Experimental Quantum Teleportation Quantum systems for Information Technology

Experimental Quantum Teleportation Quantum systems for Information Technology Kambiz Behfar Phani Kumar

Contents • Concept of Quantum Teleportation Introduction Quantum Teleportation Circuit Theoretical Results • Experimental Realization Principles Entangled States Outside Teleportation Region Inside Teleportation Region Measured Coincidence Rate Summary

Quantum Teleportation: Teleportation means: a person or object disappear while an exact replica appears in the best case immediately at some distant location. ● Bennett et al. (1993) have suggested that it is possible to transfer the quantum state of a particle onto another particle-the process of quantum teleportation-provided one does not get any information about the state in the course of this transformation. ● Application: ● Teleportation can be used in place of wiring in a large quantum computer. ● To Build a distributed system (e. g. a quantum multicomputer). and so on

Quantum Teleportation Circuit H M 1 M 2 XM 2 ZM 1

Proof

QT Circuit

Theoretical Results A complete Bell-state measurement can not only give the result that the two particles 1 and 2 are in the anti-symmetric state, but with equal probabilities of 25% we could find them in any one of the three other entangled states. After successful teleportation particle 1 is not available in its original state any more, and therefore particle 3 is not a clone but is really the result of teleportation.

Principle of Quantum Teleportation – – – – Alice has particle 1 Alice & Bob share EPR pair Alice performs BSM causing entanglement between photon 1 and 2 Alice sends classical information to Bob performs unitary transformation Teleporting the state not the particle Correlations used for data transfer Schematic idea for quantum teleportation introducing Alice as a sending and Bob as a receiving station, showing the different paths of information transfer.

Entangled States • • Type II Spontaneous Parametric down-conversion Non-linear optical process inside crystal Pulsed pump photons Creation of two polarization entangled photons 2 & 3 E 1 k(1) p = Pump k p= k(1) + k(2) E p p Ep= (2)E 1. E 2* k p k(2) E 2 Parametric down-conversion creating a signal and idler beam from the pumppulse. Energy and momentum conservation are shown on the right side.

Experimental Realization • UV pulse beam hits BBO crystal twice • Photon 1 is prepared in initial state • Photon 4 as trigger • Alice looks for coincidences • Bob knows that state is teleported and checks it. • Threefold coincidence f 1 f 2 d 1(+45°) in absence of f 1 f 2 d 2 (-45°) • Temporal overlap between photon 1, 2 Experimental set-up for quantum teleportation, showing the UV pulsed beam that creates the entangled pair, the beamsplitters and the polarisers.

Outside Teleportation Region • For distinguishable photons, with p=0. 5, 2 photons end in different O/P ports • Photon 3 polarization undefined! • So, d 1, d 2 have 50% chances of receiving photon 3 • => 25% probability for both f 1 f 2 d 1 and f 1 f 2 d 2 threefold coincidences • P(f 1 f 2 d 1) = P(f 1 f 2 d 2) = 0. 25

Inside Teleportation Region – Indistinguishable photons interfere! – Input state – If f 1, f 2 both click, then teleportation occurred and only d 1 f 1 f 2 coincidences should occur and d 2 f 1 f 2 should be 0 – Teleportation (d 1 f 1 f 2 coincidences) achieved with 25% prob.

Experimental Demonstration Theoretical and experimental threefold coincidence detection between the two Bell state detectors f 1 f 2 and one of the detectors monitoring the teleported state. Teleportation is complete when d 1 f 1 f 2 (+45°) is present in the absence of d 2 f 1 f 2(-45°) detection.

Measured Coincidence Rates

Summary • Deduced from the basic principles of quantum mechanics, it is possible to transfer the quantum state from one particle onto another over arbitrary distances. • As an experimental elaboration of that scheme we discussed the teleportation of polarization states of photons. • But quantum teleportation is not restricted to that system at all. One could imagine entangling photons with atoms or photons with ions, and so on. • Then teleportation would allow us to transfer the state of, for example, fast decohering, short-lived particles onto some more stable systems. • This opens the possibility of quantum memories, where the information of incoming photons could be stored on trapped ions, carefully shielded from the environment. • With this application we are in heart of quantum information processing.