Physicists have blasted through the previous record of 25 km for the teleportation of quantum information, bringing us even closer to a quantum internet with secure connections.
No, we still can’t teleport people or objects. But teleporting less tangible things, like magnetic fields or quantum information about particles, definitely lies in the realm of possibility. Scientists have been teleporting quantum information between particles for some time now, but new technology has allowed a team at the U.S. National Institute of Standards and Technology to achieve a distance of 102 km, 4 times the previous record.
So what exactly is quantum teleportation, and how does it work? It’s the transfer of a particle’s quantum state, or information about its properties and structure, to another distant particle, without needing the particles to actually travel that distance. This process relies on “quantum entanglement,” a phenomenon where two particles are so tightly bound that whatever happens to one particle instantaneously happens to the other. Likewise, measuring the state of one particle allows scientists to determine the state of its entangled twin.
But until scientists measure the state of one particle, its information remains unknown, and the possible states are “superpositioned” in time. If these superpositioned quantum states line up with each other, they are “in phase,” while if they don’t line up, they are “out of phase” and cancel each other out.
The NIST team started with a single photon beam in a superposition of two possible quantum states, either “early” or “late,” and used a crystal to split the photon into two entangled daughters: a helper photon and an output photon. These two photons are now entangled, and the output photon is sent on its way through a 102 km fiber optic cable.
Then they made a third input photon with a known quantum state — either “early” or “late,” or a superposition of both. They sent the input and helper photons towards a beam splitter, which could either let the photon pass through in a straight line towards one detector or send it ricocheting at an angle towards a second detector. These detectors time the arrival of each photon, and when the photons arrive at staggered times, they know that the helper and input photons are either in opposite states or superpositioned in different ways.
Meanwhile, the output photon is still entangled with the helper photon, so the physicists knew that it had the opposite quantum state from the input photon. In this way, they teleported the opposite quantum state of the input photon across 102 km of optic fibers, without any interaction between input and output. The output photon’s quantum state was confirmed with another detector at the end of the cable. This record-breaking distance was made possible by new single-photon detectors that were far more sensitive, and could pick up the few output photons that made it all the way down the cable. Lasers erode as they travel such a long distance, which loses most of the quantum information by the end of the cable.
So other than another awesome achievement in quantum physics, what does this have to do with us? The “early” or “late” quantum states of photons can translate to another sort of binary data — 0s and 1s, for instance. Teleportation of binary data over such long distances would prevent any interference or hacking in transport, making for super-secure encryption of Internet communications, and higher speeds as well.
But first the technology has to further develop. The perfect staggered arrival times between helper and input photons only happen about 25 percent of the time, so the research team must work to increase the efficiency of the laser transmissions. Another inconvenience comes from the necessary equipment — for example, the ultra-sensitive detectors need to be maintained at only one degree above absolute zero, which isn’t very practical for real applications. But once these hurdles are overcome, we can enter a new world of communications where quantum computing is the norm.