
. 24/7 Space News .

Scientists separate a particle from its properties
by Staff Writers
Grenoble, France (SPX) Jul 31, 2014

Pictured are Yuji Hasegawa, Tobias Denkmayr, Stephan Sponar, Hartmut Lemmel, and Hermann Geppert. Image courtesy Vienna University of Technology.

Researchers from the Vienna University of Technology have performed the first separation of a particle from one of its properties. The study, carried out at the Institute Laue-Langevin (ILL) and published in Nature Communications, showed that in an interferometer a neutron's magnetic moment could be measured independently of the neutron itself, thereby marking the first experimental observation of a new quantum paradox known as the 'Cheshire Cat'.

The new technique, which can be applied to any property of any quantum object, could be used to remove disturbance and improve the resolution of high precision measurements.

The idea of a Quantum Cheshire Cat was proposed theoretically last year. It is based on the well known character from Alice in Wonderland who can vanish leaving his smile behind. In quantum physics, the term refers to an object whose properties can be separated from its physical location so that the two can be measured at different places.

While this is clearly not possible in our everyday experience, where objects are spatially linked to their properties, the laws of Quantum Mechanics allow it to be achieved.

Quantum mechanics already tells us that particles can be in different physical states at the same time, a phenomenon known as superposition. For example if a neutron beam is divided in two using a crystal, individual neutrons do not have to decide which of the two paths to take. Instead, they can travel along both paths at the same time in a quantum superposition.

"This experimental technique is called neutron interferometry", says Professor Yuji Hasegawa from the Vienna University of Technology. "It was invented here at the Atominstitut in the 1970s, and it has turned out to be the perfect tool to investigate the foundations of quantum mechanics."

To see if the same technique could separate the properties of a particle from the particle itself, Yuji Hasegawa brought together a team including colleagues Tobis Denkmayr, Hermann Geppert and Stephan Sponar from Vienna, together with Alexandre Matzkin from CNRS in France, Professor Jeff Tollaksen from Chapman University in California, and Hartmut Lemmel from the Institut Laue-Langevin to develop a brand new quantum experiment.

Their aim was to get neutrons at the ILL to travel along a different path from its magnetic moment - a property describing the particle's coupling strength to an external magnetic field. The neutron's magnetic moment has a directional preference, a property called spin.

In the experiment the neutron beam was split into two paths with different spin directions. The upper beam path had a spin parallel to the neutrons' direction of flight whilst the spin of the lower beam pointed in the opposite direction.

After the two beams were recombined the experimental detector was set up so that only neutrons with spin parallel to the direction of motion - implying that those travelling along the upper path - are detected. "This is called postselection", says Hermann Geppert. "The beam contains neutrons of both spin directions, but we only detect a selection of the neutrons."

The team then introduced a filter, which absorbs some of the neutrons, in the lower beam path. This did not change the number of detected particles. However, when the very same filter was introduced in the upper beam path, the number of detected neutrons was reduced.

Things get tricky, when the location of the neutron spin is measured: the spin can be slightly changed using a magnetic field. When the two beams are recombined appropriately, they can amplify or cancel each other.

This is exactly what can be seen in the measurement, if the magnetic field is applied at the lower beam - but that is the path, which the neutrons are actually never supposed to take. A magnetic field applied to the upper beam, on the other hand, does not have any effect.

"By preparing the neutrons in a special initial state and then postselecting them, we can achieve a situation in which both possible paths in the interferometer are important for the experiment, but in very different ways", says Tobias Denkmayr.

"Along one of the paths, only an interaction with the particles themselves has an effect, but the other path is only sensitive to a magnetic spin coupling. The system behaves as if the particles were spatially separated from their properties."

The success of this unique type of quantum experiment was dependent on making so called 'weak measurements' to avoid the collapse of the superposition in accordance with the laws of quantum mechanics.

"These weak measurements give you less information," explains Hartmut Lemmel, instrument leader on S18, the ILL's crystal thermal neutron interferometer on which the Cheshire Cat was observed.

"As a result you need to do lots of observations to achieve any sort of certainty that you have seen what you think you have seen. This was only possible due the strength of the neutron source available at the ILL which can uniquely provide the numbers of neutrons required to run these repeat experiments."

With their landmark observation suitably vindicated, questions turn to the potential impact of their fundamental discovery. One application might high precision measurements of quantum systems which are often affected by disturbance.

"Consider a quantum system that has two properties: you want to measure the first one very precisely but the second makes the system prone to perturbations. The two can be separated using a Quantum Cheshire Cat, and possibly the perturbation can be minimized", says Stephan Sponar.


Related Links
Institut Laue-Langevin
Understanding Time and Space


Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review

Measuring the Smallest Magnets
Rehovot, Israel (SPX) Jul 29, 2014
Imagine trying to measure a tennis ball that bounces wildly, every time to a distance a million times its own size. The bouncing obviously creates enormous "background noise" that interferes with the measurement. But if you attach the ball directly to a measuring device, so they bounce together, you can eliminate the noise problem. As reported recently in Nature, physicists at the Weizmann ... read more

Manned Moon Mission to Cost Russia $2.8 Bln

Tidal forces gave moon its shape

Riddle of bulging Moon solved at last

China's biggest moon challenge: returning to earth

NASA Mars Rover Curiosity Nears Mountain-Base Outcrop

Absence of Russia Instrument On NASA Mars Rover Not Political

Mars 2020 rover will carry tools to make oxygen

NASA Mars Curiosity Rover: Two Years and Counting on Red Planet

NEEMO 18 Aquanauts Complete Underwater Mission

Orion Tests Set Stage for Mission

NASA's IBEX and Voyager spacecraft drive advances in outer heliosphere research

Captains of industry explore space's new frontiers

China's Circumlunar Spacecraft Unmasked

China to launch HD observation satellite this year

Lunar rock collisions behind Yutu damage

China's Fast Track To Circumlunar Mission

Europe's Fifth and Final Resupply Ship Launches to Station

Science and Spacesuit Work While ATV-5 Preps for Launch

Russian Cargo Craft Launches for 6-Hour Trek to ISS

ISS Crew Opens Cargo Ship Hatch, Preps for CubeSat Deployment

AsiaSat 8 Successfully Lifts Off

SpaceX launches AsiaSat8 into orbit via Falcon 9 rocket

United Launch Alliance Launches Two Rockets in Just Four Days

United Launch Alliance Marks 85th Successful Launch

Young binary star system may form planets with weird and wild orbits

Hubble Finds Three Surprisingly Dry Exoplanets

Astronomers come up dry in search for water on exoplanets

Hubble Finds Three Surprisingly Dry Exoplanets

NASA Experts, Russia Sign Radiation Safety Protocol Despite Sanctions

Center for Orbital Debris Education and Research Recruits Industrial Affiliates

Military training and simulation revenues to remain steady

Printing the Metals of the Future
