Understanding Quantum

Two people, one in Tokyo and one in London, undergo the same questionnaire. They have no idea what questions they will be asked. They cannot talk to each other. In fact, they don’t even know of each other's existence. Yet they give the same answers to all the questions. This strange situation occurs in quantum physics. Entangled particles give the same results when subjected to the same measurement, no matter how far apart they are from each other.

Look through a glass window. What do you see? The outside world? A reflection of yourself? A superposition of both? Quantum systems can be in a superposition of different configurations: being here and there, moving left and right, or being one colour or the other simultaneously..

Bits are the basic unit of information. Every email you read, music you listen to or film you watch is a stream of 0s and 1s. Information can also be encoded in quantum systems, such as atoms or photons. And because they can be in quantum superposition, they can encode a 0 and a 1 simultaneously.

A transporter must deliver parcels to N different houses. What is the shortest route they can take? This everyday problem turns out to be astonishingly hard to solve even for the best computers: they basically have to look at all possible combinations of routes. Similar problems involve finding the key to an encrypted message or the most stable configuration of a molecule. However, a quantum computer that explores the quantum superpositions of the different routes can arrive at the optimal solution much faster.

Computers are devices that store and process information in the form of bit strings (sequences of 0’s and 1's). Internally, these bits correspond to two distinguishable hardware configurations, like two different levels of current in an electrical circuit. A quantum computer also stores and processes information, but unlike standard computers, it uses quantum systems such as atoms or electrons to encode information. It can thus use quantum properties such as superposition or entanglement to solve problems that are infeasible even for the best supercomputers. For instance, quantum computers could provide great benefits in healthcare with new drugs, or agriculture with more sustainable fertilisers, or perhaps even help us in the quest for a more sustainable world thanks new materials and better batteries.

What is your name? What is your name? What is your name? I hope you gave the same answer every time. Quantum systems are not so coherent and can give different answers for the same measurement. In quantum physics, although we cannot predict with certainty the results of a measurement, we can tell the probabilities of occurrence. But this does not mean that we have no control over quantum systems. In fact, scientists can design experiments so that the answers are not completely random, but the probability of the sought answer is increased.