Researchers have developed a new source of high-purity single photons that can operate at room temperature. The source is an important step towards practical applications of quantum technology, such as highly secure communication based on quantum key distribution (QKD).
“We have developed an on-demand way to generate high-purity photons in a scalable, portable system that operates at room temperature,” said research team member Helen Zeng from the University of Technology Sydney in Australia. “Our single-photon source could advance the development of practical QKD systems and can be integrated into a variety of real-world quantum photonic applications.”
In the magazine Optica Publishing Group Optical letters, Zeng and colleagues from Australia’s University of New South Wales and Macquarie University describe their new single photon source and show that it can produce more than ten million single photons per second at room temperature. They also integrated the single-photon source into a fully portable device capable of performing QKD.
The new single-photon source uniquely combines a 2D material called hexagonal boron nitride with an optical component called a hemispherical solid immersion lens, which increases the source’s efficiency sixfold.
Single photons at room temperature
QKD offers impenetrable encryption for data communication by using the quantum properties of light to generate secure random keys to encrypt and decrypt data. QKD systems require robust, bright sources that emit light as a string of single photons. However, most single-photon sources today do not perform well unless they operate at cryogenic temperatures hundreds of degrees below freezing, which limits their usefulness.
Although hexagonal boron nitride has already been used to create a single-photon source operating at room temperature, until now researchers had not been able to achieve the efficiency needed for worldwide application. real. “Most of the approaches used to improve single-photon sources of hexagonal boron nitride rely on precise positioning of the emitter or the use of nano-fabrication,” Zeng said. “This makes devices complex, difficult to scale, and difficult to mass-produce.”
Zeng and his colleagues set out to create a better solution by using a solid immersion lens to focus photons from the single-photon emitter, allowing more photons to be detected. These lenses are commercially available and easy to manufacture.
The researchers combined their new single-photon source with a custom-built, portable confocal microscope that can measure single photons at room temperature, creating a system capable of performing QKD. The single-photon source and confocal microscope are housed in a rugged case that measures only 500 x 500 millimeters and weighs about 10 kilograms. The case is also designed to cope with vibration and stray light.
“Our simplified device is easier to use and much smaller than traditional optical table setups, which often take up entire labs,” Zeng said. “This allows the system to be used with a range of quantum computing schemes. It could also be adapted to work with existing telecommunications infrastructure.”
Demonstration of quantum cryptography
Tests of the new single photon source showed that it could achieve a single photon collection rate of 107 Hz while maintaining excellent purity, meaning that each pulse had a low probability of containing more than one photon. It also showed exceptional stability over many hours of continuous operation. The researchers also demonstrated the system’s ability to perform QKD under realistic conditions, showing that secure QKD with 20 MHz repetition rates would be feasible over several kilometres.
Now that the researchers have established proof that their wearable device can perform complex quantum cryptography, they plan to perform further tests on its robustness, stability and efficiency during encryption. They also plan to use the new source to perform QKD under real-world conditions, rather than inside the lab. “We are now ready to turn these scientific advances in quantum 2D materials into technology-ready products,” said Igor Aharonovich, who led the project.
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