The researchers deployed a programmable switch to adjust how much data goes to each user by selecting and redirecting wavelengths of light carrying the different data channels, making it possible to increase the number of users without adding to photon loss as the network gets bigger. This new approach, say the researchers, addresses an issue barring the development of quantum networks that are big enough to reliably support more than a handful of users.
If photons are lost, quantum information is lost – a problem that tends to happen the farther photons have to travel through fiber optic networks.
"We show a way to do wavelength routing with just one piece of equipment – a wavelength-selective switch – to, in principle, build a network of 12 to 20 users, maybe even more," says Andrew Weiner, Purdue’s Scifres Family Distinguished Professor of Electrical and Computer Engineering. "Previous approaches have required physically interchanging dozens of fixed optical filters tuned to individual wavelengths, which made the ability to adjust connections between users not practically viable and photon loss more likely."
Instead of needing to add these filters each time that a new user joins the network, say the researchers, engineers could just program the wavelength-selective switch to direct data-carrying wavelengths over to each new user – reducing operational and maintenance costs as well as making a quantum internet more efficient. The wavelength-selective switch also can be programmed to adjust bandwidth according to a user's needs, which has not been possible with fixed optical filters.
For a quantum internet, say the researchers, forming connections between users and adjusting bandwidth means distributing entanglement, the ability of photons to maintain a fixed quantum mechanical relationship with one another no matter how far apart they may be to connect users in a network. Entanglement plays a key role in quantum computing and quantum information processing.
"When people talk about a quantum internet, it's this idea of generating entanglement remotely between two different stations, such as between quantum computers," says Navin Lingaraju, a Purdue Ph.D. student in electrical and computer engineering. "Our method changes the rate at which entangled photons are shared between different users. These entangled photons might be used as a resource to entangle quantum computers or quantum sensors at the two different stations."
The researchers' wavelength-selective switch is based on similar technology used for adjusting bandwidth for today's classical communication. The switch, say the researchers, is also capable of using a "flex grid," as classical lightwave communications now uses, to partition bandwidth to users at a variety of wavelengths and locations rather than being restricted to a series of fixed wavelengths, each of which would have a fixed bandwidth or information carrying capacity at fixed locations.
"For the first time," says Weiner, "we are trying to take something sort of inspired by these classical communications concepts using comparable equipment to point out the potential advantages it has for quantum networks."
The researchers say they are working on building larger networks using the wavelength-selective switch. For more, see "Adaptive bandwidth management for entanglement distribution in quantum networks."
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