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Free space QKD over an atmospheric channel was demonstrated in 1996 for the first time. Since then, several prepare-and-measure and entanglement-based schemes have been implemented (for a detailed overview, see). All of these systems use single-photon detectors, and therefore have to employ spatial, spectral and/or temporal filtering in order to reduce background light. In our system, we use an alternative...
A detection-time-bin-shift scheme for polarization encoding QKD is proposed. This scheme reduces cost and overcomes the security loss caused by dead-time and unbalanced characteristics of detectors. This scheme is experimentally demonstrated with the B92 protocol.
Summary form only given. Consider a pair of collinear frequency-degenerate photons-a biphoton, which can be obtained by spontaneous parametric down-conversion (SPDC). Being a three-state quantum system, it is a ternary analog of a qubit. Its state vector is |/spl psi/>=c/sub 1/|2,0>+c/sub 2/|0,2>+c/sub 3/|1,1>, with |n,m>,n+m=2 denoting n X-polarized photons and m Y-polarized photons...
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