Science News

Spooky Diamonds a Step Towards Quantum Computing

Sun, 4th Dec 2011

Diana O'Carroll

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This week, researchers from the UK, Canada and Singapore have accomplished quantum entanglement on the macro scale, entangling two millimeter-sized diamonds.

Typically we think of objects moving and interacting according to classical mechanics – i.e. Newton’s Second Law – you apply a force to one object and it will cause it to accelerate in a particular direction. But in quantum mechanics there are extra complications, such as entanglement, where an action performed on one object will affect another - even if they are at a distance: something described by Einstein as ‘spooky’.

diamonds entangledStudying these quantum effects on objects any larger than an atomic particle is tough because there is so much environmental noise. Once in the ‘macroscopic’ scale, there are too many extra factors which are difficult to eliminate. The usual approach is to lower the temperature and so reduce thermal noise. Publishing in the journal Science, a team led by Ian Walmsley of Oxford University, took millimetre-wide pieces of diamond and tried to look at them in a more typical environment with an ambient temperature. To get around the problem of other noisy interactions that could interfere with results, they shortened the experiment to a matter of femtoseconds, and they did this using laser pulses.

Next came the entanglement, which they achieved by setting up a beam-splitter and detectors. They fired two laser pulses at each diamond, 350 femtoseconds apart. The second pulse picked up the energy the first pulse left behind before reaching the detector as an especially-energetic photon. If the system were classical, the second photon should pick up extra energy only half the time – only if it happened to hit the diamond where the energy was deposited in the first place.

But in 200 trillion trials, the team found that the second photon picked up extra energy every time. That means the energy was not contained within each diamond, but that they shared the same state as if they were one system. It had already been predicted that this could be done with larger objects at ambient temperature, but actually doing it is something else altogether so – although brief - this may be a step towards some real-world quantum computing, where entanglement allows you to store far more complex information than binary digits.



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fractal geometry in forest?psychic entanglement of biotwins?  clone might do better? CZARCAR, Mon, 5th Dec 2011

So what created that entanglement?
The durations of the laser?

Thanks for the explanation though, what I've seen of it before made no sense, but this do. So they took two diamonds, of a same inner structure, and size and mass too? Then they induced energy, by a laser, in both, using two short 'pulses' at each diamond simultaneously.

If the system, the two diamonds now was defined as, was 'classical', then you shouldn't expect the second pulse to become stronger as it passed through the diamond into the detector more than half of the times, that as 'classically' the energy is expected to be 'localized' to the spot where the laser hit it?

How do they define it? If you impart a momentum, why shouldn't it spread through the whole diamond every time you do it, why only half of the time?

Because of the pulses short durations apart limited each photons momentum spreading inside the diamond? Or is there something more to it, can you define it as them not losing any energy, other than in the direction of their motion?

But accepting the definitions/assumptions there seems a entanglement, as all secondary pulses had more energy when detected.

In this case, are we talking of waves or photons btw?

"They fired two laser pulses at each diamond, 350 femtoseconds apart." which are quite long. 1000 times longer than 350 attoseconds if I got it right? And we've got down to 12 attoseconds measuring, so would that be measure as photons or waves?

They seem to treat it as photons though? So how did they define that, through the detector?

Ahh okay, ( 350 femtoseconds apart) but what was the duration of the lasers firing? Somehow it feels as 'scales' plays an important role here :) yor_on, Tue, 6th Dec 2011

I am still a bit lost with what they actually did, and most of the article is stuck behind the PayWalls.

Here is the main figure:

Diamonds are an interesting choice because light can be reflected internally, perhaps that accounts for some of the priming between pulses.

Anyway, is it the diamonds that are entangled, or the light pulses? CliffordK, Wed, 7th Dec 2011

Very nice question Clifford. Depends on how you look at it I guess :) I would say that they define it as it is the diamonds that now are entangled. The problem might then be that if they are, the entanglement then should cover the whole of the system? Meaning that this light pulse/photons sent that somehow not is expected to disperse into the whole of the diamond(s) under the firings, later, when looked at the whole experiment yet..Is expected.. to cover the same whole that earlier was treated as 'pinpointing'? yor_on, Wed, 7th Dec 2011

You might want to look at it as a result of 'wave functions'. Then the diamonds disappear, instead you have a mathematical equation symbolizing the 'system'. In the case of before firing you then will have two wave functions describing each one of the diamonds (ignoring laser etc). After the firing the diamonds represent one same wave function mathematically if entangled. That is on a theoretical plane though, not considering that those diamonds actually is there at all times. yor_on, Wed, 7th Dec 2011

Ahh sweet, they split the light in a beam splitter, so the light hitting the diamonds are/is already entangled :) as it has a same origin. Then what you do to one 'side' of the 'wave function' that this light (now split into two parts but still being one wavefunction) represent should be reflected in the other 'side'.

Ouch, that is wrong, splitting the light the definition is that you can deflect one of its two paths without changing its common 'wave function', so what I should mean here is the final measurement. And as always that gives me a headache. How can we change its path without interacting? Only if assuming 'fields' and that the 'field' also is what creates the entanglement, maybe??

So maybe I'm wrong there, maybe they don't define it as the diamonds that are entangled?

It becomes slightly weird, in that if I assume that they do mean that the diamonds now are 'entangled' as a whole 'wave function' then it seems to me that I can do this same thing on my cup and telly too? Which then by definition should mean that they too becomes entangled. Assuming that what 'entangles' is the light/photons? Or is this only expected in Raman-active media like a diamond?

Why? yor_on, Wed, 7th Dec 2011 CZARCAR, Wed, 7th Dec 2011

Very nice Czarcar.

"But because of the experimental design, there is no way of knowing which diamond is vibrating. "We know that somewhere in that apparatus, there is one phonon," Walmsley says. "But we cannot tell, even in principle, whether that came from the left-hand diamond or the right-hand diamond."

In quantum-mechanical terms, in fact, the phonon is not confined to either diamond. Instead the two diamonds enter an entangled state in which they share one phonon between them."

So it is the setup of the experiment that defines it. But it still doesn't answer the question if I can 'entangle' my cup with my telly this way? If the definition craves for the experimenters not to 'know' the specific locations of from where those vibrations come, then it is highly mystical :) from a classic perspective.

Then again, assuming that this is right everything can, and ultimately will, be entangled, assuming that you don't know, right :)

Well defining it as 'phonons' vibrating in a lattice you can entangle about anything with anything using split light, but I don't know if you can say that is is the whole of the diamonds that now are entangled? Only if assuming that this vibration is 'existing' in the whole of the diamond as it seems to me? But defining it as a shared wave function then?

If I do define it that way it seems to me that I'm also stating that the macroscopic 'diamonds' must 'vibrate/resonance' with that phonon, am I right? And that makes me wonder if you can thread a 'entanglement' on a 'entanglement' resonance wise? Weird idea, but it's been on my mind.

What I mean here is that for a single particle there may, depending on how you create the entanglement, be one or more particles it is entangled too. But for a macroscopic diamond, described by those particles, the 'vibrations' should become a composite, making it entangled through the universe, maybe :) eh, possibly, etc ::))

As I said, it's a really weird question/idea.

I do like it though. and using that idea as a argument for the 'size' of something? I can now eh, 'state' that with all particles existing, finding one entanglement per particle, I halved the universes 'size'. Assuming that macroscopically all objects are 'coupled' through entanglements, to all other objects, then our macroscopic universe has no 'size' at all :)

Which is very weird, so a better choice would be to assume that as all 'particles' comes from a Big Bang in the mainstream definition, they should all be entangled to all other particles, from the universes very beginning.

Which leaves you to define how a entanglement is 'broken'. yor_on, Wed, 7th Dec 2011

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