Generates 10 million+ single photons per second, increasing the efficiency of single photon sources by 6 times

In a paper published March 23 in Optics Letters [1], researchers at the University of Technology Sydney, the University of New South Wales, and Macquarie University in Australia have developed a new high-purity single-photon source and can operate at room temperature. The source is an important step toward practical applications of quantum technology, such as highly secure communications based on quantum key distribution (QKD).

The new single-photon source uniquely combines a two-dimensional material called hexagonal boron nitride with an optical component called a hemispherical solid immersion lens, which increases the efficiency of the light source by a factor of six, i.e. at room temperature More than 10 million single photons can be generated every second. They also integrated the single-photon source into a completely portable device that can perform QKD.

Lead author of the paper, Helen Zeng from UTS, said: "We have developed a method to generate high-purity photons on demand in a scalable and portable system that operates at room temperature. Our single photon The source can advance the development of practical QKD systems that can be integrated into a variety of real-world quantum photonic applications."

Single-photon source at room temperature

QKD utilizes the quantum properties of light to generate secure random keys for encrypting and decrypting data, providing airtight encryption for data communications. QKD systems require robust, bright light sources that emit light as a train of single photons.

However, most single-photon sources today only work well at low temperatures in excess of -200°C, otherwise their performance is poor, which limits their practicality.

In the traditional BB84 quantum key distribution protocol, a single photon source generates the single photon required for encoding.

While hexagonal boron nitride has previously been used to make single-photon sources that operate at room temperature, until now, researchers have been unable to achieve the efficiencies needed for real-world applications. "Most methods for improving hexagonal boron nitride single-photon sources rely on precisely positioning the emitter or using nanofabrication, which makes the device complex and difficult to scale up and mass-produce," Zeng said.

Zeng and colleagues set out to create a better solution, using a solid immersion lens to focus photons from single-photon emitters, allowing more photons to be detected. These lenses are commercially available and easy to manufacture.

The researchers combined the new single-photon source with a custom-built portable confocal microscope that can measure single photons at room temperature, creating a system that can perform QKD. The single photon source and confocal microscope are housed in a robust package measuring only 500 x 500 mm and weighing approximately 10 kg. The package can also handle vibration and stray light.

The single photon source and confocal microscope are housed in a robust package that is only 500 x 500 mm and weighs about 10 kg.

"Our streamlined device is easier to use and much smaller than traditional optical bench setups, which typically take up an entire lab, allowing the system to be used with a range of quantum computing schemes," Zeng said. It also Adapt to existing telecommunications infrastructure."

Demonstrate quantum cryptography

The researchers' tests of the new single-photon source showed that it can achieve a single-photon collection rate of 107 Hz while maintaining good purity -- meaning that the probability of each pulse containing more than one photon is low. It also exhibits exceptional stability over many hours of continuous operation. The researchers also demonstrated the system's ability to perform QKD under realistic conditions, showing that safe QKD at a repetition rate of 20 MHz is feasible over a range of several kilometers.

Now that the researchers have demonstrated that their portable device can perform complex quantum cryptography, they plan to further test its robustness, stability and efficiency during encryption, using a new source in real-world rather than laboratory conditions Execute QKD below. "We are now ready to translate these scientific advances in quantum two-dimensional materials into technologically mature products," said Igor Aharonovich, who led the project.

Link:

[1] https://opg.optica.org/ol/abstract.cfm?uri=ol-47-7-1673

[2] https://phys.org/news/2022-03-single-photon-source-paves-quantum-encryption.html