Quantum teleportation

Quantum teleportation is a way to send special kinds of information, called quantum information, from one place to another. Unlike in science fiction stories where people or objects can move instantly, quantum teleportation only moves this tiny bit of information. The person sending it doesn’t even need to know exactly what the information is, but they do need to send a regular message to the person receiving it. Because of this, quantum teleportation can’t happen faster than light can travel.

The idea of quantum teleportation was first shared in a science paper in 1993 by a group of scientists. Not long after, in 1997, scientists were able to show it really works in experiments. Since then, scientists have used quantum teleportation with many different kinds of tiny particles, like photons, atoms, and even electrons. The farthest it has been sent is a huge distance of 1,400 kilometers, using a special satellite called Micius.

Non-technical summary

In the world of tiny particles, there is a special way to move information from one place to another, called quantum teleportation. This is not like magic where things disappear and reappear; it only moves the information about a tiny particle, called a qubit. A qubit can be in two states at once, unlike a regular bit that is either 0 or 1.

To make this work, two particles need to be linked in a special way, called entanglement. This means that when you look at one particle, you instantly know about the other, even if they are far apart. The person sending the information mixes their particle with one of the entangled particles and sends some results through a regular channel. The person receiving the information uses these results to recreate the original information. This way, the information is moved without ever being copied or moving faster than light.

Protocol

Quantum teleportation needs a few special tools to work. First, we need a way to send two regular pieces of information between two places. We also need a pair of tiny particles, called qubits, that are linked together in a special way — this is called an entangled Bell state. One of these linked qubits goes to place A, and the other goes to place B.

Here’s how it works:

1. One qubit from the linked pair is sent to place A, and the other to place B.
2. At place A, we look closely at the linked qubit and the qubit we want to send. This tells us one of four possible results, which we can write down using two regular pieces of information. After this, the qubits at place A are no longer needed.
3. We send these two pieces of information from place A to place B. This is the slowest step because it can’t go faster than light.
4. Depending on the result we sent, the linked qubit at place B might be in one of four states. We use the two pieces of information to change the qubit at place B just enough so that it now matches the original qubit we wanted to send.

This way, the special property of the original qubit is moved from place A to place B, even though we never actually moved the particle itself!

Experimental results and records

Work in 1998 checked the first ideas, and by August 2004, the distance for moving quantum information was increased to 600 meters using special glass wires called optical fiber. Since then, scientists have kept increasing this distance. It went up to 16 kilometers, then 97 kilometers, and now stands at 143 kilometers. This last record was set in open-air tests between two astronomical observatories in the Canary Islands, done between parts of the Instituto de Astrofísica de Canarias. More recently, in September 2015, another test reached 102 kilometers over optical fiber. For experiments with materials, the farthest distance was 21 meters.

One special type of this process, called "open-destination" teleportation, was shown in 2004 using five linked particles of light. Scientists have also moved the combined state of two tiny parts of information. In April 2011, they moved wave packets of light up to a bandwidth of 10 MHz while keeping their special properties. In August 2013, they achieved a more reliable way to move quantum information. On May 29, 2014, scientists found a reliable method for moving data using quantum teleportation. In February 2015, scientists in China moved multiple pieces of quantum information over 150 meters. In 2016, they did it over 6.5 kilometers, and in September 2016, over 6.2 kilometers in Calgary. By December 2020, they moved information over 44 kilometers with very high accuracy.

Researchers have also moved information between clouds of gas atoms, which is interesting because these clouds are large groups of atoms.

It is possible to move special operations too. In 2018, scientists at Yale moved a certain operation between tiny bits of information.

First suggested in 1993, quantum teleportation has been shown in many different ways. It has been done using two levels of a single particle of light, a single atom, a trapped ion, and two particles of light together. In 1997, two groups did the experiment. The first group was led by Sandu Popescu in Italy, followed by a group led by Anton Zeilinger.

The results from Popescu's group showed that regular methods alone could not copy the movement of certain light states. Zeilinger's group made pairs of linked particles of light using a process called parametric down-conversion. They made sure the particles could not be told apart by when they arrived. The particles were sent through special filters to make their timing much longer. They used a method to check the link so they could recognize when the special property moved from one particle to another.

In one of Zeilinger's early tests, the first particle of light was set at a 45° angle. Quantum teleportation was proven when both particles were found in a certain state, which happens 25% of the time. Two detectors were placed to record when both particles arrived together, which showed the state. If the detectors recorded together and the third particle was found at a 45° angle, it proved the information had moved.

Zeilinger's group later did an experiment over 144 kilometers between two islands in the Canary Islands, La Palma and Tenerife. They used special tools to make sure the particles stayed linked even over such a long distance. They shared the linked state between the two places, acting like two characters, Alice and Bob. Alice did a measurement on her particle and sent the result to Bob, who then used it to change his particle to match the original state.

The results showed that the moved information matched the original very well, better than what regular methods could do, even though there was a lot of loss over the long distance.

In 2004, another test was done over the Danube River in Vienna, moving information over 600 meters through a special glass wire under the river. Alice measured her particles and sent the results to Bob, who then changed his particle to match. The moved information matched very well, better than regular methods.

For a different kind of test, three tiny bits were used: the sender's bit, a helper bit, and the receiver's bit, which was linked with the helper. Calcium ions were used as the bits. Two bits were prepared in a linked state, and the third was set randomly. By shining light on them, scientists could measure the states. The results showed good matching, better than what regular methods could do.

In a big step, scientists moved information from the ground to a satellite launched on August 16, 2016, called Micius, flying about 500 kilometers high. They moved the information over distances from 500 to 1,400 kilometers. The moved information matched well with the original.

Quantum teleportation has also been done over regular internet cables at the same time as normal internet traffic. This shows that quantum and regular internet can share the same cables.

In April 2025, researchers at the University of Illinois Urbana-Champaign moved information with 94% accuracy using a special method with tiny light structures made of indium, gallium, and phosphide. This made the process much better than before.

Formal presentation

Quantum teleportation is a way to send special bits of information, called qubits, from one place to another without moving the actual particles. Imagine you want to send a secret message to a friend far away. In quantum teleportation, the message is sent using a special pair of particles that are linked together, called entangled particles.

First, the person sending the message, Alice, needs to have one particle from an entangled pair. The other particle of this pair is with the person receiving the message, Bob. Alice also has the special message particle she wants to send. By doing a special measurement on her two particles, Alice can figure out which of four possible results she got. She then sends this result to Bob using regular bits of information. With this information, Bob can use a simple action on his particle to make it match the original message Alice wanted to send. This way, the message is "teleported" from Alice to Bob without either of them ever moving the particles themselves.

Certifying quantum teleportation

When testing how well quantum teleportation works, scientists look at how close the final quantum state is to the original. They use a measure called average fidelity to see if the teleportation is better than what could be done with regular, classical methods.

For teleporting certain types of quantum states, classical methods can only reach an average fidelity of 2/3. If a quantum teleportation method beats this number, it is considered successful. However, scientists can use different ways to measure how different the states are, and each method might give a different result. This means a teleportation method might seem successful with one measuring tool but not with another.

Alternative notations

Quantum teleportation can be shown in pictures using special drawings called Penrose graphical notation. There are many ways to write down the steps for quantum teleportation. One common way uses symbols for tiny operations called quantum gates.

In these pictures, a special change can be made using two simple gates: the Walsh-Hadamard gate and something called the Controlled NOT gate.

Entanglement swapping

Further information: Quantum entanglement swapping

Quantum teleportation can be used to connect particles in a special way, even if they are far apart. Imagine three friends: Alice, Bob, and Carol. If Alice and Bob have particles that are connected, and Bob shares his particle with Carol through teleportation, then Alice’s particle becomes connected to Carol’s particle. This means Alice and Carol can now work together with their particles, even though they never met!

This process is important for building networks where particles can share information over long distances. Scientists use special measurements and adjustments to make sure the particles stay connected correctly.

Generalizations of the teleportation protocol

The basic way to move quantum information from one place to another can be changed in many ways. One way is to use systems with more levels than the simple ones usually used. This was talked about in the first paper about quantum teleportation.

Another way is to use systems that can keep going forever, which was tried for the first time in an experiment.

Using special connections between more than two places lets the person sending the information choose to send it to many receivers at once, or to send information that needs more than one person to understand it. This can also let some people decide if others are allowed to get the information.

Logic gate teleportation

Main article: Quantum gate teleportation

Quantum teleportation lets us move quantum information from one place to another. Imagine Alice has a special quantum state she wants to send to Bob, who is far away. They share a special connection called an entangled state. By using this connection and some clever measurements, Alice can send the quantum information to Bob without even knowing exactly what it is.

This process is important for building quantum computers and networks because it helps move information around without disturbing the delicate quantum states.

Local explanation of the phenomenon

A local way to understand quantum teleportation was suggested by David Deutsch and Patrick Hayden. They thought about it using the many-worlds idea of quantum mechanics. In their view, the two pieces of information Alice sends to Bob hold special, hard-to-reach details that help move the quantum state from one place to another. This ability for quantum information to travel through normal channels and stay safe is what makes quantum teleportation work.

Recent developments

Quantum teleportation is still new, and scientists are working to understand and improve it. One area of focus is using special arrangements of logic gates to reduce errors in quantum computers. These arrangements help protect the information being moved and need fewer resources.

Researchers have also looked at moving information using higher dimensional quantum states, called qudits. Another important development is improving the quality of the information being sent by using a different kind of information method. This helps keep the information clear and accurate. Scientists have also shown that it's possible to move quantum information to particles that already have some information, which can help improve future calculations.