Quantum teleportation

Besides quantum computations, entanglement has also been at the core of other active research such as quantum teleportation [32, 33], dense coding [34, 35], quantum communication [36], and quantum cryptography [37]. It is believed that the conceptual puzzles posed by entanglement have now become a physical source of novel ideas that might result in applications. 

D. Bouwmeester, A.K. Ekert, A. Zeilinger, The Physics of Quantum, Information Quantum Cryptography, Quantum Teleportation, Quantum, Computation (Springer, 2000)... 

Finally, I would like to say a few words about entanglement in communication, as the last caveat to the Jozsa-Linden theorem. I will just use the example of quantum teleportation. 

In quantum teleportation, Alice is given a state pm = ip)(ip whose identity is unknown to her. She may do anything she wishes to this state and then she communicates with Bob via only a classical communication channel. Bob s aim is to create a state pout which best resembles the original state. 

Entanglement is a vital information resource employed in quantum teleportation, dense coding and quantum computation [Nielsen 2000], The fundamental role played by the entanglement in quantum information science was discussed in part I this part of the book is devoted to the generation and characterization of the entanglement of photons and their usage in quantum communication and computation protocols. 

Approximate versions of the translational EPR state, wherein the -function correlations are replaced by finite-width (Gaussian) distributions, have been shown to characterize the quadratures of the two optical-field outputs of parametric down-conversion, or of a fiber interferometer with Kerr nonlinearity. Such states allow for various schemes of continuous-variable quantum information processing such as quantum teleportation [Braunstein 1998 (b) Furu-sawa 1998] or quantum cryptography [Silberhorn 2002], A similar state has also been predicted and realized using collective spins of large atomic samples [Polzik 1999 Julsgaard 2001]. It has been shown that if suitable interaction schemes can be realized, continuous-variable quantum states of the original EPR type could even serve for quantum computation. 

Quantum teleportation was first proposed in 1993 [Bennett 1993] and the year after for the special case of continuous variables [Vaidman 1994]. Teleportation is extremely important since direct transport of physical states is often hindered by exponential decoherence. With quantum teleportation the information is cleanly separated into a classical part, which can be transmitted over arbitrary distances, and a quantum mechanical part, which only needs to interact locally. 

The first prototype of quantum cryptographic apparatus came into existence around 1990 [147]. In the meantime, quantum cryptography has become a well-known technique of communication in a provably secure way, and together with an intensive research in the held of quantum computers it has given rise to a whole new branch of science quantum information theory [148]. Viewed from this perspective, quantum cryptography today is only a subset of a broad held of quantum communications that also include quantum teleportation, quantum dense coding, quantum error-correcting codes, and quantum data compression. 

The trick is, however, that the quantum teleportation we are going to describe, will not violate the Heisenberg principle because the mechanical quantities needed will not be measured and the copy made based on their values. 

P. van Loock S. L. Braunstein. Multipartite Entanglement for Continuous Variables A Quantum Teleportation Network. Physical Review Letters 1999 Jun 17 84(15) 3482-3485. 

D. Bouwmeester, J-P Wan, K. Mattie, M. Eibl, H. Weinfurter, A. ZeiUnger, Experimental quantum teleportation, Nature 390 (1997) 575. 

In this same year quantum teleportation is created by Charles Bennett and collaborators. 

MJk. Nielsen, E. Knill, R. Laflamme, Complete quantum teleportation using nuclear magnetic resonance, Mitore396(1998)52. 

Charles H. Bennett is an IBM fellow at IBM Research, where he has worked on various aspects of the relation between physics and information. He received his bachelor s degree from Brandeis University, majoring in chemistry, and his Ph.D. from Harvard in 1970 for molecular dynamics studies (computer simulation of molecular motion). His research has included work on quantum cryptography, algorithmic information theory, and quantum teleportation. He is an IBM fellow, a fellow of the American Physical Society, and a member of the National Academy of Sciences. 

---