Quantum Key Distribution: BB84

Investigate quantum key distribution through the BB84 protocol.

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Question

How can two people create a secret key and detect someone listening to the quantum channel?

An eavesdropper must measure the states, and the disturbance appears as errors in the shared key.
An eavesdropper must measure the states, and the disturbance appears as errors in the shared key.

Goals

  • Simulate state preparation, measurement, and key sifting in BB84.
  • Measure the errors caused by an intercept-and-resend attack.

Method

Send random quantum states in two incompatible measurement bases.

  • Let Alice choose random bits and bases, and let Bob measure in random bases.
  • Keep only positions where their bases agree and compare a sample for errors.
  • Insert an eavesdropper and observe how the quantum bit error rate changes.