The effect of focusing on polarization qubits
Netanel H. Lindner, Daniel R. Terno · Journal of Modern Optics · 2005
When a photon with well-defined polarization and momentum passes through a focusing device, these properties are no longer well defined. Their loss is captured by describing polarization by a 3× 3 effective density matrix. Here we show that the effective density matrix corresponds to the actual photodetection model and we provide a simple formula to calculate it in terms of classical fields. Moreover, we explore several possible experimental consequences of the ‘longitudinal’ term: limits on single-photon detection efficiency, polarization-dependent atomic transitions rates and the implications on quantum information processing.