**Quantum Information, so what is it?**

**Answer 1:**Quantum information theory hovers in an odd way between mathematics and physics, and constitutes a general framework for thinking about quantum systems. It is based around the slippery notion of "information", and provides a powerful language in which to describe the abstract properties of quantum states that are independent of their particular physical realisations. Because of this it has a broad scope and finds application in very different areas of quantum physics.

**Answer 2:**Often an area of physics is associated with a range of length-scales or energies, however in contrast quantum information theory is associated with regimes of "non-classicality". Such regimes can occur at any length-scales and any energies. Within these non-classical regimes, quantum systems no longer possess properties in the familiar sense. This fact lies at the heart of what is so strange about quantum theory, and teasing out its implications is a surprisingly subtle and deep problem.

**Answer 3:**Quantum information theory could be described as "

*the physics of mathematics*". What do I mean by this? Well, back in pre-history we saw horses roaming around and fruit on trees and said "

*I see 2 horses...*" or "

*There are 2 apples ready to fall.*.." and then gradually we realised that it is possible to abstract away from these statements a common concept - the number "2". Such concepts can be analysed independent of their particular realisations (independent from the substrate) and studying mathematics/numbers means that any statement we deduce can be applied to any instance in the real world. Moreover these abstractions can be communicated between people or transformed through computational processes acting on particular encodings (either in the human mind, carved into stone, or inside a computer). However these substrate-independent patterns must still obey the Laws of Nature, and those laws are given by quantum theory. Quantum information theory therefore determines how fundamental physical laws constrain abstract concepts like "computation" or "proof". It is a remarkable fact that the difficulty of doing mathematics (such as factoring a number into primes) depends on the laws that are running in the universe in which you reside!