UQ physicist builds on Einstein and Galileo's work

June 2, 2017, University of Queensland
In the new quantum test of the Einstein equivalence principle, free fall of atoms in quantum superpositions on different mass-energies, |a> and |b>, was compared to the free fall of atoms with a well-defined, classical mass-energy |a>. In all previous tests of this principle, the objects were in classical mass-energy states. Credit: Dr Magdalena Zych

Sixteenth century scientist Galileo Galilei threw two spheres of different mass from the top of the Leaning Tower of Pisa to establish a scientific principle.

Now nearly four centuries later, a team of Italian physicists has applied the same principle to objects using a novel scientific method proposed by UQ physicist Dr Magdalena Zych, reported today in Nature Communications.

Dr Zych, from the ARC Centre of Excellence for Engineered Quantum Systems, said the work could lead to the development of new sensors with applications in the study of volcanic eruptions and earthquakes, in searching for mineral deposits, in navigation of Earth and space, and in high-precision measurements of time, frequency and acceleration.

Mathematician and physicist Albert Einstein described the principle last century and it became known as 'Einstein's equivalence principle' for atoms whose mass is in a quantum superposition state.

Dr Zych said the principle played a vital role in physicists' understanding of gravity and space-time.

"The principle contends that the total inertial and gravitational mass of any objects are equivalent, meaning all bodies fall in the same way when subject to gravity," she said.

"Our research team conducted a quantum version of the Leaning Tower test."

The novel approach was first proposed by Dr Zych and University of Vienna and Austrian Academy of Science researcher Professor Caslav Brukner.

"Our test relied on a unique quantum feature: superposition," Dr Zych said.

"In relativistic physics, the total mass of a system depends on its internal energy.

"In quantum theory, a system can occupy two or more different energy states 'at once'. This is called quantum superposition, which means a quantum system may occupy different mass-energies concurrently."

A team led by Professor Guglielmo Tino of the University of Florence and Rome's Istituto Nazionale di Fisica Nucleare (National Institute for Nuclear Physics) designed and realised the experiment.

"The spheres in Galileo's Leaning Tower example were replaced by rubidium atoms," Dr Zych said.

"The tower was replaced by a scheme developed by Professor Tino's team that is based on Bragg atom interferometry.

"The experiment confirmed the validity of the Einstein equivalence principle for quantum superpositions with a relative precision of a few parts per billion."

Explore further: One clock with two times: When quantum mechanics meets general relativity

More information: G. Rosi et al, Quantum test of the equivalence principle for atoms in coherent superposition of internal energy states, Nature Communications (2017). DOI: 10.1038/NCOMMS15529

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not rated yet Jun 03, 2017
This article doesn't provide much information. In Planck's electronic model of the atom, there are many possible energy states. Heavier atoms have more possible energy states. The energy states are defined by the model of the atom. In the case of "superposition" there can be two simultaneous energy states. One of them must be of much higher energy, since none of the energy states leads to destruction of the atom.
Jun 03, 2017
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Da Schneib
3.7 / 5 (3) Jun 03, 2017
So, this is interesting; it appears to show the superposition state as a separate energy level. The paper is open access, but a little dense. The findings are not collected in a summary, so you pretty much have to understand them from the two graphs of the measurements.

The implications of this for the weak equivalence principle are the most interesting part, and I'm still trying to understand them, but off the top of my head this appears to confirm that the superposition is different, in terms of its mass-energy content, from either of the alternatives it superposes.

More later when I've had time to consider it.
4.2 / 5 (5) Jun 03, 2017
that the superposition is different, in terms of its mass-energy content,

Wouldn't that mean that information and energy aren't inextricably connected? That would be pretty amazing
(Didn't we have an article on physorg recently about a way to have a current without information transmission, too?)
4.2 / 5 (5) Jun 03, 2017
Wouldn't that mean that information and energy aren't inextricably connected?

Why would it mean that? And how would that square with results from eg.

"Maxwell's demon demonstration turns information into energy"

"Maxwell's demon as a self-contained, information-powered refrigerator"

"Physicists create first photonic Maxwell's demon"
5 / 5 (4) Jun 03, 2017
I was thinking in terms of entanglement not classifying as information transmission. However it is quantum information so there's correlation involved between the states.

It was just a gut feeling that something iffy would be going on with the information content of the system. Probably not, though. Have to think a bit more on this.
Da Schneib
4.3 / 5 (6) Jun 03, 2017
Had a longer look at the paper and I think I was right in my initial impression. The experiment uses three populations: one in a lower hyperfine state, one in a higher, and one in superposition. The experimental apparatus then checks the differences in both momentum and gravitation between the first and second states, and the first and third. The difference in momentum between the first and third is less than the difference between the first and second, and in both cases equal to the difference between them gravitationally. This not only confirms that GRT applies to quantum states, but also confirms that the equivalence principle does too.

This is an extremely elegant experiment. Unfortunately the fact it worked as expected doesn't expose any new gravity physics, but it is a very good confirmation of the ultimate compatibility between GRT and the SM. When we find quantum gravity, it will not overturn GRT but supplement it.
Da Schneib
4.3 / 5 (6) Jun 03, 2017
And one more thing: the experiment also confirms that the superposition state lies somewhere between the lower and upper hyperfine levels, which is intuitive but not definitive without experimental evidence, which is now available.

It really is extremely elegant.
Da Schneib
4.3 / 5 (6) Jun 03, 2017
Incidentally it's worth reading up on Bragg's Law and atom interferometry to understand just how this experiment works. What this setup is is an atom interferometer that uses Bragg scattering to measure the flight of, essentially, rubidium-87 atoms that are Bose-Einstein condensed into the various populations of the hyperfine states using lasers, then used in the atom interferometer. This atom interferometer is in a vertical configuration that allows it to function as a gradiometer.

As I said, a very elegant experiment. Also quite sexy from a technological perspective.
3.7 / 5 (6) Jun 03, 2017
Da Schneib: Thank you for your extensions to the article's explanation. These are comments well worth reading.
Da Schneib
5 / 5 (1) Jun 04, 2017
Sure, @Emcee. I try to put these things into fairly simple terms that will be comprehensible to most people with a technical background, perhaps with a bit of study.
Jun 04, 2017
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Jun 04, 2017
This comment has been removed by a moderator.
4.3 / 5 (6) Jun 05, 2017
This is another

Post citations to peer reviewed science. Post experimental results. Or don't post anything at all. Especially don't post conceited bags of wind like "science has not yet realized". If it hasn't, get it peer reviewed. Or stop posting.

I expect "stop posting" is all you'll qualify to do.

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