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Pulsed laser delivers single photons on demand

16 Oct 2013

“Breakthrough” research project at University of Sydney progresses quantum computing technology.

A development in photonics that will help the creation of extremely compact optical chips just 100µm across and enable the delivery of one photon at a time, has been achieved by researchers at the University of Sydney, Australia.

"Our achievement has applications in the development of complex quantum technologies, including completely secure communications, quantum measurement, the simulation of biological and chemical systems and quantum computing,” said Dr Alex Clark, leader of the research team from the Australian Research Council Centre of Excellence for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS). Carried out at the University of Sydney's School of Physics, the research is published in Nature Communications.

The work of Clark’s team is part of a wider collaboration involving Australian and international universities, including Macquarie University, Australia, the University of St Andrews and the University of York, both UK , as well as the Australian Defence Science and Technology Organisation.

The importance of being able to develop a chip that can deliver one photon at a time at high rates is to provide scalability for a wide range of quantum technologies that are expected to enhance computing and communications infrastructure.

Scalability refers to the ability to use many photon sources in parallel to carry out complicated tasks. "It is easy for us to generate photons at high rates, but it's much harder to ensure they come out one by one because photons are gregarious by nature and love to bunch together," said Matthew Collins, a PhD student from CUDOS at the University of Sydney, who is lead author of the Nature Communications article.

"For that reason the quantum science community has been waiting for more than a decade for a compact optical chip that delivers exactly one photon at a time at very high rates."

Pulsed source

The creation of a single photon in an optical circuit has been possible for some years, but previous demonstrations have been difficult to implement and scale up or have been excessively noisy. This has limited single photon technologies to being either very slow or having a high probability of error. "We have now shown how multiple imperfect sources of photons on a single chip can be combined to produce a much higher quality source," said Dr Clark.

In the Sydney demonstration the photons are generated from a pulsed laser. Professor Ben Eggleton, CUDOS Director and co-author of the research, explained, "A key breakthrough for this research was the CUDOS development of photonic chips that effectively slow light. This makes single photon generation more likely, reducing energy demands and allowing extremely compact devices with lengths no longer than 200µm."

"The smaller these systems are, the more we can fit onto a chip, and the more we can fit onto a chip the more likely we are to guarantee a single photon when we want it," said co-author Associate Professor Michael Steel (Macquarie University), CUDOS' Science Leader for Quantum Integrated Photonics.

The team says that their next step is to integrate all the components of this scheme onto a single chip such that an on-demand “push button” single photon source can be deployed in future photonic quantum technologies. “This result presents a major milestone for CUDOS and for the field in general. We are especially pleased with the successful collaboration between CUDOS and DSTO,” said Professor Eggleton.

About the Author

Matthew Peach is a contributing editor to optics.org.

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