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| 2000 | Wang, Jin, Wiseman, H. M. and Milburn, Gerard J. (2000) Non-Markovian Homodyne-Mediated Feedback on a Two-Level Atom: a Quantum Trajectory Treatment. |
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Quantum feedback can stabilize a two-level atom against decoherence (spontaneous emission), putting it into an arbitrary (specified) pure state. This requires perfect homodyne
detection of the atomic emission, and instantaneous feedback. Inefficient detection was considered previously by two of us. Here we allow for a non-zero delay time (tau) in the feedback circuit.
Because a two-level atom is a nonlinear optical system, an analytical solution is not possible. However, quantum trajectories allow a simple numerical simulation of the resulting non-Markovian
process. We find the effect of the time delay to be qualitatively similar to that of inefficient detection. The solution of the non-Markovian quantum trajectory will not remain fixed, so that the
time-averaged state will be mixed, not pure. In the case where one tries to stabilize the atom in the excited state, an approximate analytical solution to the quantum trajectory is possible. The
result, that the purity (P=2Tr [ rho /sup 2/]-1) of the average state is given by P=1-4 gamma tau (where gamma is the spontaneous emission rate) is found to agree very well with the numerical
results.
| |  Dr Howard Wiseman,  Professor Gerard Milburn | | eSpace Record: |
http://espace.library.uq.edu.au/view/UQ:11174
| | | | | Links: | Alternative Location |
| Keywords: | Spontaneous emission, Atom-photon collisions, Quantum optics | | |
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