French quantum computing startup Alice & Bob SAS today announced a significant advancement in cat qubit technology to reduce errors in quantum computers.

Named after the Schrödinger’s cat thought experiment, cat qubits are a type of superconducting qubits developed by Alice & Bob to make quantum computers more robust and resistant to errors. Cat qubits address the issue where traditional qubits, which can be in a state of 0, 1 or a “superposition” of both, are sensitive to their environment. Any disturbance can cause a qubit to “decohere” and lose its superposition state, leading to computational errors.

The new advancement in quantum error correction involves “squeezing” cat qubits, compressing their quantum state in a way that optimizes error suppression. The squeezing process has been demonstrated by Alice & Bob to deliver 160 times better bit-flip error rates than standard cat qubits on the same chip.

The squeezing process works by compressing the quantum state of a cat qubit, increasing the separation between its basis states to enhance error suppression. The method allows for improved bit-flip protection without the need to inject additional photons, which could otherwise introduce phase-flip errors.

Making a cat qubit larger by adding photons strengthens its resistance to bit-flip errors, but it also raises the risk of phase-flip errors when photons escape the system. Squeezing provides an alternative approach, optimizing the balance between these error types to ensure more stable quantum operations, the company says.

“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.”

For quantum algorithms to run successfully, all errors must be corrected throughout their execution. With squeezing minimizing phase-flip errors while maintaining low bit-flip rates, error correction becomes more efficient, enabling practical applications in areas such as chemistry and materials science.

The results, on paper at least, are impressive. In an 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 with 160 times fewer bit-flip errors and 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 Raphael Lescanne, co-founder and chief technology officer of Alice & Bob.

Squeezing also resulted in a 50% reduction in Z-gate infidelity — errors in the application of the Z-gate (a quantum phase-flip operation) that can degrade the accuracy of quantum computations. Alice & Bob expect two-qubit gates to similarly gain from these performance enhancements.

Ultimately, the enhancement helps with scaling toward 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, the company says.

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