PAPER: Quantum statistical physics, condensed matter, integrable systems Precise measurement of coupling strength and high temperature quantum effect in a nonlinearly coupled qubit-oscillator system

摘要

We study the coherence dynamics of a qubit coupled to a harmonic oscillator with both linear and quadratic interactions. As long as the linear coupling strength is much smaller than the oscillator frequency, the long time behavior of the coherence is dominated by the quadratic coupling strength g_2. The coherence decays and revives at a period 2π/g_2, with the width of coherence peak decreasing as the temperature increases, hence providing a way to measure g_2 precisely without cooling. Unlike the case of linear coupling, here the coherence dynamics never reduces to the classical limit in which the oscillator is classical. Finally, the validity of linear coupling approximation is discussed and the coherence under Hahn-echo is evaluated.