Quantum computers are gaining pace. They promise to provide exponen­tially more computing power for certain very tricky problems. They do this by exploiting the peculiar behaviour of quantum particles, such as photons of light.

However, quantum states of particles are very fragile. The quantum bits, or qubits, that underpin quantum computing pick up errors very easily and are damaged by the environ­ment of the everyday world. Fortunately, we know in principle how to correct for these errors. Quantum error correc­ting codes are a method to protect, or to nurture, qubits, by embedding them in a more robust entangled state of many particles. Now, a team led by researchers at Bristol's Quantum Engineering and Techno­logy Labora­tories (QETLabs) has demons­trated this using a quantum photonic chip.

The team showed how large states of entangled photons can contain indi­vidual logical qubits and protect them from the harmful effects of the classical world. The Bristol-led team included researchers from DTU in Copenhagen who fabri­cated the chip. Caterina Vigliar said: “The chip is really versatile. It can be programmed to deliver different kinds of entangled states called graphs. Each graph protects logical quantum bits of infor­mation from different environ­mental effects.”

Anthony Laing, co-Director of QETLabs, said: “Finding ways to effi­ciently deliver large numbers of error pro­tected qubits is key to one day delivering quantum computers.” (Source: U. Bristol)

Reference: C. Vigliar et al.: Error-protected qubits in a silicon photonic chip, Nat. Phys. 17, 1137 (2021); DOI: 10.1038/s41567-021-01333-w

 Link: Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK