In an effort to do practical quantum computerResearchers are developing bigger and better quantum networks with capabilities that will complement and extend the capabilities of quantum computing. In other words, creating a functioning quantum network that can exchange many qubits safely, over long distances, could be a useful end goal completely independent of the quantum computer race.
In this spirit, Cisco launched quantum network software system September 25. The networking giant's technology could help create more powerful quantum sensors, secure position checkAnd quantum imaging technology– to list only three of them a number of new non-computer applications For quantum networks.
The team also has a hybrid goal in mind, says Ramana Kompellavice president and head of the company's research department Cisco in San Jose, California: quantum networks that can work with classical computers and conventional computer networks.
“This is a very interesting area for us because until now classical computing has not had access to a quantum network,” says Kompella. “But imagine if you had access to a quantum network, what new capabilities could you actually realize?” TOompella has answer to his own question. “We can protect classical networks with quantum signals, detecting eavesdroppers over long distances. fiber optic communications,” he says.
How does quantum work? Entanglement Secure networks?
To do this, the system relies on the fact that quantum signals common to their sensing network communicate with each other through quantum entanglement. “We are introducing entangled photons into optical fiber,” he says. “And if an attacker tries to intercept the fiber, they will end up breaking the entanglement, allowing us to detect them.”
Kompella adds that entanglement transmitted over network distances has other classical computing applications: high frequency trading And fintech“And maybe you can achieve ultra-precise time synchronization with entanglement-based networks,” he says.
The Cisco quantum network system is built on the basis practical quantum network chip company unveiled in May, which uses existing fiber optic lines, generates up to 200 million pairs of entangled photons per second and operates on standard telecommunications wavelengths.
But a new component Cisco recently introduced is software. The compiler that the company has now released allows the programmer to write in IBM's Python-based language. Quantum computer language Qiskit. And the Cisco compiler takes care of the technical details of the network, such as optimizing connections between quantum processors and fine-tuning error correction strategies.
“We hide the complexity of the physical layer,” says Reza Nejabatihead of quantum research at Cisco, “which allows algorithm developers to play with the quantity processors and how processors connect to each other to optimize their algorithms.”
“The compiler takes that high-level target, breaks it down, and then implements the network side of the equation,” Kompella adds.
Hoi-Kwong Loprofessor electrical and computer engineering from the University of Toronto, says Cisco is protecting an underappreciated part of the larger quantum technology world.
“Investment is key,” Lo says. “Although billions of research dollars are invested in quantum computing every year, startupsinvestment in quantum network startups is lagging.”
According to Ronald Hansonprofessor nanoscience at Delft University of TechnologyV NetherlandsCisco's work is a key next step. But this is just the next step.
“What Cisco is introducing now is not really the first of its kind,” Hanson says. “But the fact that Cisco is working on several of these different elements of quantum networking, coupled with their experience and strengths in classical networking technologies, makes the progress exciting and will stimulate the quantum networking industry as a whole.”
What will it take to scale quantum networks?
According to Nejabati, the biggest limitation of the Cisco system currently is the limitation of the physical distance that one photon can travel before it is absorbed by another photon. optical fiber myself.
“Our hardware and software technologies allow us … to cover distances of up to one hundred kilometers with a high-quality, high-performance network,” says Nejabati.
Law says that physics, specifically a law called “no-cloning theorem“, arguing that individual quantum bits can never be completely replicated, making the implementation of large-scale quantum networks particularly challenging.
“The big challenge is to create quantum repeaters,” Lo says. “Optical fibers are lossy, and to overcome the distance limitation, we need quantum repeaters.”
Law's group, for example, is exploring encoding a qubit signal not into another single photon, but into a cluster of entangled photons. IEEE spectrum traced back Lo's group's initial work on this method in 2015 and their experimental testing confirming the principle of operation in 2019.
On the other hand, says Hanson, making quantum repeaters is not the only path forward for next-generation quantum network technology.
“Simply exchanging photons is not, in our opinion, the most interesting technology because many use cases remain inaccessible,” says Hanson. “Instead, our goal is to create… entanglement on demand: by combining the propagation of entanglement through photonic channels with long-lived quantum memory—a buffer of entangled qubits ready for use.”
In this way, Hanson says, quantum entanglement can be stored like energy in a battery or terabits on a hard drive, and used when users on both ends of the network want to share quantum information.
“Buffer entanglement will open up an interesting range of applications beyond [quantum cryptography] that promise to deliver real benefits,” says Hanson. “It will be interesting to see when Cisco takes the step to use this technology in its networks.”
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