48
3 Introducing Quantum Key Distribution
3.4 State-of-the-Art Experiments
In this Section we provide a brief and incomplete overview of the most recent experimental achievements in QKD. More complete and elaborated reviews can be found
in [6, 7, 16].
In October 1989 Bennett, Brassard and other scientists implemented for the first
time a QKD protocol, specifically the BB84 protocol [17, 18]. The experiment was
carried out in a laboratory and was characterized by the transmission of polarized
light over (just) 32.5 cm.
Since then much progress has been made, also thanks to the interest and investments of governments and companies [19, 20]. Current QKD implementations can
reach secret key rates of the order of Mbits
−1 over about 50 km of telecom fibre
[21–23]. By exploiting wavelength division multiplexing (WDM), scientists have
multiplexed 194 QKD channels over the same fibre reaching an aggregate key rate
of 172.6 Mbits
−1 [24].
In view of implementing QKD in existing optical networks, it has been demonstrated that QKD can be multiplexed alongside classical data channels amounting to a
total of 18.3 Tbit s
−1 of classical datarate [25], which is the typical datarate achieved
nowadays in telecom fibres. To the same aim, QKD has successfully undergone field
tests on commercial telecom fibres [26–28].
Thanks to novel architectures and security proofs, namely measurement-deviceindependent QKD (Chap. 5) and twin-field QKD (Chap. 6), it has been possible to
extend the achievable distance of QKD on telecom fibres to over 400 km [29–32],
with the record currently being set to 509 km by a twin-field QKD protocol [33].
By using free-space optical links, such as satellite-to-ground links, it is possible to
extend the maximum distance of QKD even further. In 2017, Chinese and Japanese
research groups independently realized the first QKD protocols in free-space using
low-Earth-orbit satellites [34, 35]. In particular, the Chinese group led by Prof. Pan
implemented QKD over 1000 km between the satellite and a ground station [34],
including a quantum-secured video call between Beijing and Vienna [36]. More
recently, Prof. Pan’s group performed entanglement-based QKD between two ground
stations separated by 1120 km using a satellite as the source of the entangled states
[37].
Appendix
In this Appendix we prove some statements made in the main text, whose articulated
proof would have altered the cohesion and flow of the text.
3 Introducing Quantum Key Distribution
3.4 State-of-the-Art Experiments
In this Section we provide a brief and incomplete overview of the most recent experimental achievements in QKD. More complete and elaborated reviews can be found
in [6, 7, 16].
In October 1989 Bennett, Brassard and other scientists implemented for the first
time a QKD protocol, specifically the BB84 protocol [17, 18]. The experiment was
carried out in a laboratory and was characterized by the transmission of polarized
light over (just) 32.5 cm.
Since then much progress has been made, also thanks to the interest and investments of governments and companies [19, 20]. Current QKD implementations can
reach secret key rates of the order of Mbits
−1 over about 50 km of telecom fibre
[21–23]. By exploiting wavelength division multiplexing (WDM), scientists have
multiplexed 194 QKD channels over the same fibre reaching an aggregate key rate
of 172.6 Mbits
−1 [24].
In view of implementing QKD in existing optical networks, it has been demonstrated that QKD can be multiplexed alongside classical data channels amounting to a
total of 18.3 Tbit s
−1 of classical datarate [25], which is the typical datarate achieved
nowadays in telecom fibres. To the same aim, QKD has successfully undergone field
tests on commercial telecom fibres [26–28].
Thanks to novel architectures and security proofs, namely measurement-deviceindependent QKD (Chap. 5) and twin-field QKD (Chap. 6), it has been possible to
extend the achievable distance of QKD on telecom fibres to over 400 km [29–32],
with the record currently being set to 509 km by a twin-field QKD protocol [33].
By using free-space optical links, such as satellite-to-ground links, it is possible to
extend the maximum distance of QKD even further. In 2017, Chinese and Japanese
research groups independently realized the first QKD protocols in free-space using
low-Earth-orbit satellites [34, 35]. In particular, the Chinese group led by Prof. Pan
implemented QKD over 1000 km between the satellite and a ground station [34],
including a quantum-secured video call between Beijing and Vienna [36]. More
recently, Prof. Pan’s group performed entanglement-based QKD between two ground
stations separated by 1120 km using a satellite as the source of the entangled states
[37].
Appendix
In this Appendix we prove some statements made in the main text, whose articulated
proof would have altered the cohesion and flow of the text.