MIT Researchers Harness Nanoparticles for a New Source of Quantum Light
A team of scientists from the Massachusetts Institute of Technology (MIT) has made a significant stride in the development of optical quantum computers. Led by Prof. Moungi Bawendi and graduate student Alexander Kaplan, the researchers have developed a new source of quantum light using nanoparticles of novel materials. This new development could prove a game-changer for optical quantum computers, making them more scalable and affordable without the need for complex equipment.
Quantum computers traditionally use spins of single electrons or ultra-cold atoms as quantum bits or qubits, similar to classical bits. However, around two decades ago, scientists proposed using photons – particles of light – as qubits. Using photons for this purpose eliminates the need for expensive and complex equipment and only requires optical mirrors and detectors.
The team from MIT used CsPbBr3 nanocrystals, inorganic lead halide perovskite materials made of cesium (Cs), lead (Pb), and bromine (Br), as their quantum light source. These materials are being studied for their photovoltaic properties, lightweight, and easier production process compared to silicon-based photovoltaics.
The key to optical quantum computers is the creation of photons with identical properties. These indistinguishable and identical photons must then exhibit the Hong–Ou–Mandel effect, a two-photon interference central to quantum-based systems. “If you have two photons, and everything is the same about them, you can’t say number one and number two, you can’t keep track of them that way. That’s what allows them to interact in certain ways that are non-classical,” explained Bawendi in a press release.
Lead-halide perovskites can be identified in nanoparticle form by their rapid cryogenic radiative rate, which is the rate at which photons are created. The faster the photons are emitted, the better chance there is to have a well-defined wave function. Having a well-defined wave function allows for precise control and manipulation of these properties, enabling accurate encoding, processing, and utilization of quantum information in various quantum technologies and applications.
The team observed that the perovskite nanoparticles only produced Hong-Ou-Mandel interference about half the time. While not perfect, perovskite nanoparticles can be produced in large quantities using a solution-based method, making them a more scalable and reproducible source of quantum light. “The reason other sources are coherent is they’re made with the purest materials, and they’re made individually one by one atom by atom. So, there’s very poor scalability and very poor reproducibility,” Kaplan explained, highlighting the benefits of their new approach.
This significant discovery highlights the potential capabilities of perovskite nanoparticle materials. The researchers are confident that by integrating the emitters into optical cavities, similar to what has been done with other sources, the properties of the perovskite nanoparticles can reach a competitive level.
The findings of the study were published in the journal Nature Photonics on 22nd June. These results demonstrate the unique potential of perovskite nanocrystals to serve as scalable, colloidal sources of indistinguishable single photons, marking an exciting step forward in the world of quantum computing.
