Get ready to add another gadget to your Jetsons want-it-one-day list: personal quantum encryption. Although vulnerable to man-in-the-middle attacks by kitted-up boffins with access to the fibre, quantum key distribution (QKD) is still secure enough to give nightmares to spooks already scrambling to catch up with ordinary …
Missing the point
That might be interresting in fully optical systems, but in the usual usecase, there's nothing to be gained from encrypting the connection to your ISP as the attacker most likely sits at the ISP or at the core network.
QKD ..... An Alien* Discipline for Passing Advanced Instructions to GOD
Given the sensitivity of systems and applications which are both driven and protected by SMART Wizards and SWitches deploying QKD, can one not expect to learn a great deal about how successful it proves itself to be as a spooky invincible security device manager. Such is highly classified need to know territory in fields with agents exercising lead protocols in the live operational virtual environments that control commanding CyberSpaces for CyberSpace AI Command and IT Control and Offices of Cyber Security instructing Global Operating Devices.
* Irregular and Unconventional.
Why not simple TDM
Why not just dedicate some fixed percentage of the fibre to QKD by time-division? In other words, (something like) every second, turn off the conventional transmitters at both ends for 0.1s, let the line go quiet (doesn't take long at the speed of light) and then do the QKD in that gap. You get QKD in exchange for 10% of your bandwidth. Most usages won't notice 0.1s drop-outs on a WAN.
Time-coherence between the ends is a problem solved by NTP and/or GPS.
@Nigel 11 -- A few question re your TDM proposal.
The whole concept of the Young, Townsend et al 'Quantum information to the home'/FTTH paper is indeed extremely intriguing. Your reply implies the method as presented within the paper is more complex than necessary and I think I agree with you.
Synchronously interleaving entangled qbits at an RXed power of about -88 dBm [p7 & Fig 7, p10] in what is effectively the intermodulated noise (Raman scattering) region of the fibre seems to me to be a daunting if almost impossible task. Thus questioning if there are simpler/alternative ways of tackling the QKD/key problem makes sense. Moreover, the effective data rate of the key distribution is ridiculously low--a little over 1kbps--given its context. Although the QKD data rate is sufficient for purpose, it nevertheless is exceedingly close to margins of unacceptability--at least in practical engineering terms--hence another reason to look for alternative methodologies.
Perhaps their approach was adopted to maintain FTTH compatibility/standards thus your TDM proposal would be unacceptable from this perspective. I may be way off-beam here (sorry no pun intended) but I'm unclear how your 'Time-coherence between the ends is a problem solved by NTP and/or GPS' is actually supposed to work in practice.
1. With your TDM system it's unclear to me why one needs to adapt time-coherence in the same way as that proposed in the paper.
2. If so however, then how would NTP/GPS time-coherence fit into the picture given the Inter-Symbol Interference (ISI) is limited by the ~35ps jitter of the single-photon detectors which operate within a window period of only 100ps? (The short-term GPS jitter at the RX-end would be substantially more than 100ps given proximity effects, TX/RX/pulse jitter, dialectic variations and ionospheric delays over the long TX/RX path length. Remember, c(v) is ~0.3m/ns, and correction schemas such as Carrier-Phase Enhancement (CPGPS) would, if used here, be ineffective through latency/delays.
3. Why would you use a small mark-space ratio of only 10%? If TDM dedicates clear-channel time to QKD exchange then why couldn't the exchange take place in orders of magnitude less time?
'Tis a fascinating issue, perhaps you may wish to reply.