A team of French physicians (CNRS, Institut d’Optique Graduate School, Observatoire de Paris, UPMC, Université de Bordeaux), supported by CNES and ESA, publishes a detailed study showing how two different matter waves can allow to test the principle of the universality of free fall using correlated atom interferometers. Beyond this technological « tour de force », this experiment constitutes a first step to explore space-time with quantum objects.
At first sight, General Relativity, the theory of gravitation predicting macroscopic phenomena, and Quantum Mechanics, describing the infinitesimally small, are irreconcilable. For example, the concept of time itself differs from one theory to another. In Quantum Mechanics, time is an independent external variable of evolution, while in general relativity time (or rather space-time) obeys its own dynamics.
At the heart of this latest theory, the equivalence principle states that bodies of different masses fall at the same speed if they are subject to the same gravity field. If this principle is largely verified with objects of large size, its application to the microscopic “quantum” world still gives rise to numerous questions today. Atoms cooled at a few millionths above the absolute zero in the inertial quantum sensors could start to provide answers to these questions.
To reach this goal, this team has developed an experiment allowing in a unique way to measure simultaneously the acceleration of quantum particles of different masses. 10 million atoms cooled at + 0.000001 degrees, Rubidium on one side, and Potassium, twice lighter, on the other side are sent in two simultaneous interferometers. The results are remarkable because they demonstrate that this simultaneous measurement allows to correlate two atom interferometers and reach a precision largely unsensitive to external perturbations.
Thanks to a meticulous study of all the effects which could degrade the performances of the measurement, the physicians showed this is particularly important to control the relative trajectories of the particles, and the spatial characteristics of the atomic detection as well.
The team doesn’t intend to stop at this first transitional result. By pushing further the technology of quantum sensors, they aim to reach a precision at which the equivalence principle will be tested at the quantum level. For this objective, much colder atoms are required to produce much more sensitive interferometers where matter waves propagate over larger distances. This measurement will go through operating these sensors in microgravity, within the simulator developed at Institut d’Optique d’Aquitaine or later aboard a satellite in orbit around the Earth. Beyond this test of a cornerstone of General Relativity, these ultimate sensors pave the way to explore the frontier between the quantum world and the relativistic world.
These results are published in the journal AVS Quantum Science, in the special issue « Celebrating Roger Penrose’s Nobel prize ».