Another Quantum Topic: Quantum Communication

In my recent series on quantum computing (QC), I intentionally overlooked a couple of adjacent topics: quantum communication and quantum sensing. These face some of the same challenges as QC, however I noticed a recent report on a test quantum network implemented by Cisco and Qunnect which led me to find more from Cisco on their work in quantum networking.

Early post since I will be at DVCon next week moderating a panel, among other activities.

What is the point of quantum communication?

Quantum communication is based on entanglement; two physically separated qubits whose states are nevertheless coupled so that if one somehow changes state the other “instantaneously” also changes state. This holds even if the qubits are separated by thousands of kilometers and led Einstein to call this behavior “spooky action at a distance”.

This idea prompted some to think entanglement implied faster-than-light communication. Sadly no – physical laws are not violated by this technique. Still, the concept has led quantum experts (and Star Trek enthusiasts) to label methods using this technique as “quantum teleportation”, which I’ll call QT.

The point of QT is security in the communication channel. If a third-party attempts to monitor a qubit state at either end, both qubit states immediately collapse and the information is lost. Which immediately signals an attempted hack while also destroying information before it can be revealed, valuable for cryptographic key distribution.

These methods are considered “quantum-safe” unlike “quantum-resistant” methods for protecting encrypted data, which are known to defend (classically) against Shor’s algorithm but not against as-yet unknown advances on Shor. External hacks against entanglement-based QT must (as far as I can tell) hack physics, a very tall order.

Cisco work in QT

I got my information from this Cisco article and this blog. Cisco have already developed a research prototype quantum network entanglement chip able to generate a million entangled photons per second, running at room temperature and working with existing photonic infrastructure.

Cisco’s prototype run with Qunnect suggests that this entanglement chip can be used to connect a cryogenic-based system (a superconducting QC for example) on one end to fiber and on the other end of the fiber back to another QC. Details on how this works are sparse I’m afraid but they do claim they were able to connect reliably over more than 17km, a very practical distance for the banks and other finance institutions that cluster around New York area where this trial was run.

Cisco have a higher aim, for quantum networking that could scale up QC capacity without needing to wait for qubit counts to scale up in individual QCs. A quantum network connected topology of QCs could in theory provide almost as much capability (?) as a single large QC. If this works out in practice it could be huge for QC.

Sanity checks

Quantum key distribution (QKD seems to be the most real part of this story today. China claims a 2000km QKD backbone between Beijing and Shanghai supporting banks. This has been in operation for quite a while.

The idea of connecting multiple QC nodes through a quantum internet still looks experimental. The University of Chicago is active in this area, also see the earlier Cisco reference on their quantum labs.

Interesting – a new possible path towards a large scale quantum computer and truly secure networking.

 

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