From cities in the sky to robot butlers, futuristic visions fill the history of PopSci. In the Are we there yet? column we check in on progress towards our most ambitious promises. Read more from the series here.
Jetpacks, flying cars, hoverboards, bullet trains—inventors have dreamt up all kinds of creative ways, from science fiction to science fact, to get from point A to point B. But when it comes to transportation nirvana, nothing beats teleportation—vehicle-free, instantaneous travel. If beam-me-up-Scotty technology has gotten less attention than other transportation tropes—Popular Science ran short explainers in November 1993 and September 2004—it’s not because the idea isn’t appealing. Regrettably, over the decades there just hasn’t been much progress in teleportation science to report. However, since the 2010s, new discoveries on the subatomic level are shaking up the playing field: specifically, quantum teleportation.
Just this month, the 2022 Nobel Prize in Physics was awarded to three scientists “for experiments with entangled photons,” according to the Royal Swedish Academy of Sciences, which selects the winners. The recipients’ work demonstrated that teleportation is possible—well, at least between photons (and with some serious caveats on what could be teleported). The physicists—Alain Aspect, John Clauser, and Anton Zeilinger—had independent breakthroughs over the last several decades. The result of their work not only demonstrated quantum entanglement in action but also showed how the arcane property could be a channel to teleport quantum information from one photon to another. While their findings are not anywhere close to transforming airports and train stations into Star Trek-style transporters, they have been making their way into promising applications, including quantum computing, quantum networks, and quantum encryption.
“Teleportation is a very inspiring word,” says Maria Spiropulu, the Shang-Yi Ch’en professor of physics at the California Institute of Technology, and director of the INQNET quantum network program. “It evokes our senses and suggests that a weird phenomenon is taking place. But nothing weird is taking place in quantum teleportation.”
When quantum mechanics was being hashed out in the early 20th century between physicists like Max Planck, Albert Einstein, Niels Bohr, and Erwin Schrödinger, it was becoming clear that at the subatomic particle level, nature appeared to have its own hidden communication channel, called quantum entanglement. Einstein described the phenomenon scientifically in a paper published in 1935, but famously called it “spooky action at a distance” because it appeared to defy the normal rules of physics. At the time, it seemed as fantastical as teleportation, a phrase first coined by writer Charles Fort just four years earlier to describe unexplainable spectacles like UFOs and poltergeists.
“Fifty years ago, when scientists started doing [quantum] experiments,” says Spiropulu, “it was still considered quite esoteric.” As if in tribute to those scientists, Spiropulu has a print honoring physicist Richard Feynman in her office. Feynman won the Nobel Prize in 1965 for his Feynman diagrams, a graphical interpretation of quantum mechanics.
Spiropulu equates quantum entanglement with shared memories. “Once you marry, it doesn’t matter how many divorces you may have,” she explains. Because you’ve made memories together, “you are connected forever.” At a subatomic level, the “shared memories” between particles enables instantaneous transfer of information about quantum states—like atomic spin and photon polarization—between distant particles. These bits of information are called quantum bits, or qubits. Classical digital bits are binary, meaning that they can only hold the value of 1 or 0, but qubits can represent any range between 0 and 1 in a superposition, meaning there’s a certain probability of being 0 and certain probability of being 1 at the same time. Qubits’ ability to take on an infinite number of potential values simultaneously allows them to process information much faster—and that’s just what physicists are looking for in a system that leverages quantum teleportation.
[Related: Quantum teleportation is real, but it’s not what you think]
But for qubits to work as information processors, they need to share information the way classical computer chips share information. Enter entanglement and teleportation. By entangling subatomic particles, like photons or electrons—the qubits—and then separating them, operations can be performed on one that generates an instantaneous response in its entangled twin.
The farthest distance to date that qubits have been separated was set by Chinese scientists, who used quantum entanglement to send information from Tibet to a satellite in orbit 870 miles away. On terra firma, the record is just tens of miles, traveling through fiber optic connections and through air (line of sight lasers).
Qubits’ strange behavior—acting like they’re still together no matter how far apart they’ve been separated—continues to puzzle but amaze physicists. “It does appear magical,” Spiropulu admits. “The effect appears very, ‘wow!’ But once you break it down, then it’s engineering.” And in just the past five years, great strides have been made in quantum engineering to apply the mysterious but predictable characteristics of qubits. Besides quantum computing advances made by tech giants like Google, IBM, and Microsoft, Spiropulu has been spearheading a government- and privately funded program to build out a quantum internet that leverages quantum teleportation.
With some guidance from Spiropulu’s postdoctoral researchers at Caltech, Venkata R. (Raju) Valivarthi and Neil Sinclair, this is how state-of-the-art quantum teleportation would work (you might want to strap yourself in):
Step 1: Entangle
Using a laser, a stream of photons shoots through a special optical crystal that can split photons into pairs. The pair of photons are now entangled, meaning they share information. When one changes, the other will, too.
Step 2: Open a quantum teleportation channel
Then, one of the two photons is sent over a fiber optic cable (or another medium capable of transmitting light, such as air or space) to a distant location.This opens a quantum channel for teleportation. The distant photon (labeled photon one above) becomes the receiver, while the photon that remains behind (labeled photon two) is the transmitter. This channel does not necessarily indicate the direction of information flow as the photons could be distributed in roundabout ways.
Step 3: Prepare a message for teleportation
A third photon is added to the mix, and is encoded with the information to be teleported. This third photon is the message carrier. The types of information transmitted could be encoded into what’s called the photon’s properties, or state, such as its position, polarization, and momenta. (This is where qubits come in, if you think of the encoded message in terms of 0s, 1s, and their superpositions.)
Step 4: Teleport the encoded message
One of the curious properties of quantum physics is that a particle’s state, or properties, such as its spin or position, cannot be known until it is measured. You can think of it like dice. A single die can hold up to six values, but its value isn’t known until it’s rolled. Measuring a particle is like rolling dice, it locks in a specific value. In teleportation, once the third photon is encoded, a joint measurement is taken of the second and third photons’ properties, which means their states are measured at the same time and their values are locked in (like viewing the value of a pair of dice). The act of measuring changes the state of the second photon to match the state of the third photon. As soon as the second photon changes, the first photon, on the receiving end of the quantum channel, snaps into a matching state.
Now the information lies with photon one—the receiver. However, even though the information has been teleported to the distant location, it’s still encoded, which means that like an unrolled die it’s indeterminate until it can be decoded, or measured. The measurement of photon one needs to match the joint measurement taken on photons two and three. So the outcome of the joint measurement taken on photons two and three is recorded and sent to photon one’s location so it can be repeated to unlock the information. At this point, photons two and three are gone because the act of measuring photons destroys them. Photons are absorbed by whatever is used to measure them, like our eyes.
Step 5: Complete the teleportation
To decode the state of photon one and complete the teleportation, photon one must be manipulated based on the outcome of the joint measurement, also called rotating it, which is like rolling the dice the same way they were rolled before for photons one and two. This decodes the message—similar to how binary 1s and 0s are translated into text or numeric values. The teleportation may seem instantaneous on the surface, but because the decoding instructions from the joint measurement can only be sent using light (in this scenario over a fiber optic cable), the photons only transfer the information at the speed of light. That’s important because teleportation would otherwise violate Einstein’s relativity principle, which states that nothing travels faster than the speed of light—if it did, this would lead to all sorts of bizarre implications and possibly upend physics. Now, the encoded information in photon three (the messenger) has been teleported from photon two’s position (transmitter) to photon one’s position (receiver) and decoded.
Whew! Quantum teleportation complete.
Since we transmit digital bits today using light, it might seem like quantum teleportation and quantum networks offer no inherent advantage. But the difference is significant. Qubits can convey much more information than bits. Plus, quantum networks are more secure, since attempts to interfere with quantum entanglement would destroy the open quantum channel.
Researchers have discovered many different ways to entangle, transmit, and measure subatomic information. Plus, they’re upgrading from teleporting information about photons, to teleporting information about larger-sized particles like electrons, and even atoms.
[Related: Warp speed space travel just got a tiny bit more realistic]
But it’s still just information being transmitted, not matter—the stuff that humans are made of. While the ultimate dream may be human teleportation, it actually might be a good thing we’re not there yet.
The Star Trek television and film franchise not only helped popularize teleportation but also glamorized it with a glittery dissolve effect and catchy transporter-tone. The Fly, on the other hand, a movie about teleportation gone wrong, painted a much darker, but possibly scientifically truer picture of teleportation. That’s because teleportation is really an act of reincarnation. Teleportation of living matter is risky business: It would require scanning the traveler’s information at the point of departure, transmitting that information to the desired coordinates, and deconstructing them at the point of departure while simultaneously reconstructing the traveler at the point of arrival—we wouldn’t want errant copies of ourselves on the loose. Nor would we want to arrive as a lifeless copy of ourselves. We would have to arrive with all our beating, breathing, blinking systems intact in order for the process to be a success. Teleporting living beings, at its core, is a matter of life and death.
Or not.
Formidable minds, such as Stephen Hawking, have proposed that the information, or vector state, that is teleported over quantum entanglement channels does not have to be confined to subatomic particle properties. In fact, entire blackholes’ worth of trapped information could be teleported, according to this theory. It gets weird, but by entangling two blackholes and connecting them with a wormhole (a space-time shortcut), information that disappears into one blackhole might emerge from the other as a hologram. Under this reasoning, the vector states of molecules, humans, and even entire planets could theoretically be teleported as holograms.
Kip Thorne, a Caltech physicist who won the 2017 Nobel Prize in Physics for gravity wave detection, may have best explained the possibilities of teleportation and time travel as far back as 1988: “One can imagine an advanced civilization pulling a wormhole out of the quantum foam and enlarging it to classical size. This might be analyzed by techniques now being developed for computation of spontaneous wormhole production by quantum tunneling.”
For now, Spiropulu remains focused on the immediate promise of quantum teleportation. But it won’t look anything like Star Trek. “‘Beam me up, Scotty?’ No such things,” she says. “But yes, a lot of progress. And it’s transformative.”