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What is quantum key distribution?
Quantum key distribution lets two parties share a secret encryption key while detecting eavesdropping attempts thanks to the nature of quantum measurement.
In the BB84 protocol proposed by Bennett and Brassard in 1984, the sender prepares photons in one of two randomly chosen bases. An eavesdropper who measures without knowing the basis disturbs the states, which shows up as errors in the sample bits the parties compare.
QKD’s security rests on the laws of physics rather than on computing power. In practice it has limits in distance, rate and hardware security.
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- Quantum measurement · Quantum measurement ends a qubit’s superposition and returns 0 or 1, with the result chosen at random according to the amplitudes.
- Shor’s algorithm · Shor’s algorithm factors large numbers exponentially faster than known classical methods, which is why it threatens RSA encryption.
- Quantum teleportation · Quantum teleportation is a protocol that transfers the unknown state of a qubit to another qubit using a shared entangled pair and two classical bits.