Easing uncertainty

Easing uncertainty
Heisenberg's uncertainty principle limits the precision with which complementary variables can be measured. The uncertainty, however, can be 'spread out' in broad comb-like structures, where each tooth is still relatively sharp, thus enabling precise measurements in a limited range. Credit: Christa Flühmann, ETH Zurich

Heisenberg's uncertainty principle, the fundamental impossibility of simultaneously measuring properties such as position and momentum, is at the heart of quantum theory. Physicists at ETH Zurich have now demonstrated an elegant way to relax this intrinsic incompatibility using a mechanical oscillator formed by a single trapped ion, opening up a route for fundamental studies and practical uses alike.

Heisenberg's posits that there is a fundamental limit to the precision with which so-called complementary variables, such as position and , can be measured. That is, the more accurately the speed and direction (and thus the momentum) of a quantum particle are known, the less certain we can be about its position. Remarkably, this intrinsic limitation can be relaxed when measurements extract periodic functions of position and momentum with a characteristic length and momentum scale, respectively. Simply put, the uncertainty in either variable can be spread out in broad, comb-like structures in which each tooth is still relatively sharp, thus enabling precise measurements in a limited range.

Christa Fluehmann and colleagues in the group of Jonathan Home in the Department of Physics at ETH Zurich have now explored the use of such modular position and momentum measurements to study the dynamical behaviour of a mechanical oscillator consisting of a single trapped ion. As they report in a paper that appeared online today in Physical Review X, they used sequences of multiple periodic position and momentum measurements—by varying the period, they could control whether or not one measurement disturbed the state of the following one. At specific values of the period, they found that such measurements can prevent disturbance, whereas other choices produced strong disturbance. The observation of disturbances is a signature that the single ion displays quantum-mechanical behaviour—for a classical oscillator, the modular measurements are expected to be always unperturbed.

The ability to tune the degree of disturbance between subsequent measurements opens up the possibility to perform fundamental tests of quantum mechanics. Quantum mechanics can be distinguished from classical physics by considering causal connections—how much one measurement perturbs the next—and also by looking at correlations between measurements. Fluehmann et al. explore the latter by measuring time correlators between the sequential measurements and use them to violate the so-called Leggett-Garg inequality (which is also inherently impossible with a purely classical system).

In this case, some of the violations cannot be explained by the disturbance between subsequent measurements. The relation between disturbance and violations of the Leggett-Garg inequality is subtle, but either method certifies the quantum nature of the oscillator states. Indeed, these states are among the most complex quantum oscillator states produced to date. They generalize the famed Schroedinger's cat thought experiment to eight distinct mesoscopic states, analogous to a cat finding itself at distinct stages of illness rather than being simply dead or alive.

With a view to practical implications, modular position and momentum measurement are central components of a number of proposals for computing and precision-measurement protocols that exploit periodic functions of position and momentum to escape Heisenberg's uncertainty principle. The work of Fluehmann and her co-workers provides a fundamental ingredient—measurement—for such applications, thus bringing them closer into reach.


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More information: C. Flühmann et al, Sequential Modular Position and Momentum Measurements of a Trapped Ion Mechanical Oscillator, Physical Review X (2018). DOI: 10.1103/PhysRevX.8.021001
Journal information: Physical Review X

Provided by ETH Zurich
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Apr 03, 2018
Silly philos (noumenon) come here and insist that things like uncertainty are inviolate. And then along comes actual scientists who prove them wrong.

This is why philosophy, in the words of hawking, krauss, et al, IS DEAD.

Apr 03, 2018
Silly philos (noumenon) come here and insist that things like uncertainty are inviolate. And then along comes actual scientists who prove them wrong.

This is why philosophy, in the words of hawking, krauss, et al, IS DEAD.

Philosophy is good for stuff that science can't solve. It is not dead.

Apr 04, 2018
Philosophy is good for stuff that science can't solve. It is not dead
What makes you think science can't explain everything? Philo has never explained ANYTHING.

Apr 04, 2018
I think we are seeing an interference pattern with the pattern uncertainty takes.

Apr 04, 2018
Philosophy is good for stuff that science can't solve. It is not dead
What makes you think science can't explain everything? Philo has never explained ANYTHING.

Has science explained what kind of goverment is the best or can science answer moral questions? I think not. Philosophy does not explain or give straight answers, it's more about thinking, argumentation, and being rational. I don't grasp why some science orientated persons hate philosophy like it had done them some harm.

Apr 05, 2018
Has science explained what kind of goverment is the best or can science answer moral questions?
So what is it then? And what makes you think philos came up with it?

Marx told us it was communism. Aristotle told us that democracy was next to despotism. Etc ad infinitum.
Philosophy does not explain or give straight answers
You bet it doesnt.
it's more about thinking, argumentation, and being rational
Are you saying that science isnt?? Philo is all about posturing, pretense, and argument from authority. It never gets anywhere. It never produces anything of value and never has.

It is another discipline that was meant to give the impression that authorities knew what they were talking about. But they never did until the scientific method was devised to FORCE them to admit their artifice.

Science destroyed religionist authority so academies came up with a secular equivalent. It bought them a few hundred years.

"Philosophy is dead." Hawking pbuh

Apr 05, 2018
can science answer moral questions?
What makes you think it can't? Because philos told you so? An old trick invented by religionists... take an unanswered question and use it to claim only your credo answers it.

More evidence that philo is caustic crap.

Science knows the source of morality but can't fully address it as of yet. It's the tribal dynamic - internal altruism coupled with external animosity. Can't have one without the other. It's the human variant of the mechanism that drives speciation. Biological. Genetic. Scientific.

No metaphysical voodoo bullshit necessary.

Apr 23, 2018
Silly philos (noumenon) come here and insist that things like uncertainty are inviolate. And then along comes actual scientists who prove them wrong.


The above has not in fact proven the uncertainty relations between conjugate variables wrong. You have only demonstrated your personal lack of understanding of the subject,... once again.

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