Quantum encryption keys change instantly if a hacker watches them

Traditional encryption relies on complex math that powerful computers might eventually crack, but quantum key distribution (QKD) relies on the fundamental laws of physics. In a QKD system, two parties share a secret key using individual light particles called photons. Because of the principles of quantum mechanics, the act of observing or measuring a quantum system changes it. If a third party tries to eavesdrop on the transmission, the physical state of the photons shifts immediately, alerting the senders and rendering the stolen key useless.