Abstract

The development of true single photon sources is of fundamental scientific and technological importance, and such sources are particularly important for secure communication via quantum key distribution, or quantum cryptography. Although modulated lasers have been used to successfully transmit quantum keys over relatively short distances in free space, it has been shown that this method of transmission is insecure from certain types of eavesdropping attack, due to the inevitable emission of pulses containing more than one photon. It is also standard to modulate the source until, on average, each pulse contains 0.1 photons (to limit the chances of two photon emission), which therefore reduces the effective bit rate by a factor of ten. The electrically driven, surface acoustic wave (SAW) single photon source, as proposed by Foden et al [Phys. Rev. A. 62, 1803 (2000)], offers the prospect of relatively high GHz frequency operation, and therefore high bit-rate. If the SAW source could be made to operate in the mid-IR, it would also offer the prospect for secure, long distance, free space communication at wavelengths that exhibit favourable characteristics. The fundamental building block of the SAW single photon source is a lateral, quantum well n-i-p junction, and in this talk I will describe a novel technique for the fabrication of such junctions. Using this technique we have fabricated lateral n-i-p junctions in InSb/InAlSb quantum wells, and I will describe the progress this represents towards the challenging goal of fabricating a mid-IR single photon source.