Interactions between photons are easier than ever. Great progress in the performance of an international team

Their achievements are described in Nature PhysicsAdditional advances in research should translate into the development of more advanced quantum devices. As Peter Laudall explains, he and his colleagues have been working on the deterministic interface of single-photon quantum dots for more than 15 years. In the course of the research, a method based on nanowaveguides was developed, which was used in the case of deterministic single-photon sources and multi-photon entanglement sources.

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Another use for them, however, is to perform nonlinear operations on photons. Attempts were made as early as 2015, but then difficulties emerged in understanding the underlying physics behind this complex, single-photon and nonlinear interaction. Scientists also realized the possibility of building quantum photon gates and photon sorters.

In the new experiments, Laudall and the rest of the team used the efficient and coherent coupling of a single quantum emitter to a nanophoton waveguide. The goal was to induce nonlinear quantum interactions between groups of photon waves. The quantum dot, which behaves like a two-level atom, has played an important role in the research. It is embedded in a waveguide made of a photonic crystal.

The interactions between photons should facilitate the construction of quantum gates and photon sorters

In such systems, the coupling is deterministic, so even a single photon fired into the waveguide interacts with the quantum dot. Sending pulses containing two or more photons causes quantum correlations because only one photon at a time can interact with a quantum dot. By controlling the duration of the quantum pulse, we can tune these correlations as well as the interaction between photons.Laudall explains

Scientists, using the method they developed, were able to control a photon with a second photon. In practice, this means that they were able to induce a nonlinear interaction between a photon and a photon. Thanks to the further development of this technology, it should be possible to create quantum photonic gates or deterministic photon sorters, which are necessary for example in quantum amplifiers.

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Another research author, Hannah Le Jennick, adds that she and her colleagues are trying at a basic level to understand how the quantum states of light affect the journey through a single quantum dot. They also want to use the nonlinear interactions between the photons to simulate the vibrational dynamics of the molecules.