Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 32: Transport: Quantum Coherence and Quantum Information Systems - Part 2

TT 32.13: Talk

Thursday, March 30, 2006, 17:15–17:30, HSZ 304

How fat is Schrödinger’s cat? — •Benjamin Abel, Florian Marquardt, and Jan von Delft — Ludwig-Maximilians-Universität, Arnold Sommerfeld Center for Theoretical Physics and Center for Nanoscience,Theresienstr. 37, 80333 München

Recent experiments have tried to produce superpositions of "macroscopically distinct" quantum states, e.g. in small superconducting quantum interference devices (SQUIDs) or in microwave cavities. These superpositions are commonly referred to as "Schrödinger cat states" (1). In this work, we provide an answer to the following important question: "How ’macroscopic’ is such a superposition?". We present a general measure of the distance between two arbitrary many-body states forming such a superposition, going beyond previous works that only considered a special class of possible states (2). After illustrating its general features, we apply our measure to experiments employing three-junction SQUIDs (Mooij), where the ground state at half a flux quantum is a superposition of clockwise and counterclockwise flowing supercurrents: |Ψ>=(|left>+|right>)/√2.

[1] E. Schrödinger, "Die gegenwärtige Situation in der Quantenmechanik", Naturwissenschaften, 48, 807, 49, 823, 50,844 (1935).

[2] W. Dürr, C. Simon, and J. I. Cirac, Phys. Rev. Lett. 89, 210402 (2002).

[3] J. E. Mooij, et al., Science 285, 1036 (1999).