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Introduction

## Quantum Systems

A quantum system is a region of space that obeys the laws of quantum mechanics as opposed to classical mechanics. We say that this system is isolated from all others. And we say that interactions with all other micro or macroscopic systems (the environment of the system) are only there to take measurements of the system, thus by interaction the system collapses from its wavefunction and obeys the laws of classical mechanics again, making the system no longer a quantum one.

## Philosphy of Quantum Mechanics (Epistemic vs Ontic interpretations of Quantum Theory)

**Epistemic Interpretation:**

Epistemology is, according to Encyclopaedia Brittanica, "The philosophical study of the nature, origin and limits of human knowledge." (Citation). In regards to quantum mechanics this means that we only concern ourselves with what it is possible to know. The quantum world is that of probability, we can define nothing with certainty until it is actually measured and thus epistemically trying to talk about anything prior to a measurement of a quantum system is a waste of time as it is merely a gap in human knowledge that we can never bridge.

Perhaps one of the fundamental issues with this interpretation is the very basis of it and the inherent ambiguity of it all. This is the fact that it assumes that no quantum system is worth talking about until it is measured. Where, however do we draw the line between a quantum system and a classical one? It is easy to say that we draw this distinction based on the laws the system obeys, one quantum mechanics, one classical, but then we must ask at what exact point does this thin line occur? At what size does something suddenly flip from nice, simple SUVAT to the frankly horrible world of QM?

**Ontic Interpretation:**

Ontology however, is not the study of knowledge but that of being. Ontological interpretations of quantum mechanics thus say that to place no significance on the mess of ambiguity that is the wave function of a quantum system is to ignore what makes the system a whole. Niels Bohr went as far as saying that we should ignore all information we glean by measuring the system as it is so fundamentally changed by our measurement that it is no longer of any use.

Unfortunately all of these are just interpretations of formalisms anyway and cannot be tested in any way as simply by measurement collapse the wave function of a system and thus cannot know what was going on prior to the collapse. None of these interpretations can actually make predictions of anything and are thus not theories in their own right, they are merely people desperately philosophising to try and understand something that by definition seems impossible to gain a true understanding of.

## Teleportation

One potential application of entanglement is development of technology that could potentially introduce teleportation. The term itself is misleading because as discussed below, the overall effect is similar to teleportation despite the process itself not being 'teleportation' as seen in pop culture. The term 'teleportation' in the context of quantum mechanics refers to a protocol described below.

**Use of Entanglement in Teleportation**

(please feel free to review/change this, this might be v wrong)

Although quantum entanglement does not itself transfer information, it can be used to aid communication. Suppose we want to teleport a particle A, and that two particles B and C are entangled,C is placed at a different location to A and B. A can then be made to interact with the entangled B and C to form a three-particle entangled system. A measurement of the state of B is taken and this information is sent to the location of C. By entanglement, we now know the state of A, as it is the same as the state of B and this infomation can be used to specify the state of C such that it is identical to the state of A. We have therefore `teleported` A to the location of C, however no matter was actually transferred, only quantum information in the form of qubits at the speed of light.

**Some references, not laid out properly**

https://www.britannica.com/topic/epistemology -Accessed 23/10/2018

https://plato.stanford.edu/entries/qt-issues/#MeasProb
Accessed 23/10/2018

https://arxiv.org/abs/0712.1318
Accessed 23/10/2018

'The undivided universe' -David Bohm and Basil J Hiley, edition published 2009, first published in 1993 by Routledge, New York

https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1521-3978(199811)46:6/8%3C855::AID-PROP855%3E3.0.CO;2-Q -i used the pdf of this

https://stanford.library.sydney.edu.au/archives/sum2010/entries/qm-relational/ - used this as a reference