Quantum photonics with microcavities in diamond

An important method for enhancing the efficiency as well as spatial and spectral properties of single photon emitters is coupling of the emitters to optical cavities. In order to strongly influence the emitter's properties it is mandatory to keep the cavity volume extremely small, i.e. on the order of the emission wavelength.

We follow two approaches:

• coupling of NV centers in nanodiamonds to fiber-based microcavities
• fabrication of microcavities based on photonic crystals in diamond

For realization of fiber-based microcavities we produce micro mirrors by laser machining the front facet of a glass fiber, yielding very small diameter mirrors (~ 30 µm) with very strong radii of curvature. Diamond nanocrystals containing NV centers are spin coated onto a plane mirror, realizing a linear cavity of few micron length. We observe emission of single NV centers into modes of the fiber cavity.

Photonic crystals in diamond are produced from quasi-single crystal diamond films on an iridium film by ion etching (focused ion beam milling). First test structures with simple microcavities yield cavity Q-factors around 500, limited by fabrication tolerances. Our theoretical design studies show that Q-factors of up to 300,000 and very small modal volumes could be achieved.