Why Quantum?

Quantum mechanics was developed and refined during the first half of the last century, as the branch of physics required to understand matter at the atomic, nuclear and fundamental particle levels, and to understand light at the level of single quanta, or photons. It has since proved to be an invaluable tool in understanding the building blocks of all the information technologies (IT) we use in the modern world, such as: electronic circuits that underpin computers and all the other devices we rely on every day; lasers and optoelectronic components that underpin communications technologies and numerous home, consumer and personal devices. Indeed, quantum mechanics has aided the repeated improvements of all these technologies to the state-of-the-art from which we benefit today.

The fundamental features of quantum physics, which determine how atoms and photons behave, run counter to our intuition and everyday experience. Quantum systems can be in multiple states at the same time – this is termed superposition (of states). Furthermore, quantum systems, even when separated by large distances, can be correlated more strongly than any correlations familiar to us – such systems are termed entangled. Finally, when any of us try to measure or interact with a quantum system to learn about what it is doing, we inevitably and irreversibly disturb it. This relationship between disturbance and information gained is fundamental. It is not something that we will overcome by building better measurement devices and probes in the future – it is built into Nature.

These fundamental features of quantum mechanics were appreciated in the early stages of its development. However, study of these features was viewed as a somewhat academic pursuit – undertaken only to understand the basis of this part of physics. They didn’t affect our macroscopic and “classical” (meaning non-quantum) lives. Fifty years ago there was no inkling at all that these quantum behaviours would ever contribute to our daily lives. Even today, the electronic, optical and other components that comprise our conventional IT do not exhibit these counter-intuitive behaviours. However, things are now changing. Over the last few decades – initially just theoretically or abstractly, but increasingly now as actual prototype devices – it has been realised that these fundamental features of quantum physics can play centre stage in completely new technologies. These new “quantum technologies” have the potential to outperform our conventional IT, or even achieve some tasks impossible with our usual stuff. The benefits could arise across IT: in computing and processing, in sensing and imaging, and in communications.

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