Industry & Era
Quantum Supremacy
The milestone at which a quantum computer performs a specific task faster than any classical computer could.
Definition
Quantum supremacy (also called quantum advantage in some contexts) refers to the point at which a quantum computer demonstrates the ability to perform a specific computation faster than the best available classical computers or supercomputers. The term was popularized after Google's 2019 announcement that its Sycamore processor had achieved this milestone for a specific mathematical sampling task.
In depth
Quantum supremacy is the demonstration that a quantum computer can perform some task that no classical computer can do in reasonable time, regardless of whether the task is useful. John Preskill coined the term in 2012. The first claim came from Google in October 2019, when its 53-qubit Sycamore chip sampled the output of random circuits in about 200 seconds, a task Google estimated would take the best supercomputer 10,000 years. IBM disputed the estimate, arguing that a different method would take about two and a half days, and later simulations using tensor networks reduced the gap further.
Other groups followed. USTC in China reported supremacy with the Jiuzhang boson sampling machines, starting in 2020, and with the superconducting Zuchongzhi processors in 2021 and 2025. Google's 2024 Willow chip ran a random circuit benchmark on 103 qubits in under five minutes, with a classical estimate of 10 to the 25 years. These claims are repeatedly tested by classical researchers, and results have been narrowed by improved algorithms, so the status of each claim is contested.
Many in the field now prefer the term quantum advantage, partly because supremacy has unfortunate connotations, and partly because the goal is useful advantage on meaningful tasks, not artificial benchmarks. Supremacy experiments are still valuable as tests of hardware and of the theory of computational hardness, and they motivated the development of cross-entropy benchmarking and better classical simulation methods.
Technical Definition
Google's 2019 claim involved random circuit sampling — a task with no direct practical application, but one that is believed to be exponentially hard for classical computers. The Sycamore chip's result was later challenged and partially rebutted by improved classical simulations, illustrating that 'supremacy' claims for specific tasks are often contested and that the boundary between 'hard for classical' and 'achievable quantumly' is still being defined.
Visual Explanation: An Analogy
Quantum supremacy is like a new type of runner completing a specific kind of race faster than any human — impressive and significant, but not the same as being better at all races. The task may be specially chosen to suit the quantum runner's strengths.
Key facts
| Item | Detail |
|---|---|
| Coined | John Preskill, 2012 |
| Google Sycamore (2019) | 53 qubits, about 200 seconds versus an estimated 10,000 years |
| Google Willow (2024) | 103 qubits, under 5 minutes versus an estimated 10^25 years |
| USTC | Jiuzhang (photonic, 2020) and Zuchongzhi (superconducting, 2021 and 2025) |
| Classical response | Tensor network and GPU methods have repeatedly cut estimates |
Where the idea comes from
The concept comes from Preskill's 2012 essay, building on work by Boixo, Aaronson, and others on sampling hardness. The 2019 Nature paper by Google's team was the first claim, followed by many others.
Real-World Use Cases
- Marking a historical milestone in quantum computing development
- Motivating further investment and research in quantum hardware
- Prompting debate about how to fairly measure and compare quantum and classical performance
How it differs from related ideas
- Supremacy concerns a task beyond classical reach, and advantage usually implies a useful or practically meaningful task.
- A supremacy claim is tied to the best known classical algorithms, which can improve.
- Sampling tasks differ from decision problems, but hardness results exist for them.
Common Misconceptions
- Quantum supremacy on one specific task does not mean a quantum computer is generally more powerful than a classical computer for all tasks.
- The term 'supremacy' is sometimes replaced by 'quantum advantage' to avoid implying broader superiority.
Frequently asked questions
What is quantum supremacy?
A demonstration that a quantum computer can do a specific task that classical computers cannot do in reasonable time, even if the task has no practical use.
Has it been achieved?
Several groups claim it, starting with Google in 2019, though classical researchers have disputed or narrowed some claims.
Why do some researchers avoid the term?
Because of its connotations and because the focus is shifting to useful quantum advantage.
Related Terms
Keep exploring
- Algorithm: Random Circuit Sampling (Quantum Supremacy Experiments)
- Algorithm: Boson Sampling
- Hardware: Google Sycamore
- Hardware: Google Willow
- Hardware: Xanadu Borealis