How could a quantum network be constructed to handle 10,000 clients concurrently?

Question

The C10k Problem is a classical computing problem whose name (C10k) is a numeronym for concurrently handling ten thousand connections.

How could a quantum network be constructed to handle 10,000 clients concurrently?

Answer 1

Enabling network sockets to handle 10k clients at the same time with over 1 gigabit per second Ethernet (the C10k problem), is different from making a quantum computer that can handle 10k qubits concurrently. Remember 10k bits is only 1.25kB which is not even enough to store a typical operating system.

If you want to consider each qubit as a "client" in some generalization of the C10k problem, then the answer to your question depends on whether or not you need a universal gate set to be applicable between each of the 10,000 qubit connections. If so, the largest quantum computers with a universal gate set are the 50-qubit machine by IBM and the 72-qubit machine by Google (which has been announced but not shown to the public yet).

You mention D-Wave, which makes non-universal quantum annealers. If each qubit is considered a "client", it is true that the D-Wave 2000Q has 2048 qubits, but not all of them can be connected to any other qubit. This is the connectivity graph for a typical D-Wave machine. Notice that each qubit can only be connected to at most 6 other qubits. To get 10,000 qubits in this arrangement, you just need to create more of these "unit cells" of 8 qubits each. What's pictured here is the D-Wave One which has 16 units cells of 8 qubits each (8 x 16 = 128 total qubits). The D-Wave Two had 64 units cells of 8 qubits each (8 x 64 = 512 qubits). The D-Wave 2X had 132 unit cells (8 x 144 = 1152 total qubits), and the D-Wave 2000Q has 256 unit cells (8 x 256 = 2048 total qubits).

For 10,000 qubits you just need 1250 units cells (8 x 1250 = 10,000). After that point D-Wave says that a re-design would need to be required, perhaps in the size of the unit cells, or in going from 2D to 3D, or in the physics itself.

Answer 2

In the comments to my answer the OP has written:

In the universal gate case you stated the largest systems are <100. How could it reach 10k?

Well I have good news for you. Four days ago D-Wave announced at the AQC conference that they can now do YY coupling:

Here you can see the superconducting circuit that gives you ZZ and YY coupling at the same time:

I cannot show you more of their "preview" presentation, but expect for them to publish something very soon.

Why is YY coupling significant? It is because in 2007, Jacob Biamonte and Peter Love from D-Wave proved that XX + ZZ is enough for universal quantum computation. XX and YY are equivalent up to a rotation, so they could easily have instead said that YY + ZZ is universal.

Now that D-Wave has engineered a universal set of couplers, it should be possible to have a 10,000 qubit universal quantum computer when they extend to 1250 units cells (since 8 x 1250 = 10,000, see my first answer).

I'm sorry that there's no literature references for this yet, but the picture tells the whole story, and I'm afraid that until D-Wave publishes something, this is the "source" for the information. This is how you can cite this answer.