Experimental motivation and empirical consistency in minimal no-collapse quantum mechanics (Q819157)

The first half of this paper presents three ``Schrödinger-cat'' type experiments. Each is intended as a real, not ``thought'', experiment, represented by a superposition that meets the author's two conditions of a ``cat state''. First the superposed states show ``extensive difference'', i.e. ``they must differ macroscopically in some extensive value'' (p115) and second there is a sufficient ``degree of entanglement'', i.e. ``the number of correlations that would need to be measured to distinguish this state from a mixture must be sufficiently large'' (ibid). The first experiment comes from coherent quantum tunneling in SQUIDS (superconducting quantum interference devices). The superposition is between zero-fluxoid and one-fluxoid states, localized in the left and right well of potential, each corresponding ``to a classical persistent-current state and thus to macroscopically distinguishable directions of the super-conducting current''(p116). The presence of the superposition can be indirectly measured by a static spectroscopic measurement of the energy difference, and furthermore the macroscopic variable, ``the trapped flux through the SQUID ring'', can also be controlled in the experiment. (p118) Following a clear and detailed description of the experiment, with illustrations, and its formal representation, there follows a discussion of interpretation. While the superposition is not itself a current of definite direction, ``it can be decomposed into two such currents of opposite direction''. This decomposition is ``a primarily formal procedure'' and yet also ``the physical relevance of this decomposition and the meaning of the superposition then manifests itself as a current that oscillates between clockwise and counterclockwise directions'' (p119). Localization is in ``flux space'' rather than ``position space'', and this ``preferred basis'' is explained in decoherence theoretical terms as stemming from system-environment entanglement (p120). The second and third experiments are similarly presented in detail, with illustrations and formal analysis, followed by an interpretive discussion. The second experiment comes from matter-wave interferometry, specifically the carbon atoms in the C\(_{70}\) molecule passing through a diffraction grating. These are ``complex and massive'' enough to be classical solid objects rather than atoms, yet are described by single states with interference effects (p121). The third experiment is Bose-Einstein condensation, where an atomic boson gas confined by a magnetic trap is cooled down to low temperatures, and the de Broglie wavelength of each atom becom es long in comparison with the distance between particles. The second half of the paper is more generally interpretive. Section 3 is a single page on ``the status of physical collapse models''. We are told these add ``physical elements'' to interpret quantum theory, and while the experiments so far proposed do not disprove them, the author argues that all apparent physical collapses can be explained as due to decoherence (p133). Section 4 looks at the problem of a non-circular derivation of Born's Rule in the relative-state framework. A kind of ``complementarity'' between ``local events'' and the ``global entangled quantum state'' is proposed, with discussion of the notion of ``envariance'' (p135). Section 5 considers the ``Objectification of observables'', including why only a subset of possible states in Hilbert Space are observed. The ``environment as witness'' and ``quantum Darwinism'' approaches are discussed. Section 6 considers ``Decoherence in the perceptive and cognitive apparatus'' (p138). Since Schrödinger's equations are considered universally valid, questions arise about our own perception of ``outcomes'', and how Schrödinger's dynamics apply to our own perception and even out own ``consciousness'' (ibid). Superpositions of firing and non-firing neuronal superpositions are finally described, before a brief summary of the paper and a comprehensive bibliography of 151 references.