Paris – March 11, 2025 – Fault-tolerant quantum computing company Alice & Bob today announced what they said is a significant advancement in cat qubit technology to reduce errors in quantum computers.
Cat qubits are a relatively recent innovation in superconducting qubit designs that Alice & Bob has been pioneering since 2020 and that recently made headlines thanks to AWS’ (Amazon Web Services) release of their first quantum chip, Ocelot, which also uses cat qubits to run quantum error correction.
By “squeezing” cat qubits—compressing the quantum state in a way that optimizes error suppression—Alice & Bob has demonstrated 160x better bit-flip error rates than standard cats on the same chip as demonstrated in its latest paper preprint. This significant improvement reinforces the relevance of cat qubits as a scalable solution for fault-tolerant quantum computers.
“Standard cats, those that are not squeezed, offer significant advantages, but their bit-flip improvements come at a cost on the phase-flip error channel,” said Raphael Lescanne, CTO and co-founder of Alice & Bob. “By squeezing our cats, we can enhance bit-flip protection without compromising phase-flip performance, making the correction of phase-flips more manageable in the long run.”
These bit-flip errors, along with phase-flip errors, are major obstacles standing in the way of useful quantum computing at scale. Many current solutions to quantum error correction are highly resource intensive and require significant hardware overhead. Cat qubits, however, make bit-flips so rare that error correction is reduced from a 2D problem (scaling quadratically) to a 1D problem (scaling linearly), enabling simpler error correction with dramatically fewer resources.
Making a cat qubit larger makes it robust against bit-flip errors. However, injecting a higher number of photons, which increases the size of a cat qubit, also increases the possibility of one of them escaping the system, resulting in a phase-flip error. Because of this tradeoff between bit-flip and phase-flip errors, the number of photons injected must be optimized to reduce both error types as much as possible.
In the cat qubit platform, the separation of the two basis states of a cat qubit ensures robust protection against bit-flip errors. While injecting photons is the primary method used to separate these states, squeezing offers an additional solution. By compressing the quantum state to minimize overlap and increase separation between states, squeezing cat qubits can improve error suppression and correction without injecting additional photons.
“The goal with squeezing is to make every photon count,” said Anil Murani senior researcher and Fellow Expert at Alice & Bob. “Our latest innovation makes our cat qubits more well-rounded and squeezes even greater protection out of them, which will ease the requirements on error correction.”
The successful execution of quantum algorithms requires that all errors are corrected for the duration of the run time. To intrinsically reduce bit-flips by design, the number of photons in the cat qubit can be increased arbitrarily at the expense of phase-flips, which are left to be corrected by error correction codes. Thanks to squeezing, phase-flip errors are now minimized given the same bit-flip error rates, so phase-flips can be addressed by error correction more easily. This ensures that both error types are corrected, a key requirement for enabling useful applications in chemistry, materials science and more.
In the experimental demonstration, an average of 4.9 photons in cat qubits without squeezing showed a bit-flip lifetime of 138 milliseconds – a figure that already exceeds the best superconducting platforms. With squeezing, already at 4.1 photons, the bit-flip lifetime jumped to 22 seconds, 160x fewer bit-flip errors, with no increase in phase-flips.
“By enhancing qubit performance without modifying circuit design, this simple yet effective technique positions our platform to deliver high-fidelity logical qubits at an even smaller fraction of the cost of alternative approaches,” said Lescanne.
Squeezing also resulted in a 50% reduction in Z-gate infidelity, and Alice & Bob expects two qubit gates to similarly gain from these performance enhancements.
As Alice & Bob’s platform scales to universal fault-tolerant quantum computing, squeezing cat qubits will reduce the costs required for quantum error correction to solve currently intractable problems across many industries.
