Quantum Teleportation


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Quantum Teleportation

  1. 1. Quantum Teleportation
  2. 2. Experimental Demonstration of Teleportation <ul><li>Two EPR source </li></ul><ul><li>Photons #2 and #3 produced in state </li></ul><ul><li>Photon #4 is a trigger which indicates that photon #1 was sent to Alice </li></ul><ul><li>Photon #1 is linearly polarized by P </li></ul>
  3. 3. Experimental Demonstration of Teleportation 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. if both D1 and D2 click, Alice has As we have seen, if Alice measures , Bob’s photon’s state is
  4. 4. Experimental Demonstration of Teleportation In actual test P was set to +45 0 and Bob set his beam splitter to +/-45 0 Teleportation would than be demonstrated by coincidence on detectors D1D2D4 and no coincidence on D1D2D3
  5. 5. 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. 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% . The probability for D1D2D3 or D1D2D4 coincidence is 25%
  6. 6. Generation of Entangled Photon Pairs <ul><li>Early experiments (in the 60s) employed atomic cascade in calcium to generate correlated photons. </li></ul><ul><li>Calcium atoms where exited to the 4p 2 1 S 0 level by UV laser at 227.5 nm </li></ul><ul><li>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. </li></ul>
  7. 7. Generation of Entangled Photon Pairs <ul><li>in the 80s and 90s new sources of correlated pairs with higher flux rates were developed by techniques of nonlinear optics </li></ul><ul><li>The correlated phonon pairs where generated by the down-conversion process </li></ul><ul><li>This process conserves angular momentum and energy and linear momentum (phase matching conditions): </li></ul>
  8. 8. Generation of Entangled Photon Pairs <ul><li>The phase matching conditions require that the beam emerge in two cones of different polarization </li></ul><ul><li>The two entangled photons correspond to the intersection of the two cones </li></ul><ul><li>There is no way to know the origin of each photon, so a pair of photons in the intersection points is in the state: </li></ul><ul><li>The optical phase may be controlled with compensator plates. </li></ul><ul><li>By setting φ equal to 0 or π we can produce either of the Bell states with negative correlation </li></ul>
  9. 9. 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%
  10. 10. Single-Photon interference experiments