Cisco is working to extend its networking leadership into the age of quantum computing.
The company revealed a prototype Thursday of what it calls a "universal quantum switch," one that understands the encoding modalities of different types of quantum computers so they can be networked in the same way classical computers are today.
The switch works at room temperature and can hook into existing fiber optic networks. Unlike today's commercial photonic switches, these switches preserve the quantum entanglement of photons, allowing them to convey complex quantum states.
"Cisco's quantum network greatly expands the possibilities of quantum computing by allowing the networking of several smaller quantum computers into an effectively larger one, even if the underlying physics of the quantum computers are substantially different," said Mark Horvath, a Gartner analyst, in an email.
In February, Cisco, in partnership with Qunnect, set up a quantum network over a noisy commercial fiber optic conduit from Brooklyn to the 60 Hudson Street telecommunication carrier hotel in Manhattan. They were able to convey 5,400 qubit pairs per hour over the 17.6-kilometer route, about 10,000 times faster than any previous experiments, Cisco researchers asserted.
"Cisco Quantum's recent validation results from working with Qunnect in NYC were fascinating and good evidence of solid advancements, proving quantum networking can work over distances and without supercooling," said Jim Frey, Omdia principal analyst for networking, in an email.
A need for quantum networking
Quantum computing promises to solve complex problems too difficult for today's classical computers, in areas such as financial modeling, drug discovery, weather exploration and logistics planning.
Even after decades of research, however, quantum computers are still far from where they need to be to run these complex workloads, which would require hundreds of thousands or even millions of quantum bits -- or qubits -- to model.
Today's most powerful quantum computers, however, can juggle at most only a few thousand qubits at once, and with vigorous research in the next few years, that number might only jump to the low tens of thousands.
"There's a big gap between the number of qubits we need and the number of qubits we have," said Vijoy Pandey, senior vice president and general manager of Outshift, Cisco's emerging technologies and incubation group, during a press conference this week.
So, it would be natural to borrow a technique from the high-performance computing community and lash quantum computers together to get the required power needed to tackle these jobs in a distributed manner.
A network of computers would scale faster than trying to vertically build up a single computer, Pandey argued.
"In order to reach the total compute capacity needed for quantum computing to be broadly viable, and to make the system secure, it will be necessary to chain quantum computers together via quantum networking," Frey agreed.
Cisco doing what it does best
Cisco's universal quantum switch works just like a typical data center switch but adjusted for quantum traffic. It accepts the incoming quantum signal, internally converts it to a neutral common modality for routing, and sends it out in the correct modality for the receiving system -- preserving the quantum state all the while.
Classical internet routing differs from what would be required for the quantum realm. The internet operates on a store-and-forward approach, but a quantum network must establish an open path between the source and destination first to share the entanglement state.
"For now, we think of quantum networking as completely different from classical networking. Distributing quantum states is a completely separate way of doing things," said Ramana Kompella, Cisco fellow and head of Cisco research, during the press conference.
Quantum computing states are fragile. A pair of photons can be entangled to produce a qubit, and the more photons you can entangle, the more information you can convey. Moving a quantum state from one processor to another, called teleportation, requires preserving each qubit's entanglement properties. But electromechanical noise can easily destroy a qubit. The more devices a state of qubits passes through, the more a potential loss of fidelity compounds.
Different quantum systems have different encoding modalities, much like early classical computers were incompatible with one another. IBM quantum systems have a different modality, for instance, from those built by Atom Computing. This is not vendor lock-in for its own sake, Kompella said. Different applications favor different modalities.
Cisco partnered with both IBM and Atom for this switch, which will support four modalities:
- Polarization, where the orientation of light waves carries information.
- Time-bin, where the timing of light pulses carries information.
- Frequency-bin, where the color or frequency of light is used to carry information.
- Path, where the physical or spatial path carries information.
"We don't know which of these technologies will be dominant," said Reza Nejabati, head of Cisco quantum research and quantum labs, during the press conference. "So the network can support any of them."
Fast switching was also imperative. The Cisco switch can reconfigure connection in as little as a nanosecond, while consuming less than a milliwatt of power.
Key to the switching process is a silicon-based quantum state converter, which, using quantum tomography, converts qubits into an internal encoding format for routing. They are then converted back, without being measured or destroyed, to their original encoding, or to one of the other encoding formats, at their destination.
Unlike other qubit management approaches, the switch can operate at room temperature, thanks to the frequency of telecommunications fiber optic channels and the internal encoding format.
The work builds on previous Cisco research as part of its Outshift quantum incubation program, including a quantum network entanglement chip to link the quantum computers to the network, and a network-aware quantum compiler that orchestrates quantum algorithms across multiple quantum processors -- handy for error correction.
The next steps for quantum networking
The Cisco universal switch is still in the prototype phase. It will be several years before it is released commercially, as the supporting stack for end-to-end operation needs to be finalized. For instance, the company will need to build a repeater of some sort because quantum signals can only travel about 100 kilometers or so.
In the more immediate term, researchers will post a paper explaining the technology on ArXiv.
"This is a seismic breakthrough that will bring solutions into reach for many problems that were years beyond today's existing generation of quantum computers," Horvath said.
In addition to putting quantum computing on a more solid commercial footing, quantum networking may open up new uses on its own, Kompella said.
For instance, a quantum network could give high-frequency trading (HFT) firms a competitive edge. An HFT firm might run across multiple data centers, and when it makes a purchasing decision in one data center, it should replicate as quickly as possible in the other locations.
Today, the network is the bottleneck for HFT, in that it limits the speed at which that information can be moved to near the speed of light. Quantum communications could beat what was previously thought to be the physical upper limit by coordinating the decision-making process ahead of time through entanglement.
"Coordinated decisions [that run] faster than the speed of light actually give you a substantial advantage compared to any classical strategy," Kompella said.
