Final answer:
Quantum Key Distribution detects eavesdroppers by noticing disturbances in the interference patterns caused by unauthorized measurements of the quantum states of photons, which are indicators of eavesdropping attempts.
Step-by-step explanation:
Quantum Key Distribution (QKD) leverages the principles of quantum mechanics to detect the presence of an eavesdropper. When a third party tries to intercept the quanta (usually photons) carrying the key, their quantum state is altered due to the measurement process - an effect predicted by the Heisenberg's uncertainty principle. This alteration can be detected as a disturbance in the interference patterns that result when quantum objects like photons exhibit wave-like behavior.
In a QKD system, a series of photons are encoded with information (bits of the cryptographic key) and sent to the receiver. If an eavesdropper tries to measure these photons to learn the key, the act of measuring disturbs their quantum states because photons, electrons, and atoms display both wave and particle characteristics. This disturbance changes the interference pattern and can be detected, alerting the legitimate parties to the presence of an eavesdropper. The PhET Explorations on Quantum Wave Interference delve into this behavior by allowing users to visualize how wave patterns change when quantum particles are measured.