Quantum computers pose an existential threat to modern encryption. Within four years, Google and IBM say they'll deploy quantum machines powerful enough to break the sophisticated cryptography protecting banking transactions, government IDs, and classified communications, a threat scenario experts call Q-Day.

The "Q" stands for quantum. Q-Day marks the theoretical moment when these machines become capable enough to decrypt data currently considered unhackable.

How do quantum computers shatter encryption?

While traditional computers use binary digits that have values of either one or zero, quantum computers use qubits which have values of both simultaneously. Superposition means that quantum computers can evaluate several computations at once and therefore can solve any problem very quickly compared to traditional computers.

Imagine routing: a traditional computer looks for the right way by testing several routes before reaching the desired destination. But quantum computers look at the whole map immediately and find the optimal route instantly.

When this speed is applied to cryptography, modern encryption becomes ineffective. It is because contemporary cryptography uses mathematical problems that take so much time for traditional computers that it would take thousands of years to solve them.

Quantum computing is compared to the state of artificial intelligence five years back by Google’s CEO Sundar Pichai. Google and IBM have made it clear that they will be ready with commercially viable quantum technologies by 2030, adding credence to the idea of a Q-Day.

Cryptocurrency firms find themselves at a special risk. Bitcoin and blockchain rely on encryption techniques which can potentially be exploited by quantum computers.

Companies operating in the field of telecommunications, financial services, and government have started working on what are known as 'quantum-safe cryptography techniques', which are resistant to quantum attack. This marks the biggest cryptographic breakthrough since the creation of the internet.

"It could all prove a false alarm," researchers acknowledge. "But more companies are preparing as if quantum computing is genuinely coming toward us."

That preparation itself signals institutional confidence that Q-Day isn't if but when.