What Should We Make of Google’s Claim of Quantum Supremacy?

  • Google achieved a significant technical milestone, but we have much further to go to achieve practical, production-scale applications using quantum computers. Quantum supremacy in a niche, specialized, contrived “task” does not imply the achievement of quantum supremacy for any real-world application let alone for all potential applications of quantum computing.
  1. Generate a random sequence of quantum logic gates (called a circuit). This is classical code.
  2. Run the randomly-generated circuit. This is really the only part of the algorithm which is actually a quantum algorithm.
  3. Measure the results (qubits). They call this sampling. This transitions from the quantum code to classical data, producing one classical bit for the quantum state of each qubit.
  4. Rerun the circuit and measure the qubits a million times — since quantum computers are probabilistic rather than deterministic as classical computers are. They collect a million samples.
  5. Compare the result to a simulation of the quantum circuit on a classical computer to make sure they agree.
  6. You can only do that up to a certain circuit size before it becomes very slow on a classical computer.
  7. Then they extrapolate how long that simulation would take for the maximum circuit size which could be run on the quantum computer, and that’s where Google gets the 10,000 years number reported in the press.
  1. A notable milestone in quantum computing. The first time a quantum computer performed a computation which is not easily performed on a classical computer.
  2. Great to show that any algorithm can achieve supremacy over classical computing, even if contrived.
  3. Very nice hardware advance, distinct from supremacy itself.
  4. A notable feat of engineering.
  5. Great to achieve 50 working qubits.
  6. Great to achieve longer coherence time.
  7. Great to have a complete grid topology for qubit connectivity.
  8. Will enable a wider and deeper range of proof of concept implementations.
  9. The hype and attention will likely boost quantum computing R&D investment, venture capital funding for startups, corporate spending on quantum computing, and overall attention to the technology and its potential applications.
  1. There is still no universal, mathematically precise, and technically verifiable definition for the term quantum supremacy. Even Prof. John Preskill, who coined the term in 2012, does not have a precise, technically-verifiable definition of the term. Most recently he referenced the termto describe the point where quantum computers can do things that classical computers can’t, regardless of whether those tasks are useful.” We get the general idea, but generality and verifiable science are not quite the same thing. I like my own definition, but the essential pair of problems with the term is that classical computers are a moving target, constanting improving, and our technical abilities to develop algorithms to exploit classical computers are also constantly improving. Even if physics and hardware may have limits, our cleverness and problem-solving abilities don’t appear to have any limits.
  2. Not quite as dramatic a milestone as the hype suggests. Too contrived. Not a commonly recognized real-world application.
  3. IBM has also managed to engineer a 53-qubit machine — and it’s now available, rather than simply a research project.
  4. IBM disputes Google’s claim of quantum supremacy. It’s debatable and depends on your perspective. Technically, I think IBM has a good point, but Google’s results are still impressive.
  5. Not really heralding a new era yet. Incremental evolution rather than a true quantum leap. Besides I don’t think any credible scientist should be talking that way, using such hyperbolic language — scientists do best when focusing on the science, not… marketing.
  6. Barely achieved quantum supremacy, by just a few qubits.
  7. Disappointed that they failed to get their previously announced 72-qubit machine working properly. There was a media report that “linking together 72 qubits proved too difficult to control.
  8. Not a real algorithm which solves a real problem. Contrived — simply to achieve the narrow theoretical goal of quantum supremacy, in a very narrow sense.
  9. More of a clever ruse than a sincere attempt to show applicability to well-known real-world problems.
  10. Niche use case only, for now.
  11. Unclear when the work might be extended to a real algorithm which solves a recognizable real-world problem.
  12. Unclear if the work is ever likely to extend to real algorithms which solve real problems.
  13. Not a universal solution for all applications and all problems.
  14. Overly-broad term which misleads people and suggests we are further along than we actually are.
  15. Unclear when or if the machine can become a production-quality machine publicly available in the cloud.
  16. Unclear how much further the current technology can be evolved.
  17. We’re still in the proof of concept stage for applications, with no sign of when we might transition to production-scale applications.

Timeline — How it all played out

Google’s achievement of quantum supremacy was not actually a surprise at all — Google did a good job of telegraphing their quantum supremacy intentions well in advance of the deed.

What’s next?

What should we look for next?

  1. Basically, now we wait — for use cases in each application category to gradually achieve quantum supremacy, one use case at a time, slowly over time, as hardware and ability to design algorithms that exploits that hardware gradually advances. Which practical use case will be first? Nobody knows, yet.
  2. Will Google turn this research project into a production machine? More than one machine?
  3. Will someone attempt to reproduce Google’s results on the IBM 53-qubit machine?
  4. Will someone attempt to reproduce Google’s results on some other machine? IonQ with trapped ions? Honeywell? After all, reproducibility is supposed to be a hallmark of science.
  5. What will be the next incremental advance in qubits and coherence time?
  6. Might we see some dramatic technological breakthrough over the next year or two, or only gradual, incremental progress?
  7. When will we see significant quantum supremacy — an interesting number of applications where quantum supremacy has been achieved?
  8. When will we see true quantum supremacy — quantum supremacy across a wide range of categories of applications, for most of the compute-intensive application categories.
  9. When will we see the ENIAC moment — a significant production application on beefier hardware?
  10. When will we see the FORTRAN moment — an expressive higher-level programming language which dramatically simplifies algorithm development and enables widespread mainstream usage?
  11. When will we see quantum algorithmic breakout — both hardware and algorithm development, as well as a trained workforce achieve a critical mass which enables widespread mainstream usage?
  12. When will we see a true universal quantum computer, which combines classical and quantum computing in the same machine with zero latency to transition between the two modes of computing?



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