Experiments in quantum entanglement

[Vincent Neave]

Two or three years ago there was an interview in a science journal with a physicist who had worked on the large hadron collider. The interviewer asked what he wanted to do next,and he replied that he'd like to do some experiments in quantum entanglement but had no funding. Apparently donations flooded in from around the world and enabled him to proceed. He was expecting results within a year or so.

Then my PC died and, after replacing it I had forgotten the name of the scientist (it's my age). Since then I have searched in vain for his results. Does anyone know about whom I am talking and whether or not his experiments were successful?

Incidentally I regularly re-route all the cables behind my PC so that they all run freely but when I clean up behind it they are always tied in complex knots. I believe that quantum entanglement may be responsible for this.

 

[DrChinese]

Does anyone know about whom I am talking and whether or not his experiments were successful?

Not sure who you are talking about, but there are a lot of quantum entanglement experiments performed every year (hundreds at least). Is there a specific side of entanglement you are specifically trying to research?

For example, here is a recent article by one of the top teams:

http://arxiv.org/abs/quant-ph/0201134
Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping

"Quantum teleportation strikingly underlines the peculiar features of the quantum world. We present an experimental proof of its quantum nature, teleporting an entangled photon with such high quality that the nonlocal quantum correlations with its original partner photon are preserved. This procedure is also known as entanglement swapping. The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons that never interacted our results directly confirm the quantum nature of teleportation. "

 

[Vincent Neave]

Thank you,

The scientist I am referring to was interviewed on BBC radio. The experiment he was describing was to investigate a mathematical paradox which (if I recall correctly) indicates that if one of a pair of entangled photons were slowed down and the other were not, one could indicate change in the polarity of the other one of the pair before it had actually happened!

I found this possibility so intriguing that I have remembered all that whilst forgetting the most important part, his name.

Oh! and by the way, research is far too grand a word, I am just an interested layman.

 

[DrChinese]

Thank you,

The scientist I am referring to was interviewed on BBC radio. The experiment he was describing was to investigate a mathematical paradox which (if I recall correctly) indicates that if one of a pair of entangled photons were slowed down and the other were not, one could indicate change in the polarity of the other one of the pair before it had actually happened!

I found this possibility so intriguing that I have remembered all that whilst forgetting the most important part, his name.

Then you may enjoy the specific link I provided above. In this case, the entangled photons are detected (and violate a Bell inequality) BEFORE they are entangled. Oh, and they have never been in contact with each other either. How's that for a paradox!

There are a number of experiments in this area, often called Delayed Choice experiments. Here is one of the key ones:

http://arxiv.org/abs/quant-ph/9903047
A Delayed Choice Quantum Eraser

"This paper reports a "delayed choice quantum eraser" experiment proposed by Scully and Druhl in 1982. The experimental results demonstrated the possibility of simultaneously observing both particle-like and wave-like behavior of a quantum via quantum entanglement. The which-path or both-path information of a quantum can be erased or marked by its entangled twin even after the registration of the quantum."

 

[Vincent Neave]

Thanks Dr. Chinese, though I'm not sure if I can wrap my head around it.
In "The Emporer's New Mind" by Professor Roger Penrose he proposes the theory that as the electrical and chemical processes in our brains operate at a quantum level, there is a possibility that we may never be able to fully understand our consciousness. But if he is correct, then this weirdness may well even effect the way we perceive reality. I have referred to this obliquely in a rather "out of the box" discussion in the PF lounge Skepticism and Debunking section.

 

[KipIngram]

I am very interested in this general topic. I would like to attempt to perform an experiment in optics based on quantum entanglement myself - in my own lab. I will be funding this privately, so I need an experiment that has reasonable cost (hundreds to low thousands of dollars).

I am interested in the most "overtly smoking" gun I can possibly get - I'd prefer not to have to wave my hands and talk about "this ensemble vs. that ensemble" when interpreting the results. My first attraction to this project was reading about the Kim et. al. quantum eraser project. That lost its "glow" for me, though, when I realized that manipulating the idler photons did not change the behavior of a consistent set of signal photons - instead the experiment splits the signal (and idler) photons into two batches and notes that one batch exhibits interference while the other does not.

To make matters even worse in this experiment, there are really *two* batches of signal photos that show interference, but if you combine them the interference exactly cancels.

Once I understood these things that particular experiment didn't interest me as much. What I would like to find, ideally, is an experiment where performing (or not performing) measurements on a *pure stream* of photons, which are each entangled with partners in another pure stream, will have an overt and measurable effect on the partner stream. In other words, I'd like to be able to switch interference on and off in the target stream my manipulating the idler stream.

Has any experiment demonstrated entanglement in such an overt fashion?

At this time I don't necessarily feel the need to demonstrate non-locality - I don't require space-like separation of the manipulation and the effect. I'm willing to "believe" that once I split the signal and idler photons in some way that they are then "classically separated"; I seek to demonstrate that they are still entangled in spite of this.

Thanks in advance for advice and guidance.


Kip Ingram, PhD (University of Texas at Austin College of Engineering, 1992)

 

[DrChinese]

...What I would like to find, ideally, is an experiment where performing (or not performing) measurements on a *pure stream* of photons, which are each entangled with partners in another pure stream, will have an overt and measurable effect on the partner stream. In other words, I'd like to be able to switch interference on and off in the target stream my manipulating the idler stream.

Has any experiment demonstrated entanglement in such an overt fashion?

Welcome to PhysicsForums, Kip!

The issue is that what you are describing is not really possible. If you could do as you describe, you could send a signal from point A to point B. Since quantum entanglement has nonlocal components, that signal could exceed c. That obviously isn't going to fly.

There is really no way to see that there is entanglement except by correlating results. That means bringing together information from Alice and Bob.

 

[KipIngram]

Wow - thanks for the extremely fast answer. I'm aware of the basic issues you invoke in your answer, but I hadn't grasped their connection to my question. You've given me a new thing to go off and think about. Now I should be able to "lower my standards" in a rational way and figure out what my "home experiment" target should be.


Kip Ingram

 

[Vincent Neave]

Wow,

I never guessed that my curiosity could have triggered such an erudite discussion.

If you have any success, Kip, I'd love to hear about it.

Vincent