Solving single photon detector problems

Quantum key distribution(QKD) could be the most significant application in quantum information theory. Recent years, QKD distance improved dramatically but is still restricted. The main problem is that the bit error rate(QBER) caused by single photon detector(SPD) dark counts is out of control as the distance increases. If this problem can be solved, QKD can be implemented over arbitrarily long distance. However, previous solutions often result in impractical requirements such as superconductors while they can only reduce dark count rate to finite low levels. Here we present a scheme with today's technologies only, solving SPD problems. Our scheme demonstrates that imperfect detectors can provide nearly perfect results, namely the QBER caused by dark counts can be reduced to arbitrarily low while detective efficiency can be improved to arbitrarily high. As a consequence, QKD distance is not limited by the imperfect SPD any more. For example, it can be improved from hundreds of kilometers to thousands without high-technology detectors. Therefore, our result might change the research point in QKD devices from SPD to others. On the other hand, it is worth noting that similar schemes can be applied for reducing measurement errors or improving the performance of source.Comment: 13 pages, 7 figure