Quantum Supremacy Shown with the Odd-Cycle Game
Why in the news
A simple, easily checked game gave a fresh demonstration of quantum supremacy in April 2025, unlike earlier tests built on very complex problems such as random circuit sampling.
Key facts
- Quantum supremacy: a quantum device beating the best classical computers at a defined task.
- Game: points on a circle with an odd count must get two colours with neighbours differing, which is impossible. Alice and Bob, unable to talk, answer referee questions: same point means same colour, adjacent points means different colours.
- Best classical win rate: 83.3% for a 3-point circle.
| Item | Outcome |
|---|---|
| Set-up | Two strontium atoms, 2 m apart, entangled by lasers |
| Games | 101,000 on circles of 3 to 27 points |
| Win rate | 97.8%; the rest lost to entanglement noise |
| Supremacy shown for | Circles up to 19 points |
Significance
- Uses just two qubits, against Google’s 53-qubit Sycamore.
- Easier verification; shows the strongest quantum correlations recorded between separated particles.
- Could suit restricted-communication tasks like rendezvous: for 1 million meeting points, Grover’s algorithm needs about 1,000 steps rather than 1 million.
Exam angle
- Terms: entanglement, qubit, Grover’s algorithm.
- Atoms: strontium; numbers: 83.3% vs 97.8%.