Entangled photon pairs generated by quantum light sources can be used for quantum computing and cryptography

A new device composed of semiconductor rings generates pairs of entangled photons, which can be used in photon quantum processors.

Quantum light sources generate entangled photon pairs, which can be used in quantum computing and cryptography. A new experiment has demonstrated a quantum light source made from semiconductor gallium nitride. This material provides a multifunctional platform for device manufacturing, previously used in on-chip lasers, detectors, and waveguides. Combined with these other optical components, new quantum light sources have opened up the potential to construct complex quantum circuits on a single chip.

Quantum optics is a rapidly developing field, where many experiments use photons to carry quantum information and perform quantum calculations. However, in order for optical systems to compete with other quantum information technologies, quantum optical devices need to be reduced from desktop size to microchip size. An important step in this transformation is the development of quantum light generation on semiconductor chips. Several research teams have accomplished this feat using materials such as aluminum gallium arsenide, indium phosphide, and silicon carbide. However, in addition to quantum light sources, fully integrated photonic circuits also require a series of components.

In order to ultimately establish such a complete circuit, Zhou Qiang and his colleagues from the University of Electronic Science and Technology of China turned their attention to gallium nitride. This material is renowned for its application in the first batch of blue LEDs, a development recognized by the 2014 Nobel Prize in Physics. Recent studies have shown that gallium nitride grown on sapphire can be used for many quantum optical functions, such as lasers, optical filtering, and single photon detection. "The gallium nitride platform provides broad prospects for advancing photonic quantum chips in the near future," Zhou said.

In order to manufacture gallium nitride quantum light sources, Zhou and his colleagues grew a layer of material thin film on a sapphire substrate, and then etched a diameter of 120 in the thin film μ The ring of m. In this structure, photons can propagate in a loop, similar to the way sound waves propagate on the curved walls of a whispering gallery. Next to the ring, researchers etched a waveguide for transmitting infrared laser. The coupling between two optical elements allows some laser photons to enter the ring from the waveguide.

In the experiment, the detector recorded the spectrum of the waveguide output light, revealing the discrete decrease of multiple wavelengths. These decreases correspond to resonance in the ring - when the wavelength of a specific photon fits an integer within the circumference of the ring. Resonant photons in waveguides can enter the ring and be trapped inside.

However, due to an effect called four wave mixing, resonant photon pairs entering the ring sometimes annihilate, causing a new pair of resonant photons to be generated and leave through the waveguide. It is expected that the two photons in each exit pair will be entangled with each other. To verify this entanglement, the research team measured the overlapping photons, indicating that they produce interference patterns - light and dark stripes - during imaging. In contrast, non entangled pairs produce a broad bright spot.

The interference level is a measure of the degree of photon entanglement. The degree of entanglement generated by gallium nitride rings is comparable to the level measured by other quantum light sources, Zhou said. "We demonstrate that gallium nitride is a good quantum material platform for photon quantum information, where the generation of quantum light is crucial," he said.

"In recent years, quantum optics has developed at an astonishing speed," said Thomas Walther, a quantum optics expert at the Technical University of Darmstadt in Germany. He said that moving forward will require small, sturdy, efficient, and relatively easy to manufacture components. Therefore, Zhou and his colleagues have demonstrated that gallium nitride is a promising material for manufacturing pump sources, quantum light sources, and single photon detectors. He said providing a platform for all these devices would be an important step forward, as it could reduce the cost of manufacturing such systems and make them more compact and robust than they are now.

Source: Laser Net