Midterm Colloquium by Thomas Aktor – Niels Bohr Institute - University of Copenhagen

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Midterm Colloquium by Thomas Aktor

Quantum information brings with it both great advantages and great disadvan-tages. One of the big problems stems from the nocloning theorem of quantummechanics. When a classical signal travels through cables it is subject to losses,and these are classically compensated for, by amplifying the signal at regularinterval. However and because of the fact that you cannot copy quantum infor-mation, it cannot be amplified. Hence sending a signal any significant distancerequires a special trick. This trick is known as quantum teleportation, and requires sender and receiverto share an entangled state. Entangled states can be hard to maintain over largerdistances due to interactions with the environment, but using what is known as"entanglement swapping", one can acquire these states. The idea is to "trade in"or "swap" small segments of entanglement with one "big" entangled state. Thescheme using this entanglement swapping to distribute entanglement is commonlycalled a quantum repeater. In my midterm colloquium I will go through some of different effects, one hasto deal with when concerned with quantum information, particularly the no-cloning theorem and its consequences. I will go on talking about entanglementand teleportation, and its importance to the quantum repeater scheme. I will then talk about the quantum repeater and go through a specific repeaterprotocol know as the DLCZ protocol, which is a probabilistic scheme, that usesthe storage of a photon in an atomic ensemble and linear optics to establish en-tanglement that grows polynomial as a function of distance. Lastly I will finishof my colloquium talking about an experimental implementation of the DLCZprotocol using ion crystals.