Free-space Polarization-selective Microcavity based on Chiral Metasurfaces

Summary

Developing a new type of Fabry-Pérot cavity that allows improved control of the atoms’ emission into the cavity mode will result in enhancement of the efficiency and fidelity of quantum state transfer from photons to atoms and back. This in turn can be used to improve the performance of quantum networks and repeaters, as well as sensors based on atoms inside Fabry-Pérot cavities. In this project we design and fabricate Fabry-Pérot microcavities that trap only one polarization of light. A Fabry-Pérot cavity is an optical resonator formed by two parallel mirrors or reflective surfaces. When the frequency of light matches the spacing between the mirrors, photons can enter through the mirrors and become trapped inside the cavity, which can then be used to enhance their interactions with the medium between the mirrors. Alternatively, when an atom in an excited state is placed inside the cavity, the cavity will encourage the atom to emit light that matches the cavity, which is one of the phenomena on which laser is based. In our work, the microcavity consists of two metasurfaces that act as chiral polarization-selective (dichroic) mirrors and that tightly confine one type of circularly polarized optical field in the free space between them, while remaining transparent to light of the opposite circular polarization. We propose to realize free space Fabry-Pérot cavities by fabricating reflective and focusing metasurfaces on the tips of optical fibres. Finally, this project has the potential to improve the performance and scalability of quantum information platforms that rely on cavity quantum electrodynamics, and possibly trapped ions as well, by realizing optical cavities with smaller mode volumes, compact footprint, and chirality-enhanced light-atom coupling.

Figure 1. Proposed polarization-selective cavity based on fiber-mounted patterned surfaces with nanoscale features (metasurfaces) that in this case act as focusing mirrors for left-handed circularly polarized light and as lenses for right-handed circularly polarized light.