Inside the company that sells quantum entanglement

Medhi Namazi wants to sell you quantum entanglement.

He and his colleagues at Qunnect have spent nearly a decade building devices that make the sharing of quantum entangled particles of light, or photons, practical enough to be used for unhackable communication.

At Qunnect’s headquarters in Brooklyn, New York, large tables are filled with lasers, lenses, special crystals and other tiny components that scientists use to manipulate light. They are all destined to be neatly packaged in bright magenta boxes and then shipped off to other builders of future communications technology.

Against the backdrop of the stunning New York skyline, Namazi opens a box for me, revealing electronics that at first glance don’t seem particularly remarkable. But if you stack several of these boxes together, you get what the company calls a Carina rack—and the Carina rack can make remarkable quantum things happen.

In February, Qunnect’s team used these racks to perform “entanglement swapping” over 10 miles of fiber optic cables connecting Brooklyn and Manhattan via a commercial data center.

Entanglement swapping is when the property of quantum entanglement is transferred from one pair of photons to another. Once photons are entangled, they are extremely sensitive to any attempt to tamper with them, making it nearly impossible to steal information stored within them. With switching, it will then be possible to extend this unhackable property into a long-distance quantum internet.

Qunnect reliably switched quantum entanglement between 5,400 pairs of photons every hour while the network ran autonomously for days. Previous best experiments switched entanglement at half that rate or less.

Before a Carina rack can perform its tricks, entangled photons must be created by a separate device. I look at the heart of this “source of entanglement” and see a small glass and metal box filled with a vapor of rubidium atoms that must be hit with laser light to produce the photon pairs. The smallest details matter here. Namazi tells me how his team was able to increase the number of entangled photons they produced by adjusting the angle at which laser beams enter the box.

Once the pairs are created, a Carina rack sends them through a fiber network across New York City, for example to labs at New York University and Columbia University.

Namazi explains how I could go about setting up my own entanglement sharing system if, for example, I wanted to send super secure messages to a friend. “If you have two of these (Carina) racks, you can have entanglement distribution within a few hours,” Namazi says.

Qunnect has such a rack in a commercial data center in Manhattan, operated by telecom company QTD Systems. When I ask QTD’s Peter Feldman about it, he echoes Namazi’s sentiments. “I don’t need to know anything about quantum physics,” he says. Devices that keep entangled photons moving through Qunnect’s network can be controlled remotely and the process can run autonomously for weeks at a time.

Attempts to build an unhackable quantum internet are not unique to New York City. Several other metropolitan quantum networks exist worldwide, including in Hefei, China and Chicago, Illinois. In each case, there is still work to be done to reach its full potential, including fixing the problem that photons are often lost over long distances.

But Namazi says having access to quantum entanglement can already be useful. Entangled photons can be mixed into streams of classical information-carrying light and act as a kind of quantum tripwire, exposing any nefarious attempts to intercept it.

Another short-term use could be to verify the identity of the person you’re exchanging sensitive information with based on their location, says Alexander Gaeta of Columbia University, who is working with Qunnect. This is again possible thanks to the quantum nature of the entangled photons. There are dozens of financial institutions in just one neighborhood in New York City that could benefit from such capabilities, says Javad Shabani of New York University. “Once you have the infrastructure, the end users will come, and they’re probably across the street.”

Although the quantum internet is still far from mainstream, during a car ride from Qunnect’s headquarters to QTD’s data center, I am struck by how much is already up and running. As I cross one of New York’s bridges, I think about how many entangled photons have also done the same. Busy quantum New Yorkers with places to be.