Quantum mechanics was developed in the first half of the 20th century, following the pioneering work of Max Planck and Albert Einstein, who proposed the notion of the quantum. This theory has revolutionized our understanding of the physical world, from elementary particles to molecules and biology. It is the basis of many everyday objects, such as electronic circuits and GPS. The second half of the 20th century saw considerable progress both in understanding the concepts and in manipulating quantum objects on a microscopic or even individual scale. We are now at a turning point, where disruptive technologies based on these fundamental concepts are leading to new applications unimaginable twenty years ago, impacting computing capacities, optimization methods and data transfer security.
We can identify four main families of applications that structure quantum technologies in most international actions and are the subject of the four thematic axes of the QuanTiP DIM:
- Quantum computing,
- Quantum simulator,
- Quantum communication,
- Quantum sensors and metrology.
Quantum computing
By replacing the classical 0/1 logic of today’s processors (bits) with that of qubits (quantum bits) based on superposition and entanglement, we theoretically obtain a “universal quantum machine” capable of considerably reducing the execution time of certain algorithms (optimization problems, machine learning, cryptography methods).
The dual challenge of quantum computing is, on the one hand, to have a large number of “physical” qubits robust to decoherence and, on the other, to design the architecture and protocols to use them as efficiently as possible. Qubits can be made from a wide variety of physical systems (ions, photons, cold atoms, superconductors, semiconductors)…
Quantum simulation
Some specific questions are inaccessible even to classical supercomputers, but do not require a universal quantum computer. The aim of quantum simulators is to answer these questions, by modeling the behavior of systems made up of numerous interacting quantum objects. The idea is to simulate the problem under study with another quantum system, easier to handle, and to explore configurations or parameter sets inaccessible to the initial system. Verification of quantum simulators is essential, and requires multidisciplinary efforts to improve theoretical models.
In progress…
Quantum communication
One of the most mature applications of quantum technologies concerns the secure exchange of information via quantum communications, which generalize quantum cryptography methods. The basis of this security is the encoding of information in quantum variables, which an eavesdropper cannot access without modifying them. The aim is to build extensive, hybrid quantum communication networks (combining several physical platforms to support quantum information and several types of encoding) and enable secure exchanges that are resistant to attack by supercomputers, whether classical or quantum.
In progress…
Quantum sensors and metrology
Whatever the physical system used (atoms, molecules, spins, optomechanical devices of micro- or nanometric dimensions), quantum sensors work by exploiting the quantum properties of matter and light to achieve very high sensitivity to external force fields. They can be used to measure a wide range of physical quantities, opening up applications in numerous fields with high societal impact, such as climate and natural resource monitoring, healthcare, positioning, navigation and dating, or natural disaster prevention. While these sensors are often limited by classical noise sources, measurement protocols exploiting quantum correlations offer the possibility of pushing their sensitivity below the standard quantum limit.
In progress…
Quantum technologies exploit the concepts of superposition and entanglement, as well as the control of individual quantum objects, to secure communications, develop ultra-sensitive sensors and revolutionize computing and digital simulation.
Quantum superposition
(© Christian Schirm)
The world is such that an object can exist in several distinct states. An object is said to be in a quantum superposition of states when it is in several of these states simultaneously. But superimposed states are fragile and quickly disappear at our scale.
Is the cat alive AND dead?
E. Schrödinger devised a thought experiment to demonstrate the paradoxical nature of quantum physics as applied to our scale: a cat is enclosed in a box with a radioactive atom, whose disintegration triggers the emission of a deadly gas into the box. If the atom is both undecayed AND decayed, then the cat is both alive AND dead! Yet when we open the box, we still observe the cat alive OR dead.
Quantum entanglement
(© shutterstock.photo)
Quantum physics allows two or more objects to exist in very special superposition states called entangled states. While a measurement of one of the entangled objects yields a completely random result
determined by the measurement itself, this measurement also instantaneously determines the state of the other objects, regardless of the distance between them.
Albert Einstein rejected the concept of quantum entanglement, calling it “phantom action at a distance”.
Entanglement is a resource for storing, transferring and processing information.
INÉGALITÉS DE BELL
J. Bell realized that there were experiments (measuring Bell inequalities) to verify whether the world was really described by quantum physics alone, or whether entanglement could in fact be described by classical hidden variables attached to entangled objects. These experiments showed that such local hidden variables cannot exist.
(© Johan Jarnestad/The Royal Swedish Academy of Sciences)
Violation de l’inégalité de Bell
A. Aspect and his team used pairs of entangled photons produced by a bright source. The two photons in a pair were separated and then measured “by surprise”, without them being able to communicate to each other how they were being measured. They gave results that were both totally random, but exactly opposite to each other, without having embedded any hidden information when they were separated.
Prix Nobel de physique 2022
The 2022 Nobel Prize in Physics is awarded to 3 physicists who have demonstrated the bizarre phenomenon of quantum entanglement, paving the way for quantum information processing: Alain Aspect, John Clauser and Anton Zeilinger.