Currently the two qubit gate error rate is listed as ~2.7e-3 (see https://quantum.cloud.ibm.com/computers?system=ibm_phoenix but note it will vary from day to day). That implies you can expect ~400 entangling gates before experiencing an error. A zero-shenanigans factoring of 21 takes ~2000 entangling gates. So it's not good enough to factor 21 in any meaningful sense.
Really what matters about this chip is that it is better suited for error correction. They have a square grid connectivity (previous IBM chips incurred fatal overheads from their heavy hex connectivity), they can actually reset their qubits now (previous IBM chips couldn't scale to long running computations because once leakage arose nothing could remove it except waiting a long time), and they have tunable couplers instead of fixed frequency ones (previous IBM chips were just doomed whenever some problem happened to land on their operating area in frequency space).
Most interesting quantum computations take millions or billions of gates. Factoring classically intractable numbers takes tens of billions of gates. No one is going to do that many quantum gates without error correction. Whenever a quantum computing company says anything other than "it made error correction better" or "it will make error correction better", you can ignore that. It's just some side quest. Maybe it's interesting in and of itself, but it's not what matters for progress.
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Currently the two qubit gate error rate is listed as ~2.7e-3 (see https://quantum.cloud.ibm.com/computers?system=ibm_phoenix but note it will vary from day to day). That implies you can expect ~400 entangling gates before experiencing an error. A zero-shenanigans factoring of 21 takes ~2000 entangling gates. So it's not good enough to factor 21 in any meaningful sense.
Really what matters about this chip is that it is better suited for error correction. They have a square grid connectivity (previous IBM chips incurred fatal overheads from their heavy hex connectivity), they can actually reset their qubits now (previous IBM chips couldn't scale to long running computations because once leakage arose nothing could remove it except waiting a long time), and they have tunable couplers instead of fixed frequency ones (previous IBM chips were just doomed whenever some problem happened to land on their operating area in frequency space).
Most interesting quantum computations take millions or billions of gates. Factoring classically intractable numbers takes tens of billions of gates. No one is going to do that many quantum gates without error correction. Whenever a quantum computing company says anything other than "it made error correction better" or "it will make error correction better", you can ignore that. It's just some side quest. Maybe it's interesting in and of itself, but it's not what matters for progress.