The manipulation of quantum systems in order to develop applications for information processing has become a very active area of quantum optics and mesoscopic physics. In previous lectures, I had studied systems of trapped ions and atoms coupled to a few photons in cavities, analyzing various methods of state preparation, estimation and reconstruction. I described the generation and measurement of states with non-classical properties, such as the entangled states of several atoms, the Schrödinger cat states of a field trapped in a cavity, or Fock states with well-defined photon numbers, and showed how the decoherence of these states could be experimentally observed.
This year, I described more general methods for synthesizing arbitrary quantum states, and tackled the problem of decoherence control by describing quantum feedback methods whose aim is to protect quantum systems from decoherence by keeping them in a given non-classical state for as long as possible. An important part of the lecture was devoted to the description of systems made up of superconducting Josephson junctions, veritable artificial atoms whose development in recent years has led to remarkable state synthesis and reconstruction experiments. I compare these experiments with those carried out with atoms and photons in quantum optics.
I have described cavity quantum electrodynamics experiments involving the non-destructive measurement of photons and the reconstruction of non-classical field states, as well as quantum feedback experiments. I have also analyzed experiments on the measurement and reconstruction of field states in circuit electrodynamics, comparing them with those in cavity quantum electrodynamics.