Quantum time evolution in a qubit readout process with a Josephson bifurcation amplifier.

Phys Rev Lett 2009 Jun 26;102(25):257003. Epub 2009 Jun 26.

NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan.

We analyzed the Josephson bifurcation amplifier (JBA) readout process of a superconducting qubit quantum mechanically by calculating the dynamics of the density operator of a driven nonlinear oscillator and a qubit coupled system during the measurement process. In purely quantum cases, bifurcation is impossible. Introducing decoherence enables us to reproduce the bifurcation with a finite hysteresis. When a qubit is initially in a superposition state, we have observed the qubit-probe (JBA) entangled state, and it is divided into two separable states at the moment the JBA transition begins. This corresponds to "projection." To readout the measurement result, however, we must wait until the two JBA states are macroscopically well separated. The waiting time is determined by the strength of the decoherence in the JBA.

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https://link.aps.org/doi/10.1103/PhysRevLett.102.257003
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http://dx.doi.org/10.1103/PhysRevLett.102.257003DOI Listing
June 2009
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References

(Supplied by CrossRef)

W. Jordan et al.
1999

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