Curriculum / Quantum Networking / Capstone: Build a Quantum Repeater Chain
Capstone: Build a Quantum Repeater Chain
Design and simulate a complete quantum repeater chain with entanglement swapping, purification, and secret key generation.
Capstone: Build a Quantum Repeater Chain
Build a complete quantum repeater chain simulation demonstrating how entanglement can be extended across multiple nodes to achieve end-to-end connectivity with high fidelity.
System Overview
You will implement a 4-node repeater chain: Alice, Repeater1, Repeater2, Bob. Each adjacent pair generates Bell pairs over a noisy fiber link; repeater nodes perform entanglement swapping to extend the range; purification improves fidelity before swapping.
Your system will demonstrate four checkpoints:
- 1.Checkpoint 1: Link entanglement, Generate noisy Bell pairs on each link with realistic fiber loss model
- 2.Checkpoint 2: Entanglement swapping, Extend entanglement from Alice→R1 and R1→R2 to Alice→R2
- 3.Checkpoint 3: Entanglement purification, Improve pair fidelity using BBPSSW before long-range swapping
- 4.Checkpoint 4: End-to-end, Chain all operations to establish Alice→Bob entanglement and verify quality
Technical Parameters
- •Segment length: 50 km per link (150 km total)
- •Fiber loss: 0.2 dB/km
- •Initial link fidelity: 0.85 (after noise model)
- •T₂ quantum memory: 100 ms
- •Link attempt rate: 1000 Hz
Without repeaters, end-to-end entanglement over 150 km requires a photon to survive 150 km of fiber: probability ≈ 0.001 (0.1%). With two repeater nodes, each link is 50 km: probability per link ≈ 0.1, and three links must all succeed: 0.001, the same! The advantage of repeaters comes from quantum memories: each 50 km link can retry independently and store its Bell pair until the other links also succeed, so the three links do not need to succeed in the same attempt. Entanglement swapping then joins the stored pairs, and purification repairs the accumulated noise. Swapping alone, without memory, would still require all three links to succeed simultaneously and would not beat direct transmission.
How this lesson works
A multi-step project that combines several concepts into one larger build, checked checkpoint by checkpoint as you go.
Part of: Quantum Networking
Build quantum networks from the ground up, entanglement distribution, quantum repeaters, the quantum internet, and satellite-based QKD.
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