Promising to solve problems that even the most powerful classical supercomputers can’t handle, Quantum computing has the potential to revolutionise fields ranging from medicine to cyber security. But what exactly is quantum computing, how does it work, and what will it mean for the world when it becomes reality? 

What is Quantum Computing? 

Traditional computers process information using bits — binary units that represent either a 0 or a 1. Every program, image, or application you use is ultimately encoded in these binary strings. Quantum computers, however, take advantage of the principles of quantum mechanics, the physics governing the behaviour of subatomic particles, to process information in an entirely different way. 

Instead of bits, quantum computers use qubits. A qubit can exist as 0, 1, or both simultaneously thanks to a property known as superposition. When combined with entanglement, where qubits become linked so that the state of one instantly influences the other, quantum computers can perform vast numbers of calculations at once. This parallelism allows them to potentially solve specific types of problems much faster than any classical computer could. 

How Quantum Computers work 

At their core, quantum computers manipulate qubits using operations known as quantum gates. These gates change the probabilities associated with a qubit’s state. The outcome of a quantum computation is not a single deterministic result, but rather a probability distribution from which the correct answer can be inferred after repeated measurements. 

Maintaining and controlling qubits is extremely difficult. They are highly sensitive to their environment, and even slight disturbances — heat, vibration, or electromagnetic radiation — can cause decoherence, collapsing their quantum states. To combat this, many quantum computers operate at temperatures close to absolute zero using complex cryogenic systems. Technologies such as superconducting circuits, trapped ions, and photonic qubits are among the various approaches being explored by companies and research institutions worldwide. 

What is Q-Day? 

Q-Day refers to the hypothetical moment when a quantum computer becomes powerful enough to break the encryption methods that currently secure much of the world’s digital communication. Today’s encryption, such as RSA and ECC, relies on mathematical problems that are practically impossible for classical computers to solve within a reasonable time frame — like factoring huge numbers into their prime components. 

However, once a sufficiently advanced quantum computer exists, these protections could be rendered obsolete. Data encrypted today could be stored by adversaries and later decrypted after Q-Day, leading to potentially catastrophic privacy and security breaches. This looming risk has led to the development of post-quantum cryptography (PQC), a set of encryption algorithms designed to withstand attacks from quantum machines. 

Shor’s algorithm 

The key breakthrough that raised concerns about Q-Day came from mathematician Peter Shor in 1994. Shor’s algorithm demonstrated that a quantum computer could factor large integers exponentially faster than the best-known classical algorithms. 

In simple terms, RSA encryption depends on the fact that while it’s easy to multiply two large prime numbers together, it’s extremely hard to reverse the process and find those primes again. Shor’s algorithm, however, could make that problem trivial for a powerful enough quantum computer. The same principle applies to other cryptographic systems built on similar mathematical assumptions. 

While no current quantum computer can yet run Shor’s algorithm at a meaningful scale, the progress being made in qubit count, error correction, and stability is steadily bringing that future closer. 

What Quantum Computing means for encryption 

Encryption is the foundation of digital trust. It protects online transactions, secures cloud data, and ensures the confidentiality of communications between individuals and organisations. The arrival of quantum computing threatens to upend this entire structure. 

Most public-key encryption systems in use today — including RSA, Elliptic Curve Cryptography (ECC), and Diffie-Hellman key exchange — rely on mathematical problems that are easy to perform one way but nearly impossible to reverse without the key. Quantum computers, through Shor’s algorithm and similar advances, would make reversing these problems feasible. 

This means that once a sufficiently advanced quantum computer is available, encrypted emails, secure websites, VPNs, and even classified government data could be exposed. Crucially, the threat is not limited to the future — data intercepted and stored today could be decrypted later once quantum capability matures. This concept is often called “harvest now, decrypt later.” 

In response, researchers and international bodies such as the US National Institute of Standards and Technology (NIST) are developing new encryption methods resistant to quantum attacks. Known collectively as post-quantum cryptography, these algorithms use mathematical structures — such as lattices, hash-based signatures, and code-based systems — that are believed to be secure even against quantum decryption techniques. 

The transition to quantum-safe encryption will be one of the largest cryptographic shifts in history. It will require governments, businesses, and service providers to update systems, reissue digital certificates, and replace protocols across global networks. Preparing early is essential, as migrating critical infrastructure after Q-Day would be too late. 

The coming Quantum tipping point 

In 2026, quantum computing is accelerating towards a tipping point that could redefine digital trust. The threat of Q-Day — when quantum systems can break today’s encryption — is often misunderstood. It won’t be a single moment of collapse, but a progressive weakening of cryptographic foundations as capability increases. 

The real danger lies in a lack of situational awareness. Many organisations simply don’t know which assets, certificates, and systems will be affected. Retrofitting encryption, especially where it is hard-coded into legacy applications, could cost over £100 million for large enterprises — making early preparation essential. 

The financial sector is among the most exposed, where any breach of confidentiality or data integrity could trigger a collapse of customer trust. Transitioning to quantum-safe encryption also introduces new challenges: larger packet sizes, higher latency, and potential incompatibility with existing hardware — particularly older switching equipment and Android devices. 

Resilience in the quantum era begins with education. Boards must recognise that encryption, once viewed as a “free” and permanent safeguard, will soon require strategic investment and governance. 

Building resilience begins now. Organisations should: 

• Challenge vendors on their post-quantum cryptography roadmaps and ensure compatibility across their product portfolios. 

• Inventory all cryptographic assets to understand exposure. 

• Collaborate across teams to centralise upgrade policies and align governance. 

The organisations that map their exposure now and begin the migration early will define the next generation of digital trust. 

“62% of technology and cyber security professionals worry about quantum computers breaking current internet encryption.” — ISACA 

What it will mean 

The arrival of practical quantum computers will have profound implications across nearly every industry. In medicine, they could accelerate drug discovery by simulating molecular interactions that are impossible for classical systems to model. In logistics and finance, they could optimise complex systems with countless variables. In materials science, they could uncover entirely new compounds and superconductors. 

Yet the greatest and most immediate impact will likely be on cyber security. The cryptographic foundations that underpin everything from online banking to national security communications will need to be replaced or upgraded long before Q-Day arrives. Governments, research institutions, and private enterprises are already working on quantum-resistant solutions to future-proof data protection. 

Beyond security, quantum computing also raises ethical, political, and economic questions. Who will control this technology? How will access be regulated? And what new inequalities might emerge between those who possess quantum capabilities and those who do not? 

Quantum computing represents both a breakthrough and a challenge. It will unlock unprecedented computational power and transform science and industry, but it also threatens to undermine the digital security infrastructure that modern society depends upon. 

As Q-Day approaches — whether years or decades away — preparation will be essential. The race is no longer just to build the first quantum computer, but to ensure that when it arrives, we’re ready for the world it will change. 

How Integrity360 can help 

At Integrity360, we help organisations prepare for tomorrow’s threats today. Our experts work with clients to assess their encryption readiness, strengthen data protection strategies, and implement proactive cyber security measures that evolve alongside emerging technologies like quantum computing. 

Through continuous testing, incident response, and managed services, we help ensure your organisation is resilient — whatever the future holds.