Scientists are able to double the lifetime of a qubit in a quantum computer

A quantum computer qubit capable of operating… 1.8 milliseconds. Admittedly, put this way, it sounds pretty short. Nevertheless, this performance, achieved by a team of Yale University researchers, more or less doubles the typical lifetime of a qubit found in a working quantum computer.

Building a functional quantum computer… The idea is like the computing holy grail of the moment, and is gathering researchers from all over the world. If this is so intriguing, it is because such a system would offer computing power unmatched to date. It can, in all likelihood, perform tasks that conventional computers struggle to overcome in the blink of an eye. However, getting one of these machines up and running is a very difficult challenge.

By turning on a qubit for 1.8 milliseconds, Yale University scientists have made a major breakthrough. Their study was published in the journal Nature. To understand them better, let’s go back to the concept of computers and qubits and try to see why they are so difficult to control.

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A quantum computer is a machine that performs calculations based on the principles of quantum physics. That is, in short, the science concerned with the behavior of matter and light at the microscopic or atomic level. By actually studying how matter behaves at this scale, researchers have identified entirely new principles of physics. Among these principles is “quantum superposition,” which has become one of the keys to quantum computing. Specifically, “quantum superposition” is a principle that explains how something seemingly confusing to us somehow exists “in two states at once.”

When applied to computing, this principle is very useful: it makes it possible to use qubits to perform calculations. What is a qubit? To understand that, we have to go to the basic definition of computer. In a “classic” computer, the basic unit of information is the “bit”. It can be either “0” or “1”. It is these combinations of 0’s and 1’s that make up the codes that make computers possible to program. In a quantum computer, not bits, but “qubits” or quantum bits. This is where the principle of superposition comes into play. In fact, thanks to that, a qubit can somehow be both 0 and 1, and even in the states between the two: 01, 10, 11… Thanks to this superposition, a quantum computer can use such a large amount of computing power. . However, this strength can also be a weakness. In fact, qubits are very sensitive to external disturbances.

Most of the time, it’s actually atoms. Overall, the idea is to succeed in isolating the atoms that make up the qubits, while allowing them to interact with each other in good time, in order to perform quantum calculations. But despite all the precautions taken, errors can occur very quickly in quantum calculations. ” Quantum computers are inherently more sensitive to perturbations and therefore always require error correction mechanisms, otherwise errors propagate uncontrollably through the system and information is lost.
“, explains thus Press release from the University of Innsbruck Regarding error correction method.

Fix errors without creating more

So, not by eliminating these errors, but by managing them when they occur, the Yale University researchers were able to keep their qubits in working order for longer. The idea of ​​correcting errors made by quantum computers over time is not new, and recently researchers have been actively working on the subject. A so-called “redundancy” is one of the keys that allows this correction. In classical computing, redundancy is the idea of ​​having multiple copies of data: if an error occurs, the two results are different, so it is easy to conclude that there is an error.

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In quantum computing, it’s a bit more complicated. In fact, according to the “no cloning” theorem (another principle of quantum physics), it is impossible to “copy” quantum information. However, some scientists have already managed to develop sets of functions that allow the redundancy principle: Redundancy can be achieved by distributing logical quantum information across the complexity of many physical systems, for example many individual atoms. », for example, explained a group of Austrian researchers who worked on the subject in 2022.

Schematic of an experimental quantum error correction system. © Michel Devoret et al.

According to the Yale researchers, this is the first time such a principle has actually been used in real time during an experiment. And for good reason: introducing these entanglements into the system is an additional source of perturbation for the qubits, which can prove counterproductive. ”
For the first time, we show that making the system highly redundant and actively detecting and correcting quantum errors improves the resilience of quantum information. “, explains physicist Michael Devoret of Yale University In a press release. ” Our experience shows that quantum error correction is a real practical tool “.

If they were able to confirm this method, it was not really due to a capital innovation. ” This conclusion is not the result of an invention “, explains Volodymyr Sivak, a researcher at Google and formerly of Yale University. ” It’s actually a combination of different technologies that have been developed over the last few years and we’ve incorporated them into this test. “. Of course, there is still a long way to go when doubling the operating time of a qubit is seen to be equivalent to 1.8 milliseconds. However, it is not enough to disturb the enthusiasm of scientists. ” Our experience confirms a fundamental assumption of quantum computing, and it makes me very excited about the future of the field.
», Volodymyr Shivak rejoices.

Source: Nature

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