Grant: Research Tools and Instruments

Atmospheric turbulence, caused by rapidly moving air cells with slightly different pressures, is the common obstacle for any ground-based observations. Perhaps the most readily observed consequence of turbulence is the twinkling of the stars in the night sky, which are speckled and blurred upon a closer look through a telescope. In the context of optical communication, atmospheric turbulence is detrimental for transmitting information as the light can be severely distorted and perturbed, severely limiting the distance over which this information can be sent. Adaptive optics is the unrivalled solution for correcting and reversing these undesirable distortions caused by turbulence on light travelling through Earth's atmosphere, enabling the secure transmission of information over much larger distances.There have been numerous efforts during the last century on increasing communication security by implementing novel encoding techniques such as quantum key distribution (QKD), as well as on increasing the rate of data communication (superdense coding). Most of these techniques rely on the modulation of photon number, frequency, or the polarization of photons. Recently, I proposed a novel approach to encode and decode information onto and from transverse degrees of freedom, i.e. the orbital angular momentum (OAM) and the radial mode (RM) of photons. Unlike polarization, OAM and RM are inherently unbounded, thus they can be used for expanding the alphabet used in classical and quantum communication. Such an alphabet expansion opens a wide route to many novel protocols which were not previously available with binary quantum systems. I am thus building a novel platform for unconditionally secure quantum communications (quantum key distribution) with structured photons over the city of Ottawa. However, this technique with ""structured"" photons are inherentlymore sensitive to turbulence due to their transverse varying spatial mode structure; thus, over long distances in free-space, atmospheric turbulence becomes a major limiting factor. Here, Ipropose the use of a fast adaptive optics system that will enable the development and testing of high-dimensional quantum cryptographic protocols feasible in real-world conditions.