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We are currently living in an exciting time for quantum computing. Most leading companies like Google and IBM have 20 qubit devices. IBM has a 50 qubit prototype [0].

Google has plans to show quantum supremacy in the next couple of months: where a quantum computer will perform a task that cannot be simulated on a classical computer [1]. These near-term (5-10 year) quantum computers will likely be used for simulating quantum chemistry and solving optimization problems [2].

[0]: https://www.technologyreview.com/s/609451/ibm-raises-the-bar...

[1]: https://www.technologyreview.com/s/609035/google-reveals-blu...

[2]: https://www.nature.com/news/commercialize-quantum-technologi...

Number of physical qubits is not a meaningful measure of computational power, especially since fault tolerant computation has not been demonstrated. (In the limit of large errors, a physical qubit has zero computational power.)

D-Wave has a 2000-qubit machine.

Yes. The researchers at IBM don't use the number of qubits as a measure of the quality of the computer. They use the quantum volume [0]. I said 50 qubits because I was just parroting the press release. The reason I didn't mention D-Wave's machine is because it is not a universal quantum computer. It is a quantum annealer [1].

Google and IBM want their qubits to be of high quality (high coherence times e.t.c). One of the big obstacles right now is scaling up the number of qubits while making sure that their quality is high.

[0]: https://en.wikipedia.org/wiki/Quantum_annealing

[1]: https://www.research.ibm.com/ibm-q/resources/quantum-volume....

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