Fibonacci boost for quantum computer error correction

Technology News | July 21, 2022

By Nick Flaherty

Researchers in North America have discovered a way to make qubits in quantum computers more stable with a technique they call a ‘second dimension of time’.

By shining a quasiperiodic laser pulse sequence inspired by the Fibonacci numbers at atoms inside a quantum computer, the researchers in the US and Canada have dramatically improved the stability of trapped ion qubits, which will boost the performance of error- corrected quantum computers.

Rather than a second dimension in time, the work demonstrates an emergent dynamical symmetry-protected topological phase in an array of ten Ytterbium trapped ion qubits in Quantinuum’s System Model H1 quantum processor. This phase shows edge qubits that are dynamically protected from control errors, cross-talk and stray fields. Crucially, this edge protection relies purely on emergent dynamical symmetries that are absolutely stable to generic coherent perturbations and is a result of the quasiperiodically driven approach.

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This addresses the issue of error correction.

“Even if you keep all the atoms under tight control, they can lose their ‘quantumness’ by talking to their environment, heating up or interacting with things in ways you didn’t plan,” said Philipp Dumitrescu, who worked on the project as a research fellow at the Flatiron Institute’s Centre for Computational Quantum Physics in New York City, along with researchers in Texas, Vancouver and Massachusetts. “In practice, experimental devices have many sources of error that can degrade coherence after just a few laser pulses.”

The quasi-periodic laser-pulse is based on the Fibonacci sequence, where each part of the sequence is the sum of the two previous parts (A, AB, ABA, ABAAB, ABAABABA, etc.). This arrangement is ordered without repeating.

Using Quantinuum’s quantum computer, the researchers pulsed the laser light at the computer’s qubits both periodically and using the sequence based on the Fibonacci numbers. The focus was on the qubits at either end of the 10-atom array. In the periodic test, the edge qubits stayed coherent for around 1.5 seconds. With the quasi-periodic pattern, the qubits stayed quantum for the entire length of the experiment, about 5.5 seconds.

“With this quasi-periodic sequence, there’s a complicated evolution that cancels out all the errors that live on the edge,” he said. “Because of that, the edge stays quantum-mechanically coherent much, much longer than you’d expect.”

Some reports have called this emergent dynamical symmetry-protected topological phase a ‘second dimension’ of time.

Link to the scientific paper