Subdiffraction Distance Measurement of Dipolar Emitting Qubit Pairs

In this work, we present a possibility to measure the distance between two color centers far below the diffraction limit of light in the optical wavelength range using a confocal fluorescence microscope. For this purpose, we show how the process of fabricating nitrogen-vacancy (NV)-based qubits in diamond by ion implantation with lithography masks is carried out. These masks contain small holes down to 80 nm in diameter in which the qubits are formed. A method to systematically identify the spots with exactly two qubits, the photons of which are polarized perpendicular to each other, is introduced. Further, an optical polarization dependent photoluminescene measurement principle is shown to determine the projected color center distances in several spots between 16 and 95 nm. It is thus possible to precisely determine the positions and distances of two quantum bits with a standard deviation of less than 10 nm for most measurements. This will enable a simple, systematic procedure for finding suitable qubit systems for quantum applications.