Single-Photon Emitter Pushing us Closer to Quantum Technology

To achieve quantum technology, we need to create a non-classical source of lights that can produce a single photon at a time and accomplish this on-demand. Researchers at EPFL have now developed one of these single-photon emitter that can operate at room temperature. Based on quantum dots grown on cost-efficient silicon substrates.

Designing non-classical light sources that can produce, on-demand, precisely one photon at a time. Is one of the primary requirements of quantum technologies. However, although the initial presentation of such a “single-photon emitter,” or SPE, goes back to the 1970s. Their reduced dependability and performance have stood in the way of any meaningfully practical usage.

Traditional sources of lights like incandescent light bulbs or LEDs radiate multitudes of photons. Simply put, their likelihood of radiating a solitary photon at a time is extremely low. Laser sources can discharge streams of single photons. However, not on-demand, which indicates that. In some cases, there will be no photons whatsoever produced when we desire them to.

So the primary benefit of SPEs is that they are capable of emitting a solitary photon. And doing so on-demand in more technical terms, their single-photon purity. Which they can preserve at an ultrafast timeframe. Therefore, for a light source to qualify as an SPE, it needs to include a single-photon purity over 50%; naturally. So the closer to 100%, the closer we will be to an optimal SPE.

Silicon substrates for SPEs

Scientists at EPFL, led by Professor Nicolas Grandjean. Have created “bright and pure” SPEs based on wide-bandgap semiconductor quantum dots grown on cost-effective silicon substrates.

Quantum dots comprise gallium nitride and aluminum nitride (GaN/AlN) and feature a single-photon purity of 95% at cryogenic temperatures while preserving exceptional durability at greater temperatures, with a purity of 83% at room temperature.

The SPE additionally presents photon emission rates up to 1 MHz while preserving a single-photon purity of over 50%. “Such brightness up to room temperature is possible because of the unique electronic properties of the GaN/AlN quantum dots, which preserves the single-photon purity due to the limited spectral overlap with competing neighboring electronic excitation,” states Stachurski, the Ph.D. student that explored these quantum systems.

“A very appealing feature of GaN/AlN quantum dots is that they belong to the III-nitride semiconductor family, namely that behind the solid‐state lighting revolution (blue and white LEDs) whose importance was recognized by the Nobel prize in Physics in 2014,” said the researchers.

“It is nowadays the second semiconductor family in terms of consumer market right after silicon that dominates the microelectronic industry. As such, III-nitrides benefit from a solid and mature technological platform, which makes them of high potential interest for the development of quantum applications.”

An essential future action will be to see if this system can discharge one photon and only one per laser pulse, which is crucial for establishing its performance.

“Since our electronic excitations exhibit room temperature lifetimes as short as 2 to 3 billionth of a second, single-photon rate of several tens of MHz could be within reach,” said the authors. “Combined with resonant laser excitation, which is known to significantly improve single-photon purity, our quantum-dot platform could be of interest for implementing room-temperature quantum key distribution based on a true SPE, as opposed to current commercial systems that run with attenuated laser sources.”

Originally published by: phys.org

Reference: Johann Stachurski et al, Single photon emission and recombination dynamics in self-assembled GaN/AlN quantum dots, Light: Science & Applications (2022). DOI: 10.1038/s41377-022-00799-4