Formulas Used
The following formulas define the parameters governing the qubit-resonator interaction.
Detuning (Δ) | Δ = 2π⋅(fq−fr) | fq = qubit frequency fr = resonant frequency |
Dispersive shift | g2/Δ | g = qubit-resonator coupling strength |
Lamb shift | g2/Δ | |
AC Stark shift | n.(2.g2/Δ) | n = Number of photons in the cavity |
Total qubit shift | Lamb Shift + AC Stark Shift | |
Purcell decay rate (ΓP ) | ΓP = κ.(g/Δ)2 | κ: resonator bandwidth |
Purcell decay time (TP) | TP = 1/ΓP | |
Critical photon number (ncrit) | ncrit = Δ2/4g2 | |
Resonator quality factor (Q) | Q=2π⋅fr/κ | |
Power Associated with Photons in the Cavity | Pin=n⋅ℏ⋅(2π⋅fr)⋅κ |
When the number of photons in the resonator exceeds the "critical photon number," the dispersive Hamiltonian approximation becomes invalid. As a result, the critical photon number defines the maximum power level of the resonator probe signal required to ensure an approximate QND (quantum non-demolition) measurement.
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