· quantum computing · 3 min read

# An illustrated guide to quantum computing, including qubits, algorithms, challenges, government support, and “Q-day”, when a quantum computer cracks encryption

They call it Q-day. That is the day when a robust quantum computer will be able to crack the most common encryption method used to secure our digital data. Q-day will have massive implications for all internet companies, banks and governments — as well as our own personal privacy. We know that this will happen one day. The only question is when. For the moment, quantum computers, which exploit the spooky physics of subatomic particles, remain too unstable to perform sophisticated operations for long. IBM’s Osprey computer, thought to be the most powerful quantum computer yet developed, only has 433 qubits (or quantum bits) when most computer scientists consider it would take 1mn to realise the technology’s potential. That may still be a decade away. But in 1994 the American mathematician Peter Shor wrote an algorithm that could theoretically run on a powerful quantum computer to crack the RSA encryption protocol most commonly used to secure online transactions. The RSA algorithm exploits the fact that while it is very easy to multiply two large prime numbers, no one has yet discovered an efficient way for a classical computer to perform the calculation in reverse. Shor showed how a quantum computer could do so relatively easily.

Quantum computing relies on the strange properties of subatomic particles, such as electrons and photons, that can exist in a superposition of two states at the same time. This means that a quantum bit, or qubit, can be both 0 and 1 simultaneously, unlike a classical bit that can only be either 0 or 1. By manipulating qubits in certain ways, quantum computers can perform parallel computations on multiple possibilities at once, rather than sequentially as classical computers do. This gives them a huge speed advantage for solving certain types of problems, such as finding the prime factors of large numbers, which is the basis of the RSA encryption algorithm.

However, qubits are also very fragile and prone to errors, as they can easily lose their quantum state due to any interaction with the environment. This is called decoherence, and it limits how long quantum computers can stay in a quantum state and how many qubits they can reliably use. To overcome this challenge, researchers are developing various techniques to isolate, control, and correct qubits, as well as designing new quantum algorithms that can tolerate noise and errors. The ultimate goal is to build a robust quantum computer with millions of qubits that can achieve quantum supremacy, or the ability to outperform any classical computer on a given task.

The race to build such a quantum computer is intensifying among governments, corporations, and start-ups around the world, as they see the potential benefits and risks of quantum technology. Quantum computers could help us discover new materials and drugs, optimize complex systems and processes, and create new methods of communication and computation. But they could also undermine the security of our current encryption systems and expose our sensitive data to hackers and adversaries. That is why many experts are calling for a pause on new AI models and a development of new cryptography systems that are secure against both quantum and classical attacks.

Quantum computing is not a distant future; it is happening now. And we need to be ready for it.

### Key takeaways

- Quantum computing uses qubits that can be in a superposition of two states at once, enabling parallel computations on multiple possibilities.
- Quantum computers can solve certain problems much faster than classical computers, but they are also very noisy and error-prone due to decoherence.
- Quantum computing poses a serious threat to the security of our digital data, as it could break the RSA encryption algorithm that protects most of our online transactions.
- The race to build a robust quantum computer with millions of qubits is on among governments, corporations, and start-ups around the world.
- We need to develop new cryptography systems that are secure against both quantum and classical attacks, as well as ethical and social guidelines for using quantum technology.

Read more:

- An illustrated guide to quantum computing, including qubits, algorithms, challenges, government support, and “Q-day”, when a quantum computer cracks encryption
- Single-GPU Systems Will Beat Quantum Computers for a While: Research
- Disentangling Hype from Practicality: On Realistically Achieving Quantum Advantage
- Single Nvidia GPU speeds past the physics-straining might of a quantum computer