1 / 12

Quantum communication via entanglement

Quantum communication via entanglement. Myungshik Kim Queen’s University, Belfast. Contents. Dense coding Bell-state measurement Entanglement swapping Quantum teleportation Entanglement concentration.

preston-ramos
Download Presentation

Quantum communication via entanglement

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quantum communication via entanglement Myungshik Kim Queen’s University, Belfast

  2. Contents • Dense coding • Bell-state measurement • Entanglement swapping • Quantum teleportation • Entanglement concentration

  3. Dense codingBennett+Wiesner, PRL 69,2881 (1992), Mattle&Zeilinger, PRL 76, 4656 (1996) • Using entanglement, by sending one qubit, two-qubit information can be transmitted. • Coding? Two-qubit information coded in four operations I, x, y, z: x:(, ), y:(, ), z:(,) • Steps? • Share an entangled pair between sender and receiver • The sender applies one of the unitary operations to his particle then the entangled pair becomes one of the four Bell states. • The sender transmits his particle to the receiver.

  4. D1 D1 Bell-state measurement • Problem: How to identify the four Bell states. • Two Bell states can be identified: Both photons leave the beam splitter via the same output port except . • When coincidence between D1 and D2 or D2 and D1 , incident photons were in . • When D1 and D1 or D2 and D2 incident photons were in +. • Otherwise we do not know. • How do we discern all four Bell states? D2 D2 BS PBS Lutkenhaus, PRA 59, 3295 (1999) It is not possible to discern all four Bell states by using a combination of linear devices

  5. Bell-state measurement Entangler 2 Entangler 1 Entanglement swappingC.H. Bennett et al., PRL 70,1895 (1993) • With use a Bell-state measurement, it is possible to swap entanglement.

  6. Pan & Zeilinger, “experimental entanglement swapping”, PRL 80, 3891 (1998)

  7. Quantum teleportationBennett, “teleporting an unknown quantum state via dual classic & EPR channels”, PRL 70, 1895 (1993) Classical information (1,2,3,4) • Teleport quantum information by sending classical information. • What is quantum/ Classical information? Bell-state measurement Unitary transformation Unknown state Entangler

  8. Quantum teleportation for a qubit : Pauli spin operators

  9. Check points • Quantum measurement? • Why not measure the unknown state to find a & b and send the classical information to the receiver? • Quantum copying? • Does it violate the cloning theorem? • Superluminal communication? • Any violation of the Relativity? • Is it more efficient than sending the quantum information? • because entanglement is very fragile. • Possible to concentrate entanglement. Entanglement teleportation: Lee & Kim, PRL 84, 4236 (2000)

  10. Entanglement concentration-pure stateBose & Knight, PRA 60, 194 (1999) • Consider two pair of non-maximally entangled particles (they are identically entangled) • For the outcomes  of the Bell measurement, the other two particles are maximally entangled. Bell measure Entangler 2 Entangler 1

  11. :PBS Entanglement concentration-mixed stateKwiat et al., Nature 409, 1014 (2001); Pan & Zeilinger, Nature 410, 1067 (2001) • Assume a mixed state • For coincident counting of ()a and()b, the two other particles are in

More Related