Teleported light (new Danish experiment)

[Martin]

http://physicsweb.org/articles/news/10/10/6/1?rss=2.0

 

===sample quote===

5 October 2006

Danish physicists have managed to light-up a cloud of atoms using light teleported from a source half a metre away.

 

Since Charles Bennett and his team first proposed quantum teleportation in 1993, science fiction enthusiasts have had to be content with frustratingly prosaic examples of the principle. However, at the University of Copenhagen in Denmark, physicists have passed a milestone that will help to bring some practical applications of teleportation within sight (Nature 443 557).

 

Glowing caesium

“This is the first time teleportation has been achieved between the ‘flying’ medium of light and the ‘stationary medium’ of atoms,” said Eugene Polzik of Copenhagen. “Such teleportation could serve as a main building block of a quantum network connecting distant quantum processors.”

 

Quantum teleportation cleverly evades one of the best known peculiarities of quantum states – their inability to be measured precisely. Only some of the information of a quantum state can be learned in a single measurement, and once that measurement is made, the quantum state is effectively destroyed....

===endquote===

[Skye]

I'm getting a Page Not Found error on the link.

 

Just to be clear, have they 'teleported' quantum states between entangled photons and atoms?

[YT2095]

Quantum teleportation cleverly evades one of the best known peculiarities of quantum states – their inability to be measured precisely. Only some of the information of a quantum state can be learned in a single measurement, and once that measurement is made, the quantum state is effectively destroyed....

===endquote===

 

I`m guessing that`s due to the Heisenberg indeterminacy/uncertainty principle?

the mere act of observing it, somehow alters it (or words to that effect).

 

btw, Nice Find Martin!, more posts like this please

 

 

edit: Skye it worked perfectly for me, maybe you could try: http://physicsweb.org/articles/news/

and then look for the Oct5 article (currently at the very top) called "Now you see it, now you don`t".

click that one

[Skye]

Thanks YT, but the original link is working now too.

 

Makes more sense with the link.

[Martin]

Thanks YT, but the original link is working now too.

 

Makes more sense with the link.

 

Here is another link. It is to a German newletter from one of the Max Planck institutes, describing the Danish research.

 

this is maybe clearer and not so sketchy:

http://idw-online.de/pages/de/news178248

 

the result was published yesterday in Nature magazine 4 October issue, I gather, but that usually takes a subscription to get access

[5614]

Just to quote part of that second site:

 

The concept of quantum teleportation - the disembodied complete transfer of the state of a quantum system to any other place - was first experimentally realised between two different light beams. Later it became also possible to transfer the properties of a stored ion to another object of the same kind. A team of scientist headed by Prof. Ignacio Cirac at MPQ and by Prof. Eugene Polzik at Niels Bohr Institute in Copenhagen has now shown that the quantum states of a light pulse can also be transferred to a macroscopic object, an ensemble of 1012 atoms (Nature, 4 October 2006). This is the first successful case of teleportation between objects of a different nature - the one representing a "flying" medium (light), the other a "stationary" medium (atoms). The result presented here is of interest not only for basic research, but also primarily for practical application in realising quantum computers or transmitting coded data (quantum cryptography).

The point of me showing you that quote is just to make clear that this is quantum teleportation. Only the quantum state is being teleported, not the actual light. This quantum state can be teleported in various ways, usually a laser is used, meaning that the data is transferred at the speed of light (speed of the light from the laser) and so nothing is actually being transferred faster than c.

 

I know many of you know, just pointing out for those who are not so sure.

[Martin]

... and so nothing is actually being transferred faster than c.

 

I know many of you know, just pointing out for those who are not so sure.

 

thanks 5614, your clarification and careful phrasing is helpful.

[Skye]

Ok, I was wondering how they would 'choose' which quantum states of the atoms to entangle. It makes sense with the magnetic moment. Could you entangle other states of the atoms with other photons to store more information?

[Martin]

hey 5614!

Skye has a question.

don't wait for permission----venture an explanantion or a guess.

 

BTW here is the technical paper for this research. that is often a help in understanding the popularized version (shouldnt it be the other way round )

 

http://arxiv.org/abs/quant-ph/0605095

Quantum teleportation between two mesoscopic objects: a photonic pulse and an atomic ensemble

Jacob Sherson, Hanna Krauter, Rasmus K. Olsson, Brian Julsgaard, Klemens Hammerer, Ignacio Cirac, Eugene S. Polzik

21 pages, 5 figures

 

"Quantum teleportation is one of the main paradigms in quantum information science. It is an important ingredient in distributed quantum networks, and can also serve as an elementary operation in quantum computers. In this paper we demonstrate for the first time quantum teleportation between two objects of different nature: a pulse of light and a material object. A quantum state encoded in a mesoscopic light pulse is teleported onto an atomic ensemble containing 10^12 Cesium atoms. The teleportation is performed at a distance of 0.5m, and this distance can be increased limited primarily by losses in the transmission of the light. The teleportation is deterministic, with a fidelity of 0.58+-0.02 for coherent states with a mean photon number of 20 and a fidelity of 0.61+-0.02 for states with 5 photons - significantly higher than any classical state transfer can possibly achieve. Quantum teleportation between the carrier of information - light - and the storage and processing medium - atoms - is a new step towards distributed quantum networks."

[5614]

Could you entangle other states of the atoms with other photons to store more information?

hey 5614!

Skye has a question.

don't wait for permission----venture an explanantion or a guess

Thanks Martin' date=' I didn't answer as I'm not really certain. We need Severian or Swansont to answer.

 

If I were to guess I would say no, because:

 

Whenever I've seen the maths it always involves a two state system, shown as [math']|0\rangle[/math] and [math]|1\rangle[/math]. I've never seen further variables or states mentioned.

 

A system is described by one quantum state, although this can be described in different ways, for example a wavefunction or a set of quantum numbers, it is still one quantum state per system. In fact, and this convinces me that I'm correct, the definition of a quantum state is*: "the quantum state of a system completely describes all aspects of the system".

 

*quote from Wikipedia, I know it's wiki, but I think it's correct and wiki worded it better than me, so I used it!

 

If the (ie. the one and only) quantum state describes the entire system, then there is no second state. What other state did you have in mind?

 

This is all my thoughts. It would be good if someone more knowledgable could comment on the above.

 

In fact, I've just been reading a bit more and I think I know what Skye is getting at. There are many quantum numbers which combine to make what is known as the quantum state, ie. magnetic and spin numbers, as well as several others.

 

If we were only teleporting part of the quantum state, say the magnetic number, then we could teleport that magnetic number and, say, the spin. However we are not teleporting part of the state. We are teleporting the entire quantum state and all the quantum numbers associated with it. We are teleporting every part of the whole system. When you teleport the state you teleport every single individual property, leaving no extras behind which you could teleport seperately or additionally.

 

All of the 'other states' are included in the all-encompassing quantum state, which you are teleporting. Leaving no other property behind which you could use to store additional data.

 

So I'm now even more convinced that the answer is no! Not that I'm necessarily right, just that I think I have convinced at least myself!

[Martin]

good show 5614!

 

BTW look on page 7 and 8 of the technical paper.

 

===quote===

The question then arises: how many photons can be contained in a state that can be reliably teleported? The upper limit in our experiment is set by the fluctuations and uncertainty of the classical gain and the coupling parameter ?. Obviously if the set of quantum states to be teleported contains large photon number states, fluctuations of the classical gain will lead to large uncontrolled displacements of the teleported state with respect to the input state, and hence to the decrease in the fidelity. We have run several series of teleportation experiments with mesoscopic photon numbers 0=n (vacuum), 500,180,45,20,5=n . The benchmark classical fidelity 4 for a Gaussian distribution of coherent states with the width n is given by 12 1 + + = n n F class n . The experimental quantum teleportation yields the results which are significantly higher than the corresponding classical benchmark values: 02.064.02 ±=F ; 02.061.05 ±=F ; 02.059.010 ±=F ; 02.058.020 ±=F ; 02.056.0300 ±=F . The effect of the atomic decoherence and losses of light on the teleported state has been modeled in 12. For our experimental values this model predicts, e.g, 66.05 =F , which is close to the observed value. Note that the size of the atomic object onto which the teleportation is performed contains hundreds of billions of atoms. However, the number of excitations in the ensemble, of course, corresponds to the number of photons in the initial state of light. Those excitations are coherently distributed over the entire ensemble.

===endquote===

just as an intuitive thing,

 

the more photons state you try to imprint on the Alice atoms, the lower the FIDELITY with which you will recover the state from the Bob atoms.

 

as they increased the number of photons from 2, to 5, to 10, to 20 ...

the fidelty kept going down.

 

to me this suggests an intuitive reaction to Skye's question. does it you too?

 

with a given resource (like this fixed number of cesiums) the more complex the state you try to transfer the more you will degrade the fidelity of transmission

[5614]

Took me a while, but I think I understand, this is hard for me.

 

with a given resource (like this fixed number of cesiums) the more complex the state you try to transfer the more you will degrade the fidelity of transmission

That's a good answer, but I interpretted Skye's question differently.

 

I read it as: in a system with one atom and one photon, can you teleport a second state, at the same time, onto the same atom. To which I answered: no, an atom can only hold one quantum state. Changing any part of the system gives it a new quantum state. One atom can only hold one state.

 

Your (Martin's) answer is better because it takes a more real life situation in which there are "hundreds of billions of atoms". In this system, as you increase the number of states (ie. the number of photons) being stored on the set of atoms, the fidelity will decrease.

 

If that was intuitive; "don't wait for permission----venture an explanantion or a guess" .