Inside the company selling 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 sharing 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 researchers use to manipulate light. They are all destined to be neatly packaged into bright magenta boxes and then shipped to other builders of the communication technologies of the future.

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

In February, Qunnect’s team used these racks to perform “entanglement swapping” across 17.6 kilometres of fibre-optic cables connecting Brooklyn and Manhattan via a commercial data centre.

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

Qunnect reliably swapped quantum entanglement between 5400 pairs of photons every hour as the network ran autonomously for days. Previous best experiments swapped 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 “entanglement source” and see a small glass and metal box filled with a vapour of rubidium atoms that must be hit with laser light to produce the photon pairs. The tiniest details matter here. Namazi tells me how his team managed 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 then sends them through a network of fibre 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, say, I wanted to send super-secure messages to a friend. “If you have two of these (Carina) racks, you can have distribution of entanglement within a few hours,” says Namazi.

Qunnect keeps one such rack at a commercial data centre in Manhattan, which is operated by telecoms firm QTD Systems. When I ask QTD’s Peter Feldman about it, he echoes Namazi’s sentiment. “I don’t have to know anything about quantum physics,” he says. Devices that keep entangled photons running 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 aren’t unique to New York City. Several other metropolitan quantum networks exist across the world, including in Hefei, China, and Chicago, Illinois. In each case, there is still work to do to reach the full potential, including fixing the problem that photons often get 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 quantum tripwire of sorts, revealing any nefarious attempts to intercept it.

Another near-term use may be for confirming the identity of the person you are exchanging sensitive information with based on their location, says Alexander Gaeta at Columbia University, who collaborates 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 of New York City that could benefit from such capabilities, says Javad Shabani at New York University. “Once you have the infrastructure, the end users will come, and they are probably across the street.”

Though the quantum internet is still far from mainstream, during a car ride from Qunnect’s headquarters to QTD’s data centre, 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.