Cryptography Reference
In-Depth Information
chapter 6
Quantum Logic Using
Linear Optics
J.D. Franson, B.C. Jacobs, and T.B. Pittman
Johns Hopkins University
Contents
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
6.2 Challenges in Quantum Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
6.3 Linear Optics Quantum Logic Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.4 Single-Photon Source and Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
6.5 Quantum Repeaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Abstract
In order for quantum communications systems to become widely used, it
will probably be necessary to develop quantum repeaters that can extend
the range of quantum key distribution systems and correct for errors in the
transmission of quantum information. Quantum logic gates based on linear
optical techniques appear to be a promising approach for the development of
quantum repeaters, and they may have applications in quantum computing as
well. Here we describe the basic principles of logic gates based on linear optics,
along with the results from several experimental demonstrations of devices
of this kind. A prototype source of single photons and a quantum memory
device for photons are also discussed. These devices can be combined with a
four-qubit encoding to implement a quantum repeater.
6.1 Introduction
Systems for quantum key distribution have been demonstrated over limited
distances, both in optical fibers and in free space, but they have not yet been
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