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Quantum physics explains how the material world is made up. So, in this respect, quantum physics is certainly something we encounter in our everyday lives. We also encounter quantum physics daily in terms of technology.

We know that lasers are used for a multitude of purposes. Laser devices are based on quantum systems jumping between two states in sync. Band theory forms the basis for making transistors and other semi-conductor technology, which is used a lot – for instance in making (regular) computers.

Many of us have been exposed to magnetic resonance imaging (MRI) at hospitals. Such machines use the fact that small particles, like electrons and nuclei, have a quantum trait called spin.

Quantum physics also provides our most powerful microscopes – the scanning tunnelling microscope. With such microscopes you may actually see atoms.

The fact that the energy of atoms and molecules is quantized ensures that each substance has its own fingerprint which is unique for that particular substance. This enables us to identify unknown substances. Such techniques are referred to as spectroscopy.

Quantum phenomena, such as entanglement for instance, are also used to perform extremely accurate measurements. Entanglement is also exploited to provide secure communication. This is an example of how quantum physics is used within information technology.

And now we are closing in on what is referred to as the second quantum revolution: quantum computing.

In traditional data processing, information is formulated in terms of sequences of zeros and ones – bits. In a quantum context, we can allow for bits which are a mixture of both – both 0 and 1 simultaneously.

More importantly: When several quantum bits are put together, we are able to construct mixes of all possible sequences of zeros and ones. Consequently, the information content of quantum information does not increase just a little as you add one more bit. In fact, it doubles with every quantum bit!

In a quantum computer, such mixtures of sequences may be processed in one single computation. In such a process, some bit sequences may be reinforced while others may be diminished – or even fully cancelled. Exploiting these possibilities for constructing efficient algorithms is far from trivial. But it may be done. Many examples are known, and devising new ones is ongoing work.

Improving the quality of quantum computers is also ongoing work. As larger and less noisy quantum computers are being built, this may actually change the world – for everyone, not just those with a particular interest.

What is quantum computing not

A quantum computer is not a computer which is faster per se. And quantum algorithms are not regular algorithms with a magic quantum speedup.

Quantum computing is different, more general. It gives us more leeway when it comes to processing data. It may be exploited to find more efficient solution to specific problems.

You will not replace your home computer with a quantum computer any time soon, probably never. Most of the specific problems for which there is a quantum advantage belongs to the realm of high performance computing.

Not even in this realm will quantum computers take over completely. When quantum computers run quantum algorithms, they will do so in tandem with traditional, classical computers.

Quantum computing is a different, more general way of handling data – a way that allows for algorithms which cannot be run on a traditional computer.

Certain problems may be solved far more efficiently on a quantum computer. And in certain cases, quantum computers will be able to solve problems which simply cannot be solved on a traditional machine – ever. So which problems and solutions are we talking about? Actually, there is a whole zoo of quantum algorithms (quantumalgorithmzoo.org).

One of the most important ones, Shor’s algorithm, is used to find large prime numbers. This may sound rather academic. However, the ability to find large primes fast may actually be devastating to much of the encryption schemes which are used today.

Several quantum algorithms, including Shor’s algorithm, require large quantum computers with very little noise to run. Such machines do not yet exist. But there are quantum schemes which are robust against a bit of noise.

Many of these algorithms are optimization methods. Better, more efficient methods for optimization will impact areas such as material technology, logistics and artificial intelligence – only to name a few.

But the most direct application of quantum computing, is to calculate the characteristics of actual quantum systems – such as atoms and molecules. In fact, this was the original motivation for launching the idea of the quantum computer in the first place – back in the 80s. The potential for application is large also in this regard – within fields such as the chemical industry and pharmacy.

Towards the end of the 19th century, researchers had come to realize that light is a type of waves. However, in the early 1900s, it was discovered that light would behave as particles in certain phenomena.

At the same time, most scientists had finally come to agree that matter consists of particles, atoms. This is when the French nobleman Luis de Broglie launched the following idea: Since light is not just waves but also particles, perhaps matter is not just particles but also waves?

And he was right!

Quantum physics, which describes small things such as nanostructures, molecules, atoms, nuclei and even smaller particles, is different from traditional Newtonian physics in so many ways. Since a particle is also a wave, it does not possess any particular position nor velocity – at least not from the outset.

Entanglement is another odd quantum phenomenon. Two “quantum balls” may very well be in a state in which one is blue and the other one is red – without any of them having a definite colour from the outset. The colour will, however, be determined if you observe it. But suppose that we observe one of the balls and find that it is red, how can the other ball instantaneously know that it is supposed to be blue – irrespective of the distance between the balls?

Yet another oddity is the fact that confined systems, quantum systems which are bound, can only be observed to have specific sets of energies. The energy is quantized. This way each substance has its own unique fingerprint of possible energies.