Smart atomic cloud solves Heisenberg's observation problem

Smart atomic cloud solves Heisenberg's observation problem
The atomic part of the hybrid experiment is shown. The atoms are contained in a micro-cell inside the magnetic shield seen in the middle. Credit: Ola J. Joensen

Scientists at the University of Copenhagen have developed a hands-on answer to a challenge linked to Heisenberg's Uncertainty Principle. The researchers used laser light to link caesium atoms and a vibrating membrane. The research, the first of its kind, points to sensors capable of measuring movement with unseen precision.

When measuring atom structures or light emissions at the by means of advanced microscopes or other forms of special equipment, things are complicated due to a problem which, during the 1920s, had the full attention of Niels Bohr and Werner Heisenberg. And this problem, dealing with inaccuracies that taint certain measurements conducted at level, is described in Heisenberg's Uncertainty Principle, which states that complementary variables of a particle, such as velocity and position, can never be simultaneously known.

In a scientific report published in this week's issue of Nature, NBI researchers demonstrate that Heisenberg's Uncertainty Principle can be neutralized to some degree. This has never been shown before, and the results may spark development of new measuring equipment, and new and better sensors.

Professor Eugene Polzik, head of the Quantum Optics (QUANTOP) at the Niels Bohr Institute, led the research, which involved the construction of a vibrating membrane and an advanced atomic cloud locked up in a minute glass cage.

Light 'kicks' object

The Uncertainty Principle emerges in observations conducted via a microscope operating with , which inevitably will lead to the object being kicked by photons. As a result of those kicks, the object begins to move in a random way. This phenomenon is known as quantum back action (QBA), and these random movements put a limit to the accuracy with which measurements can be carried out at quantum level. To conduct the experiments at NBI, professor Polzik and his collaborators used a tailor-made membrane as the object observed at quantum level.

In recent decades, scientists have tried to find ways of 'fooling' Heisenberg's Uncertainty Principle. Eugene Polzik and his colleagues came up with the idea of implementing the advanced atomic cloud a few years ago. It consists of 100 million caesium atoms locked in a hermetically closed glass cell, explains the professor:

"The cell is just one centimeter long, 1/3 of a millimeter high and 1/3 of a millimeter wide, and in order to make the atoms work as intended, the inner cell walls have been coated with paraffin. The membrane, whose movements we observed at quantum level, measures 0.5 millimeters, which actually is a considerable size from a quantum perspective."

The idea behind the glass cell is to deliberately send the laser light used to study the membrane movements through the encapsulated atomic cloud before the light reaches the membrane, explains Eugene Polzik: "This results in the laser light-photons 'kicking' the object—i.e. the membrane—as well as the , and these 'kicks,' so to speak, cancel out. This means that there is no longer any quantum back action—and therefore no limitations as to how accurately measurements can be carried out at quantum level."

How can this be utilized?

"For instance, when developing new and much more advanced types of sensors for analyses of movements,", says professor Eugene Polzik. "Generally speaking, sensors operating at quantum level are receiving a lot of attention these days. One example is the Quantum Technologies Flagship, an extensive EU program which also supports this type of research."

The fact that it is, indeed, possible to 'fool' Heisenberg's Uncertainty Principle may also prove significant in relation to better understanding gravitational waves—waves in space moving at the speed of light. In September of 2015, the American LIGO experiment published the first direct registrations and measurements of gravitational waves stemming from a collision between two very large black holes. However, the equipment used by LIGO is influenced by quantum back action, and the new research from NBI may prove capable of eliminating that problem, says Polzik.


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More information: Quantum back-action-evading measurement of motion in a negative mass reference frame, Nature (2017). nature.com/articles/doi:10.1038/nature22980
Journal information: Nature

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Jul 13, 2017
The first question that comes to my mind is; are the researchers 'fooling' the quantum medium? Or are they 'fooling' themselves?

Guess we'll have to wait and see how many other researchers will attempt to duplicate these experiments. And how many of those results will, perhaps,support these scientists conclusions.

Jul 13, 2017
This comment has been removed by a moderator.

Jul 14, 2017
OK, the way I read the linked abstract they are not circumventing Heisenberg Uncertainty but the quantum limit (which is a combination of uncertainty of the measurement apparatus and the measured object). The uncertainty in the measurement apparatus is affected by the back reaction and it is that part which they could dampen.
So measurement is still ultimately limited by the Heisenberg Uncertainty in the object.

Jul 14, 2017
Heisenberg never made any sense anyway. Having extensive math education, I keep thinking that inasmuch as math makes a good clerk out of you if you are good at it, the clerkiness of its logical mechanics leads to small un-noticed errors, like dividing by zero or mishandling limits, etc, such that whatever comes after that may look good but be worthless except as a BS'ing demo for the naive.

Plain fact is that all systems are affected by measurement. In electrical systems, the lower the 'impedance' of the tool, the more that tool affects the system when loaded by the system. We in Heisenberg's day simply did NOT have high enough impedence tools in order to not destroy the femtometer scale systems we were trying to measure. In addition, let us all be clear that an 'observation' IS a measurement due to the means we use to 'observe'.

Jul 16, 2017
My comment - see removed above by the moderator was: Ha?
Because this is what article deserves.

However I have an answer for Osiris1: It has not much to do with Heisenberg, but with the quantum uncertainty of any quantum system. Mathematics in the basis of the equations brings it over and over when you can solve equations for any system. Therefore, it is synonymous, Heisenberg principle and quantum uncertainty. This is why I am with the first commenter, rrwillsj, on this one: either this is a bad experiment, a hoax, or they are fooling themselves.


Jul 16, 2017
Interesting, so the backreaction allows the measurement to circumvent Heisenberg uncertainty of the measuring apparatus. All that remains is the uncertainty of the measured phenomenon.

I think there was an article on this same thing approached from the theoretical side, suggested for LIGO, fairly recently on physorg. Let's see if I can find it. The difference, of course, being that these guys have done it in the lab, not just in theory.

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