Atomic spontaneous decay, a basic and fundamental phenomenon, arises from the coupling of the atom to the electromagnetic field – a system with an infinite number of degrees of freedom. In conventional atomic physics the coupling is weak such that the atomic emission rate is much smaller than the atomic frequency.
We showed that with superconducting circuits we can explore a new regime, where the coupling is so large that the decay rate becomes comparable to the atomic frequency. This type of system allows for investigations of basic matter-light phenomena in a new regime.
 P. Forn-Diaz et al.,Nature Physics13,39–43.