Photon-Pressure with a Negative Mass Microwave Mode

Harmonic oscillators belong to the most fundamental concepts in physics and are central to many current research fields such as circuit QED, cavity optomechanics and photon-pressure systems. Here, we engineer an effective negative mass harmonic oscillator mode in a superconducting microwave LC circuit and couple it via photon-pressure to a second low-frequency circuit. We demonstrate that the effective negative mass leads to an inversion of dynamical backaction and to sideband-cooling of the low-frequency circuit by a blue-detuned pump field, naturally explained by the inverted energy ladder of the negative mass oscillator.