If someone intercepts the signal and attempts to read the private keys, the entanglement breaks, because measuring an entangled particle changes its state. The sender and receiver use the entangled particles to generate private keys, known only to them, that they can use to encode their messages. According to Caltech Magazine, in this scenario, a sender and a receiver build a secure communication link that includes pairs of entangled particles. Perhaps the most widely used application of quantum entanglement is in cryptography. (Image credit: ICFO) (opens in new tab) What can quantum entanglement be used for? According to NASA, it's also possible to create entangled pairs of photons, or particles of light, by either splitting a single photon and generating a pair of photons in the process, or by mixing pairs of photons in a fiber-optic cable.Īrtistic illustration of a cloud of atoms with pairs of particles entangled between each other, represented by the yellow-blue lines. One method is to cool the particles and place them close enough together so that their quantum states (representing the uncertainty in the position) overlap, making it impossible to distinguish one particle from the other.Īnother way is to rely on some subatomic process, like nuclear decay, that automatically produces entangled particles. There are many ways to entangle particles. While you may know the status of a distant particle's state, you cannot communicate this information faster than the speed of light. In other words, the limits imposed by the speed of light still hold with entangled systems. They must exchange information with each other no faster than the speed of light to confirm. An observer at the faraway particle does not know if the local observer has disturbed the entangled system, and vice versa. However, although entangled systems do not maintain locality (meaning one part of an entangled system can immediately influence a faraway particle), they do respect causality, meaning that effects always have causes. There is no generally accepted resolution to the paradox. But experiments have repeatedly confirmed that entangled particles do influence each other regardless of distance, and quantum mechanics remains verified to this day. This result is known as the EPR paradox (short for Einstein, Podolsky and Rosen), according to the American Physical Society - an effect Einstein dubbed "spooky action at a distance." He used the paradox as evidence that quantum theory was incomplete. In principle, you could place two entangled particles on opposite ends of the galaxy and still have this instantaneous knowledge, which appears to violate the limit of the speed of light. As Einstein, Podolsky and Rosen discovered, entanglement appears instantaneous: Once you have knowledge of one quantum state, you automatically know the quantum state of any entangled particles.
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