Frankfurt 2006 – scientific programme
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Q: Quantenoptik und Photonik
Q 58: Quantenkommunikation
Q 58.4: Talk
Thursday, March 16, 2006, 11:55–12:10, HVI
Effective Channels in Quantum Key Distribution — •Joseph Renes1 and Markus Grassl2 — 1University of Darmstadt — 2University of Karlsruhe
Quantum key distribution highlights the power of quantum mechanics to improve information-theoretic tasks, showing that even a modest use of quantum information can have a profound impact on which sorts of possible protocols. For distributing a secret classical key to two separated parties, only the ability to prepare, transmit, and measure quantum states is needed; delicate mulitparticle superpositions are not required. Upon completion of the quantum phase of the protocol, classical means of distilling the key can begin.
Formulating both parts of the protocol in entirely quantum-mechanical terms enables us to describe the whole enterprise as a quantum channel. From this perspective, the goal of the protocol is then to use this channel to create virtual entanglement between the parties. Then the monogamy of entanglement implies that classical keys reated from it are truly secret. While entanglement is not physically required, it arises virtually since to an eavesdropper the prepare and measure scheme is consistent with a protocol using actual entanglement.
For QKD schemes possessing a high degree of symmetry, including essentially all protocols studied to date, the effective quantum channel takes on an especially simple form. We show how to determine the relevant symmetry operations and employ them to arrive at this description. This enables us to establish the security of a wide range of protocols, including in particular those based on equiangular spherical codes.