By Stephen Nellis

SAN FRANCISCO, Feb 18 (Reuters) - Cisco Systems CSCO.O and startup Qunnect said on Wednesday that they have built and operated a quantum network between Brooklyn and Manhattan in New York which sends signals over real-world fiber optic cables and works as well as studies in labs.

The experiment, which used Brooklyn, New York-based Qunnect's hardware and Cisco's software, solved some key challenges in building such networks in existing data centers and cities.

Quantum computers tap quantum physics to perform calculations that would take conventional computers thousands of years, but they often require bulky cryogenic cooling equipment.

Qunnect CEO Noel Goddard said the company's approach requires cryogenic cooling only at one central hub, while other data centers connected to the hub can use room-temperature equipment.

Quantum computers and networks are normally sensitive to the slightest vibration from the world around them, but a research paper released by Cisco and Qunnect said the startup's technology - specifically devices called automatic polarization controllers - keeps the quantum network intact over a 17.6 kilometer (10.9 mile) stretch of fiber optic cable.

"It corrects for real-world problems," Goddard said, noting that "data centers have these tens of kilometers of fiber, and they run through all sorts of different patch panels, all of the things that make it look like a rat's nest."

Ramana Kompella, vice president and head of Cisco Research, called the experiment "foundational" to Cisco's goal of one day connecting quantum computers together inside a data center and then connecting those quantum data centers into a quantum internet.

In the short term, practical quantum networks could be used in fields such as trading stocks, Kompella said.

A quantum technique called "teleportation" can allow physically separated computers to share information instantaneously, rather than taking a few milliseconds to move information at the speed of light.

"Trading computers that are tens of kilometers away, and they want to make a coordinated decision or a stock sell or a buy, without hitting the speed of light limitations you typically have. Quantum entanglement networks can actually really help," Kompella said.

(Reporting by Stephen Nellis in San Francisco; Editing by Edwina Gibbs)

((stephen.nellis@thomsonreuters.com))