Christian Weedbrook graduated with a Bachelor of Science majoring in

maths and physics from the University of Queensland in 2003. The

following year he earned his honours degree in physics from the

Australian National University. He completed his Ph.D. degree in 2009

with the thesis: “Quantum information and quantum computation using

continuous variables”. After graduating he worked as a postdoctoral

research fellow in the Centre for Quantum Computer Technology at the

University of Queensland and briefly as a postdoctoral fellow at the

Massachusetts Institute Technology. Currently, he is a postdoctoral

fellow at the University of Toronto after being awarded the Ontario

postdoctoral fellowship and CQIQC prize postdoctoral fellowship.

We consider the security of continuous-variable quantum cryptography

as we approach the classical limit, i.e., when the unknown preparation

noise at the sender’s station becomes significantly noisy or thermal

(even by as much as a million times greater than the variance of the

vacuum mode). We show that, provided the channel transmission losses

do not exceed 50%, the security of quantum cryptography is not

dependent on the channel transmission, and is therefore incredibly

robust against significant amounts of excess preparation noise. We

extend these results to consider for the first time quantum

cryptography at wavelengths considerably longer than optical and find

that regions of security still exist all the way down to the

microwave.