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arXiv:quant-ph/0405169 · Physical Review Letters

Qutrit State Engineering with Biphotons

Yu. I. Bogdanov, Maria V. Chekhova, S. P. Kulik, Gleb Maslennikov, Andrei A. Zhukov, C. H. Oh, Meng Khoon Tey

Published Dec 1, 2004• 149 citations
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Abstract

The novel experimental realization of three-level optical quantum systems is presented. We use the polarization state of biphotons to generate a specific sequence of states that are used in the extended version of four-state QKD protocol quantum key distribution protocol. We experimentally verify the orthogonality of the basic states and demonstrate the ability to easily switch between them. The tomography procedure is employed to reconstruct the density matrices of generated states.

DOI
10.1103/physrevlett.93.230503

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The novel experimental realization of three-level optical quantum systems is presented. We use the polarization state of biphotons to generate a specific sequence of states that are used in the extended version of four-state QKD protocol quantum key distribution protocol. We experimentally verify the orthogonality of the basic states and demonstrate the ability to easily switch between them. The tomography procedure is employed to reconstruct the density matrices of generated states.
The novel experimental realization of three-state optical quantum systems is presented. We use the polarization state of biphotons in single frequency- and spatial mode to generate an arbitrary qutrits. In particular the specific sequence of states that are used in the extended version of BB84 quantum key distribution protocol was generated and tested. We experimentally verify the orthogonality of the 12 basic states and demonstrate the ability of switching between them. The tomography procedure is applied to reconstruct the density matrices of generated states.
We discuss the proof-of-principle demonstration of the extended deterministic Quantum Key Distribution (QKD) protocol based on ququarts. The experimental realization is based on the polarization degrees of freedom of two-mode biphotons, making the process of state preparation, transformation and measurement rather simple. The scheme uses only single nonlinear crystal for biphoton generation and linear optical elements for their following transformation and can be used as a base for further practical applications.
The best qubit one-way quantum-key-distribution (QKD) protocol can tolerate up to 14.6% in the error rate. It has been shown how this rate can be increased by using larger quantum systems. The polarization state of a biphoton can encode a three-level quantum system---a qutrit. The realization of a QKD system with biphotons encounters several problems in generating, manipulating, and detecting such photon states. We define those limitations and find within them a few protocols that perform almost as well as the ideal qutrit protocol. One advantage is that these protocols can be implemented with minor modifications into existing single photon systems. The security of one protocol is proved for the most general coherent attacks and the largest acceptable error rate for this protocol is found to be around 17.7%. For comparison, the security of the best possible qutrit protocol of four mutually unbiased bases was also rigorously analyzed against general attacks, with a proven bound on the acceptable error rate of 21.1%.