At some point this year, a pivotal event known as ‘Q-Day’ is anticipated to arrive, unleashing a cascade of unprecedented consequences. Cryptocurrencies are expected to plummet, gold prices could skyrocket, and the foundations of the global financial system may face severe disruption.

As governments and financial institutions rush to address a digital landscape where security has crumbled, every confidential piece of information stored online—ranging from private emails to personal search histories—could become exposed.

Public confidence in traditionally reliable financial entities may falter, prompting individuals to hoard cash and prioritize tangible assets. This could lead to a resurgence of old habits, such as tucking away savings under mattresses. In terms of secure communication, many might revert to pen and paper.

Denmark’s Saxo Bank has spotlighted this alarming scenario as its leading ‘outrageous prediction’ for 2026, suggesting a future where these events could unfold.

Interestingly, some technology experts concede that this prediction might not be as improbable as it sounds.

The term ‘Q-Day’ refers to the potential moment when an advanced quantum computer—a pinnacle of digital processing power—successfully breaches the world’s electronic security frameworks.

Such an event has long excited catastrophists, who have cited dire consequences not mentioned by the Danes, including entire cities losing power, missile silos being deactivated and nuclear submarines being tricked into surfacing in the middle of hostile fleets.

Of the world’s estimated 100 to 200 quantum computers, many are in China, which has been deeply secretive about what it’s doing with them

‘Q-Day’ is the moment a future quantum computer (pictured, as a digital image) – man’s most powerful digital processor – will crack the world’s electronic security systems

And while we may not see all this in the coming months, researchers tend to agree that a version of Q-Day could be only a few years off – and, when it hits, the fallout will be even more devastating than Saxo Bank outlined.

According to many experts, despite being hailed as the greatest technological revolution of our times, artificial intelligence is merely a warm-up act for quantum computing.

These vastly powerful computers, which can solve problems way beyond traditional PCs, have already passed the initial research and development stages.

Silicon Valley giants such as Microsoft, IBM and Google are vying for supremacy in a field of tech in which several British companies are also at the forefront.

Quantum computing harnesses the laws of quantum mechanics – the physics of how atoms, molecules and other tiny particles behave – to process information in a very different and much faster way than normal computers.

The latter use ‘bits’ (short for ‘binary digit’, the smallest unit of digital information) to process data represented as either a one or a zero. Quantum computers use minute physical particles known as ‘qubits’, which can be one, zero or, as head scratching as it sounds, both one and zero at the same time.

Yes, it’s extremely complicated, but their unique properties allow qubits to explore many possibilities at once when solving a problem, unlike bits, which can examine only one at a time, using a process of trial and error.

This allows quantum computers to hold exponentially more information and be exponentially faster, solving problems at almost unimaginable speed.

Cryptocurrencies such as Bitcoin could be particularly vulnerable, given their main selling point is they are supposedly unhackable

The challenge now is to move on from experimental machines to so-called ‘large-scale quantum computing’ by building computers with sufficient qubits and error correction to solve complicated, real-world problems.

Physicist Sir Peter Knight, one of Britain’s leading quantum scientists, said: ‘Things that could take the age of the universe to calculate, even on the most powerful supercomputer, could be performed, probably in seconds.’

However, as is typical of revolutionary technology breakthroughs, there’s a nightmarish downside: quantum computing can potentially hack into any ‘secure’ modern system.

Even the most rock-solid data-encryption algorithms will be vulnerable, posing a devastating threat to digital banking among much else. Cryptocurrencies such as Bitcoin could be particularly vulnerable, given that their main selling point is they’re supposedly unhackable.

Today’s most popular encryption systems rely on fiendish mathematical problems that traditional computers find almost impossible to solve. But for a quantum computer, they’d be a cinch.

Imagine, warn security experts, the consequences of every password and encrypted message you’ve ever sent suddenly becoming accessible to anyone who wants to look. They divide the threats into two main areas: confidentiality and authentication.

At risk would be our emails, text messages, previously anonymous social media posts (and anonymous surfing of online pornography), bank accounts, Bitcoin wallets and criminal and medical records.

The random number generators that are used by online casinos, the password on our home wifi, the smartcards that allow people into their office – all would suddenly be up for grabs.

Hospitals, power stations and banks would become putty in the hands of hackers, as indeed – most worryingly – would governments. 

As research companies develop more powerful quantum processors, Q-Day draws ever nearer. Microsoft (pictured, its Majorana 1 quantum computing chip) says a breakthrough is ‘years, not decades away’

Military experts say Q-Day would allow other countries to spy in real time on the most classified defence data, such as the location of submarines and missiles, and what satellites are monitoring.

One obvious solution would be to find better ways of encryption, but even that won’t necessarily work.

Security experts are deeply concerned because hackers and other hostile parties are already employing a so-called ‘harvest now, decrypt later’ strategy, whereby they hoover up and stockpile currently encrypted data, ready for the day when quantum computers can decrypt it.

This poses a particular risk to sensitive information such as medical records, intellectual property and government information that needs to be kept secret for many years.

Last year GCHQ, Britain’s intelligence, security and cyber agency, revealed that hackers working for the Chinese government have been running a huge operation, codenamed Salt Typhoon, that has been doing precisely this since at least 2021.

It said Beijing has targeted more than 80 countries, ‘harvesting’ data from government networks, transport, telecoms, hotels, energy suppliers and the military.

Former GCHQ cryptography chief Daniel Shiu said he considers it ‘credible’ that almost every UK citizen has had their data compromised in this way.

And while tech companies including Apple have already released advanced forms of encryption that would resist quantum computers, it cannot be applied retrospectively to data that’s been encrypted the old way.

Technical challenges to the quantum revolution and the terrible dawn of Q-Day certainly remain. Researchers need to build more and better qubits, which are notoriously error-prone and physically ‘sensitive’ to their environment.

This means they’ve traditionally had to be kept in huge buildings that are expensively isolated from vibration and light, as well as cooled to temperatures below those in outer space.

However, with consultancy giant McKinsey predicting the technology could increase the value of global businesses by as much as £967 billion by 2035, vast sums are being poured into quantum computing, including a £2.5 billion pledge from the British government to its National Quantum Technologies Programme.

And as research companies develop more powerful quantum processors, Q-Day draws ever nearer. IBM is working to build a ‘large-scale, fault-tolerant’ quantum super-computer by 2029, while Microsoft says a breakthrough is ‘years, not decades away’.

A year ago, Google unveiled its latest iteration, Willow, which can solve in under five minutes a problem that would take one of the fastest existing super-computers ten septillion years to do (that’s the figure 10 followed by 24 zeros). Which is longer, incidentally, than the existence of the universe.

Some experts say that Q-Day won’t be a single moment, but more of a gradually developing threat, and one that could be with us right now. Of the world’s estimated 100 to 200 quantum computers, many are in China, which has been deeply secretive about what it’s doing with them.

As some techies concede, Q-Day may have arrived already. We just don’t know about it yet.