An important breakthrough in quantum computing has just been announced. In a study published in Nature, researchers at Google claim that they have achieved “quantum supremacy.” A quantum computer was able to perform an operation in a fraction of the time it would take a regular supercomputer.
In the paper, the team reports that the quantum computer took 200 seconds to sample one instance of a quantum circuit a million times. The team believes that the same process would take the best supercomputer roughly 10,000 years. But IBM, a rival to Google in this field, argues that the quantum supremacy breakthrough has not yet been reached.
“Because the original meaning of the term 'quantum supremacy,' as proposed by John Preskill in 2012, was to describe the point where quantum computers can do things that classical computers can’t, this threshold has not been met,” IBM researchers Edwin Pednault, John Gunnels, and Jay Gambetta wrote in a blog post.
They also discuss how the 10,000 years claim is based on certain RAM requirements, and argue that using a different approach this estimate can be reduced to at least 2.5 days (if not fewer), with the supercomputer delivering a result with greater fidelity (the ability to reproduce the same result) than the one produced by its quantum counterpart.
The quantum processor that Google employed, known as Sycamore, was made up of 53 programmable superconducting qubits. The processor actually contains 54, but one did not work. Qubits are the quantum equivalent of regular computer bits, hence the name. Their power comes from the fact that the two states, “0” and “1”, that you would find in the binary system of a regular computer are actually in superposition.
Superposition is a quantum mechanical property in which, for example, two states can exist simultaneously, until the system is observed. This is often discussed using the concept of Schrodinger’s cat. In the famous thought experiment, a cat is locked in a box where a vial of poison can be activated by a quantum process. Without opening the box and seeing what happened, the researchers will have to conclude that the cat is both dead and alive.
Superposition is not a concept that we find in the classical world so unfortunately its accurate interpretation cannot easily be described using an analogy (see the excellent SMBC comic for more on that). What is easy to understand is that this property can be employed to reach incredible computational power.
The breakthrough, wherever you fall in the quantum supremacy debate, is an important step forward. The team is looking to get more people involved in making quantum algorithms while making quantum computing architecture more fault-tolerant.