Stuttgart runs quantum dot encryption over campus fibre for 19 hours straight

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Quantum key distribution usually relies on lasers dimmed down to single photon levels, but researchers in Germany have tried something more precise. Quantum Computing Report says teams from the University of Stuttgart, Saarland University and IFW Dresden ran an entanglement based key distribution link using a quantum dot photon source over installed campus fibre

The quantum dot emits entangled photon pairs at 779.8 nanometres. One photon from each pair is converted to 1515 nanometres, in the telecom band, using a converter that preserves its polarisation. The pairs reached about 91.4 percent fidelity to an ideal entangled state

The link ran over 1.59 kilometres of real campus fibre with total loss of just 1.09 decibels and automatic polarisation tracking. Over 19 hours of continuous operation it produced a secure key rate of 206 bits per second and an average error rate of 4.70 percent, well below the 11 percent limit for the BBM92 protocol

In total the system generated 14.2 megabits of secure key, which was used to encrypt an image with a one time pad. The authors say quantum dots with frequency conversion are viable transmitters for city scale quantum networks

Quantum dots matter because they emit photons one at a time rather than in random bunches, which closes some security loopholes. The key rate is modest and this is a preprint, but running stably for 19 hours over real fibre is an important practical step

Could quantum dots replace lasers in quantum networks? And what would it take to scale this across a city?

University of Stuttgart Deploys Quantum Dot QKD Link Using Frequency Conversion Over Campus Fiber - Quantum Computing Reportquantumcomputingreport.com