Scientists evade the Heisenberg uncertainty principle

[wolram]

https://www.sciencedaily.com/releases/2017/03/170322143233.htmDate:
March 22, 2017
Source:
ICFO-The Institute of Photonic Sciences
Summary:
Researchers report the discovery of a new technique that could drastically improve the sensitivity of instruments such as magnetic resonance imagers (MRIs) and atomic clocks. The study reports a technique to bypass the Heisenberg uncertainty principle. This technique hides quantum uncertainty in atomic features not seen by the instrument, allowing the scientists to make very high precision measurements.At the bottom of the article it states that this methodology could detect Gravitational Radiation, How is that possible?

 

[DrClaude]

Link to the (paywalled) article: http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html
Preprint: https://arxiv.org/abs/1702.08888

Measurement of spin precession is central to extreme sensing in physicshttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref1, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref2, geophysicshttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref3, chemistryhttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref4, nanotechnologyhttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref5 and neurosciencehttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref6, and underlies magnetic resonance spectroscopyhttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref7. Because there is no spin-angle operator, any measurement of spin precession is necessarily indirect, for example, it may be inferred from spin projectors at different times. Such projectors do not commute, and so quantum measurement back-action—the random change in a quantum state due to measurement—necessarily enters the spin measurement record, introducing errors and limiting sensitivity. Here we show that this disturbance in the spin projector can be reduced below N1/2—the classical limit for N spins—by directing the quantum measurement back-action almost entirely into an unmeasured spin component. This generates a planar squeezed statehttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref8 that, because spins obey non-Heisenberg uncertainty relationshttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref9, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref10, enables simultaneous precise knowledge of spin angle and spin amplitude. We use high-dynamic-range optical quantum non-demolition measurementshttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref11, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref12, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref13 applied to a precessing magnetic spin ensemble to demonstrate spin tracking with steady-state angular sensitivity 2.9 decibels below the standard quantum limit, simultaneously with amplitude sensitivity 7.0 decibels below the Poissonian variancehttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref14. The standard quantum limit and Poissonian variance indicate the best possible sensitivity with independent particles. Our method surpasses these limits in non-commuting observables, enabling orders-of-magnitude improvements in sensitivity for state-of-the-art sensinghttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref15, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref16, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref17, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref18 and spectroscopyhttp://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref19, http://www.nature.com/nature/journal/v543/n7646/full/nature21434.html#ref20.

Many quantum systems that are currently used to enhance metrological precision obey the regular Heisenberg uncertainty relations that apply to conjugate variables such as position and momentum. These systems can be 'squeezed' to reduce the uncertainty of one variable at the expense of greater uncertainty in another, and thereby to surpass the limits set by classical physics in metrology. However, spin systems and pseudo-spin systems obey different uncertainty relations because of their underlying symmetries. On the basis of these relations, the authors demonstrate simultaneous measurement of spin amplitude and spin angle beyond classical limits. This approach has potential applications in spin-based sensors and could increase the sensitivity for several applications, such as magnetic resonance measurements, in which spin relaxation rates could be correlated with precession frequency with higher precision than is currently possible.