Quantum computers are a significant challenge for science communicators for a few reasons. One, of course, is that they involve quantum mechanics, which is not intuitive. It’s also difficult to understand why they represent a potential benefit for computing. But even with those technical challenges aside – I find it tricky to strike the optimal balance of optimism and skepticism. How likely are quantum computers, anyway. How much of what we hear is just hype? (There is a similar challenge with discussing AI.)

So I want to discuss what to me sounds like a genuine breakthrough in quantum computing. But I have to caveat this by saying that only true experts really know how much closer this brings us to large scale practical quantum computers, and even they are probably not sure. There are still too many unknowns. But the recent advance is interesting in any case, and I hope it’s as good as it sounds.

For background, quantum computers are different than classical computers in that they store information and do calculations using quantum effects. A classical computer stores information as bits, a binary piece of data, like a 1 or 0. This can be encoded in any physical system that has two states and can switch between those states, and can be connected together in a circuit. A quantum computer, rather, uses qbits, which are in a superposition of 1 and 0, and are entangled with other qbits. This is the messy quantum mechanics I referred to.

For this news item, the thing you most need to understand is entanglement. Two quantum systems are entangled if their states depend upon each other. So, for example, two particles might have entangled spin where if one particle is spin up the other must be spin down. One way to think of this is that their spins must cancel each other out. One of the challenges for quantum computers is that these entangled states are very fragile. They require very low energy (meaning cold) and very isolated systems, with very little noise. Any contact with matter or energy outside the entangled system causes the quantum state to break down. For this reason entangled states like this in qubits tend to be very short lived.

For a quantum computer to work, the different qubits must be entangled but also able to communicate with each other – they have to be physically connected in some way. This creates a trade-off. The more isolated a qubit is, the less noise and therefore the longer the entanglement will last and the fewer errors will occur, but the less able it will be to communicate to other qubits. This means they have to be very close together in an isolated system. This is a very practical problem for quantum computers because it limits the size and scalability of the networks of qubits that can be created.

This is where the breakthrough comes in, as researchers have found a way to keep a quantum system isolated enough to maintain entanglement and minimize noise while simultaneously giving it the ability to communicate not only over longer distances, but theoretically scalable distances. This is how it works.

The researchers used the spin of phosphorous nuclei as their qbit. Nuclear spin has so far proven to be one of the best quantum computer media because they are very stable – it is a “clean” quantum system. They have previously demonstrated that they can maintain entanglement for 30 seconds (a relatively very long time for such systems) with <1% errors, which is also very good for a quantum system. The problem has been getting these atomic nuclei to communicate with each other. What they did is surround two phosphorus nuclei with a single electron, and this enables to two nuclei to communicate with each other. They were able to do this over a distance of 20 nanometers, which sounds like a short distance but this is the scale of modern silicon chips. So theoretically we could use existing manufacturing techniques to make quantum computer chips using this new system.

If this all pans out, it would be a massive breakthrough for quantum computers. This is because this system is scalable – you can keep adding phosphorus nuclei and connecting them together with other nuclei using this shared electron technique. The researchers say that using their technique they should be able to control the shape of the electron cloud, increasing the distance between nuclei, and including more than two nuclei together. The best case scenario is that this system leads to the ability to mass produce quantum computer chips with many qbits linked together.

These systems still won’t be on your desktop. They require expensive systems and supercooling. Quantum computers will be used by governments, corporations, and large institutions, not consumers. What can they do?

Quantum computers do not do the same kinds of calculations that classical computers do, they can do a different kind of calculation. For certain kinds of problems this means that they can accomplish in seconds or minutes what would theoretically take a classical computer billions of years to complete. This can be used for things like modeling complex systems, like the climate. This could be a boon for researchers in many fields.

But perhaps the application which gets the most interest, and the reason why governments are so interested in funding research, is quantum encryption. Once someone has a powerful-enough and accurate-enough quantum computer, every encryption system in the world is suddenly obsolete. Encryption systems generally use sufficiently complex codes that classical computers could not crack them in any usable time frame. But a quantum computer might be able to crack the classical encryption codes in seconds, rendering them useless.

The solution is to use quantum encryption – you need your own quantum computer to make the encryption so that other quantum computers cannot crack it. So yes, we are in the middle of yet another technological arms race (Mr. President, we cannot allow a quantum computing gap!), with several countries racing to build quantum computers so that they will not suddenly become vulnerable to other countries with quantum computers. This is a very real security issues. Imagine if a hostile country had access to our military secrets, or could cause havoc in our energy grids. Obviously there are other ways to secure systems from hacking, which we do, but the ability to crack any encryption would still be a problem.

However this pans out, the physics here are interesting. For now, I am keeping my eye on quantum computing. It is probably a lot further away than it sounds from many of the news items, but at the same time we do appear to be making steady process. This advance does sound significant, and we’ll just have to wait and see what happens.