Experimental Quantum Key Distribution with Decoy States

To increase dramatically the distance and the secure key generation rate of quantum key distribution (QKD), the idea of quantum decoys—signals of different intensities—has recently been proposed. Here, we present the first experimental implementation of decoy state QKD. By making simple modifications to a commercial quantum key distribution system, we show that a secure key generation rate of $165\mathrm{\text{bit}}/\mathrm{s}$, which is $1/4$ of the theoretical limit, can be obtained over 15 km of a telecommunication fiber. We also show that with the same experimental parameters, not even a single bit of secure key can be extracted with a non-decoy-state protocol. Compared to building single photon sources, decoy state QKD is a much simpler method for increasing the distance and key generation rate of unconditionally secure QKD.

Figure 1

Schematic of the experimental setup in our system. Inside Bob (Jr. Alice): Components in Bob’s (Alice’s) package of id Quantique QKD system. Our modifications: CA, compensating AOM; CG, compensating generator; DA, decoy AOM; DG, decoy generator. Original QKD system: LD, laser diode; APD, avalanche photon diode; ${\Phi }_i$, phase modulator; PBS, polarization beam splitter; PD, classical photo detector; DL, delay line; FM, faraday mirror. Solid line, SMF28 single mode optical fiber; dashed line, electric cable.