Image: Hansonlab at TUDelft
For years now, researchers have suggested that quantum communication could herald an era of "completely secure" communication—the only problem is, they haven't been able to demonstrate that it's possible, until now. Dutch researchers have, for the first time, perfected "unconditional quantum teleportation."
It's not the teleportation of physical matter, like people think of from science fiction. Instead, what's being teleported or communicated is the state of a qubit—a piece of quantum data stored on an electron or a proton. That state can be transmitted to and read from a separate qubit in another location, 100 percent of the time, and could eventually be used to send messages, e-mails, data, or even create robust quantum networks and computers that are much, much faster than what we already have.
Though similar "teleportation" has been done by researchers at the University of Maryland, their success rate was abysmal: Just one out of every 100 million attempts succeeded. Meanwhile, the Dutch researchers, who work at a lab at the Kavli Institute of Nanoscience Delft, were able to transmit the data over a distance of 10 feet each time, with plans to try it out at distances of over a kilometer in future tests. The team published their findings in Science.
Here's what it looks like:
The theory of quantum mechanics suggests that two particles can be entangled, or bonded together, so they behave in exactly the same way, no matter where they are located. Einstein once said that the behavior is "spooky action at a distance"—when you act upon one part of an an entangled pair, the other will also be affected, no matter how far away they get. However, if the state of that information is read, they will automatically be destroyed—that's why quantum communication is looked at as a theoretical gold standard for security.
"There have been a lot of ideas in the past about realizing a perfectly secure communications channel—if you have entanglement, it's always possible for the sender and the receiver to figure out if someone is listening in," Wolfgang Pfaff, one of the study's authors, told me. "In the future, it'll be possible to send information this way, and, as one of the fundamentals, you can't capture the information without me knowing."
The fact that quantum bits of data are inherently destroyed if they are read is one of the reasons why they're so secure—but it also makes working with them, and making them useful, exceedingly difficult. That difficulty is why most so-called "quantum computers" created so far haven't actuallybeen quantum computers. Pfaff's team, however, seems to have figured out how to use qubits to actually send meaningful messages without destroying the whole thing in the process.
In the lab, his team created qubits and stored them in a low-temperature diamond "prison" which allows the team to more easily study the atoms. Pfaff says the team excited the particles—two electrons and an atomic nucleus—using lasers, which entangles them and turns them into what he calls a "joint entity." They then establish what is known as a "spin" on the electrons, which can be reliably read from across the lab. The first qubit is destroyed, as expected, but is "consumed" on the other end, and the data is successfully transferred.
"The novelty is we were able to determine the outcome of the measurement every single time while preserving the fragile quantum state," he said. "If you know the outcome of that measurement, you can transfer it in real time and read it."
Here's what the whole lab setup looks like:
Image: Hansonlab at TUDelft
It's tricky stuff—basically, Pfaff and others who believe quantum computing and communications are possible are out to disprove one of Einstein's theorems—but the important thing to note is that it's appearing much more likely that this can actually be done, and scientists are making real strides toward making it a reality. Earlier this year, China announced that it would begin building the world's largest quantum communications network, and DARPA and the NSA are also working on quantum computing.
The key now is to make it possible to send actual messages—the "hello world" of quantum communications, Pfaff said. Doing that requires creating quantum memory, a way of reading and storing these states on both sides of the teleporters.
"Bit for bit, you'd send all that information, create entanglement, and repeat it until you're done with it. It requires some other technologies because we don't have memories that last long enough, but in principle, you could already do it," he said.
So, you won't be able to call up Comcast and have a quantum teleporter put into your house anytime soon, but this means that quantum computing can finally move out of the theoretical realm and into the practical one.