Real-world bell-state measurement and proof-of-principle demonstration of quantum key distribution immune to detector attacks over deployed optical fiber

Based on quantum physical properties of light, quantum key distribution (QKD) promises cryptographic key exchange with information theoretic security over an untrusted but authenticated public communication channel. However, by exploiting vulnerabilities of single photon detectors, quantum hacking attacks have recently been shown to compromise this security. Fortunately, the so-called measurement device independent QKD (MDI-QKD) protocol overcomes the threat of such attacks by implementing a timereversed, entanglement-based version of QKD. In this talk we present the first proof-of-principle demonstration of the MDI-QKD protocol, which uses attenuated laser pulses supplemented with two decoy states. Our fiber based implementation took advantage of three different locations within the city of Calgary. Its simplicity and robustness to environment-induced property variations of deployed optical fibers, along with the enhanced level of security offered by the protocol, confirms QKD as a viable technology for safeguarding secrets in transmission. Furthermore, the required Bell-state measurement with independently generated photons that have traveled over real-world fibers constitutes an important, and previously undemonstrated element of a quantum repeater.