Control of atomic state decay in cavities and microspheres

Novel methods are discussed for the state control of atoms coupled to singl e-mode and multi-mode cavities and microspheres. (1) Excitation decay contr ol: The quantum Zeno effect, i.e. inhibition of spontaneous decay by freque nt measurements, is observable in high-Q cavities and microspheres using a sequence of evolution-interrupting pulses or randomly-modulated CW fields. By contrast, in 'bad' cavities or open space, frequent measurements can onl y accelerate the decay, causing the anti-Zeno effect. (2) Location-dependen t interference of decay channels: Control of two metastable states is feasi ble via resonant single-photon absorption to an intermediate state, by engi neering spontaneous emission in a multimode cavity. (3) Decoherence control by conditionally interfering parallel evolutions: An arbitrary internal st ate of an atomic wavepacket can be protected from decoherence by interferen ce of its interactions with the cavity over many different time intervals i n parallel, followed by the detection of appropriate atomic-momentum observ ables. The arsenal of control methods described above can advance the state -of-the-art of quantum information storage and manipulation in cavities.