Quantum technologies

Abstract

Could we send information encoded in single photons possibly exploiting the wave particle duality inherent in quanta? Could we even build arbitrary processors using single quanta to encode bits of information? Within this talk I would hope to introduce you to the area of quantum information which is largely a theoretical preserve at the moment. There are however various experimental in-roads into this area, the most notable being secure key exchange using quantum cryptography. The technologies required for optical quantum information systems are essentially sources and detectors of single photons and single photon sensitivity non-linear elements. In this lecture I will discuss recent progress with single photon emission and detection. I would also hope to introduce the concept and progress towards single photon non-linear elements. I will discuss in detail two possible single photon sources. The first is a source of gated single photons based pair photon emission in parametric downconversion. The second is emission from single dye molecules diffusing in a 40nm thick layer within an optical microcavity. Both these sources have (as yet) serious limitations for any practical applications and here we highlight the progress needed to go beyond conventional weak lasers. On a more practical note many optical systems now operate at the quantum limit set by the Poisson fluctuations in detected photon number. The continuous development of photon counting detectors over the past thirty years has improved this sensitivity enormously. To optimise further we still need to improve detector performance especially in the 1-1.7micron wavelength range. Here the detectors are extremely noisy and up till now have required cooling to cryogenic temperature. I will review the development of solid state photon counting detectors highlighting recent advances in long wavelength detection.