= Cavity quantum electrodynamics
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<Cavity quantum electrodynamics> studies <chemical atoms> or related quantum emitters interacting with quantized <electromagnetic field> modes confined by a cavity. Confinement changes the available mode structure and can strengthen a single excitation's coupling to the emitter. The interaction rate, cavity loss and emitter <decoherence> determine whether coherent exchange can be resolved.
Near <resonance>, an <chemical atom> and mode can exchange excitation; far from <resonance>, <dispersive atom-cavity coupling> produces state- and photon-number-dependent shifts. In the microwave photon-box experiments described in the authored lecture, <chemical atoms> provide repeated nondestructive probes of a long-lived field, allowing photon-number jumps and nonclassical field states to be studied.<Controlling Photons in a Box and Exploring the Quantum to Classical Boundary by Serge Haroche>[Lecture opening and photon-counting discussion: confined microwave field, atom probes and quantum nondemolition measurements]{ref} A cavity's presence alone does not establish strong coupling or a particular nonclassical state.
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