Cavity cooling using ultrafast electrons

Abstract

We propose a method to cool a thermal photonic state in a cavity by passing electrons through it. Electrons are coherently split into two paths, with one path traversing the cavity, becoming entangled with its photonic state. A sequence of such entanglement interactions can achieve cooling of the cavity: e.g., a twofold reduction in thermal photon number with a 25% post-selection probability. This ``which-path''-based approach extends to other qubit oscillator systems, such as phonons in crystals or optomechanical resonators, offering a general framework for quantum oscillator cooling.