Quantum key distribution (QKD) brings the power of quantum computing to communication, using the unique properties of quantum physics to make an unhackable system. Now, a new network developed by an international team sets a path to make a dream come true: an entire city operating through quantum communication.
The quantum world is vastly different from the natural world we see around us every day, which is controlled by what quantum scientists refer to as “classical physics.” Under classical physics, an object, like the key to your house, can only be in one place at a time. Yet at the smallest quantum level, photons of light can take on what is known as a superposition, meaning that they exist in multiple places at the same time.
But superpositions come with a fascinating qualification: they fall apart if directly observed. If a scientist tried to directly observe quantum superposition, it would fall apart into two separate positions again.
So, the thinking goes, what’s true for the quantum scientist is equally true for hackers trying to push their way into an email. In QKD, those photons are sent through a quantum channel with a secret key that can be used to decrypt the message. Until now, it had only been possible between two users.
The team’s work, published Wednesday in Science Advance, has expanded that to eight users, with simulations showing as many as 32 users. The system can operate over a distance of a little over 10.5 miles or 17 kilometers.