The EPR Effect and Quantum Teleportation By Seamus O'Dunn September 24, 2012

Teleportation Teleportation is the name given by science fiction to the action of making something disappear in one place and then reappear some place else. It usually involves scanning the object, destroying it, then re-materializing it based on the information from the scan.

Teleportation cont. Teleportation has historically been dismissed by scientists, because the uncertainty principle of quantum mechanics does not allow for all the information to be extracted from an object through scanning. With the EPR effect, it is possible to transfer the information that is unscanable.

Short Overview of Quantum Mechanics Systems are characterized by wave functions. Each wave function corresponds to the ‘state’ of the system. Physical quantities are represented as operators rather than numbers. These operators operate on the wave function (state) of a system to give information about its possible values.

Short Overview of Quantum Mechanics Cont. For a given operator A and a system described by the wave function ψ. If where a 0 is a number, Then the physical quantity that A represents will have the value a 0 when the system is in the state ψ. Ψ is also called an eigenstate of A corresponding to the eigenvalue a 0.

Short Overview of Quantum Mechanics cont. In QM the physical quantities represented by two non-commuting operators (AB≠BA) cannot be known simultaneously with certainty. This is from the Heisenberg uncertainty principle.

The Einstein-Podolsky-Rosen Effect In 1935 Albert Einstein, Boris Podolsky and Nathan Rosen published a paper entitled “Can Quantum-Mechanical Description of Reality be Considered Complete?” The paper outlined what seemed like a contradiction in quantum mechanics that proved it incomplete. Inadvertently, their paper outlined the property of qm that allows for quantum teleportation.

EPR Effect in a Nutshell Two systems I and II are allowed to interact for from t=0 to t=T. Assuming that the states of I and II are known, It is possible to calculate the state of the interaction. It is not, however, possible to calculate the states of the individual systems after they are done interacting. To find the states after t=T one must use a process called wave packet decomposition.

EPR cont. Measurements made on system 1 affect the state of system 2 at a time after the duration of their interaction. This phenomenon is called quantum entanglement, and is the basis for quantum teleportation.

Quantum Teleportation QT is the transfer of quantum states (information) from one location to another. In 1993, a paper by Bennett, Brassard, Crepeau, Jozsa, Peres and Wootters proved that QT is possible. In 1998, the 1993 paper was experimentally proven. QT is not instantaneous or superluminal. Its strength lies in the ability to send quantum information along Classical channels.

QT Process teleportation.html

QT Process cont. 1. EPR pair is generated and brought to to different locations 2. A and B are scanned 3. The classical information gleaned from the scan is sent to location of C 4. Classical information is used to choose the treatment that turns C into A.

Difficulties Facing Development in QT Entangled states are very delicate. It is very hard maintain them long enough to transfer them long distances. It becomes increasingly difficult to teleport larger numbers of spins. Most interesting applications involve teleporting at least a few thousand spins at a time.

QT Applications Mastery of QT will allow for the construction of quantum computers, and perhaps eventually a quantum internet. This from the marriage of classical and quantum information processing. Communication using QT could be completely secure if the information was sent in such a way that the part sent by entanglement was needed to decode the rest. That part does not move through space, so it can't be intercepted.

QT Current Progress In May 2012 a group of scientists broke the QT record by teleporting a photon 89 miles through the open ocean air. Link to the paper: full/nature11472.html In June 2004 scientists at Los Alamos managed to teleport spin states from one atom to another 8 microns away. This is the first time massive matter has been teleported. Article: shtml shtml

Summary Teleportation was once thought impossible because it violated the Heisenberg uncertainty principle. In 1993, a paper by Charles Bennet and others showed that QT using the EPR effect would not violate the uncertainty principle and was therefore possible. In 1998, They verified this experimentally. QT has many powerful application in communications and information processing.

References Einstein, Podolsky, Rosen, “Can Quantum Mechanical Description of physical reality be considered complete?”, Physical Review, 15 May 1935: Print communications communications