A new high-purity single-photon source that can operate at room temperature has been developed by researchers. The source is a significant step toward practical quantum technology applications, such as highly secure communication based on quantum key distribution (QKD).
“We developed an on-demand method to generate photons with high purity in a scalable and portable system that operates at room temperature,” said Helen Zeng, a member of the Australian research team. “Our single-photon source has the potential to accelerate the development of practical QKD systems and can be integrated into a wide range of real-world quantum photonic applications.”
Zeng and colleagues from Australia’s University of New South Wales and Macquarie University describe their new single-photon source in the Optica Publishing Group journal Optics Letters, demonstrating that it can produce over ten million single photons per second at room temperature. They also built the single-photon source into a fully portable device capable of performing QKD.
The new 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.
We developed an on-demand method to generate photons with high purity in a scalable and portable system that operates at room temperature. Our single-photon source has the potential to accelerate the development of practical QKD systems and can be integrated into a wide range of real-world quantum photonic applications.
Helen Zeng
Single photons at room temperature
By utilizing the quantum properties of light to generate secure random keys for encrypting and decrypting data, QKD provides impenetrable encryption for data communication. QKD systems necessitate strong and bright light sources that emit light in the form of a string of single photons. Most single-photon sources today, however, do not perform well unless operated at cryogenic temperatures hundreds of degrees below zero, limiting their practicality.
Although hexagonal boron nitride has previously been used to create a single-photon source that operates at room temperature, researchers were unable to achieve the efficiency required for real-world application until now. “Most approaches to improving hexagonal boron nitride single-photon sources rely on precisely positioning the emitter or using nanofabrication,” Zeng explained. “This makes the devices complex, difficult to scale and not easy to mass produce.”
Zeng and colleagues set out to create a better solution by using a solid immersion lens to focus the photons coming from the single-photon emitter, allowing more photons to be detected. These lenses are commercially available and easy to fabricate.
The researchers created a QKD system by combining their new single-photon source with a custom-built portable confocal microscope that can measure single photons at room temperature. The single-photon source and confocal microscope are housed in a sturdy package measuring 500 x 500 millimeters and weighing around 10 kilograms. The package is also designed to handle vibration and stray light.
“Our streamlined device is much easier to use and much smaller than traditional optical table setups, which frequently take up entire labs,” Zeng explained. “As a result, the system can be used with a variety of quantum computing schemes. It could also be modified to function with existing telecommunications infrastructure.”
Demonstrating quantum cryptography
Tests of the new single-photon source revealed that it could achieve a single-photon collection rate of 107 Hz while maintaining excellent purity – that is, each pulse had a low probability of containing more than one photon. It also demonstrated exceptional stability over many hours of continuous operation. The researchers also demonstrated the system’s ability to perform QKD under realistic conditions, demonstrating that secured QKD with 20 MHz repetition rates would be feasible over several kilometers.
Now that the researchers have established proof that their portable device can perform complex quantum cryptography, they intend to test its robustness, stability, and efficiency during encryption. They also intend to use the new source to perform QKD in real-world settings rather than in the lab. “We are now ready to translate these scientific advances in quantum 2D materials into technology-ready products,” said project leader Igor Aharonovich.
