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AIP conference proceedings

Macroscopic Quantum Processors Based on Stored High-Energy Polarized Beams

Dennis Sivers

Published Jan 1, 2003• 0 citations
Publisher

Abstract

The coherent spin rotation of stored particle beams produces macroscopic states with familiar quantum properties. Because massive quantum systems with spin greater than or equal to one display instructive interference effects not accessible with spin one‐half particles, we discuss the sequential rotation and decoherence of a stored polarized deuteron beam. Experimental measurements on such systems should produce unique quantum effects.

DOI
10.1063/1.1607243

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The coherent spin rotation of stored particle beams produces macroscopic states with familiar quantum properties. Because massive quantum systems with spin greater than or equal to one display instructive interference effects not accessible with spin one‐half particles, we discuss the sequential rotation and decoherence of a stored polarized deuteron beam. Experimental measurements on such systems should produce unique quantum effects.
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Large-scale quantum effects have always played an important role in the foundations of quantum theory.With recent experimental progress and the aspiration for quantum enhanced applications, the interest in macroscopic quantum effects has been reinforced.In this review, measures aiming to quantify various aspects of macroscopic quantumness are critically analyzed and discussed.Recent results on the difficulties and prospects to create, maintain, and detect macroscopic quantum states are surveyed.The role of macroscopic quantum states in foundational questions as well as practical applications is outlined.Finally, past and ongoing experimental advances aiming to generate and observe macroscopic quantum states are presented.
In this paper we introduce a simple procedure for computing the macroscopic quantum behaviour of periodic quantum systems in the high energy regime. The macroscopic quantum coherence is ascribed to a one-particle state, not to a condensate of a many-particle system; and we are referring to a system of high energy but with few degrees of freedom. We show that, in the first order of approximation, the quantum probability distributions converge to its classical counterparts in a clear fashion, and that the interference effects are strongly suppressed. The harmonic oscillator provides a testing ground for these ideas and yields excellent results.
The ergotropy, or unitarily extractable work, of a quantum system naturally splits into incoherent and coherent contributions, respectively set by population inversion and coherences in the energy eigenbasis. We show that this split makes the coherent ergotropy of a Mach--Zehnder qubit sensitive to path predictability that the output interference fringes do not reveal. We send the path qubit, prepared as a thermal quantum battery, through two quantum-controlled interferometers built from the same elements, a fixed beam splitter and a beam splitter coherently controlled to be present or absent, differing only in the order in which these two act. The two arrangements share identical visibility, stored energy, and incoherent ergotropy at every point in the parameter space. Yet, for work extracted from the output battery alone, placing the controlled beam splitter first never yields less coherent ergotropy, and at fixed visibility and interferometric phase the difference is governed by the path predictability that this ordering creates. The same expression reappears as a purity deficit on the beam-splitter controller, so the work advantage comes with a Landauer bound on the cost of locally resetting the controller that is never larger at the same temperature. We further examine the effects of decoherence on the battery and consider a relativistic realization in which a Wigner rotation correlates the particle's spin with its path. Tracing out the spin decoheres the battery and allows the two arrangements to exhibit different coherent ergotropies even in regimes where their non-relativistic counterparts coincide. These results show that interference visibility is not a complete measure of the coherence available as work.