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 physics, and teasing out its implications is a remarkably subtle and deep problem.
Answer 3.
(Abstraction): Back in pre-history we saw horses roaming around and fruit dangling on trees. We said to each other "Today I saw two horses in the field!" or "Look, there are two apples ready to fall!". Over time, we realised that it is possible to abstract away from these concrete experiences a common abstract concept - the number "2". We then began to analyse these abstract concepts independent of their particular realisations (independent from the substrate). This lead to the study of such things as numbers and mathematics.
(Classical information): However, we also discovered we could go the other direction: from the abstract to the concrete. We discovered that our abstract thoughts and concepts could be given a physical encoding - writing was born! We first did this remarkable thing by carving strange patterns into stone, and then later by scribbling ink onto paper. Today we carve this "information" into pulses of light and electricity flowing through the internet. However, all of these methods turn out to be "the same", meaning we could take an email and carve it into stone with a chisel, or we could take an image of a stone carving and post it online. The abstract information is the same, it is only the encoding that changes.
(Quantum information): In the past few decades we have discovered that remarkably there is a second, more fundamental way of encoding information using quantum physics, and that this form is different from the "classical information" we have used for thousands of years. This new form defies our everyday intuitions, since it is based on "quantum superpositions" and "quantum entanglement". The famous example is Schrödinger's Cat, which is neither alive nor dead, but in a superposition-state of 'alive' and 'dead'. Today, instead of carving patterns into stone or pulses of electricity, we are starting to carve patterns into quantum superpositions! We call these carvings into superpositions quantum information. Quantum information theorists therefore live in the twilight world between the abstract and the concrete. They are trying to understand what strange new carvings are actually possible, how we can manipulate these carvings, and what we can do with them.
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 physics, and teasing out its implications is a remarkably subtle and deep problem.
Answer 3.
(Abstraction): Back in pre-history we saw horses roaming around and fruit dangling on trees. We said to each other "Today I saw two horses in the field!" or "Look, there are two apples ready to fall!". Over time, we realised that it is possible to abstract away from these concrete experiences a common abstract concept - the number "2". We then began to analyse these abstract concepts independent of their particular realisations (independent from the substrate). This lead to the study of such things as numbers and mathematics.
(Classical information): However, we also discovered we could go the other direction: from the abstract to the concrete. We discovered that our abstract thoughts and concepts could be given a physical encoding - writing was born! We first did this remarkable thing by carving strange patterns into stone, and then later by scribbling ink onto paper. Today we carve this "information" into pulses of light and electricity flowing through the internet. However, all of these methods turn out to be "the same", meaning we could take an email and carve it into stone with a chisel, or we could take an image of a stone carving and post it online. The abstract information is the same, it is only the encoding that changes.
(Quantum information): In the past few decades we have discovered that remarkably there is a second, more fundamental way of encoding information using quantum physics, and that this form is different from the "classical information" we have used for thousands of years. This new form defies our everyday intuitions, since it is based on "quantum superpositions" and "quantum entanglement". The famous example is Schrödinger's Cat, which is neither alive nor dead, but in a superposition-state of 'alive' and 'dead'. Today, instead of carving patterns into stone or pulses of electricity, we are starting to carve patterns into quantum superpositions! We call these carvings into superpositions quantum information. Quantum information theorists therefore live in the twilight world between the abstract and the concrete. They are trying to understand what strange new carvings are actually possible, how we can manipulate these carvings, and what we can do with them.