopic system like a cat by common experience. The question then arises at which level classical concepts take over from quantum mechanical ones. In a very clear and readable discussion of this and other paradoxes Glauber has pointed out that the noise inevitably associated with the amplification process accompanying the measurement of a microscopic system leaves the cat in a mixed state rather than a pure one.
Abstract In this paper we re-investigate the core of Schrödinger’s “cat paradox”. We argue that one has to distinguish clearly between superpositions of macroscopic cat states |☺〉 + |☹〉 and superpositions of entangled states |☺, ↑〉 + |☹, ↓〉 which comprise both the state of the cat (☺=alive, ☹=dead) and the radioactive substance (↑=not decayed, ↓=decayed). It is shown, that in the case of the cat experiment recourse to decoherence or other mechanisms is not necessary in order to explain the absence of macroscopic superpositions. Additionally, we present modified versions of two quantum optical experiments as experimenta crucis. Applied rigorously, quantum mechanical formalism reduces the problem to a mere pseudo-paradox.