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Google and the XPrize Foundation have launched a $5 million (£4 million) competition to develop real-world applications for quantum computers that benefit society – accelerating progress on one of the UN’s Sustainable Development Goals, for example . The principles of quantum physics suggest that quantum computers could perform very fast calculations on specific problems, so this competition could expand the range of applications where they have an advantage over conventional computers.

In our everyday lives, the way nature works can generally be described by what we call classical physics. But nature behaves very differently on tiny quantum scales – below the size of an atom.

The race to harness quantum technology can be seen as a new industrial revolution, progressing from devices that utilize the properties of classical physics to those that utilize the weird and wonderful properties of quantum mechanics. Scientists have spent decades trying to develop new technologies taking advantage of these properties.

Given how often we are told that quantum technologies will revolutionize our everyday lives, you might be surprised that we have yet to look for practical applications by offering a prize.

However, although there are numerous examples of success in using quantum properties for greater precision in detection and timing, there has been a surprising lack of progress in developing quantum computers that surpass their classical predecessors.

The main bottleneck supporting this development is that the software – which uses quantum algorithms – needs to demonstrate an advantage over computers based on classical physics. This is commonly known as the “quantum advantage”.

One crucial way in which quantum computing differs from classical computing is by using a property known as “entanglement.” Classical computing uses “bits” to represent information. These bits consist of ones and zeros, and everything a computer does comprises sequences of these ones and zeros. But quantum computing allows these bits to be in a “superposition” of ones and zeros. In other words, it is as if these ones and zeros occur simultaneously in the quantum bit, or qubit.

It is this property that allows computational tasks to be executed at once. Hence the belief that quantum computing can offer a significant advantage over classical computing as it is capable of performing many computational tasks at the same time.

## Notable quantum algorithms

Although executing many tasks simultaneously should lead to increased performance over classical computers, putting this into practice has proven more difficult than theory would suggest. In fact, there are only a few notable quantum algorithms that can perform their tasks better than those using classical physics.

The most notable are the BB84 protocol, developed in 1984, and Shor’s algorithm, developed in 1994, both of which use entanglement to outperform classical algorithms in specific tasks.

The BB84 protocol is a cryptographic protocol – a system for ensuring secure and private communication between two or more parties that is considered more secure than comparable classical algorithms.

Shor’s algorithm uses entanglement to demonstrate how current classical encryption protocols can be broken because they are based on factoring very large numbers. There is also evidence that it can perform certain calculations faster than similar algorithms designed for conventional computers.

Despite the superiority of these two algorithms over conventional ones, few advantageous quantum algorithms have been followed. However, researchers have not given up trying to develop them. Currently, there are a few main directions in research.

## Potential quantum benefits

The first is to use quantum mechanics to assist in so-called large-scale optimization tasks. Optimization – finding the best or most effective way to solve a specific task – is vital in everyday life, from ensuring traffic flow works effectively, to managing operating procedures in factory pipelines, to deciding service about what to recommend to each user. It seems clear that quantum computers could help with these problems.

If we could reduce the computational time required to perform optimization, we could save energy, reducing the carbon footprint of the many computers that currently perform these tasks around the world and the data centers that support them.

Another development that could offer far-reaching benefits is the use of quantum computing to simulate systems, such as combinations of atoms, that behave according to quantum mechanics. Understanding and predicting how quantum systems work in practice could, for example, lead to better design of medicines and medical treatments.

Quantum systems could also lead to improved electronic devices. As computer chips get smaller, quantum effects take hold, potentially reducing device performance. A better fundamental understanding of quantum mechanics could help avoid this.

While there has been significant investment in building quantum computers, there has been less focus on ensuring they will directly benefit the public. However, this now appears to be changing.

It remains to be seen whether we will all have quantum computers in our homes within the next 20 years. But given the current financial commitment to making quantum computing a practical reality, it appears that society is finally in a better position to make use of it. What precise form will this take? There’s $5 million at stake to find out.