The security of #Bitcoin comes from the difficulty of solving a certain type of math problem, called the "elliptic curve discrete logarithm problem." This problem is very difficult to solve, even for a 'quantum computer'.
Quantum computing won’t break Bitcoin:
Q(x) = (2^n)/2^x
Where Q(x) is the quantum computer power required to break Bitcoin, n is the number of qubits (quantum bits) in the quantum computer & x is the number of bits in the Bitcoin private key.
As you can see, the quantum computer would need to have twice as many qubits as there are bits in the private key in order to have a 50% chance of breaking Bitcoin. For a 128-bit private key, that would mean a quantum computer with at least 256 qubits.
Current quantum computers have around 100 qubits, so they aren’t even close to being able to break #Bitcoin.