Written by John Spizzirri
The world awaits quantum technology. Quantum computing is expected to solve complex problems that current, or classical, computing cannot. And quantum networking is essential for realizing the full potential of quantum computing, enabling breakthroughs in our understanding of nature, as well as applications that improve everyday life.
But making it a reality requires the development of precise quantum computers and reliable quantum networks that leverage current computer technologies and existing infrastructure.
Recently, as a sort of proof of potential and a first step toward functional quantum networks, a team of researchers with the Illinois‐Express Quantum Network (IEQNET) successfully deployed a long-distance quantum network between two U.S. Department of Energy (DOE) laboratories using local fiber optics.
The experiment marked the first time that quantum-encoded photons — the particle through which quantum information is delivered — and classical signals were simultaneously delivered across a metropolitan-scale distance with an unprecedented level of synchronization.
The IEQNET collaboration includes the DOE’s Fermi National Accelerator and Argonne National laboratories, Northwestern University and Caltech. Their success is derived, in part, from the fact that its members encompass the breadth of computing architectures, from classical and quantum to hybrid.
“To have two national labs that are 50 kilometers apart, working on quantum networks with this shared range of technical capability and expertise, is not a trivial thing,” said Panagiotis Spentzouris, head of the Quantum Science Program at Fermilab and lead researcher on the project. “You need a diverse team to attack this very difficult and complex problem.”
And for that team, synchronization proved the beast to tame. Together, they showed that it is possible for quantum and classical signals to coexist across the same network fiber and achieve synchronization, both in metropolitan-scale distances and real-world conditions.
Classical computing networks, the researchers point out, are complex enough. Introducing the challenge that is quantum networking into the mix changes the game considerably.
When classical computers need to execute synchronized operations and functions, like those required for security and computation acceleration, they rely on something called the Network Time Protocol. This protocol distributes a clock signal over the same network that carries information, with a precision that is a million times faster than a blink of an eye.
With quantum computing, the precision required is even greater. Imagine that the classical network time protocol is an Olympic runner; the clock for quantum computing is The Flash, the superfast superhero from comic books and films.
To assure that they get pairs of photons that are entangled — the ability to influence one another from a distance — the researchers must generate the quantum-encoded photons in great numbers.
Knowing which pairs are entangled is where the synchronicity comes in. The team used similar timing signals to synchronize the clocks at each destination, or node, across the Fermilab-Argonne network.