August 13, 2015

Reprogrammable optic chip has complete flexibility in processing of photons and is a pathway to quantum computing

Researchers from the University of Bristol in the UK and Nippon Telegraph and Telephone (NTT) in Japan, have 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

silicon based quantum optics lab-on-a-chip.

Journal Science - Universal linear optics

Science - The on-ramp to the all-optical quantum information processing highway

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.


Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons, and their measurement with a 12-single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with an average fidelity of 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies.

Editors Summary Complex quantum optical circuitry

Encoding and manipulating information in the states of single photons provides a potential platform for quantum computing and communication. Carolan et al. developed a reconfigurable integrated waveguide device fabricated in a glass chip (see the Perspective by Rohde and Dowling). The device allowed for universal linear optics transformations on six wave-guides using 15 integrated Mach-Zehnder interferometers, each of which was individually programmable. Functional performance in a number of applications in optics and quantum optics demonstrates the versatility of the device's reprogrammable architecture.

Abstract - The on-ramp to the all-optical quantum information processing highway

Since the first formulations of quantum mechanics in the early 20th century, it became clear that the enormous complexity of quantum-mechanical systems presented intractable computational problems. Richard Feynman was the first to turn this problem on its head. He asked whether we could exploit this quantum complexity to construct a computer based on these same quantum mechanical principles, offering exponential algorithmic improvements, and whether such a computer could efficiently simulate quantum systems that our classical computers are unable to simulate. This challenge initiated the field of quantum computing and is today a major field of research in the physics and computer science communities. One hurdle has been to construct devices that match the flexible programmability of classical computers. On page 711 of this issue, Carolan et al. (1) present a step in that direction, a fully reconfigurable optical waveguide circuit that can be programmed to implement arbitrary linear optics transformations on up to six optical modes.

SOURCES - University of Bristol, Eurekalert, Journal Science

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