Integration of Strong Fluorescent Nanodiamonds into Direct Laser Written Polymer Waveguides for Quantum Sensing

I report on the integration of quantum emitters into novel three dimensional polymer waveguides on an optical chip, fabricated by two-photon lithography. The waveguide is used to address the integrated emitters optically for state initialization and state readout before and after coherent manipulation of the emitter’s internal degree of freedom. Since the waveguides presented feature a high confinement of the guided optical mode, they support small bend radii down to 40 μm, facilitating high integration densities. The novel coupler design developed in this thesis features the opportunity to simultaneously couple light into input ports and detect the light exiting the waveguide network ports, using one single microscope objective. A detailed parameter study of these waveguides with lengths up to millimeters is presented and beamsplitting devices are shown. In contrast to waveguides made from glasses or semiconductor material, the polymer waveguides are capable of integrating nanoparticles containing quantum emitters inside the waveguide. Since the fundamental waveguide mode has its maximum inside the waveguide, this maximizes the coupling strength of emitter and guided modes. The quantum emitters I integrate into the polymer waveguides are negatively charged nitrogen-vacancy (NV) centers in nanodiamonds. Embedded into a waveguide, the NV center ensemble in a single nanodiamond acts as a waveguide-integrated quantum probe, where the waveguide plays two roles: It guides the laser light used for initialization and readout to the NV centers and it guides the fluorescent light from the NV centers to the detector. Noticeably, the NV center does not have to lie in the focal plane of the microscope objective, but may also be raised above the substrate in a free standing waveguide section, which might be used to immerse the quantum probe into a gaseous or liquid sample volume. I show the equivalence of the state readout via the fluorescent light directly obtained from the nanodiamond and the fluorescent light guided through the waveguide, which proves the absence of significant noise due to autofluorescence from the waveguide material. Further, for the first time Rabi nutations are remotely detected via a waveguide, showing that the coherence properties of the NV center are preserved when embedded into the photoresist. This will enable to harness nonclassical states of the NV center for remote quantum sensing.