matpompili OP t1_isybhxw wrote

Yeah that's a great question!

How do we generate the pairs? We use an entanglement protocol called Single-Click-Entanglement (you can read details about it here:, essentially we make the node emit a photon that's entangled with our communication qubit. A second node does the same. We bring the two outputs on a beam-splitter, and if we detect a photon on the other side we have entangled the two communication qubits. Most of the time the photons get lost along the way, and the attempt fails, but once every while we get a click from the photon detector (hence the name of the protocol) that tells us that an entangled state has been made and we can stop trying.

How do we verify entanglement? Once the protocol succeeds, we know we have an entangled state. To characterize it we use a measurement procedure called quantum state tomography, that by measuring the same state many times in different ways can tell how good it is.

How long do they last? In our experiments they last a few tens of a second, which is very long compared to other quantum platforms, and compared to how long it takes to do operations on the qubits (hundreds of nanoseconds).

What can you do with it? Entangled states are at the basis of many (all?) quantum network applications. Just like for quantum computers, we don't really know yet all the things we'll be able to use it for. You can find many more details here:


matpompili OP t1_isu5g1b wrote

Alright, lemme try: IF the AI has access to multiple full-fledged quantum computers, IF those computers are connected by a quantum network many many many times better than what we have done here (which is state of the art right now), IF we don't realize the only prototype we have of this thing is being used without our authorization and we don't pull a plug, THEN a rouge AI could MAYBE run some algorithms faster than it could on other computers it has stolen.

But if such an AI was available, I would ask it to please please keep my devices on resonance so I can do more useful stuff in the meantime.


matpompili OP t1_isst5eq wrote

Thanks! I would say this was just as much innovation at the physical layer (running quantum network operations in real time) than at the link layer and above (implementing for the first time an entanglement distribution service, keeping track of entangled qubits and states delivered, assigning them to different quantum applications and so on).

The link layer we implemented is completely agnostic to the physical layer implementation, so the job for the developers on a different platform would be to be able to receive a set of instructions from the link layer and to execute the required operation on the hardware and reply with one of the expected outcomes, you can see a list of commands/replies here
Then you can run the exact same Python-based apps we ran on our diamond devices on other platforms, with no other changes (the only caveat is that if the platform does not support some quantum gates, the link layer needs to be made aware of that, such that it can convert the application to use a different set of gates)


matpompili OP t1_issrydd wrote

Yes! I believe one of the really exciting things is that once you abstract functionality in these layers, people from different backgrounds and with different expertise can contribute in their niche.
Building Reddit would have been unimaginable to the people that first laid out the cables to connect the first computers, but here we are. Once you make a technology available to people, they will come up with amazing things you would have never imagined.


matpompili OP t1_isq7f52 wrote

Without communication between the two sides, no: imagine you are in a closed room, no communication to the outside, and have one of the spins.
You measure it repeatedly, and you get random outcomes: 0, 1, 1, 0, 0.
The other side got 1, 0, 0, 1, 1, but since neither you nor the other side has a way to change what those bits are going to be, all you have after measuring is a correlated list of random numbers.
The fundamental problem, is that you have no way to tell whether the other side has done anything to their spin. If the other side had not done anything, you could have totally gotten the same string of random bits!


matpompili OP t1_isq5v6a wrote

The problem with your argument is that you cannot force the system to go "left" or "right".
All that entanglement gives you is: either the two spins go "left-right", or they go "right-left", but you cannot force the system in one of the two options.
So when you measure your spin, and you get "left", you know that the other spin will be right, but you have no way to imprint a message on this process.
You can only use this as a correlated source of random events (which is why it is so useful for cryptography)


matpompili OP t1_isq2vd1 wrote

Yes, precisely. One great application of this would be connecting many smaller quantum computers into one large quantum computer, similar to what we do today for supercomputers. It's impossible to build one huge CPU with PetaFLOPS capabilities, but you can put thousands of normal CPUs together if you have a network.


matpompili OP t1_isq0qyp wrote

Hi! The quantum entanglement itself does happen instantaneously, but it cannot be used to send messages faster than the speed of light. A good analogy is the following, from John Bell:

«The situation is further complicated by the fact that there are things which do go faster than light. British sovereignty is the classical example. When the Queen dies in London (may it long be delayed) the Prince of Wales, lecturing on modern architecture in Australia, becomes instan taneously King.»

So the entanglement effect is instantaneous, like the transfer of sovereignty, but until the information reaches the other side it is not known. So you cannot use entanglement to communicate faster than the speed of light.


matpompili OP t1_ispxfh4 wrote

We developed and implemented a building block for connecting future quantum computers in networks.
You can think of it as the very first messages exchanged by computers at the birth of the Internet (1970s), not really "useful" yet for corporations, but will be the basis for what is to come :)