Quantum Teleportation

Experimental Demonstration of Teleportation

• Two EPR source

• Photons #2 and #3 produced in state

• Photon #4 is a trigger which indicates that photon #1 was sent to Alice

• Photon #1 is linearly polarized by P

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Experimental Demonstration of Teleportation

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Only the following states can be detected unambiguously:

Furthermore, it is easier to detect since it is the only case in which the photons

go to different detectors.12

if both D1 and D2 click, Alice has 12

As we have seen, if Alice measures , Bob’s photon’s state is12

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Experimental Demonstration of Teleportation

In actual test P was set to +450 and Bob set his beam splitter to +/-450

Teleportation would than be demonstrated by coincidence on detectors D1D2D4 and

no coincidence on D1D2D3

Experimental Demonstration of Teleportation

If #1 and #3 arrive at different times – no interference and D1

and D2 click simultaneously with 50% prob.

In this case no teleportation occurs, thus D3 and D4 click with

50% prob.

The probability for D1D2D3 or D1D2D4 coincidence is 25%

If #1 and #2 arrive to BS at the same time interference can

occur and Alice can make Bell-state measurement. We would

then expect the coincidence rate D1D2D3 to drop to zero, with

D1D2D4 remaining at 25% .

Generation of Entangled Photon Pairs• Early experiments (in the 60s) employed atomic cascade in calcium to generate correlated photons.

• Calcium atoms where exited to the 4p2 1S0 level by UV laser at 227.5 nm

• Initial and final states are both with J=0 and of the same even parity. This demands that the emitted photons carry no net angular momentum and polarization correlation properties required for the EPRB experiments.

Generation of Entangled Photon Pairs• in the 80s and 90s new sources of correlated pairs with higher flux rates were developed by techniques of nonlinear optics

• The correlated phonon pairs where generated by the down-conversion process

• This process conserves angular momentum and energy and linear momentum (phase matching conditions):

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Generation of Entangled Photon Pairs• The phase matching conditions require that the beam emerge in two cones of different polarization

• The two entangled photons correspond to the intersection of the two cones

• There is no way to know the origin of each photon, so a pair of photons in the intersection points is in the state:

• The optical phase may be controlled with compensator plates.

• By setting φ equal to 0 or π we can produce either of the Bell states with negative correlation

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Single-Photon interference experiments

When there is no path length difference, only one detector clicks

When the path length difference is larger than coherence length coincidence on D1 and D2 occurred with 50%

Single-Photon interference experiments