Quantum computing FAQs

Here are some commonly-asked questions about quantum computing and their answers.
What is a quantum computer, and why all the effort to build one?

Just as classical computing is based on classical physics, quantum computing is based on quantum physics: it exploits the "weirdness" of quantum physics (its probabilistic nature, and the phenomena of superposition and entanglement) to create machines far more powerful than the ones we're used to using in everyday life.  Quantum computers won't be just faster than even the most advanced of classical computers, they will work in a fundamentally different way - and will therefore be capable of tackling complex computing tasks that aren't even conceivable for existing machines.

How far have we got?

Many organisations around the world have already succeeded in building simple quantum computers with a limited number of "qubits" (the most basic unit of information), and demonstrating simple algorithms.  But qubits are notoriously fragile, difficult to control, and prone to errors i.e. "noisy".  Connecting them together requires an enormous engineering effort; current machines don't yet have enough qubits to be able to spare any for error correction.  This era of quantum computing is often referred to as "noisy intermediate-scale quantum computing" (NISQC), and represents the near-term possibilities for quantum computers.  As well as advancing both hardware and software for NISQC approaches, we are also investigating the longer-term possibilities of a universal fault-tolerant quantum computer (UFTQC) which would use logical qubits and quantum error correction, and could be programmed to do any task.  Through the previous Networked Quantum Information Technologies Hub (NQIT), we have successfully demonstrated all of the building blocks of a universal quantum computer.

What makes the QCS Hub different?

We believe that the best approach to building a quantum computer is a modular one (as is often the case in technology): rather than trying to build as many qubits as possible into one system, we are investigating how to interlink modules containing just a few qubits each, thereby allowing for scalability while minimising the potential for error.  We think this is our best chance of building a truly universal quantum computer that could be programmed to do any task.

Does this mean the end of "normal" computers?

Probably not for a long time.  Silicon computers - such as your smart phone or desktop - are very good at what they do.  The first quantum computers will initially be research machines used by labs and businesses, not least because they are very expensive to make.  They may eventually find their way into the home but would probably exist side-by-side with normal computers, at least initially.

Are quantum computers good for the environment?

Quantum computers promise to use less power in the long run, because they use the smallest systems possible i.e. individual atoms.  But the first few generations of machines will be clunky (like all new technology), and will typically use similar power to a server farm, such as those already operated by internet companies.  In the end though, we hope our work will help to dramatically reduce the power used by computers, which is a significant concern.

Aren't quantum computers a threat to security?

It's true that one of the first "killer apps" of quantum computers was an algorithm that would be able to read encrypted messages on the Internet.  However, this is only one application, and many more exist and are yet to be discovered.  There are research groups around the world working on quantum cryptography, which would be secure even against a quantum computer.  Quantum cryptography is already being used by banks and very critical applications; by the time quantum computers can read secure messages on the Internet, the Internet itself may already be using quantum cryptography.

Are we playing with technology we don't understand?

Quantum effects have been understood and heavily researched for over 120 years.  A lot of the materials and devices we use every day (like the flash memory on our phones) have been made possible due to our understanding of quantum physics.  To most people, quantum physics may seem weird and complicated, but this is because we live in a world where we cannot see the quantum nature of the universe directly; instead, we're used to seeing things working on a macroscopic level.  Scientists have tested and used the theories of quantum physics very thoroughly, and it is considered the most well-tested and accurate theory we have.  This knowledge has led to an explosion of quantum technology, with the 21st-century being dubbed the "quantum century" in the same way that the late 20th-century was dubbed the "silicon age".  Whether we like it or not, the future is quantum: the challenge for the UK is to get ahead of the curve, rather than fall behind.