BB84 Quantum Key Distribution Protocol

A
Alice (Sender)
B
Bob (Receiver)
Quantum Channel (Photons)
Public Classical Channel

Alice's Random Bit Generation

Index a (bit value) b (basis bit)

Alice's Basis Selection Rules

(a, b) Basis Quantum State
(0, 0) Z |0⟩
(1, 0) Z |1⟩
(0, 1) X |+⟩
(1, 1) X |−⟩

Bob's Received Photons

Index Received State
|0⟩
|1⟩
|+⟩
|−⟩
Alice randomly chooses bit values (a) and bases (b)
Photons are traveling through the quantum channel...

Basis Comparison and Key Generation

Index Alice's a Alice's b Bob's b' Bob's a' Basis Match Status

Alice's Key

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Bob's Key

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