Single-Photon Source Could Help Secure Quantum Data

Researchers have found a way to generate very rapid single-photon light pulses, a discovery that could be used to secure quantum data transfer.

Single-photon pulses offer data security, because any attempt to intercept the data can be detected immediately. The challenge has been to produce pulses that are fast enough to transfer data in high volumes.

Electrically-tunable on-demand on-chip single photon source enabled by a strong Purcell effect. Courtesy of John O'Hara.

In a waveguide-coupled quantum dot-photonic crystal cavity system, researchers at the University of Sheffield placed a nanocrystal (i.e., a quantum dot) inside a cavity within a larger crystal (i.e., a semiconductor chip). When researchers shined a laser on the quantum dot it absorbed energy, which was emitted in the form of a photon. The laser light bounced around inside the cavity that held the quantum dot, speeding up photon production.

To separate the photons carrying data information from the laser light, researchers funneled the photons away from the cavity and into the semiconductor chip.

The Sheffield team’s technique is based on a phenomenon known as the Purcell effect.

Researchers demonstrated a photon emission rate about 50 times faster than would be possible without using their technique. Researchers say that, although their approach does not achieve the fastest photon light pulse yet developed, it has an advantage because the photons produced are all identical — an essential quality for many quantum computing applications.

On-chip single photon source array. Courtesy of John O'Hara.

Professor Mark Fox said that the use of photons to transmit data makes it possible to use the fundamental laws of physics to guarantee security.

“It’s impossible to measure or ‘read’ the particle in any way without changing its properties. Interfering with it would therefore spoil the data and sound an alarm," Fox said. "Our method also solves a problem that has puzzled scientists for about 20 years — how to use the Purcell effect to speed up photon production in an efficient way.

“This technology could be used within secure fiber optic telecoms systems, although it would be most useful initially in environments where security is paramount, including governments and national security headquarters,” Fox said.

The research was published in Nature Nanotechnology (doi:10.1038/s41565-018-0188-x).