AI Article Synopsis
- MDI-QKD (Measurement-device-independent quantum key distribution) is a secure method for transmitting encrypted keys that is resistant to attacks on the detection system, allowing for untrusted relays in the network.
- Recent advancements have been made in fiber-based MDI-QKD implementations aimed at improving distance, key rates, and network verification, but free-space applications have been challenging due to atmospheric turbulence.
- Researchers successfully conducted the first free-space MDI-QKD over a 19.2-km urban channel by employing adaptive optics, precise time synchronization, and frequency locking, paving the way for future satellite-based MDI-QKD and long-distance quantum experiments.
Article Abstract
Measurement-device-independent quantum key distribution (MDI-QKD), based on two-photon interference, is immune to all attacks against the detection system and allows a QKD network with untrusted relays. Since the MDI-QKD protocol was proposed, fiber-based implementations aimed at longer distance, higher key rates, and network verification have been rapidly developed. However, owing to the effect of atmospheric turbulence, MDI-QKD over a free-space channel remains experimentally challenging. Herein, by developing a robust adaptive optics system, high-precision time synchronization and frequency locking between independent photon sources located far apart, we realized the first free-space MDI-QKD over a 19.2-km urban atmospheric channel, which well exceeds the effective atmospheric thickness. Our experiment takes the first step toward satellite-based MDI-QKD. Moreover, the technology developed herein opens the way to quantum experiments in free space involving long-distance interference of independent single photons.
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