When Heroes (now streaming on Peacock!) hit the airwaves in September of 2006, few characters were as immediately beloved as the appropriately named Hiro Nakamura. Granted the ability to manipulate space-time, Hiro could not only slow down, speed up, and stop time, he could also teleport from one place to another. That’s a useful skill if you need to get to a specific point in time and space to fight an evil brain surgeon or prevent the end of the world. It’s also useful if you want to build the quantum internet.
Researchers at QuTech — a collaboration between Delft University of Technology and the Netherlands Organization for Applied Scientific Research — recently took a big step toward making that a reality. For the first time, they succeeded in sending quantum information between non-adjacent qubits on a rudimentary network. Their findings were published in the journal Nature.
While modern computers use bits, zeroes, and ones, to encode information, quantum computers us quantum bits or qubits. A qubit works in much the same way as a bit, except it’s able to hold both a 0 and a 1 at the same time, allowing for faster and more powerful computation. The trouble begins when you want to transmit that information to another location. Quantum computing has a communications problem.
Today, if you want to send information to another computer on a network, that’s largely accomplished using light through fiber optic cables. The information from qubits can be transmitted the same way but only reliably over short distances. Fiber optic networks have a relatively high rate of loss and rely on cloning bits and boosting their signal in order to transmit over significant distances. Qubits, however, can’t be copied or boosted. That means that when and if information is lost, it’s lost for good, and the longer the journey the more likely that is to happen.
That’s where Hiro Nakamura comes in, or at least his quantum counterpart. In order to reliably transmit quantum data, scientists use quantum teleportation, a phenomenon that relies on entanglement or what Einstein called "spooky action at a distance."
As with all things quantum, understanding entanglement isn’t the easiest endeavor but, for our purposes, we’ll simplify. When two particles are entangled, they share a connection, regardless of the physical distance between them. By knowing the state of one entangled particle, you can instantly know the state of the other even if its out of view. It’s sort of like making two people share a single pair of shoes. If you know the first person is in possession of the right shoe, then you know the second person has the left.
Using that spooky connection, scientists can transmit information between the two particles and that information appears at one particle and vanishes at the other instantly. That’s where the analogy to teleportation comes in. First, it’s here, then it’s there, without the need for a journey along cables. Importantly, only information is transferred, not any physical matter. Our teleportation technologies aren’t at BrundleFly levels just yet.
Quantum teleportation isn’t exactly new. It’s been done before, but always between two directly connected entangled particles. In communications parlance, it’s the quantum equivalent of talking to your friend in the next room using two cans connected by a string. In order to create a true quantum network, we need to be able to transmit data between non-adjacent nodes using intermediaries.
In this case, researchers wanted to transfer information between nodes named Alice and Charlie, using Bob as a go-between. To make that happen Bob created an entangled state with Alice and stored his portion of the entanglement in a bit of quantum memory. Next, Bob repeats that process with Charlie. Then, using what researchers at QuTech describe as “quantum mechanical sleight of hand,” Bob completes a measurement and passes on the entanglement between Alice and Charlie.
Once that’s done, Charlie prepares the information he wants to send and completes a complicated measurement between his message and his half of the entanglement with Alice. Quantum mechanics goes to work, and the information vanishes on Charlie’s end and appears on Alice’s.
This has some important implications for the future of communication. First, using quantum teleportation networks avoids the threat of packet loss over fiber optic cables. Second, it effectively encrypts the information at Alice’s end. In order to decode the information, you need to know the result of the calculation Charlie performed. The third thing builds upon the first; despite the immediate transfer of quantum information, we are still bound by the speed of light. As you know, the cosmic speed limit isn’t just a suggestion, it’s the law. Sending the calculation information to Alice in order to decode the information relies on more traditional communications bound by light speed. No getting around it.
While this is an important step toward a quantum internet, in order to build the sorts of networks we’ll need for everyday use, we’re going to need a lot more nodes. But, hey, even today’s global communications network started with a single telephone.