When we finally have a quantum internet you’ll be able to simultaneously like and dislike this video. But we don’t. So I hope you like it. The world is widely regarded as being well and truly into the digital age, also called the information age. No longer are economies and industries solely characterised by the physical goods they produce, and in fact some of the largest companies in the world produce no physical goods at all: digital information is a commodity in its own right. As discussed in a previous episode, this worldwide digital economy is fundamentally reliant on certain cryptographic processes. Currently these processes work in the realm of classical cryptography, but one day soon this may not be enough and so quantum cryptographic methods and algorithms are being developed. However, it’s one thing to design a protocol, it’s something else entirely to build a system to support it. To understand what needs to be done we need to get to the foundations of quantum mechanics - we need to talk about quantum information theory.