Progressing Towards Economical and Secure Quantum Networks

Canadian and US Researchers have made a crucial breakthrough towards enabling quantum networks to be economical and really secure from attack.

The experiments, by the team from the University of Calgary, the California Institute of Technology and the National Institute of Standards and Technology, Colorado, establish the viability of a measurement-device-independent quantum key distribution (QKD) system, based on easily available hardware.

QKD provides a technique of provably secure communication. A number of QKD systems, including commercial systems, have been created during the last three decades, and vital elements such as maximum transmission and secret key rates have constantly enhanced.

The team’s results, published today in the Quantum Science and Technology journal, reveal how they used economical and commercially available hardware such as field-programmable gate arrays (FPGA) electronics and distributed feedback (DFB) lasers, which enable time-bin qubit preparation and time-tagging and active feedback systems that allow for compensation of time-variable properties of photons after transmission via deployed fiber.

Quantum hacking over the past decade has also shown, however, that the specifications of components and devices used in actual QKD systems never perfectly agree with the theoretical description used in security proofs, which can compromise the security of real QKD systems.

Raju Valivarthi, First Author

Valivarthi added, “For instance, so-called ‘blinding attacks’ exploit vulnerabilities of single photon detectors (SPDs) to open a side-channel, via which an eavesdropper can gain full information about the (assumed-to-be) secure key. Making practical QKD systems secure against all such attacks is a challenging task.”

Senior Author Dr. Qiang Zhou said,“Our MDI-QKD system includes four parts: qubit preparation module, Bell state measurement (BSM) module, control module, and time-tagging module, which allows key generation from qubits in randomly prepared states. It is worth to note that our control module in the demonstration is further improved to control the polarization and arrival-time of photons traveling from Alice and Bob to Charlie, which ensures their indistinguishability at the moment of the BSM.”

Our experimental demonstration paves the way for MDI-QKD-based star-type quantum networks with kbps secret key rates spanning geographical distances of more than 100 km.

Professor Wolfgang Tittel, Group leader