Researchers at the Massachusetts Institute of Technology have designed a new type of quantum light source using lead salt perovskite nanoparticles

Most traditional quantum computing uses the spin of supercooled atoms or individual electrons as quantum bits, which form the foundation of such devices. By comparison, if light is used to replace physical entities as basic quantum bits, ordinary lenses and optical detectors can replace expensive devices to control the data input and output of quantum bits.

Based on this, chemistry professors Moungi Bawendi and graduate student Alexander Kaplan from the Massachusetts Institute of Technology designed a new type of quantum light source using a common solar photovoltaic material (lead salt perovskite nanoparticles) and demonstrated that the material has a fast low-temperature radiation rate and can emit single photon streams with the same characteristics. Although this work is currently only a basic study of the functions of these materials, it is expected to pave the way for new optical quantum computers and quantum teleportation devices for communication. This achievement was published in Nature Photonics under the title "Hong Ou Mandel interference in colonial CsPbBr3 perovskite nanocrystals" (DOI: 10.1038/s41566-023-01225-w).

Microscopic imaging of perovskite nanoparticles
Kaplan said that by combining photons similar to qubits with some common linear optical devices, people can build a new quantum computer. The key to the entire research lies in not only generating these photons, but also ensuring that each photon accurately matches the quantum properties of previous photons. Generally speaking, the truly significant paradigm shift in scientific research is the shift from requiring very special and expensive optical devices to requiring only simple and common equipment.

Bawendi explained that they utilize these identical and indistinguishable single photons and interact with each other. This inseparability is very important. If two photons are identical, you cannot distinguish which is the first and which is the second. There is no way to track them, which is why they are allowed to interact. Kaplan said that if people want photons to have this very special property, which is well defined in terms of energy, polarization, spatial mode, temporal mode, and everything that can be encoded using quantum mechanics, they also need a single photon light source with very good quantum performance.

In the experiment, the research team used lead salt perovskite nanoparticles as luminescent materials. Lead halide perovskite thin films are lighter and easier to process than the widely used silicon based photovoltaic materials today, and have received widespread attention as potential next-generation photovoltaic materials. Unlike other colloidal semiconductors, lead halide perovskite in the form of nanoparticles has extremely fast low-temperature emissivity. The faster light is emitted, the more likely the output is to have a clear wave function. Therefore, the rapid radiation rate enables lead halide perovskite nanoparticles to uniquely emit quantum light.

To test that the designed single photon source indeed has this indistinguishable characteristic, the standard test is to detect a specific type of interference between two photons called red Euclidean interference. Kaplan stated that this phenomenon is at the core of many quantum based technologies, so proving its existence has become the standard for confirming that photon sources can be used for these purposes. But the materials that meet this testing requirement are very few, almost just a handful. Although the new light source designed by the research team is not yet perfect and only generates HOM interference in about half of the cases, it has significant improvements in scalability compared to other light sources and can be integrated into other devices. Because other light sources use very pure materials and are composed of one atom after another, their scalability and repeatability are relatively poor.

In contrast, perovskite nanoparticles are made in solution and then simply deposited on the substrate material. What we do is simply spin coat it onto the surface of ordinary glass, "Kaplan said. But in this way, they also observed a phenomenon that could only be seen under very strict production processes before.

The research team stated that the importance of this work lies in the hope that it can encourage people to study how to further enhance functionality in various device architectures. They are fully confident that integrating this new light source into an optical cavity will bring its performance to a competitive level.

Source: China Optical Journal Network