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Monday, March 02, 2009
12:30 PM - 1:30 PM
T-DO Conference Room

Quantum Lunch

The Size of Macroscopic Superposition States: How Big is Your Cat?

K. Birgitta Whaley
University of California, Berkeley

Realization of true macroscopic quantum superposition states has significant implications for our fundamental understanding of quantum mechanics. The ability to construct and control quantum superpositions of large numbers of particles is also central to large scale quantum information processing. The extreme superposition expressed by Schrödinger’s cat epitomizes such states and current experiments seek to realize “cat” states made from larger and larger numbers of particles in a variety of physical systems. Yet theoretical understanding of the true “size” or “Schrödinger cattiness” of a quantum superposition in a strongly interacting quantum system composed of large numbers of elementary particles is lacking. I shall describe measures to assess the cattiness and present applications to superposition states of Bose gases trapped in double well potentials and to superpositions of superconducting flux qubits. Microscopic analysis of the latter for the micronscale qubits accessible with current technology leads to the surprising result that although the supercurrent is carried by ~10^6 – 10^10 electrons, a mesoscopic number, the number of microscopic degrees of freedom participating in the superposition is far less than this, of order 10^1-10^3.

Host: Malcolm Boshier