MIT researchers have discovered that new photovoltaic nanoparticles can emit streams of identical photons, potentially paving the way for new quantum computing technologies and quantum teleportation devices.
The device emits a stream of single photons and could provide the basis for optical quantum computers.
Using new materials that have been widely studied as potential new solar photovoltaics, researchers from WITH have shown that nanoparticles of these materials can emit a stream of single, identical photons.
While the work is currently a fundamental discovery of the capabilities of these materials, it could eventually pave the way to new optical-based quantum computers as well as possible quantum teleportation devices for communication, the researchers say. The results were published June 22 in the journal Photonics of naturein a report by graduate student Alexander Kaplan, chemistry professor Mungi Bawendi and six others at MIT.
The microscopic image shows the uniformity of the size of the perovskite nanocrystals. Credit: Courtesy of the researchers
Most concepts for quantum computing use ultracold atoms or the spins of individual electrons to act as the quantum bits or qubits that form the basis of such devices. But about two decades ago, some researchers proposed the idea of using light instead of physical objects as basic qubit units. Among other advantages, this would eliminate the need for complex and expensive equipment to control the qubits and input and retrieve data from them. Instead, simple mirrors and optical detectors would be needed.
“With these qubit-like photons,” Kaplan explains, “you can build a quantum computer with just ‘homemade’ linear optics, provided you have properly prepared photons.”
The preparation of these photons is the key thing. everyone photon must exactly match the quantum characteristics of the previous one, and so on. Once that perfect match is achieved, “the really big paradigm shift is changing from the need for very sophisticated optics, very sophisticated equipment, to the need for simple equipment. The thing that needs to be special is the light itself.
Then, Bavendi explains, they take these single photons, which are identical and indistinguishable from each other, and interact with each other. This indistinguishability is crucial: if you have two photons and ‘everything is the same about them and you can’t tell number one and number two, you can’t track them that way. It allows them to interact in certain ways that are not classical.”
Kaplan says that “if we want the photon to have this very specific property, to be very well defined in energy, polarization, spatial mode, time, all the things that we can encode quantum mechanically, the source has to be very well defined and quantum mechanically .”
The source they ended up using was a form of lead-halite perovskite nanoparticles. Thin films of lead halide perovskites are widely pursued as potential next-generation photovoltaics, among other things, because they can be much lighter and easier to process than today’s standard silicon-based photovoltaics. In nanoparticle form, lead-halide perovskites are distinguished by their blindingly fast cryogenic emission rate, which distinguishes them from other colloidal semiconductor nanoparticles. The faster the light is emitted, the more likely the output will have a well-defined wave function. Thus, the fast emission rates uniquely position the lead-halide perovskite nanoparticles to emit quantum light.
To test whether the photons they generate do indeed have this indistinguishable property, a standard test is to detect a specific type of interference between two photons known as Hong-Ou-Mandel interference. This phenomenon is central to many quantum-based technologies, Kaplan says, and therefore demonstrating its presence “is the hallmark of confirming that a photon source can be used for these purposes.”
Very few materials can emit light that meets this test, he says. “They can almost be counted on one hand.” While their new source is still not perfect, producing HOM interference only about half the time, other sources have significant trouble achieving scalability. “The reason the other sources are consistent is that they are made of the purest materials and are individually made one by one, atom by atom. So it has very poor scalability and very poor reproducibility,” Kaplan says.
In contrast, perovskite nanoparticles are made in solution and simply deposited on a substrate material. “We’re basically just spinning them on a surface, in this case just a plain glass surface,” Kaplan says. “And we’re seeing them engage in these behaviors that were previously only seen under the most rigorous training conditions.”
So while these materials may not be perfect yet, “They’re very scalable, we can make a lot of them. and currently they are very unoptimized. We can integrate them into devices and we can further improve them,” Kaplan says.
At this stage, he says, this work is a “very interesting fundamental discovery” showing the possibilities of these materials. “The importance of the work is that we hope it can encourage people to look at how to further improve them on different device architectures.”
And, Bavendi adds, by integrating these emitters into reflective systems called optical cavities, as has already been done with the other sources, “we have full confidence that integrating them into an optical cavity will raise their properties to the level of the competition. ”
Reference: “Hong–Ou–Mandel Interference in Colloidal CsPbBr3 perovskite nanocrystals” by Alexander EK Kaplan, Chantal J. Krajewska, Andrew H. Prope, Weiwei Sun, Tara Sverko, David B. Berkinski, Hendrik Utsat, and Mungi G. Bavendi, 22 Jun 2023, Photonics of nature.
DOI: 10.1038/s41566-023-01225-w
The research team includes Chantal Krajewska, Andrew Prope, Weiwei Sun, Tara Sverko, David Berkinski, and Hendrik Utsat. The work was supported by the US Department of Energy and the Natural Sciences and Engineering Research Council of Canada.