‘Spooky action at a distance’ demonstrated in single-particle quantum experiment for first time

A team of scientists have for the first time successfully demonstrated the non-local collapse of a particle’s wave function in an experiment using a single particle.

Using homodyne detectors to measure the particle, and quantum tomography to map the effect of those measurements, the scientists, from Griffith University and the University of Tokyo, were able to verify single-particle quantum entanglement an unusual form of entanglement that could prove invaluable for quantum computing and communications.

While quantum entanglement usually refers to two particles that are bound by opposing spins, the directions of which will only be set when they are observed, single particles can also be entangled, meaning their wave function – ie the equation that defines their likely location and behaviour – can cover any distance.

In other words, a single entangled particle can only be in one place at a given time, but it can be located over a very large distance. When the particle is measured, the wave function will instantly collapse to a set location.

Professor Howard Wiseman at the Centre for Quantum Dynamics. Image courtesy of Griffith University.

Professor Howard Wiseman at the Centre for Quantum Dynamics. Image courtesy of Griffith University.

This was demonstrated by the scientists, who split a single photon between their labs in Japan and Australia, but was previously regarded as an unlikely phenomenon by Albert Einstein.

Almost 90 years ago, he used single-particle entanglement as evidence that quantum mechanics was incorrect, deriding non-local wave function collapse as “spooky action at a distance”.

“Einstein never accepted orthodox quantum mechanics and the original basis of his contention was this single-particle argument,” explained Professor Howard Wiseman, director of Griffith University’s Centre for Quantum Dynamics.

“This is why it is important to demonstrate non-local wave function collapse with a single particle.”

While taking issue with quantum mechanics, Einstein proposed an alternative hypothesis for the particle’s behaviour.

“Einstein’s view was that the detection of the particle only ever at one point could be much better explained by the hypothesis that the particle is only ever at one point, without invoking the instantaneous collapse of the wave function to nothing at all other points.”

Although this alternative theory seems more acceptable to the human brain, Wiseman and his colleagues have shown it to be incorrect.

“Rather than simply detecting the presence or absence of the particle, we used homodyne measurements enabling one party to make different measurements and the other, using quantum tomography, to test the effect of those choices,” he explained.

“Through these different measurements, you see the wave function collapse in different ways, thus proving its existence and showing that Einstein was wrong.”

The research was published today in Nature Communications.


Journal reference: Fuwa M, Takeda S, Zwierz M, Wiseman HM, Furusawa A. Experimental proof of nonlocal wavefunction collapse for a single particle using homodyne measurements. Nature Communications 06 March 2015. doi:10.1038/ncomms7665.


 

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Juno mission: Jupiter’s magnetic field is even weirder than expected

It has long been known that Jupiter has the most intense magnetic field in the solar system, but the first round of results from NASA’s Juno mission has revealed that it is far stronger and more misshapen than scientists predicted.

Announcing the findings of the spacecraft’s first data-collection pass, which saw Juno fly within 2,600 miles (4,200km) of Jupiter on 27th August 2016, NASA mission scientists revealed that the planet far surpassed the expectations of models.

Measuring Jupiter’s magnetosphere using Juno’s magnetometer investigation (MAG) tool, they found that the planet’s magnetic field is even stronger than models predicted, at 7.766 Gaus: 10 times stronger than the strongest fields on Earth.

Furthermore, it is far more irregular in shape, prompting a re-think about how it could be generated.

“Juno is giving us a view of the magnetic field close to Jupiter that we’ve never had before,” said Jack Connerney, Juno deputy principal investigator and magnetic field investigation lead at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“Already we see that the magnetic field looks lumpy: it is stronger in some places and weaker in others.

An enhanced colour view of Jupiter’s south pole. Image courtesy of NASA/JPL-Caltech/SwRI/MSSS/Gabriel Fiset. Featured image courtesy of NASA/SWRI/MSSS/Gerald Eichstädt/Seán Doran

At present, scientists cannot say for certain why or how Jupiter’s magnetic field is so peculiar, but they do already have a theory: that the field is not generated from the planet’s core, but in a layer closer to its surface.

“This uneven distribution suggests that the field might be generated by dynamo action closer to the surface, above the layer of metallic hydrogen,” said Connerney.

However, with many more flybys planned, the scientists will considerable opportunities to learn more about this phenomenon, and more accurately pinpoint the bizarre magnetic field’s cause.

“Every flyby we execute gets us closer to determining where and how Jupiter’s dynamo works,” added Connerney.

With each flyby, which occurs every 53 days, the scientists are treated to a 6MB haul of newly collected information, which takes around 1.5 days to transfer back to Earth.

“Every 53 days, we go screaming by Jupiter, get doused by a fire hose of Jovian science, and there is always something new,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio.

A newly released image of Jupiter’s stormy south pole. Image courtesy of NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles

An unexpected magnetic field was not the only surprise from the first data haul. The mission also provided a first-look at Jupiter’s poles, which are unexpectedly covered in swirling, densely clustered storms the size of Earth.

“We’re puzzled as to how they could be formed, how stable the configuration is, and why Jupiter’s north pole doesn’t look like the south pole,” said Bolton. “We’re questioning whether this is a dynamic system, and are we seeing just one stage, and over the next year, we’re going to watch it disappear, or is this a stable configuration and these storms are circulating around one another?”

Juno’s Microwave Radiometer (MWR) also threw up some surprises, with some of the planet’s belts appearing to penetrate down to its surface, while others seem to evolve into other structures. It’s a curious phenomenon, and one which the scientists hope to better explore on future flybys.

“On our next flyby on July 11, we will fly directly over one of the most iconic features in the entire solar system – one that every school kid knows – Jupiter’s Great Red Spot,” said Bolton.

“If anybody is going to get to the bottom of what is going on below those mammoth swirling crimson cloud tops, it’s Juno and her cloud-piercing science instruments.”