Single-photon sources for quantum information processing

Contacts:

Niels Gregersen, DTU Fotonik, 4525-3789 (ngr@fotonik.dtu.dk)

Jesper Mørk, DTU Fotonik, 4525-5765 (jm@fotonik.dtu.dk)

Fig. 1: Scanning electron micrograph (left) and optical field profile (right) of the nanowire single-photon source.

The photonic nanowire is a semiconductor cylinder placed on a substrate (Fig. 1). By embedding a quantum dot single photons can be emitted, and they couple to the fundamental mode of the nanowire with a probability of almost 100 %. The photonic nanowire is thus a promising platform for a highly efficient single-photon source. The applications include secure communication based on quantum key distribution, optical metrology and quantum information processing and computing.

However, the efficient transmission of light from the nanowire into an optical fiber and also the implementation of electrical contacts (Fig. 2) while maintaining the high efficiency pose challenges.

Fig. 2: Sketch of the electrically pumped photonic nanowire single-photon source with top and bottom gold contacts (red sections) emitting light into an optical fiber.

To address these, an understanding of the light-matter interaction is necessary and this requires a solution to the electromagnetic problem. First, the light-matter coupling between the QD and the optical field must be evaluated and this is done by calculating the local density of states. Then the light emission from the nanowire must be determined to ensure that the photon is transmitted towards the optical detection system.

In this theoretical project, the students will perform numerical simulations to solve the electromagnetic problem for a realistic photonic nanowire-based single-photon source. Starting with Maxwell’s equations, the students will determine the optical modes (Fig. 3) of the nanowire. This will be performed using semi-analytical and numerical methods (Fourier Modal Method/Finite Elements). From here the project will continue depending on the students interests.

Fig. 3: Numerical simulation of the electric field profile of the fundamental mode in a nanowire.