With that said and the fact that more enterprise organizations are also putting their eyes on quantum computing means that the ruling held by blockchain currencies may start coming to an end. IOTA in that case is not affected at all.
When Quantum computers show up on the scene, most current cryptography (and cryptocurrencies) will be no longer secure. For this reason engineers and mathematicians are already starting to look for cryptography unbreakable by quantum computers.
What is Post-quantum cryptography
Post-quantum cryptography refers to cryptographic algorithms (usually public-key algorithms) that are thought to be secure against an attack by a quantum computer. This is not true for the most popular public-key algorithms, which can be efficiently broken by a sufficiently large quantum computer. The problem with the currently popular algorithms is that their security relies on one of three hard mathematical problems: the integer factorization problem, the discrete logarithm problem or the elliptic-curve discrete logarithm problem. All of these problems can be easily solved on a sufficiently powerful quantum computer running Shor’s algorithm.
A very good comparison on blockchain technology used by Bitcoin and IOTA’s algorithm is presented here.