One- and Two-Photon Counting Methods in the Spectroscopy of a Single Impurity Center
It was shown in the last chapter that relaxation of off-diagonal elements of the density matrix is determined by a rate constant 1/T 2. This constant results from the interaction with phonons and tunnelons. In Part VI, when we study coherent effects like optical free induction decay or photon echo, we shall see that these off-diagonal elements contain information concerning the phase of the electronic excitation. Therefore T 2 is called the phase relaxation time or dephasing time. The constant T 2 depends on temperature and this dephasing time increases when the temperature decreases. However, the dephasing time T 2 is less than the fluorescence lifetime T 1 by a significant factor, even at T = 4.2 K.
KeywordsTriplet State Rabi Frequency Photon Pair Triplet Level Quantum Trajectory
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