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The development of a single-photon source opens the door for effective quantum encryption


A novel high-purity single-photon source that can function at ambient temperature has been created by researchers. The source represents a significant step toward actual quantum technology applications, such as extremely secure communication based on quantum key distribution (QKD).

“We created an on-demand method to produce high purity photons in a scalable and portable device that functions at room temperature,” said Helen Zeng, a member of the research team from Australia’s University of Technology Sydney. “Our single-photon source has the potential to accelerate the development of realistic QKD systems and can be incorporated into a wide range of real-world quantum photonic applications.”

Zeng and colleagues from Australia’s University of Novel South Wales and Macquarie University report their new single-photon source in the Optica Publishing Group journal Optics Letters, demonstrating that it can create over 10 million single photons per second at ambient temperature. They also built the single-photon source into a completely portable device capable of performing QKD.

The novel single-photon source is the first to combine a 2D material known as hexagonal boron nitride with an optical component known as a hemispherical solid immersion lens, increasing the source’s efficiency by a factor of six.

At ambient temperature, single photons

QKD provides unbreakable encryption for data transfer by generating safe random keys for encrypting and decrypting data using the quantum characteristics of light. QKD systems need strong and brilliant light sources that produce light in the form of a string of single photons. However, most single-photon sources currently function poorly unless operated at cryogenic temperatures hundreds of degrees below zero, limiting their use.

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Although hexagonal boron nitride has previously been utilized to generate a room-temperature single-photon source, researchers have not been able to attain the efficiency required for real-world deployment. “The majority of technologies utilized to enhance hexagonal boron nitride single-photon sources focus on accurately placing the emitter or on nano-fabrication,” Zeng said. “As a result, the gadgets are complicated, difficult to scale, and tough to mass manufacture.”

Zeng and colleagues set out to develop a better solution by focusing the photons emitted by the single-photon emitter using a solid immersion lens, enabling for more photons to be detected. These lenses are commercially accessible and simple to make.

The researchers created a QKD system by combining their novel single-photon generator with a custom-built portable confocal microscope that can analyze single photons at ambient temperature. The single-photon source and confocal microscope are contained in a sturdy container measuring 500 × 500 millimeters and weighing roughly 10 kg. The package is also designed to handle vibration and stray light.

“Our simplified system is considerably simpler to operate and much smaller than typical optical table configurations, which sometimes take up whole laboratories,” Zeng said. “As a result, the system may be employed with a variety of quantum computing approaches. It might potentially be modified to operate with current telecoms infrastructure.”

Quantum cryptography demonstration

The novel single-photon source demonstrated a single-photon collection rate of 107 Hz while retaining outstanding purity, implying that each pulse had a low possibility of carrying more than one photon. It also shown outstanding stability over long periods of continuous operation. The researchers also proved the system’s capacity to conduct QKD under realistic settings, demonstrating that secured QKD with 20 MHz repetition rates is viable across long distances.

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After proving that their portable device can execute complicated quantum cryptography, the researchers want to evaluate its resilience, stability, and efficiency during encryption. They also want to utilize the new source to execute QKD in the field rather than in the lab. “We are now poised to translate these scientific discoveries in quantum 2D materials into technology-ready goods,” stated project leader Igor Aharonovich.

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