Theoretically, quantum computers could harm bitcoin in particular and cryptocurrencies in general. But the problem is, according to experts, it will take at least 20-30 years for quantum computers to develop powerful enough to harm current bitcoin technology. That means quantum computing technology lags behind Bitcoin technology, and that also means when quantum computing reaches a level where it can harm Bitcoin, Bitcoin will also evolve and reach new heights at that time.

So, theoretically and mathematically, quantum computers are harmless to bitcoin, both now and in the future.