06 Feb 2014 No Comments

## Are Coherent States of Light Classical or Quantum?

I gave this answer on Physics Stack Exchange to the following question: Coherent states of light, defined as:$$|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum_{n=0}^\infty \frac{\alpha^n}{n!}|n\rangle$$ for a given complex number $\alpha$ and where $|n\rangle$ is a Fock state with $n$ photons, are usually referred to as the most classical states of light. On the other hand, many quantum protocols with no […]

09 Feb 2014 No Comments

## Just How Much Data Can We Stuff Through an Optical Fibre?

This question on Physics Stack Exchange asks what the theoretical bandwidth of an optical fibre is. Let’s explore this question. The short answer is that a good order of magnitude rule of thumb for the maximum possible bandwidth of an optical fibre channel is about 1 petabit per second per optical mode for up to […]

by Rod Vance in Optics, Physics Tags: FIbre Optical Telecommunications, Noise, Optical Fibre, Quantum Shot Noise, Shannon Capacity Theorem, Shannon-Hartlee Theorem, Signal-to-Noise, Squeezed State