A new protocol for quantum communication that works in the presence of channel noise and loss has been experimentally demonstrated. Quantum secure direct communication (QSDC) involves sending messages securely and directly over a quantum channel. Now, Jianyong Hu and co-workers from Shanxi University and Tsinghua University have developed a single-photon frequency coding scheme for QSDC. The protocol operates by encoding information into the frequency spectrum of a block of single photons rather than into the individual photons themselves. Analysis suggests that the scheme is more robust against channel noise and loss, which usually severely degrade quantum communication. It also eliminates the need for quantum error correction. Experiments implementing the frequency coding scheme with 16 frequency channels (to represent binary numbers 0000 to 1111) achieved a transmission rate of 4 kilobytes per second.
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