= Dark count
{title2=$r_{\rm dark}$}
A registered detector event occurring without an incident signal <photon>. For a <single-photon avalanche diode>, internally generated carriers can trigger the same avalanche as an absorbed <photon>. The dark-count rate $r_{\rm dark}$ is the mean number of these events per unit <time> under specified operating conditions. Such events can contaminate <coincidence counting> and increase the <quantum bit error rate> in <quantum key distribution>.
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