Researchers from the American University of Rutgers (Rutgers University), IBM and a number of other scientific organizations have demonstrated a method that allows a quantum computer to independently monitor and correct errors while it is running, without stopping the calculation. It’s as if a car could change a flat tire while still driving along the highway at high speed.
Image source: eurekalert.org
Regular consumer computers work with bits—ones and zeros. Quantum machines use qubits, which can be in several states at the same time. This feature gives them enormous computing power to solve complex problems, such as creating new drugs. There’s a problem, however: qubits are incredibly finicky. The slightest noise, temperature change or electromagnetic waves can disrupt their state, turning precise calculations into meaningless chaos.
Until now, the main dream of engineers was to create a fault-tolerant quantum computer, that is, a device that is not afraid of failures. In a new work published in the journal Nature Physicsresearchers have shown that this is possible. They used one of the most powerful modern IBM Quantum Heron chips, containing 156 qubits, and involved a chain of 100 qubits, programming the system to alternate between two competing tasks.
Next, the system constantly “mixed” information between the qubits, deliberately creating disorder, and at the same time checked their state, restoring order. An analogy can be drawn with a room where objects are constantly changing places (chaos), and a special controller periodically places them in specified places (order).
As a result, it turned out that everything depends on the frequency of interventions. If there were few checks, chaos won. But when the system began checking and resetting qubits often enough, an unexpected effect occurred. The entire group of hundreds of qubits suddenly synchronously moved from a state of disorder to a stable, controlled state. Physicists call such a sharp jump a phase transition – the same term used to describe, for example, the transformation of water into ice.
«This was a real test of theory in practice.says Jedediah Pixley, a professor of physics at Rutgers and one of the authors of the study. — We had to do these checks not just once, but thousands of times in a row while the machine was running. And the hardware did the trick».
The story of this discovery began with a friendly dispute. In 2021, at his wife Pixley’s birthday party, his colleague Sriram Ganeshan argued that the strange quantum effect could be explained by the laws of ordinary physics. The loser had to treat the winner to blueberry ice cream. Pixley lost, but as a result, this dispute led to the creation of a new theory, which IBM specialists then helped test.
Now scientists are confident that they have found the key to controlling quantum chaos. Although the advent of full-fledged quantum computers capable of solving problems inaccessible to any other machine today is still a long way off, this experiment showed that the path to their creation is open.
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