Quantum Entanglement: Effects on Particle 'b

[jnan014]

If you have two particles 'a' and 'b' which are entangled with each other and you observe the state of 'a' so consequently you know the state of 'b', if you destroy 'a' will the state of 'b' become unknown again?

Cheers
Jake

 

[Chipset]

I doubt it. Basically, imagine equation:
a + b + 1 = 0;
here we know what a equals to: a = -b - 1, same applies to b.
If we would measure b, for example, and find out that b=3, then we would know what a equals to: a + 3 + 1 = 0; a = -4.
Now the relationship is broken, so we can set b to anything -- a doesn't care as long as it exists independently.

The fun part is that when relationship (entanglement) persists, values "swing" back and forth and so it's impossible to predict what will happen.

 

[actionintegral]

Hi Chipset,

I like your way of explaining entanglement. It seems like you have reached the heart of the matter without using big words.

Do you have an equally intuitive description for Bell's theorem?

 

[DrChinese]

If you have two particles 'a' and 'b' which are entangled with each other and you observe the state of 'a' so consequently you know the state of 'b', if you destroy 'a' will the state of 'b' become unknown again?

Cheers
Jake

In your example: NO, because the superposition of states has collapsed. (At least with respect to the non-commuting operators that were measured.) They are essentially no longer entangled.

 

[RandallB]

If you have two particles 'a' and 'b' which are entangled with each other and you observe the state of 'a' so consequently you know the state of 'b', if you destroy 'a' will the state of 'b' become unknown again?

Have you carefully thought through how an optical experiment of entanglement actually works?
With photon ‘a’ & ‘b’ how did you detect the state of ‘a’ ?
Do you think you still have a photon to do anything with, even after you gain whatever information you could from it from the photo-detector. Hasn’t it been destroyed as its energy was used to stimulate the detector.

Even when testing electrons after doing anyone test on a electron you cannot do second test on that same electron and consider it to “be the same” as in expecting the second test to guarantee giving you the same results as if the first test had not been preformed.

 

[bruce2g]

Have you carefully thought through how an optical experiment of entanglement actually works?
With photon ‘a’ & ‘b’ how did you detect the state of ‘a’ ?
Do you think you still have a photon to do anything with, even after you gain whatever information you could from it from the photo-detector. Hasn’t it been destroyed as its energy was used to stimulate the detector.

Even when testing electrons after doing anyone test on a electron you cannot do second test on that same electron and consider it to “be the same” as in expecting the second test to guarantee giving you the same results as if the first test had not been preformed.

The simplest experiment would involve two entangled photons, A and B, and a polarized filter, set to a specific value, let's say 90 degrees. Since they are entangled, the two photons will show the same polarization when they are measured, though the polarization is undetermined until one of them is measured.

If photon A passes through the filter and is detected, then we know that photon B will also pass through a 90 degree filter. Photon A has been destroyed at this point, since it either was stopped by the filter or by the detector; Photon B will retain the polarization value forever, unless it is altered or destroyed by another event.

 

[wm]

The simplest experiment would involve two entangled photons, A and B, and a polarized filter, set to a specific value, let's say 90 degrees. Since they are entangled, the two photons will show the same polarization when they are measured, though the polarization is undetermined until one of them is measured.

If photon A passes through the filter and is detected, then we know that photon B will also pass through a 90 degree filter. Photon A has been destroyed at this point, since it either was stopped by the filter or by the detector; Photon B will retain the polarization value forever, unless it is altered or destroyed by another event.

Question: Was photon A polarized at 90 degrees before it was measured?

 

[RandallB]

The simplest experiment ...

Not sure why your directing your comments to me - aren’t just repeating what I just said

Did you mean to address this tojnan014 on how the OP answers its own question.

Question: Was photon A ...?

Not sure why you are here WM; shouldn’t you be fixing the links on your crackpot site?; you promised to be done by last month.

 

[bruce2g]

Not sure why your directing your comments to me - aren’t just repeating what I just said

Did you mean to address this tojnan014 on how the OP answers its own question.

Sorry about that, yes, it intended for the originator.

 

[bruce2g]

Question: Was photon A polarized at 90 degrees before it was measured?

No, the fact that it went through a 90 degree filter doesn't mean it was 90 before it hit the filter. On average, half of the A photons will go through the filter, and they can do so with any polarization.

And, no matter what the angle is, if A goes through a filter at that angle, then so will B.

 

[mgelfan]

Hi Chipset,

I like your way of explaining entanglement. It seems like you have reached the heart of the matter without using big words.

Do you have an equally intuitive description for Bell's theorem?

No offense to chipset, but he hasn't exactly 'explained' quantum entanglement. As far as I'm aware, nobody has been able to do that yet.

Events (or the quantum probabilities related to those events) at, say, two detectors, A and B, are called quantum entangled when their combined detection rate, or probability thereof, P(AB) can't be expressed as the product of the individual detection rates, or probabilities), P(A)P(B).

But the 'nature' of quantum entanglement is unknown.

An intuitive description of Bell's Theorem might be along these lines:
In the archetypal optical Bell test setup, if the polarizer at A is offset from the horizontal (0 degrees in a unit circle) setting at a = 30 degrees, and the polarizer at B is offset in the other direction from the horizontal at b = 30 degrees, then the angular difference of this joint setting, (a,b), is 60 degrees (or two times the offset of either a or b). The angular difference is usually called Theta.

One representation of Bell's Theorem says, in effect, that the correlation at a 60 degree angular difference between a and b (at Theta = 60 degrees) should be exactly twice what it is at Theta = 30 degrees. But (according to qm, and apparently experimentally) it isn't.

A simple Bell-type inequality might be,

N(a, not b) + N(b, not c) >= N(a, not c),

where a, b and c are three values or properties (or not) of objects in some grouping of objects. For example, the group of objects might be the words in this post and the values or properties might be letters (say, a, b and c). So that, for example, N(a, not b) refers to the number of words in this post that contain the letter a but not the letter b, and so on.

But the objects, and values or properties exhibited (or not) by those objects, can be virtually anything -- and the above inequality is always true.

 

[actionintegral]

Thanks, mgelfan - I will think on this and get back to you

 

[DrChinese]

In principle: I think it would be possible to take 2 entangled particles and perform a spin measurement on them. That would collapse their spin states. But I don't think it would collapse the states of other non-commuting observables... would it?

 

[Dense]

This is pretty neat:

Quantum teleportation between light and matter
Veröffentlicht am: 05.10.2006

Veröffentlicht von: Dr. Olivia Meyer-Streng
Max-Planck-Institut für Quantenoptik

Kategorie: überregional
Forschungsergebnisse, Publikationen
Informationstechnologie, Mathematik und Physik
Druckansicht



The concept of quantum teleportation - the disembodied complete transfer of the state of a quantum system to any other place - was first experimentally realized 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).
Since the beginning of the nineties research into quantum teleportation has been booming with theoretical and experimental physicists. Transmission of quantum information involves a fundamental problem: According to Heisenberg's uncertainty principle two complementary properties of a quantum particle, e.g. location and momentum, cannot be precisely measured simultaneously. The entire information of the system thus has to be transmitted without being completely known. But the nature of the particles also has the solution to this problem at the ready: This consists in the possibility of "entangling" two particles in such a way that their properties become perfectly correlated. If a certain propertie is measured in one of the "twin" particles, this determines the corresponding property of the other automatically and with immediate effect.

With the help of entangled particles successful teleportation can be achieved roughly as follows: An auxiliary pair of entangled particles is created, the one being transmitted to "Alice" and the other to "Bob". (The names "Alice" and "Bob" have been adopted to describe the transmission of quantum information from A to B.) Alice now entangles the object of teleportation with her auxiliary particle and then measures the joint state (Bell measurement). She sends the result to Bob in the classical manner. He applies it to his auxiliary particle and "conjures up" the teleportation object from it.

Are "such "instructions for use" merely mental games? The great challenge to theoretical physicists is to devise concepts which can also be put into practice. The experiment described here has been conducted by a research team headed by Prof. Eugene Polzik at Niels Bohr Institute in Copenhagen. It follows a proposal made by Prof. Ignacio Cirac, Managing Director at MPQ, and his collaborator Dr. Klemens Hammerer (also at MPQ at that time, now at University of Innsbruck, Austria).

First the twin pair is produced by sending a strong light pulse to a glass tube filled with caesium gas (about 1012 atoms). The magnetic moments of the gas atoms are aligned in a homogenous magnetic field. The light also has a preferential direction: It is polarised, i.e. the electric field oscillates in just one direction. Under theses conditions the light and the atoms are made to interact with one another so that the light pulse emerging from the gas that is sent to Alice is "entangled" with the ensemble of 1012 caesium atoms located at Bob's site.

Alice mixes the arriving pulse by means of a beam splitter with the object that she wants to teleport: a weak light pulse containing very few photons. The light pulses issuing at the two outputs of the beam splitter are measured with photodetectors and the results are sent to Bob.

The measured results tell Bob what has to be done to complete teleportation and transfer the selected quantum states of the light pulse, amplitude and phase, onto the atomic ensemble. For this purpose he applies a low-frequency magnetic filed that makes the collective spin (angular momentum) of the system oscillate. This process can be compared with the precession of a spinning top about its major axis: the deflection of the spinning top corresponds to the amplitude of the light, while the zero passage corresponds to the phase.
To prove that quantum teleportation has been successfully performed, a second intense pulse of polarised light is sent to the atomic ensemble after 0.1 milliseconds and, so to speak, "reads out" its state. From these measured values theoretical physicists can calculate the so-called fidelity, a quality-factor specifying how well the state of the teleported object agrees with the original. (A fidelity of 1 is equivalent to a perfect agreement, while the value zero indicates that there has been no transfer at all.) In the present experiment the fidelity is 0.6, this being well above the value of 0.5 that would at best be achieved by classical means, e.g. by communicating measured values by telephone, without the help of entangled particle-pairs.

Unlike the customary conception of "beaming", it is not a matter here of a particle disappearing from one place and re-appearing in another. "Quantum teleportation constitutes methods of communication for application in quantum cryptography, the decoding of data, and not new kinds of transportation", as Dr. Klemens Hammerer emphasizes. "The importance of the experiment is that it has become possible for the first time to achieve teleportation between stationary atoms, which can store quantum states, and light, which is needed to transmit information over wide distances. This marks an important step towards accomplishing quantum cryptography, i.e. absolutely safe communication over long distances, such as between Munich and Copenhagen." [O.M.]

Contact:
Prof. Dr. Ignacio Cirac
Chair of Physics, TU München
Managing Director, Max Planck Institute of Quantum Optics
Hans-Kopfermann-Strasse 1
D-85748 Garching
Telephone: +49 - 89 / 32905 705 / 736
Fax: +49 - 89 / 32905 336
E-Mail: ignacio.cirac@mpq.mpg.de
www.mpq.mpg.de/cirac[/URL]

Dr. Olivia Meyer-Streng
Press & Public Relations Office
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Strasse 1
D-85748 Garching
Telephone: +49 - 89 / 32905 213
Fax: +49 - 89 / 32905 200
E-Mail: [email]olivia.meyer-streng@mpq.mpg.de[/email]


URL dieser Pressemitteilung: [url]http://idw-online.de/pages/de/news178248[/url]
[/quote]

 

[Careful]

This is pretty neat:

Well, I will wait for the paper with all the details which will probably reveal that local realism is as alive as ever. I am not impressed with a fidelity of 60 percent (of the measured coincidences I presume, no mentioning of efficiencies and so on here), the distance between alice and bob is 0.5 meter, so the locality loophole is wide open too...
Anyway, given the historical victorious cries about the Aspect experiment as well as the local realist follow-up papers, I presume it is best to remain calm ...

I do not mean to imply that the experiment is not an accomplishment, just that one has to be cautious about the conclusions one draws from this.

Careful

 

[Chipset]

No offense to chipset, but he hasn't exactly 'explained' quantum entanglement. As far as I'm aware, nobody has been able to do that yet.

Well, I didn't really set my goal to explain what's within quantum entanglement or otherwise I'd probably be preparing my Nobel prize speech right now :)

In principle: I think it would be possible to take 2 entangled particles and perform a spin measurement on them. That would collapse their spin states. But I don't think it would collapse the states of other non-commuting observables... would it?

Why should it?

Do you have an equally intuitive description for Bell's theorem?

I believe that mgelfan has explained that but you can imagine Bell's theorem as simple lack of determinism when in quantum world. That is, you cannot expect coin to be thrown and 50% of the times land on tail as would be expected.

 

[RandallB]

Well...but you can imagine Bell's theorem as simple lack of determinism when in quantum world. That is, you cannot expect coin to be thrown and 50% of the times land on tail as would be expected.

Not true
QM does expect 50% and experiment shows this. Just like the "entangled" coin being tested at another time and place also has 50%. What is unexpected is that the matched "entangled" coins give these random results in coordination with each other. That is they are correlated with no apparent means of using a pre-determined unknown hidden variable of a HVT to account for it. Addressing this fixed and determined HV is all that Bell deals with; it has nothing to do with the philosophy of determinism.

In fact Bell does not care if classical physics is deterministic or non-deterministic. It only cares about finding a HV to show that reality is “LOCAL” or if not implying that reality must therefore be “NON-LOCAL” this is all Bell can do. Even as the experiments show that Non-Local must be the case for reality; Bell offers no means to help decide between Non-Local Theories.
Non-Local theories (QM, BM, MWI, Strings, M, etc,) each must look for a way to prove there case Bell will not help. (Note: some of the Non-Local theories have their own version of “local” within their theory – don’t confuse that with Bell Local)

 

[DrChinese]

Well, I will wait for the paper with all the details which will probably reveal that local realism is as alive as ever. I am not impressed with a fidelity of 60 percent (of the measured coincidences I presume, no mentioning of efficiencies and so on here), the distance between alice and bob is 0.5 meter, so the locality loophole is wide open too...

Careful, I still get confused about your position.

The only reason the items you mention would matter is IF the actual values, with "perfect" measurements (to your satisfaction), were different from the QM predicted values. Is this what you are imagining to going to result? I thought your opinion was that even if existing Bell tests are confirmed to your satisfaction in the future, you argue that local reality is not excluded because Bell's assumptions are a bit too simplistic to lead to an absolute rejection of LR.

 

[Careful]

Careful, I still get confused about your position.

The only reason the items you mention would matter is IF the actual values, with "perfect" measurements (to your satisfaction), were different from the QM predicted values. Is this what you are imagining to going to result? I thought your opinion was that even if existing Bell tests are confirmed to your satisfaction in the future, you argue that local reality is not excluded because Bell's assumptions are a bit too simplistic to lead to an absolute rejection of LR.

Right, but there are subtleties involved in these scenario's too (actually I have to check out all the details of the paper before I comment any further).

Careful

 

[DrChinese]

Right, but there are subtleties involved in these scenario's too (actually I have to check out all the details of the paper before I comment any further).

Careful

OK, thanks.

 

[Chipset]

Randall, ugh, I probably see it now -- had some problems with it too :\ Oky-doky, so Bell theorem makes entanglement actually a field which passes "pseudoscientific idiocy" check through statistical predictions?

 

[Careful]

Ok, did not read the paper yet, but let me ask a very simple question : ``how can you determine the state of a single particle ?´´. I mean what is the *exact* definition of a ``fidelity factor'' (on the entire sample space) and so on ?? I would for sure appreciate an answer.

Careful

 

[RandallB]

Oky-doky, so Bell theorem makes entanglement actually a fi...

NO, Bell hasn’t made or shown anything to BE anything.
All Bell was intended for or can ever do is help find the HVT, or show where and how the HV (Hidden Variable) exists. Much to the disappointment of Bell the “local” HV he looked for seems to have been shown not to be possible. Or if you like you could say Bell 'shows' reality must BE non-local; but is shows us no more than that.

This non-local thing is a big paradox, but once you accept the reality must be Bell Non-Local, you can solve the Bell and Double-Slit paradoxes with Non-Local solutions. BUT there is more than one non-local way to do that, and Bell is not designed or able to help decide between them.
Example, QM Entanglement solves the problem; but BM, using a non-local to Bell but “local” within the BM theory view, gives a solution without “super-position” or “entanglement”. Other theories can give non-local solutions as well in other various “ways” or “interpretations” of “reality”. This leaves lots of room for “debate” between those theories at least IMO none of the arguments among them are conclusive or can use Bell productively to decide between them.

You can learn a lot by studying things like BM, Strings, M, WMI, etc but Bell will not help you pick a “best” one. And I still feel QM is the most important one to gain some understanding of.

And as for getting frustrated over studying, understanding, interpreting, learning, and defining; just what it the world is going on with Bell ‘entanglement’ plus the single particle Young’s double Slit experiments – that has to be the most fun and fascinating of them all!

 

[selfAdjoint]

Or if you like you could say Bell 'shows' reality must BE non-local; but is shows us no more than that.

I may be cruisin' for a bruisin' but here's a question. Since the theories Bell was considering were also classical-realist, shouldn't we say instead that he set up the possibility of experiments which, if performed successfully, could demostrate that Nature is not classical-realist-local?

Since that is (C & R & L), its negation would be ~C or ~R or ~L.

 

[RandallB]

I may be cruisin' for a bruisin' but here's a question. Since the theories Bell was considering were also classical-realist, shouldn't we say instead that he set up the possibility of experiments which, if performed successfully, could demostrate that Nature is not classical-realist-local?

Since that is (C & R & L), its negation would be ~C or ~R or ~L.

I don’t think what Bell the man was considering is significant – just what Bell the theorem does or can do.
IF given that the theorem shows reality is non bell local or ~L then yes you would have ~(C & R & L) but not because of anything from C or R.

However, if by R you mean the “realist view” and not “reality” then I think ~L would demand ~R as well; as 'local' is required by R IMO.
Example if some much more impressive experiment were to Prove MWI true that would be a new but valid reality, but in agreement with ~R as it would not be a “realist view” but need a “nuvo-WMI realist view”.

On the C side of the issue some new version of reality (M or something)might be able to displace GR and recover Classical, but if so I don’t think we could know how until such a solution were discovered.

 

[wm]

I may be cruisin' for a bruisin' but here's a question. Since the theories Bell was considering were also classical-realist, shouldn't we say instead that he set up the possibility of experiments which, if performed successfully, could demostrate that Nature is not classical-realist-local?

Since that is (C & R & L), its negation would be ~C or ~R or ~L.

Dear selfAdjoint, I'd like join you in that cruising.

Since the theories Bell considered are naive-realist* (NR) and Einstein-local (EL), Bell sets up the possibility of tests which demonstrate that Nature is not-NR or not-EL. Given the results of these tests, and with EL supported by relativity (and in the absence of tachyons), we conclude that Nature is not-NR. QED.

PS: Some will say that Bell (1964) is not NR because his definition of lambda appears to be unrestricted. However, the mathematical manipulations that Bell makes (in two un-numbered equations at the top of page 198) are only satisfied by objects which are NR. So to admit the validity of the manipulations is to restrict the domain of lambda to NR.


*In my terms: A naive-realist believes that a mercury-in-glass thermometer correctly measures the temperature of a thimble full of liquid. A classical-realist is not so inclined.