Abstract
Quantum secure direct communication (QSDC) is an important quantum
communication branch, which realizes the secure information transmission
directly without encryption and decryption processes.
Recently, two table-top experiments have demonstrated
the principle of QSDC. Here, we report the first long-distance QSDC experiment,
including the security test, information encoding, fiber transmission and
decoding. After the fiber transmission of 0.5 km, quantum state fidelities of
the two polarization entangled Bell states are 91% and 88%, respectively, which
are used for information coding. We theoretically analyze the performance of
the QSDC system based on current optical communication technologies, showing
that QSDC over fiber links of several tens kilometers could be expected. It
demonstrates the potential of long-distance QSDC and supports its future
applications on quantum communication networks.
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