“cat qubit” resists errors in record time

Researchers have created a quantum bit known as a “cat qubit” that can withstand errors inherent in quantum computers for more than 10 seconds – or 10,000 times longer than previously tested. This unprecedented level of control will reduce the number of qubits needed for error correction by almost 10 times, paving the way for reliable and practical quantum computers.

Unlike bits in classical computers, which process information in binary form (0 or 1), qubits can take the form of any combination of the two at the same time (quantum superposition). This aspect logically allows quantum computers to greatly exceed the processing power of conventional computers, allowing them to solve problems that are usually considered intractable. However, their capabilities have so far been poorly demonstrated due to their vulnerability to computational errors and the size limitations of current quantum systems.

Indeed, qubits are extremely fragile and difficult to stabilize. Any external “noise” can lead to their collapse and loss of their quantum nature, thereby triggering the process of decoherence. When decoherence occurs before the task (algorithm) completes execution, the result becomes unreadable because the information stored in the qubit is lost. Decoherence somehow affects the superposition state of the qubit and thereby disrupts its ability to process information.

Thus, decoherence leads to errors (known as “bit flipping”) in quantum computing systems. Although a classical computer is very reliable in calculations, the best quantum versions will allow an error of 1000 operations. Moreover, the difficulty of maintaining coherence increases as the number of qubits increases, so the most advanced quantum processors have difficulty exceeding 100 qubits. However, a device suitable for practical use would require several thousand qubits.

To solve this problem, about 10 years ago, physicists proposed a new type of qubit called a “cat qubit.” Inspired by the famous “Schrödinger’s cat experiment”, this type of qubit will be able to self-correct its errors, causing a quantum superposition similar to the state of the famous cat in the box (the cat is considered potentially dead and dead). alive until his box is opened).

However, experimental demonstration of this ability (self-correction) poses a serious challenge. In a new study published in the journal Naturea team from Ecole Normale Supérieure (France) and French quantum computing startup Alice & Bob, describes the first cat qubit that can withstand errors of more than 10 seconds – or 10,000 times longer than those obtained in previous experiments.

10,000 times better error tolerance

To create the cat qubit, the researchers used a superconducting resonator (or oscillator). It’s a chip riddled with tiny superconducting circuits and a light-catching hole in the middle. Once inside the hole, the light can vibrate in two different ways. Instead of making it oscillate in one direction, the team allows it to move in both directions at once, creating a state of quantum superposition similar to that of Schrödinger’s cat thought experiment—hence the name.

However, for several years, researchers were still detecting bit changes every few milliseconds, despite the successful creation of the cat qubit. They recently realized that the problem was in the way they measured the state of the produced qubit. By revising their protocol, they were able to control the cat qubit without flipping for 10 seconds.

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Thus, this first functional cat qubit could pave the way for the development of reliable and useful quantum computers. Indeed, such computers could allocate more cat qubits for computation, rather than reserving them solely for error correction. According to the study’s experts, this new type of qubit will reduce the number of qubits needed for error correction by almost 10 times compared to current devices using superconducting circuits.

However, it is important to note that bit flips are not the only types of errors that cat qubits must correct. Indeed, their resistance to change may make them more vulnerable to other types of errors. Although the results obtained by the researchers in this study represent significant progress, many challenges remain to be addressed before real-world applications can be considered.

Source: Nature