The Technical Reason Quantum Computers Haven't Factored 21 Yet
By
ingve
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Summary
The article explains why quantum computers, despite factoring 15 in 2001, haven't yet factored 21 in 2025. It debunks the misconception that this indicates lack of progress, revealing that the reason is more technical and surprising - the quantum circuit used for 15 doesn't scale well to 21 due to fundamental differences in the mathematical operations required. The piece contrasts the specific quantum logic gates and operations needed for each number, showing that 21 presents unique challenges that aren't simply a matter of scaling up from the 15-factoring approach.
Key quotes
· 4 pulledIn 2001, quantum computers factored the number 15. It's now 2025, and quantum computers haven't yet factored the number 21.
It's sometimes claimed this is proof there's been no progress in quantum computers.
But there's actually a much more surprising reason 21 hasn't been factored yet, which jumps out at you when contrasting the operations used to factor 15 and to factor 21.
The circuit (the series of quantum logic gates) that was run to factor 15 can be seen in Figure 1b of 'Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance'.
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