Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2009-06-04
Physical Review B 80, 184509 (2009)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
15 pages, 7 figures
Scientific paper
We theoretically describe the weak measurement of a two-level system (qubit) and quantify the degree to which such a qubit measurement has a quantum non-demolition (QND) character. The qubit is coupled to a harmonic oscillator which undergoes a projective measurement. Information on the qubit state is extracted from the oscillator measurement outcomes, and the QND character of the measurement is inferred by the result of subsequent measurements of the oscillator. We use the positive operator valued measure (POVM) formalism to describe the qubit measurement. Two mechanisms lead to deviations from a perfect QND measurement: (i) the quantum fluctuations of the oscillator, and (ii) quantum tunneling between the qubit states $|0>$ and $|1>$ during measurements. Our theory can be applied to QND measurements performed on superconducting qubits coupled to a circuit oscillator.
Burkard Guido
Chirolli Luca
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