QM. First, a theory to explain "mysteries"

Quantum Mechanics (QM) is, with relativity, one of the major theoretical backbones that was defined at the beginning of the previous century. First used to explain "anomalous phenomena" such as blackbody radiation, this theory rapidly explained the internal structure of atoms and molecules. It also raised fundamental questions about our perception of the real world, and quantum theory of measurement became, after many years of arguments, one of the most intriguing but fascinating facets of QM which lead to the recent development of applications in communication of computing.

How QM has led to test Physics much better than ever before?

Another intriguing aspect of quantum mechanics, sometimes called the "wave-particule" duality, states that, as the quantum wavefunctions that describe material objects obey a wave-type equation (the Schrödinger Equation), wave should exhibit a matter behavior, rapidly observed with the measurement of electromagnetic quanta : the photon. Conversly, matter should exhibit a wave behavior and the best known proof for that is the ability to build up interference fringes. Efforts and progress made in the last 30 years allowed to first build experiments that proved this reciprocal behavior. In addition, it paved the way to the development of new apparatus relying on matter-wave (electron, neutrons, atoms and more and more complex molecules) optics and matter wave interferometry. These techniques have enabled tests of the fundamental laws of physics with significantly greater sensitivity than ever before. Such experiments expand the range of validity of our understanding of the physical world and allow us to establish the limits at which our understanding fails. Novel quantum interactions, such as atomic collisions at temperatures lower than a few millionths of a kelvin, are now being studied. Recent progress has led to the dramatic observation of manifestly quantum-mechanical behavior of matter on a truly macroscopic scale.

What's new in the Quantum World?

More recently, we have been able to enter "more directly" right into the quantum world. The achievement of nanostructure on semiconductor devices, where transport phenomena rely on single electron dynamics and exhibit quantum behavior such as quantum Hall effect or Josephson oscillation opened new fields of research in electronics, semiconducting devices, as well as the superconductors (the 2003 Nobel price actually celebrated the HTS discovered in 1986). Reaching milliKelvin temperature proved to be another step into the quantum world, where fluids stat to have permanent flows and where the wave nature of the fluid drives its properties. Finally, the demonstration of novel quantum systems such as Bose-Einstein condensates (BECs) holds the promise of enabling new and important technologies. Experiments with laser-cooled atoms in space will allow investigations of matter in new regimes not achievable on Earth, and will support new developments and realizations of breakthrough technologies such as the atom laser — a bright source of coherent, propagating matter waves analogous to coherent propagating light waves of the optical laser — and ultraprecise atomic clocks.

Space : a low gravity environment for more precision in measurement...

The threshold between "classical" and "quantum" matter is often seen as on of the most mysterious crossover in nature, since the symmetry properties often break here. Studying nature’s symmetries and how they break (change in pattern) will reveal some of the rules that determine natural processes. Just as a perfectly symmetrical pond can be broken into rings by a stone’s throw, the more perfect symmetry of the early universe was broken by infinitesimal changes that produced all the diversity we observe today. By understanding how such changes occur, we can predict how nature will behave. This understanding can help us to develop products that improve human lives. It may also help to unite our fundamental theories about the universe. Already, a recognition of symmetry between the electromagnetic and weak forces has united theories describing them, and the search continues or uniting all four forces. By pursuing the following research destinations, we shall contribute to an understanding of the patterns that rule atoms, the universe, and life within it. Nevertheless, studying for example a fluid, or a superfluid on Earth is difficult because the weight at the top of the sample presses down on the liquid at the bottom, making the fluid denser at the bottom. A low-gravity environment makes a sample uniform, allowing scientists to measure more precisely what happens when an ultra pure system such as liquid helium passes into a superfluid state.

...and to test quantum effects in large macroscopic systems like superfluids

Understanding such transitions in matter, especially at the critical point where there is no distinction between two phases, is one of the unresolved questions of our age. Fluids naturally have a convective flow on Earth, where the lighter fluid goes to the top and the heavier to the bottom. Patterns form as a given fluid rises and falls, but it is not predictable under what conditions (velocities) patterns will form. When the fluid starts out, it is uniform; when the pattern emerges, we see a break in symmetry.

Condensed helium (superfluid) and cold alkali atoms (Bose-Einstein Condensates) are unique testbeds displaying quantum effects even in large macroscopic systems. When we cool atoms so that they condense into one quantum state (so that they’re at the same lowest-energy state), a single wave function describes their motions. Phonons (density waves going through atoms) and vortices (whirlpools of moving atoms) are excitations known to exist in this state.

...ultimate limits...

Well-posed studies of these macroscopic quantum systems in a low-gravity environment can answer important open questions such as the nature of the transition, possible application of these macroscopic quantum effects and the ultimate limits of matter wave devices.