Fig. 4: Security for experimental quantum cryptograms.
a The semidefinite programming framework extracts a secure region of operation (turquoise) as a function of errors and losses. Our measured experimental performance (em = 0.0328 ± 0.0001; lm = 0.2239 ± 0.0150) is indicated by the blue dot, and lies within the secure region. Error bars propagate Poisson errors on coincidence counts. b The dishonest success probability pd (green, upper bound) and honest success probability ph (red, lower bound) are displayed as a function of the number of quantum states N required to verify one bit of the cryptogram. These are derived using a Chernoff bound argument (see Supplementary Information)54. As an example, an experimental token containing λ = N = 4.2 × 106 quantum states (vertical blue dashed line) achieves an honest success probability very close to ph ~ 1 and a dishonest success probability pd = 5.9 × 10−45.
