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New optical chip lights up the race for quantum computer

“The silicon based quantum optics lab-on-a-chip”

The Bristol team from left to right: Chris Sparrow, Chris Harrold, Jacques Carolan, Dr Anthony Laing.

Press release issued: 14 August 2015

The microprocessor inside a computer is a single multipurpose chip that has revolutionised people’s life, allowing them to use one machine to surf the web, check emails and keep track of finances. Now, researchers from the University of Bristol in the UK and Nippon Telegraph and Telephone (NTT) in Japan, have pulled off the same feat for light in the quantum world by developing an optical chip that can process photons in an infinite number of ways.

It’s a major step forward in creating a quantum computer to solve problems such as designing new drugs, superfast database searches, and performing otherwise intractable mathematics that aren’t possible for super computers. 

The fully reprogrammable chip brings together a multitude of existing quantum experiments and can realise a plethora of future protocols that have not even been conceived yet, marking a new era of research for quantum scientists and engineers at the cutting edge of quantum technologies.  The work is published in the journal Science on 14 August.

Since before Newton held a prism to a ray of sunlight and saw a spectrum of colour, scientists have understood nature through the behaviour of light.  In the modern age of research, scientists are striving to understand nature at the quantum level and to engineer and control quantum states of light and matter. 

A major barrier in testing new theories for quantum science and quantum computing is the time and resources needed to build new experiments, which are typically extremely demanding due to the notoriously fragile nature of quantum systems.

 This result shows a step change for experiments with photons, and what the future looks like for quantum technologies.

Dr Anthony Laing, who led the project, said: “A whole field of research has essentially been put onto a single optical chip that is easily controlled. The implications of the work go beyond the huge resource savings.  Now anybody can run their own experiments with photons, much like they operate any other piece of software on a computer.  They no longer need to convince a physicist to devote many months of their life to painstakingly build and conduct a new experiment.”

The team demonstrated the chip’s unique capabilities by re-programming it to rapidly perform a number of different experiments, each of which would previously have taken many months to build.

Bristol PhD student Jacques Carolan, one of the researchers, added: “Once we wrote the code for each circuit, it took seconds to re-programme the chip, and milliseconds for the chip to switch to the new experiment. We carried out a year’s worth of experiments in a matter of hours. What we’re really excited about is using these chips to discover new science that we haven’t even thought of yet.”

The device was made possible because the world’s leading quantum photonics group teamed up with Nippon Telegraph and Telephone (NTT), the world’s leading telecommunications company. 

Professor Jeremy O'Brien, Director of the Centre for Quantum Photonics at Bristol University, explained: “Over the last decade, we have established an ecosystem for photonic quantum technologies, allowing the best minds in quantum information science to hook up with established research and engineering expertise in the telecommunications industry. It’s a model that we need to encourage if we are to realise our vision for a quantum computer.”

The University of Bristol's pioneering ‘Quantum in the Cloud’ is the first and only service to make a quantum processor publicly accessible and plans to add more chips like this one to the service so others can discover the quantum world for themselves. 

The Article has been published in the journal Science : Universal Linear Optics, Carolan et al, 14th August 2015

Further information

Published in the journal Science : Universal Linear Optics, Carolan et al, 14th August 2015


Jacques Carolan is PhD student at the Centre for Quantum Photonics at the University of Bristol.

Dr Anthony Laing is a research fellow at the Centre for Quantum Photonics at the University of Bristol.  His interests include theory and experiments in quantum computation and simulations, and quantum communication.

Professor Jeremy O’Brien is Director of the Centre for Quantum Photonics at the University of Bristol. He holds a Royal Academy of Engineering Chair in Emerging Technologies. His work is focused on the development of photonic quantum technologies.

The Centre for Quantum Photonics is part of the Bristol Quantum Engineering Technology (QET) Labs.

The room within which this chip resides is what one would expect from a state-of the art quantum optics laboratory: There is a heavy optical bench onto which components are bolted down, stabilising  the path of single photons by distances equal to fractions of a human hair; lights are turned down low and the room hums with the operation of machinery.  But in amongst all this is a chip that would look perfectly at home inside your average desktop computer.  A single optical device made with glass and silicon via commercial fabrication techniques; sits neatly packaged, with electrical and optical connectors, receiving electrical commands and single particles of light.  “This chip has been fabricated and packaged up, so that we never need to re-align it” explained University of Bristol PhD student, Jacques Carolan. “It sits there, and we can perform literally 1000s of different experiments in a single day—this was simply unthinkable a few years ago”.

A quantum computer based on photons is known to have major components that live in a group known as the Unitaries. What’s been known, but untested for some time, is a recipe to build an optical device that can build any unitary. We have been able to implement this recipe with our chip: It has 6 optical inputs and 6 optical outputs, which means it can perform absolutely any unitary of size 6. What’s even more exciting is that this is entirely scalable and our demonstration opens up the possibility of being able to implement this on larger and larger devices.” This complete flexibility in what is possible is termed ‘universality’ and is a critical step in the design of a universal quantum computer – albeit at modest scale.  The Bristol team have made great strides towards designing and building a large scale universal quantum computer and are currently working on the engineering challenges that will ultimately result in such a device.