Here’s how quantum teleportation works

In October 2022, the Nobel Prize in Physics was awarded to three scientists – Alain Aspect, John Clauser and Anton Zeilinger – whose work demonstrated that teleportation is possible between photons. A photon is the smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light.

According to the Royal Swedish Academy of Sciences which selects the winners, 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,” reads a report by American digital magazine, Popular Science.

 Tech giants like Google, IBM and Microsoft have made strides in quantum computing by building quantum computers.

According to Shang-Yi Ch’en professor of physics at the California Institute of Technology, and director of the INQNET quantum network program, “Teleportation is a very inspiring word. It evokes our senses and suggests that a weird phenomenon is taking place. But nothing weird is taking place in quantum teleportation.”

Prof. Spiropulu has been spearheading a government- and privately funded program to build out a quantum internet that leverages quantum teleportation together with her postdoctoral researchers at Caltech, Venkata R. (Raju) Valivarthi and Neil Sinclair.

According to the trio, the following five steps shows how  state-of-the-art quantum teleportation would work:

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.

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.

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.)

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.

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.

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.