Prolonged control of cat qubits: a breakthrough in quantum computing published in “Nature”

Quantum tomography protocol based on the holonomic gate.

The QUANTIC team, comprising researchers from the Laboratoire de Physique de l’École Normale Supérieure (LPENS), Mines Paris – PSL and the Institut National de Recherche en Sciences et Technologies du Numérique (INRIA), in partnership with start-up Alice & Bob, has succeeded in performing quantum operations on a highly stable qubit. The breakthrough lies in the fact that the bit-flip time measured on this qubit exceeds 10 seconds. This breakthrough paves the way for more powerful and stable quantum calculations, with applications in fields ranging from cryptography to molecular modeling and artificial intelligence.

The qubit

In quantum computing, the “qubit” is the equivalent of the “bit” in classical computing, a “bit” representing the most elementary unit of data, which can be either a 0 or a 1. A bit flip, or bit-flip, therefore refers to the involuntary change of a bit’s value from 0 to 1 or vice versa. This seemingly innocuous event can have far-reaching implications, particularly in systems where precision is paramount.

In quantum computing, qubits are therefore the basic units of information, and their stability is crucial to the proper functioning of quantum systems. However, qubits are notoriously sensitive to environmental interference, leading to errors in calculations. To overcome this problem, scientists have developed protected qubits, of which the cat qubit is a particularly promising example.

Phase-flip and bit-flip time measurements for cat qubits.

The cat qubit

The “cat qubit” owes its curious name to its unique quantum behavior. Unlike conventional qubits, which are often prone to computational errors, cat qubits are intrinsically protected against certain forms of error. Indeed, a cat qubit is the encoding of a qubit in a quantum state composed of two diametrically opposed conditions at the same time, thus putting it in the quantum state of Schrödinger’s famous cat. The use of cat qubits makes it possible to limit the error rate inherent in conventional quantum computers, offering a promising solution for the quantum technologies of the future.

Quantum control of a cat qubit with bit-flip times exceeding ten seconds

In this study, the researchers took the decisive step of controlling a cat qubit for more than 10 seconds. This achievement is based on the use of two-photon dissipation, a phenomenon that stabilizes quantum states while enabling their manipulation. Two-photon dissipation involves the simultaneous absorption of two photons of the same or different frequencies, with the aim of exciting a molecule in a given state (usually the ground state) to a higher-energy electronic state. By controlling the phase of quantum superpositions without compromising error protection, the researchers have demonstrated the viability of this approach for future quantum technologies.

This breakthrough heralds the development of numerous research topics and applications in the field of quantum computing. By enabling extended bit-flip times and precise qubit control, this breakthrough could lead to the creation of more reliable, high-performance quantum systems. From cryptography to the simulation of molecules and the optimization of artificial intelligence, the potential applications of this technology are vast and revolutionary.

Find out more:

Article “Quantum control of a cat qubit with bit-flip times exceeding ten seconds” – Nature (2024).

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