Quantum optics of single atoms

[PHY]

In recent years there has been increasing interest in systems capable to generate photon fields containing a preset number of photons. This has chiefly arisen from applications for which single photons are a necessary requirement, such as secure quantum communication and quantum cryptography. Photon number states or Fock states are also useful for generating multiple atom entanglements in strongly coupled systems such as the micromaser. The generated field and the pumping atoms are in an entangled state, this entanglement can be transferred by the field to subsequent atoms, leading to applications such as basic quantum logic gates. For our experiments we employ a micromaser having a cavity Q of 4 × 1010 corresponding to a photon lifetime of 0.3s which is the largest ever achieved in this type of experiments. A source of single photons or, more generally, arbitrary Fock states is also a useful tool for further investigations of atomfield interaction. It can be used to obtain the reconstruction of purely quantum states of the radiation field as represented by the Fock states. Recently we succeeded to combine an ion trap with an optical cavity. With this system also single photons in the visible spectral region can be produced on demand.

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