In an office overlooking an old shipyard in Brooklyn, I am learning that I may have walked over some entangled quantum light on my way here.
Since the previous evening, researchers at Qunnect have been sending particles of light, or photons, through a 34-kilometre-long loop of optical fibre underneath New York. Their approach preserves the special quantum property of entanglement that will allow them to eventually use this loop as a starting point for a quantum internet.
In a quantum internet, devices communicate by exchanging quantum particles, like photons, that encode lots of complex information at once. This encoding is fundamentally different from the way electronic signals carry information between our computers and phones because it takes advantage of properties that don’t exist for non-quantum objects. The biggest promise of quantum networks is that they will transmit information more securely than any existing network, rendering what we share online nearly unhackable.
Advertisement
The key quantum ingredient for this security is entanglement. For two entangled particles, if one is tampered with, the other instantly changes its properties. This alerts the user that their communication has been compromised.
To make their test network, Qunnect’s researchers had to build a device called an entanglement source that generates entangled photons. It utilises rubidium atoms that release entangled photons when hit by carefully calibrated lasers. The device is the size of a shoe box, works at room temperature and can plug into existing fibre networks.
The number of entangled photon pairs the device is producing and how reliably they are entangled is unprecedented – a 100-fold improvement over rates that other atom-based devices had achieved in the past, says Mehdi Namazi, Qunnect’s chief science officer.
By the time I look at Qunnect’s entanglement source, the experiment has been running for over 12 hours. For each entangled pair generated, one photon is kept in the lab while the other is sent around the loop. Tens of thousands of photons have been completing the loop every second.
Other quantum networks already exist. One network in Hefei, China, already connects 40 quantum devices, and smaller networks have been put together in Bristol in the UK, Chattanooga, Tennessee and Chicago, Illinois. There are also plans for a quantum network in Rotterdam in the Netherlands, Europe’s largest seaport.
However, these networks can’t easily plug into existing infrastructure. Rather than using rubidium atoms, they use crystals that release entangled photons after being hit by a laser. The advantage of this approach is that you get more photons so can transfer more information, but the photons aren’t the right wavelength to be used with current fibre-optic networks.
, Qunnect’s CEO, says that the team’s long-term goal is to leave the set up “always on” and keep adding other devices, like quantum memory devices that store information, without messing with the fibres that already stretch through New York. “After all, the world won’t lay whole new networks of fibre to have quantum internet,” she says.
Now, the researchers are working on adding another loop and entanglement source to their setup. This will get them closer to a quantum internet where there would be multiple quantum telecommunication hubs, each with their own entanglement source, and users would have more than one option for getting entangled photons delivered to them.
Goddard says that it is hard to predict every future use for such photons, but Qunnect wants to provide them to financial and research institutions, for instance, that need secure communication or have quantum computers.
