While the new Ant-Man movie might have you thinking that quantum computing can create a portal to an entirely different realm of reality, the truth is that the potential impact of quantum computing on the world is a lot less grandiose — and also a lot harder to achieve. Despite being a conceptual reality since the 1980s, fully functioning quantum computers are still something of a great white whale for scientists. The main reason for this is that, like your teenage years, quantum computers are notoriously unstable.
Quantum computing is said to be an answer to the problem with transistors: a type of switch found in every type of computer, from your PC gaming rig to your cell phone. They act as a switch that controls the flow of electrical volts known as bits that carry data. A bit is conceived as either a one (high voltage) or a zero (low voltage). All of the computers you interact with every day are just a combination of transistors that relay complex data and information to you.
While technology has advanced enough that we can shrink transistors to incredibly small sizes, there is a limit to how small we can make them and therefore how powerful our computers can be. This is where quantum computing comes into play. Instead of using transistors and normal bits that can only be either a one or a zero, a quantum computer uses qubits, which can be as small as photons and can be one and zero at the same time in a state called superposition. This allows a single qubit to store all the combinations of ones and zeros that store ten bits.
But qubits are incredibly unstable, reacting to the presence of other qubits or even minute environmental changes. These bugs are the main reason why fully functional quantum computing is still not a reality. If scientists can find a way to reduce the errors through a process called quantum error correction, then we have a much better chance of developing a usable quantum computer.
“It’s a necessary rite of passage that any mature quantum computing technology must go through,” Hartmut Neven, the technical director at Google Quantum AI, said at a news conference on Tuesday.
“We believe that quantum error correction is the single most important technology for the future of quantum computing,” added Julian Kelly, computer scientist at Google Quantum AI, in the briefing. “Correction of construction errors is the only known way to produce generally useful and large-scale quantum computers.”
Photo of a fully assembled quantum system at Google Quantum AI. Of particular note are the dilution refrigerator where the calculations take place, the quantum processor and quantum limited amplifiers installed in the bottom stage of the refrigerator, various cables connecting from the bottom up, and the quantum computer control electronics on the back.
Erik Lucero / Google Quantum AI
Neven, Kelly and their colleagues have developed an error correction method by using an ensemble of qubits to create a logical surface code qubit. This is able to find and correct errors without affecting the data. But there’s a catch: Paradoxically, if you scale up the set of logical qubits, you might end up creating even more logical errors.
However, Google’s team was able to create a type of qubit, called a logical surface code qubit, that reduces error rates even as the system size increases. This has brought researchers much, much closer to one of the biggest hurdles in quantum computing.
“To our delight, our team was able to demonstrate for the first time in practice that qubits protected by surface code error correction can actually be scaled to achieve lower error rates,” he said. The team published a paper about their findings in the journal Nature on February 22.
For the study, the researchers created a superconducting 72-qubit quantum processor. Then they tested the computer with two surface codes of different lengths: longer and shorter. They discovered that the longer surface code had better qubit performance, with an error rate of 2.914 percent. In contrast, the smaller surface code had an error rate of 3.028 percent.
This may seem small to the layman, but it is in fact a huge improvement – and signals that such logical surface code qubits could help reduce errors in quantum computing.
“What we have shown here for the first time is the system implementing error correction that was good and large enough to show that as the amount of error correction increased, the logical error was reduced by it,” explained Kelly. “This achievement completes a major scientific and engineering challenge that has existed in the community for decades.”
The authors acknowledge that this is just one study and that more research needs to be done so that logic error rates are low enough for quantum computers to become operational. However, this is a massive milestone for the system and lays the foundation for future quantum computers.
While we may not be getting quantum computers in our phones or offices anytime soon, the folks at Google just took a monumental step forward in making that a reality. Hopefully it runs smoother than their entire chatbot search engine.