Hide and seek with a quantum compass

Mar 11, 2013 by Pete Wilton
Hide & seek with a quantum compass

How would you look for something that can be in two 'places' at once? The answer, according to Oxford University research into a quantum phenomenon called superposition, seems to be to ask where it isn't rather than where it is.

'Superposition allows an atom to be simultaneously 'here' and 'there'. Electrons behave like which can point both North and South at the same time,' explains Professor Andrew Briggs of Oxford University's Department of Materials. 'This is a distinctive ; it is quite different from anything in our intuitive every day experience of the world.'

Professor Briggs tells me that you can imagine an electron as being rather like a spinning top, as it spins it generates a .

'Just as a aligns itself with the Earth's , because its energy is lower when it points that way, so a single electron in a magnetic field has a different energy depending on which way its spin points,' he says.

But in the nothing is easy: try to look directly at which way this 'quantum compass' is pointing and the very superposition you wanted to catch in the act - of it pointing north and south at the same time - is destroyed. Instead the superposition state will be replaced with one where the magnet is pointing either north or south at random.

To get around this problem Dr Richard George and others from Oxford worked with colleagues at TU Delft in the Netherlands to prepare a series of experiments.

The researchers used the magnetism of a single atom of nitrogen trapped in a high-purity diamond as their 'quantum mechanical compass'. Under , the fluoresced according to how it was magnetised.

Rather than asking, 'Is the magnet pointing north or south?' the team asked, 'Is it pointing not east?' Measurements that confirm 'not east' were still compatible with the quantum superposition of pointing both north and south at the same time. The researchers studied three successive rounds of measurement on the nitrogen quantum compass, and used correlations between different rounds to prove the presence of quantum superposition in their system.

The team recently reported the results in the journal PNAS.

'We had previously performed experiments in which the nuclei of our atoms had two states available to them. Now we have extended this to a superposition of three states, if you like North, South, and East,' Professor Briggs explains.

'The investigation involved an intermediate measurement, which was equivalent to opening one of three boxes and seeing if a ball was not in it. We showed that not only could you not tell which box had been opened; you could not even tell whether a box had been opened. This in turn, thorough some rather detailed reasoning, allowed us to prove experimentally some fundamental conjectures about the nature of reality.'

According to Professor Briggs this work is pushing the boundaries of 'quantumness' and developing techniques that will help to investigate whether applies to larger and more complex objects.

Dr George adds: 'Our confirmation of these subtle quantum predictions is an important step on the road to transplanting quantum mechanics from a theoretical and laboratory curiosity and into the devices which we use in commerce and everyday life. Our vision is to scale up and build computers in which every 'bit' is replaced with a 'quantum bit' that uses superposition as an integral part of their operation.'

Explore further: Simon's algorithm run on quantum computer for the first time—faster than on standard computer

More information: www.pnas.org/content/early/201… /1208374110.abstract

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User comments : 16

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antialias_physorg
4.3 / 5 (6) Mar 11, 2013
Very good example that you can get information on something by observing what it is not.
While you never get ultimate information that way you DO increase the predictive power you have over the entire system.
Tektrix
not rated yet Mar 11, 2013
I might add that "ultimate information" is not going to happen, at least if thermodynamics has anything to say. However, according to the same rules, "ultimate disinformation" is unavoidable.
El_Nose
5 / 5 (2) Mar 11, 2013
Hijacking post --- but not trolling -- same topic -- entanglement

Have you guys read this??

http://www.extrem...an-light

interesting and I wonder if other institutions will comment or verfiy

ValeriaT
1 / 5 (3) Mar 11, 2013
interesting and I wonder if other institutions will comment or verfiy
It's rather confirmation of older results - the Chinese just replicated them. From perspective of AWT it's evident, that the entanglement must be mediated with faster-than-light interactions (gravitational/scalar/longitudinal waves of vacuum, analogous to sound waves, which are connecting the phenomena at the water surface). The only reason, why the string theorists didn't claimed the entanglement as the evidence of extradimensions already is, it violates the Lorentz symmetry at the same moment.
ValeriaT
1 / 5 (3) Mar 11, 2013
Sorry, the correct illustration of the above experiment is here. From the animation it's evident, with observing of the state of two photons from threesome entangled we can deduce the state of the remaining photon reliably, despite we will not observe it directly. The photons must somehow exchange their state faster, than the detector can notify.

Does such an observation violate special relativity? Actually not, because the photons don't move, they just change their state in synchrony. It similar to observation of "ninja cat" - you're feeling, something strange happens there, but you cannot observe it directly.
Tausch
not rated yet Mar 11, 2013
Our experiment can be described as a game played by two opponents (Alice and Bob) who take alternate turns to measure a shared system. The system they share may or may not obey the axioms of MR. For the purposes of the game, Bob assumes he may rely on the MR assumptions being true and only Alice is permitted to manipu-
late the system between measurements. If Bob is correct to as-
sume MR holds, the game they play is constructed in his favor;
however, "paradoxically," the exact same sequence of operations
will define a game that favors Alice when a quantum-coherent
description of the system is valid.
http://www.pnas.o...full.pdf

MR(Macrorealism[Classical Mechanics])

Bob can not explain his statistical results. There are no correlations between independent events. Classically.
vacuum-mechanics
1 / 5 (3) Mar 11, 2013
'Superposition allows an atom to be simultaneously 'here' and 'there'. Electrons behave like tiny magnets which can point both North and South at the same time,' explains Professor Andrew Briggs of Oxford University's Department of Materials.…
Professor Briggs tells me that you can imagine an electron as being rather like a spinning top, as it spins it generates a magnetic effect.

Yes, this is what we always were told, but the problem is that no explanation how electron spins could generate magnetic field? Maybe this electron mechanism could help us to understand it.
http://www.vacuum...21〈=en
event
not rated yet Mar 11, 2013
Hijacking post --- but not trolling -- same topic -- entanglement

Have you guys read this??

http://www.extrem...an-light

interesting and I wonder if other institutions will comment or verfiy

I have read it and it's an interesting test. The so-called spooky action at a distance is thought to be instantaneous and this test only shows that the 'action' is faster than the degree of accuraccy of the experiment, so it places a lower speed limit, at best.
Zep Tepi
not rated yet Mar 11, 2013
Reminds me of an old thought experiment;

There is a fork in the road. There are two trolls at this fork. One on one fork and one on the other. One path goes to heaven and the other to hell.

One troll always lies and the other always tells the truth. You can only ask one question but you dont know which troll is the truth teller or the liar.

What would your question be?

Tausch
1 / 5 (1) Mar 12, 2013
Do you always tell the truth?
rubberman
not rated yet Mar 12, 2013
Do you always tell the truth?


If you ask this they will both answer yes. Still can't tell.
I would ask what color the sky is over the road to heaven. Since you can all see the sky it'll be pretty clear who is lying.
Mumrah
not rated yet Mar 12, 2013
Hijacking post --- but not trolling -- same topic -- entanglement

Have you guys read this??

http://www.extrem...an-light


You may be interested in this, although it doesn't seem like they've got round to trying the actual experiment yet.

http://www.seattl...0227.php
gwrede
1 / 5 (2) Mar 12, 2013
I'm with Einstein here. There's no such thing as Spooky Action at a Distance. It's merely about Hidden State. (Now I'll hear all about Bell and local state.)

The better clock you have and the longer the distance, the faster the speed you get. If your gear is "perfect", then you'd get an infinite speed. While even this doesn't prove Spooky Action to be false, it at least kind of urges us to start looking at entanglement as a "property" of particles.

Oh, and my question to the troll would be "Would the other troll say this way leads to heaven?"
Tausch
1 / 5 (2) Mar 12, 2013
A troll who always lies has only yes as an answer.
The question is asked only once to an isolated troll.

Color is not an absolute.
Tausch
1 / 5 (2) Mar 12, 2013
The truth for the truth teller harbors inconsistency.
The liar must maintain consistency .
Tausch
1 / 5 (2) Mar 12, 2013
The fallacy arises from language. All language falls short.
The truth can measure nothing.

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