Optical switches are devices that allow rerouting an incident optical signal to different ports and play a vital part in fiber optic
communication networks. The realization of future quantum networks and quantum communication applications require
so-called quantum switches, which, in contrast to classical optical switches, have to be treated quantum mechanically. In
particular, quantum switches can be prepared and operated in coherent superposition states.
We propose the experimental implementation of a fiber based quantum switch, for which the internal state of a single
laser-cooled atom defines the output port of the incident light field. The key element of this proposal is a novel type of
optical whispering-gallery-mode microresonator. It allows one to reach the regime of strong coupling, where a single atom is
sufficient to drastically change the transmission properties of the resonator. The coupling of light into and out of this so-called
bottle microresonator is realized with very low losses using tapered optical fibers. This fiber integration in conjunction with
the extremely high optical quality of the resonator enables the realization of a highly efficient quantum switch with properties
adequate for real applications.
In addition to its potential use in quantum communication, an intrinsic property of this quantum switch is that it allows one to
efficiently generate matter-light entanglement as well as highly entangled multi-photon states as, e.g., Schrödinger cat states.
This is interesting both from an applied and from a fundamental point of view because the number of entangled particles can
easily be adjusted, thus allowing the quantitative study of the transition from the quantum mechanical behaviour of the switch
to the classical regime.