Quantum Teleportation

Here we explain the idea using clocks as an easy example. A quantum state is a state where we do not know the time. When we measure it, it becomes a fixed, classical state such as “3AM” or “6AM.” One type of quantum state is called an EPR pair. This is a pair of quantum states where the times are unknown, but they always differ by 3 hours.

Quantum teleportation is a technique that transfers this “unknown time” state to a clock located somewhere else, while keeping the time unknown throughout the process. It is known that the original quantum state is destroyed during this process. This is required by a fundamental rule of quantum physics called the no-cloning theorem.

Let us look at a concrete example. In the figure on the right, the source state S and the EPR pair A and B are all quantum states, so their times are unknown. However, let us assume that if we were to measure them, their times would be 2AM, 3AM, and 6AM, respectively (with A and B differing by 3 hours). Quantum teleportation consists of three steps. In the first step, Alice measures the difference between A and S, and finds that S is 1 hour earlier than A. In the second step, Alice sends this information to Bob. In the third step, Bob advances B by four hours. These 4 hours come from the 3-hour difference between A and B, plus the 1-hour difference between S and A. As a result, B changes from 6AM to 2AM, matching S. Alice and Bob have successfully transferred the time of S to B without ever knowing the actual times of S, A, or B.

The quantum teleportation technology being developed in ASPIRE for gravitational-wave detectors is more complicated, but the basic principle is the same.