We present a quantum electrodynamic treatment of the photon-assisted tunneling sidebands that arise when an electron tunnels through a discrete electron state that is interacting with a coherent field. Virtual spontaneous emission of photons by the electron due to its interaction with the vacuum fluctuations of the electromagnetic field leads to an asymmetry in the sideband spectrum not present in the classical limit. For the case of strong coupling between the electron state and the electromagnetic field there can be significant differences between the quantum and classical results, even in the limit of high fields.

• Received 23 April 1998

DOI:https://doi.org/10.1103/PhysRevB.58.12617