DARK STATES AND DE BROGLIE WAVE OPTICS

The techniques of laser cooling have now become sufficiently developed that the focus has shifted toward interesting applications such as th e quantum domain of atomic motion. This topic is characterized by the failure of the classical description in which atoms move as point part icles whose trajectories can be known: instead, atomic motion must be described as the optics of de Broglie waves. For example, when the de Broglie wavelength lambda(dB) exceeds lambda(optical), then a classica l description is insufficient (Bose condensation is done in the dark, and the quantum condition becomes lambda(dB) > nearest neighbor distan ce). One of the most fascinating topics of quantized atomic motion in a laser field derives from optical dark states that can even occur in the simplest (two-level) atoms, where there are no magnetic sublevels and the polarization is irrelevant. In spite of the simplicity of this two-level atom case however, the more interesting cases occur in mult ilevel atoms where the internal magnetic states and external quantum s tates of atomic motion become truly entangled. Schrodinger called such states ''the heart of quantum mechanics'' because they led to puzzles such as his famous ''cat'' and the EPR paradox.