Project 1: The Quantum Coin Flip - Superposition and Measurement
Build a circuit that produces a perfect 50/50 quantum coin flip.
Project Overview
| Attribute | Value |
|---|---|
| Difficulty | Level 1: Beginner |
| Time Estimate | Weekend |
| Main Language | Python |
| Alternative Languages | Q#, Java |
| Knowledge Area | Superposition |
| Tools | Qiskit or Cirq |
| Main Book | “Quantum Computation and Quantum Information” by Nielsen & Chuang |
What you’ll build: A single-qubit circuit that creates a superposition and measures it repeatedly.
Why it teaches quantum: Superposition is the foundational quantum phenomenon.
Core challenges you’ll face:
- Creating a balanced superposition
- Running repeated measurements
- Interpreting randomness statistically
Real World Outcome
You will see near-equal counts for 0 and 1 after many shots.
Example Output:
$ python coin_flip.py --shots 1000
Counts: 0=498, 1=502
Verification steps:
- Increase shots to see convergence
- Compare to classical random generator
The Core Question You’re Answering
“How does a single gate create two outcomes at once?”
This is the essence of superposition.
Concepts You Must Understand First
Stop and research these before coding:
- Hadamard gate
- Why does H create equal amplitudes?
- Book Reference: Nielsen & Chuang, Ch. 2
- Measurement
- Why do we only see classical outcomes?
- Book Reference: Nielsen & Chuang, Ch. 2
- Probability vs amplitude
- Why do probabilities come from squared magnitudes?
- Book Reference: Nielsen & Chuang, Ch. 2
Questions to Guide Your Design
- Shot count
- How many shots do you need for stable ratios?
- How will you display results?
- Comparison
- Will you compare to a classical RNG to show differences?
- How will you visualize variance?
Thinking Exercise
Hadamard on |0>
| Write the state vector after applying H to | 0>. |
Questions while working:
- Why do you get 50/50 probabilities?
- What happens if you apply H again?
The Interview Questions They’ll Ask
Prepare to answer these:
- “What is superposition?”
- “What does the Hadamard gate do?”
- “Why are measurement outcomes probabilistic?”
- “How does shot count affect results?”
- “What is the difference between amplitude and probability?”
Hints in Layers
Hint 1: Starting Point Build a circuit with a single Hadamard gate.
Hint 2: Next Level Run the circuit multiple times and gather counts.
Hint 3: Technical Details Plot the ratio of 0s and 1s as shots increase.
Hint 4: Tools/Debugging Check that counts approach 50/50 with more shots.
Books That Will Help
| Topic | Book | Chapter |
|---|---|---|
| Hadamard gate | Nielsen & Chuang | Ch. 2 |
| Measurement | Nielsen & Chuang | Ch. 2 |
| Probability | Nielsen & Chuang | Ch. 2 |
Implementation Hints
- Use a simulator backend.
- Keep circuits minimal for clarity.
- Repeat runs to show statistical convergence.
Learning Milestones
- First milestone: You can create a superposition state.
- Second milestone: You can measure and interpret results.
- Final milestone: You can explain probabilistic outcomes.