Applied Physics

Directing Single Photons

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Science  07 Oct 2011:
Vol. 334, Issue 6052, pp. 17-19
DOI: 10.1126/science.334.6052.17-d

Photons are ideal carriers of bits of information—they are fast, robust, and can travel long distances. For secure applications such as quantum key distribution for cryptography, the information is conveyed by single photons. Compared with classical keys, an attack on the communication channel by an eavesdropper that uses a quantum key is readily detected. Quantum dots are useful sources of single photons and can be integrated into on-chip waveguides that direct where the single photons go. However, extracting the photons from the waveguide into an external communication channel (such as an optical fiber) is often inefficient because the photons undergo internal reflection at the waveguide's interfaces. Davanco et al. have designed a system whereby a tapered fiber waveguide is coupled to a semiconductor waveguide that contains quantum dots. The geometry of the semiconductor waveguide is designed so that the properties of the generated single photons can be selected and matched to that of the tapered fiber. This matching enhances the extraction of the single photons from the semiconductor waveguide into the tapered fiber.

Appl. Phys. Lett. 99, 121101 (2011).

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