Quantum properties of light used to transmit information

Technology News | November 5, 2020

By Rich Pell

The researchers designed a nanoscale node made out of magnetic and semiconducting materials that could interact with other nodes, using laser light to emit and accept photons. The device, say the researchers, demonstrates a way to use quantum properties of light to transmit information – a key step on the path to the next generation of computing and communications systems, which promise faster, more efficient ways to communicate, compute, and detect objects and materials.

The nanoscale node consists of an array of 120-nanometer high pillars, which are themselves part of a platform containing atomically thin layers of semiconductor and magnetic materials. The array is engineered so that each pillar serves as a location marker for a quantum state that can interact with photons and the associated photons can potentially interact with other locations across the device – and with similar arrays at other locations.

This potential to connect quantum nodes across a remote network, say the researchers, capitalizes on the concept of entanglement, a phenomenon of quantum mechanics that, at its very basic level, describes how the properties of particles are connected at the subatomic level.

“This is the beginnings of having a kind of register, if you like, where different spatial locations can store information and interact with photons,” says Nick Vamivakas, professor of quantum optics and quantum physics at Rochester.

Building on previous work that uses layers of atomically thin materials on top of each other to create or capture single photons, the new device uses a novel alignment of tungsten diselenide (WSe₂) draped over the pillars with an underlying, highly reactive layer of chromium triiodide (CrI₃). Where the atomically thin, 12-micron area layers touch, the CrI₃ imparts an electric charge to the WSe₂, creating a “hole” alongside each of the pillars.

In quantum physics, a hole is characterized by the absence of an electron. Each positively charged hole also has a binary north/south magnetic property associated with it, so that each is also a nanomagnet.

When the device is bathed in laser light, further reactions occur, turning the nanomagnets into individual optically active spin arrays that emit and interact with photons. Whereas classical information processing deals in bits that have values of either 0 or 1, say the researchers, spin states can encode both 0 and 1 at the same time, expanding the possibilities for information processing.

“Being able to control hole spin orientation using ultrathin and 12-micron large CrI₃, replaces the need for using external magnetic fields from gigantic magnetic coils akin to those used in MRI systems,” says graduate student Arunabh Mukherjee, lead author of a paper on the research. “This will go a long way in miniaturizing a quantum computer based on single hole spins.”

In creating the device, the researchers say they faced two major challenges: One was creating an inert environment in which to work with the highly reactive CrI₃, while the other was determining just the right configuration of pillars to ensure that the holes and spin valleys associated with each pillar could be properly registered to eventually link to other nodes.

The first challenge was overcome through collaboration with Cornell University researchers, whose expertise in working with chromium triiodide enabled fabrication of the CrI₃ in nitrogen-filled glove boxes to avoid oxygen and moisture degradation. The second challenge, say the researchers, remains to find a way to send photons long distances through an optical fiber to other nodes, while preserving their properties of entanglement.

“We haven’t yet engineered the device to promote that kind of behavior,” says Vamivakas. “That’s down the road.”

For more, see “Observation of site-controlled localized charged excitons in CrI₃/WSe₂ heterostructures.”