Quantum Zeno effect: preventing a photon from exiting a cavity*

The quantum Zeno effect refers to the freezing of the time evolution of a quantum system subjected to repeated measurements. In this talk we try to answer the question, as to whether the Zeno effect can stop stochastic decay events like a photon jump from a cavity. There is a time scale governing the rate at which the photon in the cavity gets entangled with the environment, and therefore the decay constant of finding the photon in the cavity. Performing a projective and quantum non-demolition photon number measurement on the cavity faster than this time scale prevents the system to get entangled with the environment, thereby freezing the photon jump. To demonstrate this phenomenon, we use a 3D microwave resonator as the cavity and an auxiliary resonator as a toy environment. The auxiliary resonator is coupled to a transmon, which is continuously being readout to monitor photon jumps. Conditioning the evolution under “no jumps” on the transmon serves to experimentally show the time scale of system-environment entanglement. A second transmon which is coupled to the main  cavity can now perform the Fock state projective measurements fast enough to freeze the photon jumps.