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Quantum Communication

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  1. Quantum Communication AditiSen(De) Harish-Chandra Research Institute, India

  2. Outline Communication Communication Secure Communication Quantum Cryptography

  3. Outline Classical info transmission Communication Without security Quantum state transmission Communication Secure Communication Quantum Cryptography

  4. Outline Classical info transmission Communication Without security Quantum state transmission Communication Secure Communication Quantum Cryptography

  5. Outline Classical info transmission Communication Without security Quantum state transmission Communication Secure Communication Quantum Cryptography

  6. Communication

  7. Communication

  8. What is Communication? At least 2 parties Sender Receiver Bob Alice Communication is a process by which information is sent by a sender to a receiver via some medium.

  9. What is Communication? At least 2 parties Sender Receiver Bob Alice Communication is a process by which information is sent by a sender to a receiver via some medium.

  10. What is Communication? At least 2 parties Sender Receiver Bob Alice Communication is a process by which information is sent by a sender to a receiver via some medium.

  11. What is Communication? At least 2 parties Sender Receiver Bob Alice Communication is a process by which information is sent by a sender to a receiver via some medium.

  12. What is Communication? At least 2 parties Sender Receiver Bob Alice a process by which information is sent by a sender to a receiver via some medium.

  13. What is Communication? encodes Alice (Encoder) Sends Bob (Decoder) receives & decodes

  14. What is Communication? informationmustbeencoded in, and decodedfrom a physicalsystem. encoding/Decoding red-green balls, sign of charge of a particle. “Informationisphysical” ---Landauer Classical World Only orthogonal states Quantum World: Nonorthogonal states

  15. What is Communication? informationmustbeencoded in, and decodedfrom a physicalsystem. encoding/Decoding red-green balls, sign of charge of a particle. “Informationisphysical” ---Landauer Classical World Only orthogonal states Quantum World: Nonorthogonal states

  16. What is Communication? informationmustbeencoded in, and decodedfrom a physicalsystem. encoding/decoding red-green balls, sign of charge of a particle. “Informationisphysical” ---Landauer Classical World Only orthogonal states Quantum World: Nonorthogonal states

  17. What is Communication? informationmustbeencoded in, and decodedfrom a physicalsystem. encoding/decoding red-green balls, sign of charge of a particle. “Informationisphysical” ---Landauer Classical World Only orthogonal states Quantum World: Nonorthogonal states

  18. What is Communication? informationmustbeencoded in, and decodedfrom a physicalsystem. encoding/decoding red-green balls, sign of charge of a particle. “Informationisphysical” ---Landauer Do quantum states advantageous? Classical World Only orthogonal states Quantum World: Nonorthogonal states

  19. Classical Information Transmission via Quantum States Part 1

  20. Quantum Dense Coding Bennett & Wiesner, PRL 1992

  21. Classical Protocol Sunny Windy Snowing Raining

  22. Classical Protocol Sunny Windy Snowing Raining

  23. Classical Protocol Sunny Windy

  24. Classical Protocol Sunny Windy Snowing Raining

  25. Classical Protocol Sunny Windy Snowing Raining

  26. Classical Protocol Sunny 2 bits Windy Snowing Raining

  27. Classical Protocol Sunny 2 bits Windy Classical computer unit: Bit = one of {0, 1} Snowing Raining

  28. Classical Protocol Alice Bob Message Encoding Decoding Sunny 00 Sending Snowing Distinguishable by color 01 Windy 10 Raining 11

  29. Classical Protocol Alice Bob Message Encoding Decoding Sunny 2 bits 4 dimension Snowing Distinguishable by color Windy Raining

  30. What abt Quantum?

  31. Quantum Protocol Alice Bob Message Sunny B A Snowing Windy Singlet state Raining

  32. Bob Alice U B A Message Alice performs unitary on her particle I Sunny Snowing Windy Raining

  33. Bob Alice U B A Message Alice performs unitary on her particle I Sunny Snowing Creates 4 orthogonal states Singlet, Triplets Windy Raining

  34. Bob Alice U B A Message I Sunny Alice sends her particle to Bob Snowing Windy Raining

  35. Bob Alice B A Message I Sunny Bob has 2 particles: one of the triplets or singlet Snowing Windy Raining

  36. B A Alice Bob Decoding Message I Sunny Snowing 4 orthogonal states Possible to distinguish Windy Raining

  37. B A Alice Bob Decoding Message I Sunny Snowing 4 orthogonal states Possible to distinguish Windy Decodes message Raining

  38. B A Alice Bob Decoding Message I Sunny 2 bits 2 dimension Snowing 4 orthogonal states Possible to distinguish Windy Raining

  39. Moral Quantum Classical Vs. Task: sending 2 bits Encoding: 2 Dimensions Encoding: 4 Dimensions

  40. Moral Quantum Classical Vs. Task: sending 2 bits Encoding: 2 Dimensions Encoding: 4 Dimensions Bennett & Weisner, PRL 69, 2881 (’92).

  41. Dense Codingfor arbitrary state Hiroshima, J. Phys. A ’01; Ziman & Buzek, PRA ’03, Bruss, D’Ariano, Lewenstein, Macchiavello, ASD, Sen, PRL’ 04

  42. B A Alice & Bob share a state

  43. Encoding B A Alice’s aim: to send classical info i

  44. Encoding B A Alice’s aim: to send classical info i which occurs with probability pi

  45. Encoding Ui B A Alice performs pi , Ui

  46. Encoding Ui B A Alice performs pi , Ui she produces the ensemble E = {pi, ri}

  47. Encoding Ui B A Alice performs pi , Ui she produces the ensemble E = {pi, ri}

  48. Sending Ui B A Alice performs pi , Ui she produces the ensemble E = {pi, ri} Alice sends her particle to Bob

  49. Decoding A B Bob Alice

  50. Decoding A B Bob’s task: Gather info abti Alice