Proof that Quantom Supremacy Will Exist

The big advantage of qubits over ordinary bits is that they can exist in a superposition of states. So while an ordinary bit can be either a 1 or a 0, a qubit can be both a 1 and 0 at the same time. This means two qubits can represent four numbers at the same time, three qubits can represent eight numbers, and nine qubits, 512 numbers simultaneously. In other words, their capability increases exponentially.

That’s why it doesn’t take many qubits to outperform conventional computers. Just 50 qubits can represent 10 quadrillion numbers. A classical computer would require a petabyte-scale memory to store that number.

One way to achieve quantum supremacy is to create a system that can support 49 qubits in a superposition of states. This system doesn’t need to perform any complex calculations—it just needs to be able to explore the entire space of a 49-qubit superposition reliably.

Qubits are quantum objects that can exist in two states at the same time, and there are lots of ways of making them. For example, photons can be polarized both vertically and horizontally at the same time, atomic nuclei can spin with their axis both up and down at the same time, electrons can travel along two paths at the same time.

A good quantum system is a superconducting qubit. This is essentially a loop of metal cooled to low temperature. Set a current flowing through this loop and it will flow forever—a quantum phenomenon known as superconductivity.

This quantum nature leads to a neat trick: the current can flow in one direction and in the other at the same time. And this is what allows it to act as a qubit that can simultaneously represent both a 0 and 1.

The big advantage of superconducting qubits is that they are relatively easy to control and measure. They can also be linked to each other when several loops sit next to each other on a chip. This linking of neighbors is harder and requires another trick.

The flow of current in one direction or the other is just a low-energy configuration; put in more energy and other states are possible, too. It is these higher energy states that can interact with each other, creating bigger superpositions. In this way, neighboring loops can share the same, much more complex state.

If a chip were to be made with nine of these neighboring loops, the superconducting qubits they support can represent 512 numbers simultaneously. That is nowhere near the number of qubits required for quantum supremacy, but this offers proof that it will be possible.