I asked gpt-4

To "crack" a Bitcoin private key, in the sense of finding the private key from a given public key, is a problem that falls under the general class of quantum computing attacks called Shor's algorithm, which could factor integers and compute discrete logarithms much more efficiently than any known classical algorithm.

The Bitcoin address corresponds to the hash of a public key, derived from a 256-bit private key through the elliptic curve digital signature algorithm (ECDSA). This 256-bit key would require a quantum computer with around 3072 qubits in order to break it using Shor's algorithm, due to requirements of qubits for error correction and for storing intermediate results.

However, as of my knowledge cutoff in September 2021, we don't yet have quantum computers capable of executing Shor's algorithm on numbers anywhere near this large. The largest number factored by a quantum computer using Shor's algorithm as of 2021 was only 21, which was accomplished using just 8 qubits. In fact, there is much skepticism in the scientific community about whether it's feasible to build quantum computers of the size required to break ECDSA 256-bit keys in the near future, due to issues with error correction, qubit stability, and other technological challenges.

Moreover, even if a sufficiently powerful quantum computer was developed, the Bitcoin protocol could be updated to use post-quantum cryptographic algorithms, which are believed to be resistant to quantum computing attacks. Many cryptocurrencies are already working on post-quantum cryptographic solutions.