Scientists transmitted data for a record 102 km using secure quantum communication

Direct Secure Quantum Communication (QSDC) is a technology that uses quantum entanglement as a means of

protection of data transmitted over insecurecommunication lines. Unlike quantum key distribution, which uses quantum effects only to transmit the encryption key, QSDC applies quantum entanglement to all transmitted data. Hi-Tech told more about this technology earlier.

The key limitations of this technology remaina significant number of errors in data transmission, low speed and a limited distance over which messages can be sent. In their new work, researchers at Tsinghua University in China have developed a new protocol for QSDC that combines photon state time coding for signal monitoring and quantum states for real messages.

The researchers believe that this approach will helpprotect against quantum errors and polarization of light. They also believe that the new protocol makes systems more reliable, which in turn leads to lower error rates. And this allows you to increase the distance over which messages can be sent.

To test the operation of the protocol, researchersassembled a setup based on a laser with a repetition rate of 50 MHz, which, as the authors of the work note, can be easily upgraded to 1 GHz. Using the installation helped to transmit information over a distance of about 102.2 km (the previous record was 18 km). Scientists emphasize that the system they created significantly increased secrecy by achieving an ultra-low quantum bit error rate (less than 0.1%), which is an order of magnitude less than existing systems.

Experimental setup.FPGA - Field Programmable Gate Array, ATT - Attenuator, PC - Polarization Controller, ILP - Fiber Optic Polarizer, CIR - Optical Circulator, PBS - Polarizing Beam Splitter, FC - 90:10 Split Optical Coupler, PMFC - Saving Optical Coupler polarization, PM - phase modulator, IM - intensity modulator with an attenuation coefficient of 45.1 dB, ISO - insulator, FR - Faraday rotator with an angle of rotation of 90 °, SPD - single photon detector based on superconducting nanowires with a detection efficiency of more than 85%, frequency dark count 50 Hz and reset time 15 ns. Source: Haoran Zhang et al., Light: Science and Applications

The key limitation of the new system remains howthe researchers note that the low data transfer rate is only 0.54 bps. However, the authors of the work believe that this is enough to send an encrypted message or phone call.

Scientists believe that the ability to transmitsecure data over 100 km allows you to create long-distance networks using the new QSDC protocol based on our existing technologies. A secure exchange, according to the authors, will be able to replace some of the most vulnerable segments of the Internet in order to protect sensitive data from hackers.

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