Figure 5
From: Witnessing Quantum Coherence: from solid-state to biological systems
Detecting vacuum Rabi oscillations in a lossy cavity.
Here we use the experimental data reported in Ref. 47 to illustrate coherence-verification using our second witness Eq. (6). The circular Rydberg states with principle quantum numbers 51 and 50 for transition ω0 = 51.1 GHz are considered as the states |e〉 and |g〉, respectively. The atom-field coupling is ωR/2π = 47 KHz. For a high-Q cavity with Q = 7 × 107, the vacuum Rabi oscillation is detected by use of 
where m = n = 1. As a comparison we also checked the case when the Q-factor is so low that 2ωR < ω0/Q. For such a low-Q cavity (e.g., Q = 7 × 105), the state evolution is in the regime of irreversible transitions and obeys the classical constraint (3). Hence the value of the witness is zero.
