Photograph of the silicon photonic chip. Copyright: Nature Physics

Optical chip protects quantum technology from errors

Tuesday 28 Sep 21
by Tobias Sydradal Lund


Yunhong Ding
Senior Researcher
DTU Electro
+45 45 25 65 87


Leif Katsuo Oxenløwe
Professor, Group Leader
DTU Electro
+45 45 25 37 84


Davide Bacco
Assistant Professor
DTU Electro
+45 45 25 38 77

New quantum photonic processor uses entanglement to protect itself from errors. The feat is published in Nature Physics.

In today’s digital infrastructure, the data-bits we use to send and process information can either be 0 or 1. Being able to correct possible errors that may occur in computations using these bits is a vital part of information processing and communication systems. But a quantum computer uses quantum bits, which can be a kind of mixture of 0 and 1, known as quantum super-position. This mixture is vital to their power - but it makes error correction far more complicated.

Researchers from DTU Fotonik have co-created the largest and most complex photonic quantum information processor to date – on a microchip. It uses single particles of light as its quantum bits, and demonstrates a variety of error-correction protocols with photonic quantum bits for the first time.

“We made a new optical microchip that processes quantum information in such a way that it can protect itself from errors using entanglement. We used a novel design to implement error correction schemes, and verified that they work effectively on our photonic platform,” says Jeremy Adcock, postdoc at DTU Fotonik and co-author of the Nature Physics paper.

Read more about entanglement 

This research is important because error correction is key to developing large-scale quantum computers, which will unlock new algorithms for e.g. large-scale chemical simulations and faster machine learning.

One key application could be drug discovery. Today’s computers cannot simulate large molecules and their interactions, for example when you introduce a drug molecule to the human body. In today’s computers, the size of classical computation grows exponentially with the size of the molecules involved. But for future quantum computers, more efficient algorithms are known, which do not blow up in computational cost.

This is just one of the problems that the quantum technology of the future promises to solve, by being able to process information beyond the fundamental limits of traditional computers. But to reach this goal, we have to go small: 

"Error correction is key to developing large-scale quantum computers"
Jeremy Adcock, postdoc at DTU Fotonik

“Chip-scale devices are an important step forward if quantum technology is going to be scaled up to show an advantage over classical computers. These systems will require millions of high-performance components operating at the fastest possible speeds, something that is only achieved with microchips and integrated circuits, which are made possible by the ultra-advanced semiconductor manufacturing industry,” says co-author Yunhong Ding, senior researcher at DTU Fotonik.

To realize quantum technology that goes beyond today’s powerful computers requires scaling this technology further. In particular, the photon (particles of light) sources on this chip are not efficient enough to build quantum technology of useful scale.

“At DTU, we are now working on increasing the efficiency of these sources - which currently have an efficiency of just 1 per cent - to near-unity. With such a source, it should be possible to build quantum photonic devices of vastly increased scale, and reap the benefits of quantum technology's native physical advantage over classical computers in processing, communicating, and acquiring information, says postdoc at DTU Fotonik, Jeremy Adcock. He continues:

“With more efficient photon sources, we will be able to build more and different resource states, which will enable larger and more complex computations, as well as unlimited range secure quantum communications.”

Read the paper in Nature Physics

The transfer of knowledge – and researchers

The Nature Physics paper is the result of a collaboration between the University of Bristol, DTU and Peking University.

The University of Bristol designed the functionality and schematic of the chip, designed and performed the experiments on the chip.

Lead author of the paper is Caterina Vigliar from the University of Bristol. In 2022, she will transfer to DTU Fotonik.

DTU Fotonik did the photonic layout (exact placement of components on the silicon chip) and fabricated the chip using our cutting-edge components and fabrication facilities.

Jeremy Adcock, who is cited in this article as a postdoc at DTU Fotonik, actually started the project while working at the University of Bristol.

Jianwei Wang from Peking University also designed the chip and initiated the project while he was at the University of Bristol.

This article is edited by Jeremy Adcock and Tobias Sydradal

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