Present-day quantum computers are big, expensive, and impractical, operating at temperatures near -459 degrees Fahrenheit, or "absolute zero." In a new paper, however, materials scientists at Stanford University introduce a new nanoscale optical device that works at room temperature to entangle the spin of photons (particles of light) and electrons to achieve quantum communication - an approach that uses the laws of quantum physics to transmit and process data. The technology could usher in a new era of low-cost, low-energy quantum components able to communicate over great distances.
"The material in question is not really new, but the way we use it is," says Jennifer Dionne, a professor of materials science and engineering and senior author of the paper just published in Nature Communications describing the novel device. "It provides a very versatile, stable spin connection between electrons and photons that is the theoretical basis of quantum communication. Typically, however, the electrons lose their spin too quickly to be useful."
Jennifer Dionne | Courtesy Jennifer Dionne
The device is made of a thin, patterned layer of molybdenum diselenide (MoSe2) atop a solid, nanopatterned substrate of silicon. Molybdenum diselenide is one of a class of materials known as transition metal dichalcogenides (TMDCs) that have favorable optical properties.
"The Silicon nanostructures enable what we call 'twisted light,'" explains Feng Pan, a postdoctoral scholar in Dionne's lab and first author of this paper and a series of others exploring room-temperature quantum devices. "The photons spin in a corkscrew fashion, but more importantly, we can use these spinning photons to impart spin on electrons that are the heart of quantum computing."
Smaller, simpler, cheaper
"The patterned nanostructures are imperceptible to the human eye, about the size of the wavelength of visible light," Dionne adds. "But they help us manipulate photons very precisely to make them spin - to twist them - in a specific direction, for example, up or down."
In turn, Pan explains, this twisted light can be "entangled" with the spin of electrons to create qubits, the foundational unit of quantum communication and computation. The spin of a qubit is to quantum computing what the 1 and the 0 are to traditional binary computation.
The nanoscale optical device works at room temperature to entangle the spin of photons and electrons to achieve quantum communication. | Antony Georgiadis
To increase qubit stability, traditional quantum systems must operate at extremely low temperatures to prevent loss - or "decoherence" - of the delicate quantum state. This makes them big, costly, and impractical. The new device from Dionne's lab is small, relatively inexpensive, and pragmatic by comparison.
Room-temperature operation is a great leap forward in the race to overcome the complexities and costs of super-cooling, the researchers say. The device could eventually lead to the introduction of quantum technologies in broader applications, potentially reshaping cryptography, advanced sensing, high-performance computing, artificial intelligence, and other fields.
Material matters
Dionne and Pan targeted TMDCs for their distinctive quantum properties, teaming up with Stanford TMDC experts, professors Fang Liu and Tony Heinz. "It all comes down to this material and our Silicon chip," Pan says. "Together, they efficiently confine and enhance the twisting of light to create a strong coupling of spin between photons and electrons. This stabilizes the quantum state that makes quantum communication possible."
Dionne and Pan are now working to refine their device and exploring other TMDCs and material combinations to achieve even greater quantum performance or, potentially, to reveal additional quantum functionalities currently not possible at room temperature.
More promising still, the researchers are looking at ways to integrate their device into larger quantum networks. To do this, the field will need new and better light sources, modulators, detectors, interconnects, Dionne says. The ultimate vision is to miniaturize quantum systems to the point where they can be embedded in everyday devices, at which point they might become a ubiquitous part of the modern technological landscape - a day that is still years away.
"If we can do that, maybe someday we could do quantum computing in a cell phone," Pan says with a smile. "But that's a 10-plus-year plan."
