Quantum Optics Colloquium by Ewold Verhagen

Breaking optical reciprocity through photon-phonon interactions

Reciprocity is a symmetry that characterizes the transport of light and sound waves in the vast majority of systems. Creating nonreciprocal behaviour requires suitable ways of breaking the system’s time-reversal symmetry. This can yield functionality such as isolation and circulation, useful for the routing of classical and quantum information, and could also allow exploring topological physics for photons and phonons. While the breaking of time-reversal symmetry is usually achieved with a magnetic field, the weakness of magneto-optic interactions makes miniaturization to chip-scale devices challenging. A possible route to nonreciprocity without a magnetic field relies on a spatiotemporal modulation of the refractive index, which is straightforwardly achieved in optomechanical systems. We show that in suitable multimode optomechanical systems, the radiation pressure of an optical control field can break the symmetry of propagation of probe photons. We demonstrate optical isolation and circulation with ~10 dB contrast and low insertion loss in a high-quality ring resonator. A general theory reveals the minimal requirements to create nonreciprocity in a wide class of optomechanical systems that involve a pair of optical modes parametrically coupled to a mechanical mode. The underlying principle is related to a nonreciprocal phase incurred during photon-phonon transfer that is induced by the control field. This mechanism can be related to the Aharonov-Bohm effect for electrons, and in larger systems, it could enable the creation of topological phases of light and sound. We discuss the bandwidth and noise characteristics of optomechanical nonreciprocal devices, and their ability to route quantum states with negligible loss.

Ewold Verhagen is group leader of the Photonic Forces group in the Center for Nanophotonics at AMOLF (Amsterdam, The Netherlands) since 2013, and part-time professor of Applied Physics at Eindhoven University of Technology. His group studies light-matter interactions at the nanoscale, with a particular focus on the coupling between photons and phonons in nano-optomechanical systems. His interests include the quantum measurement and control of mechanical motion, nonreciprocal and topological transport of photons and phonons, nanoscale sensing systems, and the physics of photonic and plasmonic resonators. He previously worked as a postdoctoral fellow on quantum optomechanics at EPFL. For his PhD work at AMOLF on plasmonics and metamaterials, he was awarded the Dutch Physics Thesis Award and the FOM Valorization Chapter Award in 2010. He recently received an NWO Vidi grant (2014) and an ERC Starting Grant (2017).