Google recently announced that is has achieved “quantum supremacy.” The declaration sounds ominous, but what exactly does it mean?
The phrase was first coined by theoretical physicist John Preskill in 2012 to describe the point at which a quantum computer is able to do things that are, for all practical purposes, impossible for conventional supercomputers.
Google claims that its quantum computer, called Sycamore, was able to solve a particularly tough problem involving random numbers in just 200 seconds. Google claims the world’s fastest conventional supercomputer, Summit, which is owned by IBM, would have taken 10,000 years to solve the same problem.
IBM disputes that and says that with the right tweaking its computer could have resolved the problem in about two-and-a-half days.
Nevertheless, it’s quite an upgrade.
“Whether you say that they’ve solved a problem in 100 seconds that would take a classical computer 10,000 years or three days – the fact is it is an extraordinary speedup,” said David Awschalom, director of the Chicago Quantum Exchange and a leading scientist in the world of quantum technologies.
But Awschalom cautioned against making too much of the Google announcement.
“The Google announcement is something that is technologically quite impressive. They have demonstrated a fully functional quantum machine that solves a problem around random number generation,” he said. “I think you need to be careful not to claim that you have a machine that can outperform classical technologies more broadly because that’s not the case.”
The power of quantum computing and quantum technologies more broadly is based on the properties of quantum bits or qubits. It’s counterintuitive, but the key thing to understand is that qubits are able to exist in many different states at the same time.
“If you think of it as a little magnet it would be pointing in all directions,” said Awschalom. “That’s sort of a weird thing but that is a quantum bit.”
It’s a concept that most people find difficult to comprehend even if they work in the field.
“As (theoretical physicist) Richard Feynman often said: ‘No one understands quantum mechanics,’” Awschalom said. “You know it is working and it governs the world around us but deep within you, I don’t know anyone who has a deep intuition for quantum science.”
Another concept that can be difficult to comprehend is that the mere act of looking at a qubit changes it. And that quality may one day lead to encrypted communications that are impossible to hack.
“When the act of looking at something can change it you might think that’s a liability, but for communication it could be a fantastic asset for security,” said Awschalom. “So if I sent you a message with these quantum bits and somebody tries to eavesdrop – if they grab one of these quantum bits to try and look at them – they have changed it irreversibly. It’s a fantastic basis for security and there are many companies around the world trying to build networks based on this.”
According to Awschalom, the situation now in terms of developing quantum technologies is akin to the early days of electronics with vacuum tube transistors. Nobody could have known where that technology would eventually lead.
“When people were building vacuum tubes I don’t believe anybody thought that they were going to be building something that you could fit in your pocket that you could pull out and speak to anybody on the planet or that I can get a satellite map of the weather in France this afternoon. The point is that these things happen in ways that are really exciting and a bit unpredictable and that’s what’s going to happen with quantum technology – we’re at the vacuum tube level.”
One area of quantum research that Awschalom is particularly excited about is the idea of using quantum bits as sensors. When used in quantum computing, qubits are isolated from the outside world. But when exposed to the world they can also be “extraordinary sensors,” said Awschalom.
“Imagine you could build a probe that could take magnetic resonance imaging to the level of one molecule,” he said. “You would be able to unravel things like the structure, function and relationship of proteins and us. And very few proteins in us are understood because there is no way to probe how they react to pharmaceuticals, how they react to disease. If a quantum sensor could be used to take MRI down to single molecules it would revolutionize areas of chemistry, biology and medicine. And that’s not an overstatement.”
Another fundamental aspect of the quantum realm is the notion of entanglement – something Albert Einstein called “spooky action at a distance.” What it means is that when pairs of particles are generated and then separated even by large distances they continue to interact. And that property could lead to seemingly impossible scientific creations.
“People are proposing satellites that are quantum mechanically entangled that are essentially large aperture arrays,” said Awschalom. “What that means is you could build a space-based telescope using quantum entanglement that in principle could have the resolution to look at cities on exoplanets. You could look for civilizations across the galaxy with these types of resolutions. I’m not saying we will do that because when you have this type of technology it is hard to predict where it is going to go, but it’s very exciting.