BB84 QKD Research Project

Project Abstract

This project demonstrates a macroscopic proof-of-concept of the BB84 Quantum Key Distribution (QKD) protocol. While commercial QKD relies on single, indivisible photons to guarantee unconditional security via Heisenberg's Uncertainty Principle, this architecture emulates the logical and algorithmic validity of the protocol using classical optics.

Utilizing ESP32 microcontrollers communicating via a low-latency ESP-NOW handshake, the system synchronizes two physically isolated nodes (Alice and Bob). Motorized polarizers dictate the quantum state, while a reverse-biased BPW34 photodiode captures the intensity. A centralized server subsequently executes the sifting phase, applying dynamic thresholding to calculate the Quantum Bit Error Rate (QBER) and extract the final cryptographic key.

System Methodology

The transmission process obeys classical optics and Malus's Law to emulate quantum collapse:

State Generation: Alice generates a random bit and basis, rotating a NEMA 17 stepper motor to 0°, 45°, 90°, or 135°.
Synchronization: To account for mechanical travel time, Bob issues an ESP-NOW ready flag. Alice verifies position and issues a timestamped trigger.
Measurement: Bob measures the physical light intensity. If the hardware bases match, intensity is deterministic (100% or 0%). If mismatched, intensity is exactly 50%.
Classical Sifting: Data is pushed via WiFi HTTP GET requests to this server, where mismatches are discarded and the Sifted Key is generated.

Project Abstract

System Methodology

Hardware Stack