BB84 protocol

Definition:
The BB84 protocol is the first and most widely known Quantum Key Distribution (QKD) protocol. It was introduced in 1984 by Charles Bennett and Gilles Brassard, and its name comes from their initials and the year of publication.

Scientific context:
BB84 relies on two fundamental principles of quantum mechanics: the Heisenberg uncertainty principle and the no-cloning theorem. These principles ensure that any attempt to intercept or measure the transmitted quantum states disturbs them, thus revealing the presence of an eavesdropper.

Example in practice:
In a typical BB84 setup, the sender (often referred to as Alice) encodes bits of information using the polarization of individual photons, randomly choosing between two bases (rectilinear or diagonal). The receiver (Bob) also randomly selects a basis for each incoming photon. After transmission, Alice and Bob publicly compare the bases used, discard mismatched results, and use the remaining matching bits to generate a secure cryptographic key.

Media:
Play in Quantum Flytrap’s Virtual Lab

Did you know?
The BB84 protocol laid the groundwork for the entire field of quantum cryptography. It is still widely implemented today in fiber-based, free-space, and even satellite-based QKD systems.

Related QSNP publications:

Security of hybrid BB84 with heterodyne detection. Jasminder S Sidhu, Rocco Maggi, Saverio Pascazio and Cosmo Lupo.

Jasminder S Sidhu et al 2025 Quantum Sci. Technol. 10 025012