2003/07/28 by Frank K. Wilhelm, F. K. Wilhelm
Computer Science · Physics and Astronomy · #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum and electron transport phenomena #cond-mat.mes-hall #cond-mat.supr-con #quant-ph
paper · pdf · doi:10.1103/physrevb.68.060503
4 pages, 3 figures, accepted for publication as a rapid communication in Phys. Rev. B
arxiv created 2003/07/28 · openalex publication_date 2003/08/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
A measurement on a macroscopic quantum system does not, in general, lead to a projection of the wave function in the basis of the detector as predicted by von Neumann's postulate. Hence, it is a question of fundamental interest, how the preferred basis onto which the state is projected is selected out of the macroscopic Hilbert space of the system. Detector-dominated von Neumann measurements are also desirable for both quantum computation and verification of quantum mechanics on a macroscopic scale. The connection of these questions to the predictions of the spin-boson model is outlined. I propose a measurement strategy, which uses the entanglement of the qubit with a weakly damped harmonic oscillator. It is shown that the degree of entanglement controls the degree of renormalization of the qubit and identify that this is equivalent to the degree to which the measurement is detector dominated. This measurement very rapidly decoheres the initial state, but the thermalization is slow. The implementation in Josephson quantum bits is described and it is shown that this strategy also has practical advantages for the experimental realization.