What is quantum physics?
Quantum physics is the set of behaviours of our world when we look at it very closely. At small scales, our world is made of building blocs called atoms (for matter) and photons (for light). These blocs constantly interact with each other, and build up everything we see, taste, touch, and hear. Surprisingly, scientists have observed that when they isolate one or a small number of atoms or photons, they behave in totally unexpected manners. Atoms can travel through walls, take several trajectories simultaneously, etc. Only, when many photons and atoms interact, and bounce on one another, the weird behaviours cancel out. This is why we do not see these weird phenomena in our daily lives. In the past century, these behaviours have been observed and understood very well by scientists. We now use the term « quantum » to describe these behaviour, which we never see in our daily lives but appear at small scales.
The two central phenomena of quantum physics are superposition and entanglement.
Superposition is the fact that a particle can be simultaneously in several states, positions, orientations at once. This has been observed in a famous experiment called the « Double slit experiment » (click here for an animation of this experiment)
Entanglement is the fact that two atoms (or other small particles, or photons) can be « connected » in such a way that they become a single « entangled » object. Once entangled, the two atoms can be taken far away from one another. Because the two objects are now two parts of a single « entangled » object, an action on one atom will instantaneously influence the other atom. This phenomenon took decades to be accepted by the scientific community, because at first sight it introduces contradictions with Einstein’s results on space-time physics. Luckily, scientists have been able to prove that entanglement does not contradict any of it. One key experiment proving that entanglement is real was led by 2022 Nobel prize laureate Alain Aspect, in the 80s (click here for a nice video on the topic)
Don’t ever get fooled by quantum charlatans again
On the Internet, some people use quantum as a magic word to give scientific credibility to their personal beliefs. You should be very cautious about « quantum-ness » claims, they regularly hide a lack of scientific background. For example, quantum meditation has nothing to do with science. Also, quantum physics does not allow teleportation, as depicted in sci-fi (click here to learn about real « quantum teleportation »). If you wan’t to avoid being fooled by charlatans or even big companies (hi Guerlain 😉 ), here is a little trick: if the « quantum effect » happens at our scale (not the size of a few atoms), and at human temperature (more than 0°C), it is probably (not always of course) a hoax. If you have a doubt, send me a message so we can talk about it.
What about quantum technologies?
Quantum physics is now leveraged all around the world in order to create useful technologies. Yet, not everyone agrees on what should be called a « quantum technology ». Indeed, most modern technologies are all built based on the rules of quantum physics. Our TV screens and our smartphones are made of very small components, which are therefore subject to quantum phenomena. We would not be able to build these without knowing quantum physics. But, usually, the adjective « quantum » is used to refer to technologies which manipulate information using quantum properties of matter and light. From that perspective, technologies which merely take into account quantum effects are not « quantum technologies ». Quantum technologies exploit superposition and entanglement in order to enhance precision, security, speed or energy consumption in calculations, measurements or communication. These technologies have a very borad range of maturity. Some are already widely used, such as MRIs (medical imagery), or atomic clocks (in synchronizing satelites for GPS). Others, which you here a lot about in the news, are for the most part still far away from doing anything useful, like quantum computing. Here are the main areas of quantum technologies.
Quantum sensing: consists in measuring things using quantum objects as highly sensitive detectors. By exploiting superposition and entanglement, scientists reach record-breaking precisions for geolocation, medical imagery, … It is already in use and its outreach is rapidly growing.
Quantum cryptography: uses quantum objects to share encryption keys between users. The encryption key is guaranteed to not have been seen by any hacker thanks to quantum phenomena. Later, this key can then be used to encode and decode messages on the internet or on other « classical » networks. This system already works, but it is still limited by the high infrastructure costs, and the reduced distances on which keys can be shared. For now, it is being used by Chinese banks and institutions to encode their communications securely.
Quantum computing encompasses technologies which exploit quantum phenomena for conducting calculations. It is particularly useful to conduct simulations of quantum phenomena: to find new material, for drug development, … Quantum computing can also be used in areas with no direct link with quantum physics. Some quantum algorithms could for example help in the optimisation of fabrication processes, or for improving AI models. However, quantum computing algorithms require a very precise control of the quantum state of the system, and a large quantum system. Current quantum simulators are still limited to the simulation of very small systems, so they are not very useful yet. Most of the « groundbreaking » usecases of quantum computing are predicted to be achieveable in at least 10 years, according to most companies and researchers of quantum computing.
If you want to learn more about quantum technologies, you can find nice articles, and other suggestions on : https://lelabquantique.com/online-learning/
You can also discover the different initiatives for building quantum ecosystems by « clicking here ».
If you have any questions, or suggestion, don’t hesitate to reach out !