Amazing stuff! This could be a breakthrough!
"An international team ... has observed a long-predicted effect of gravity on a falling quantum object for the first time. The result shows that a fundamental principle at the heart of Einstein's theory of gravity remains consistent with the behavior of matter in the quantum world. ...
Now, an international team has performed an experiment that probes the point where they meet. In the study, the researchers observed a distinctive change in the quantum properties of atoms as they fell under gravity. Crucially, the effect they measured is the same one predicted when Einstein's equivalence principle, a cornerstone of his theory of gravity, is applied to a quantum object.
The equivalence principle states that for an observer in free fall, gravity should locally disappear. ...
At the heart of the experiment is a new apparatus the researchers call the Quantum Galileo Interferometer. It allowed them to do something unusual: effectively split the quantum wave associated with an atom into two paths, hold one in place while allowing the other to fall freely, and then reunite them to see how gravity had changed the falling wave. ...
The experiment ... using clouds of rubidium atoms cooled to just above absolute zero and manipulated close to the surface of a specially designed atom chip. ..."
"... The experimental team ... first used microwave pulses to put the ultracold atoms into a quantum superposition, effectively allowing each atom to travel along two different paths at once. They then used tiny electrical wires on the chip to generate precisely controlled magnetic fields.
One part of the atomic wave responded to this magnetic field, allowing the researchers to apply an upward force that exactly counteracted the downward pull of gravity. In effect, this part was held stationary relative to the laboratory and the Earth. ...
At the end of the fall, the researchers used another precisely controlled magnetic pulse to bring the two parts back together.
When the two waves were reunited, they interfered with each other. That interference allowed the researchers to measure the tiny difference in quantum phase accumulated while one was falling and the other was held still.
The phase measured in the new experiment is the same as the one predicted when Einstein's principle is applied to such a quantum wave. The result therefore provides an experimental connection between quantum physics and Einstein's theory of gravity. ..."
From the abstract:
"The unification of quantum theory and the general theory of relativity, describing gravity, is one of the most important challenges in science.
Einstein’s general theory of relativity is based on the principle of equivalence and has been confirmed to great accuracy for large bodies.
However, in the quantum domain, the equivalence principle has been predicted to take a unique form involving a gauge phase, which is equal, in the context of a measurement on Earth, to the quantum phase of a free-falling wave packet relative to its counterpart wave packet which is static in Earth’s frame.
To measure this phase, we realize a novel cold-atom interferometer in which one wave packet stays static in the laboratory frame while the other is in free fall. The observed relative phase of the wave packets confirms the predicted phase and shows that, in our low energy regime, the equivalence principle may be applied to the quantum domain.
Our observation constitutes a fundamental test of the interface between quantum theory and gravity. The new interferometer also opens the door for further probing of the latter interface, as well as to searches for new physics."
Scientists observe Einstein's gravity in the quantum world
The 2D MOT apparatus which feeds the science chamber with cold atoms.
Fig. 1. The QGI experiment to measure the phase accumulation of a free-falling particle.
