Experimental test verifies Heisenberg's measurement uncertainty principle

June 2, 2016 by Lisa Zyga feature
In the new experiment, two compatible observables, C and D, are jointly measured to approximate two incompatible observables, A and B. The approach can be represented on a sphere. Credit: Ma et al. ©2016 American Physical Society

(Phys.org)—Werner Heisenberg originally proposed the uncertainty principle in 1927, but his original proposal was somewhat different than how it is interpreted today. As a recent paper in Physical Review Letters explains, Heisenberg's original statement was about error and disturbance in a measurement process. Over the years, however, Heisenberg's original proposal has been restated in terms of the uncertainties intrinsic to quantum states. This aspect of the uncertainty principle has been studied extensively with well-developed theories and verified experimentally.

On the other hand, Heisenberg's original proposal regarding error in the measurement process is not as well understood. In the new paper, a team of researchers led by Professor Jiangfeng Du at the University of Science and Technology of China has reported an experimental test of the measurement aspect of Heisenberg's uncertainty principle using nuclear-spin qubits.

In his original proposal, Heisenberg predicted a tradeoff between error and disturbance. He suggested that when a gamma-ray microscope measures the position of an electron, the measurement inevitably disturbs the electron's momentum. The smaller the measurement error, the larger the disturbance, and vice versa. This idea was described qualitatively but a complete quantitative description is still lacking today.

In the new experiment, the researchers have verified a related tradeoff that builds on a recent proposal. In this tradeoff, measurement inaccuracies are quantified geometrically.

"In recent years, the quantification of Heisenberg's original idea has drawn lots of attention, and a number of experiments have been performed," Du told Phys.org. "However, the physical validity of some parts of the theory is in dispute. A few years ago, Busch, Lahti, and Werner proposed an innovative approach which is more sensible and persuasive. Our work is based on Busch, Lahti, and Werner's theory, and makes some improvement. We reformulated their theoretical framework and derived a new tradeoff relation which was verified by our experiment. In this sense, our work tests a fundamental aspect of quantum physics."

In order to verify the new tradeoff, the researchers had to approach the situation somewhat indirectly. According to the measurement uncertainty principle, incompatible observables, such as position and momentum, cannot be measured simultaneously. So instead, the researchers simultaneously measured two compatible observables that are designed to approximate two incompatible observables. Compatible observables can be measured simultaneously, and simulate the measurement device that introduces error and disturbance.

As expected, the experimental results verify the tradeoff, showing that the worst-case inaccuracy is determined by the incompatibility of the observables. Overall, the work provides a deeper understanding of Heisenberg's original idea about the , and could also have practical applications.

"In the future, we may consider the implications for the area of quantum information technology," Du said.

Explore further: Discovery of uncertainty relations beyond the Heisenberg

More information: Wenchao Ma et al. "Experimental Test of Heisenberg's Measurement Uncertainty Relation Based on Statistical Distances." Physical Review Letters. DOI: 10.1103/PhysRevLett.116.160405, Also at arXiv:1512.07407 [quant-ph]

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MP3Car
2 / 5 (4) Jun 02, 2016
R.I.P. Walter White......

:)
rjrocker007
1 / 5 (5) Jun 02, 2016
Interesting read. My readers of my blog would love to know this.
Hyperfuzzy
1 / 5 (9) Jun 02, 2016
Really!? Think of course a gamma ray creeps out the electron; but, QM? Based upon a black body being totally reflective!? Everything is made of these spherical electric centers, how do you build a black body? Anyway, calculations based upon a fantasy containment with quantifiable states excludes simple definition and expected results other than these which can exist but ...! The argument is circular.
arom
Jun 02, 2016
This comment has been removed by a moderator.
Da Schneib
4.2 / 5 (10) Jun 02, 2016
Because of the confusion between measurement error and intrinsic uncertainty, and because Heisenberg uncertainty has been only theoretically constrained, this indirect measurement was necessary to show that measurement uncertainty cannot alone account for the Born Rule. Quantum uncertainty is not inaccuracy. It is inherent in quantum phenomena. It leads to probabilistic, not deterministic, outcomes.

This is actually a bigger deal than it appears to be on the surface.
someone11235813
4.3 / 5 (6) Jun 02, 2016
I thought Heisenberg called it an indeterminacy rather than an uncertainty. In fact you could argue that the indeterminacy is certain.

Interesting read. My readers of my blog would love to know this.


Let me fix that for you... The reader of my blog... ie, your mum.
antialias_physorg
4.6 / 5 (9) Jun 03, 2016
This is actually a bigger deal than it appears to be on the surface.

Yes. It shows that the actual information value within a system is finite*.

*which is uncomfortably close to the "we all live in a simulation" argument.
Protoplasmix
4.3 / 5 (6) Jun 03, 2016
This is actually a bigger deal than it appears to be on the surface.
Yes. It shows that the actual information value within a system is finite*.

*which is uncomfortably close to the "we all live in a simulation" argument.
Interesting. Is the principle of stationary action (or least action) applicable?
antialias_physorg
4.4 / 5 (7) Jun 03, 2016
Interesting. Is the principle of stationary action (or least action) applicable?

Should be, but only to the conjugate variables in question as a whole (e.g. energy AND time...but not separately...but don't nail me down on that. I know it's applicable in quantum mechanics, but I'm not hip enough on the specifics to give a definite statement)
Whydening Gyre
4.2 / 5 (5) Jun 03, 2016
Waitaminit...
If you can quantify uncertainty, isn't it certain?
Hyperfuzzy
1 / 5 (3) Jun 03, 2016
Simple: In a 4D space each point is defined exactly without error, in fact, with proper set-up and stabilization time you are able to predict what you will measure. Your calibration is exact based upon the combined probe and IUT. You do understand that the field obeys superposition and and temporality. So, yea, this is a boundary condition error, everything is quantized, how do you know the minimum quantity of a thing. The thing in question is an instant sample in a tiny volume of a wavelet. Nonsense. A defined false minimum.
ursiny33
1 / 5 (4) Jun 03, 2016
The uncertainly principle in open space of particle location, in space, isn't supreme in confined dense environment like a neutron star there's no open space to occupy these are captured confined particles with no other space to exist in but the one they are in ,the opposite the certainly principle
ursiny33
1 / 5 (4) Jun 03, 2016
It would be easy for neutrons positions to move in open space by repulsion forces by proximity, so that the measurable position is unattainable in time ,observation, it would be much more difficult locked into magnetic compression of attraction to un liked charged constructions as prisoners
ursiny33
1 / 5 (4) Jun 03, 2016
In neutron star density the neutrons repulsion forces to each other and countered with a super hot quantum plasma fluid of positrons and electrons that locked magnetic compression from opposite charges
Da Schneib
4.2 / 5 (5) Jun 03, 2016
This is actually a bigger deal than it appears to be on the surface.
Yes. It shows that the actual information value within a system is finite*.

*which is uncomfortably close to the "we all live in a simulation" argument.
Interesting. Is the principle of stationary action (or least action) applicable?
Not quite sure how you're thinking of applying it. What do you have in mind?
Phys1
4 / 5 (8) Jun 03, 2016
This is actually a bigger deal than it appears to be on the surface.
Yes. It shows that the actual information value within a system is finite*.

*which is uncomfortably close to the "we all live in a simulation" argument.
Interesting. Is the principle of stationary action (or least action) applicable?

Yes it is. The wave equation, whether Schrödinger, Dirac or Klein-Gordon, is a consequence of this principle. As argued in a different thread, any wave has uncertainty.
Protoplasmix
4.3 / 5 (6) Jun 03, 2016
Not quite sure how you're thinking of applying it. What do you have in mind?
I don't know enough about it. If the principle is fundamental to conjugate variables separately then maybe it's a constraint on the information within a system?
- - -
Should be, but only to the conjugate variables in question as a whole (e.g. energy AND time...but not separately...
What would be some reasons for it not applying separately*? Are they the same reasons for expressing the significance of finite information*? How does finite information within a system support (or relate to) the simulation argument?

*for example, the number of possible eigenstates for a system
Da Schneib
4.3 / 5 (6) Jun 03, 2016
@Phys1, that's the glib answer and I almost gave it, in different words of course, but I felt that @Proto had something slightly different in mind, and it emerges that I was right. Your response is correct, but I don't think it's the answer to the question @Proto was asking.

@Proto, I'm still not sure I see how to apply the action principle here. I think that the constraint on information in the system is the uncertainty principle itself. And as @Phys1 pointed out, the action principle is fundamental to the wave equation, and the form of the wave equation is the substrate from which the uncertainty principle is derived.

(@Phys1, do you recall whether the wave equation is derived from uncertainty, or vice versa? I can't be arsed to look it up. Doesn't matter anyway; either way, the action principle and uncertainty principle are fundamentally related through the wave equations.)
someone11235813
4 / 5 (4) Jun 03, 2016
*which is uncomfortably close to the "we all live in a simulation" argument.


I heard a pretty good argument recently that gives the probability that we are in fact in a simulated world is proportional to the probability that we create one because if we did create the technology then it's virtually certain that we are in a simulated world so that means a one in five chance. The other four being, 1.It would be unethical and not undertaken, 2. we all die first, 3. we couldn't be arsed, 4. it's not technologically possible after all.
Whydening Gyre
4 / 5 (4) Jun 03, 2016
*which is uncomfortably close to the "we all live in a simulation" argument.


I heard a pretty good argument recently that gives the probability that we are in fact in a simulated world is proportional to the probability that we create the technology... one in five.

Which then begs the question -
What would a level 3 civilization do for entertainment...:-)?
Or... how would they teach History...:-)?
Hyperfuzzy
1 / 5 (3) Jun 04, 2016
QM created uncertainty. Does anyone get it?
Bookbinder
1.8 / 5 (5) Jun 04, 2016
backing off? Now calling it the 'measurement' uncertainty principle. Nice. So does this mean we can all now believe the moon exists even when we are not looking at it? Or are the quantum gods still claiming there is only a 50% chance the moon exists?
Protoplasmix
4.3 / 5 (6) Jun 04, 2016
@Proto, I'm still not sure I see how to apply the action principle here. I think that the constraint on information in the system is the uncertainty principle itself.
For conjugate pairs of variables, there doesn't appear to be a way to know what the information in the system currently is, exactly, and so exact predictions can't be made. But it is possible to know what the information was, exactly, by performing an additional measurement. What does that mean? Either there was no smeared superposition of possibilities, or the additional measurement reaches back in time? Or what?
Protoplasmix
4.3 / 5 (6) Jun 04, 2016
@Phys1, do you recall whether the wave equation is derived from uncertainty, or vice versa? I can't be arsed to look it up. Doesn't matter anyway; either way, the action principle and uncertainty principle are fundamentally related through the wave equations.
It seems to be this complementarity between wave and particle descriptions that's at the heart of various interpretations of quantum mechanics. And it's not possible to derive the Schrodinger equation (or the commutation relation [pq – qp = ih/2π] ) from an inequality (I looked it up, see 2.4 Uncertainty relations or uncertainty principle? http://plato.stan...rtainty/ ).
Da Schneib
3.9 / 5 (7) Jun 04, 2016
@Phys1, do you recall whether the wave equation is derived from uncertainty, or vice versa? I can't be arsed to look it up. Doesn't matter anyway; either way, the action principle and uncertainty principle are fundamentally related through the wave equations.
It seems to be this complementarity between wave and particle descriptions that's at the heart of various interpretations of quantum mechanics. And it's not possible to derive the Schrodinger equation (or the commutation relation [pq – qp = ih/2π] ) from an inequality (I looked it up, see 2.4 Uncertainty relations or uncertainty principle? http://plato.stan...rtainty/ ).
Been a long time since I looked at matrix mechanics, so I'd forgotten the history. Actually the uncertainty relation was derived from matrix mechanics; later, when Pauli showed that matrix mechanics and the Schroedinger wave equation were equivalent, it became clear that uncertainty could also be derived from the wavefunction.
Da Schneib
3.9 / 5 (7) Jun 04, 2016
So the answer to my question is, uncertainty was originally derived from matrix mechanics, which is equivalent to wave mechanics. I can't decide if that makes me right or wrong. ;)

Looks like *you* at least are right, @Proto: neither matrix mechanics nor wave mechanics can be derived from the uncertainty relation.
Da Schneib
4.3 / 5 (6) Jun 04, 2016
I'm still not sure I see how to apply the action principle here. I think that the constraint on information in the system is the uncertainty principle itself.
For conjugate pairs of variables, there doesn't appear to be a way to know what the information in the system currently is, exactly, and so exact predictions can't be made.
Yes, I think those two statements are equivalent. I'll weasel a little bit and say that actually, we know all the information there is; the system at that point doesn't have exact values for some variables. It's not a matter, in other words, of not being able to know what the information is; it's a matter of the information not existing.

And I'll point out that in fact that little bit of weaseling is just exactly what this article is all about.
[contd]
Da Schneib
3.9 / 5 (7) Jun 04, 2016
[contd]
But it is possible to know what the information was, exactly, by performing an additional measurement.
I would rather say, an additional *later* measurement. You'll see why in a moment.

What does that mean? Either there was no smeared superposition of possibilities, or the additional measurement reaches back in time? Or what?
In flight, at the time, there is a real superposition; only after future measurement can a consistent description of what happened be made. This is the essence of consistent histories.

To relate this to a real experiment, consider the DCQE.

A bunch of signal photons appear at the signal CCD; their positions are recorded. Is there interference? At first inspection, no. This is superposition; there is no definable interference pattern. However, information about which path the original photons, the progenitors of the signal and idler photons created at the βBBO SPDC crystal, is still available.
[contd]
Da Schneib
3.9 / 5 (7) Jun 04, 2016
[contd]
If the coincidence information for the idler photons that went to the quantum eraser is removed, and then the remaining coincidence information (which is only for the idler photons whose welcher weg information was *not* quantum erased) is used to select only those photons that were closely enough coincident with an unerased idler, the interference pattern immediately jumps out.

Now that is just about exactly what you're talking about.

Let's think it through both ways, detecting the idlers first, and then detecting the signals first. In the experiment this is done by lengthening and shortening the idler and signal paths. Jack Cramer suggested doing this with fiber optic cables. Here's what we get:
1a. The idler photons that were not erased are used to select which signal photons we will look at as the signal photons arrive. Interference.
1b. All idler photons are used. No interference.
[contd]
Da Schneib
3.9 / 5 (7) Jun 04, 2016
[contd]
2a. All signal photons are looked at. No interference.
2b. Only the signal photons that arrived coincident with an unerased idler photon are looked at. Interference.

Note that *until both the idler and signal data are available*, you will see no interference.

It's a consistent history; if the idler path is longer than the signal path, then you are waiting for the welcher weg information from the unerased idlers *when you have already received the photons that interfered*. Does that interference "exist within" those photon interactions/vertices/events? According to Bell's Theorem and the experiments that have measured Bell's Inequality, the answer is "no."
Da Schneib
3.7 / 5 (6) Jun 04, 2016
The DCQE is fascinating because it combines interference with demonstration of non-locality in both space and time and with uncertainty, all in a single nice neat little package. You can see all three of the most important differences between classical and quantum physics right there in front of you.

We cannot predict in advance of the unerased idler photons' or their proxies' arrival which signal photons will have experienced interference. But we can retrodict which ones did once all the information is available.
Protoplasmix
4 / 5 (4) Jun 05, 2016
The DCQE is fascinating because it combines interference with demonstration of non-locality in both space and time and with uncertainty, all in a single nice neat little package.
Well it's frustrating, but in a good way. If the connection between entangled particles can be considered to act or function in a "non-local, entangled" way that seemingly violates special relativity [in the effort to preserve a sense of causality], then that same attribute or rationale can be applied at the start: the geometry of the experiment is encountered (or experienced, or entangled with) as the photons are being emitted, in a way that fixes (or collapses) their paths through the experiment. If there's a cart-before-the-horse aspect to causality, it seems to me that the wave mechanics aspect is the horse and the particle of information is the cart. It's a faster horse than light [entanglement is], obviously, regardless of any physical carts and their placement. Isn't it?
Phys1
3.4 / 5 (5) Jun 05, 2016
neither matrix mechanics nor wave mechanics can be derived from the uncertainty relation.

Certainly, I would derive uncertainty - as well as matrix mechanics - from wave mechanics.
Protoplasmix
4 / 5 (4) Jun 05, 2016
late edit – of course what I'm saying is akin to pilot wave theory, which Bell pointed out doesn't have locality. So I'm probably not applying it correctly to the DCQE experiment when I say it's faster than light. But if it is, wouldn't that explain the non-locality? Are there other experiments as clever as DCQE that show it couldn't be some kind of pilot wave?

edited edit - Phys1, the Schrodinger equation can also be derived from pilot wave theory...
Da Schneib
3 / 5 (4) Jun 05, 2016
neither matrix mechanics nor wave mechanics can be derived from the uncertainty relation.

Certainly, I would derive uncertainty - as well as matrix mechanics - from wave mechanics.
Historically wave mechanics and matrix mechanics were separate and apparently competing views of quantum physics until Pauli showed they are equivalent. Today we use both of them in bra-ket equations and matrices and switch back and forth as it suits us.
Da Schneib
3 / 5 (4) Jun 05, 2016
If the connection between entangled particles can be considered to act or function in a "non-local, entangled" way that seemingly violates special relativity [in the effort to preserve a sense of causality],
It's quite important to understand here that there is no way to use this apparent superluminal connection to transmit matter, energy, or information.

All that happens is a pair of particles that share a superposed state have that state resolved. We cannot prove this occurred until we measure both particles, and then transmit the measurements one way, the other, or to a third party using an (at fastest) speed-of-light communication channel.

We cannot observe that a particle's superposed state has been resolved; all we can do is measure the particle, and that doesn't tell us what happened to it before we measured it. The situation is exactly the same with the interference in the DCQE.
[contd]
Da Schneib
3 / 5 (4) Jun 05, 2016
[contd]
then that same attribute or rationale can be applied at the start: the geometry of the experiment is encountered (or experienced, or entangled with) as the photons are being emitted, in a way that fixes (or collapses) their paths through the experiment.
It's important here to understand exactly how the DCQE works.

1. A laser emits some photons.
2. The photons pass a dual slit barrier, introducing the possibility of interference.
3. The photons enter a beta barium borate (βBBO) crystal, which performs spontaneous parametric down-conversion (SPDC) on them, converting them to two photons that share the characteristics of the original photon, particularly a location which identifies which slit they went through. These photons are of crossed polarization.
4. The photons enter a polarizer, specifically a Glan-Thompson prism (chosen for its high transmissivity) which separates the SPDC photons into polar moieties.
[contd]
Da Schneib
3 / 5 (4) Jun 05, 2016
[contd]
5. These polar (i.e., spin on the axis of the GT crystal) moieties form two beams; one is the "idler" beam, which is used as a proxy for the welcher weg (which slit) information, and the other is the "signal" beam, which is used to form interference (or not, depending on whether the idlers are measured to determine the welcher weg information).
6. The idler beams (from the two slits) are sent to two beam splitters (one for each slit) which pass 50% of the photons, and reflect the rest.
7. The reflected idler beams are detected to determine the welcher weg information, thus ensuring that their entangled signal photons will not show interference.
8. The transmitted idler beams are mixed through another beam splitter, erasing their welcher weg information, and then detected by two detectors, thus ensuring that their entangled signal photons will show interference.
9. The timing of each idler photon is used to select their entangled signal photons.
[contd]
Da Schneib
5 / 5 (2) Jun 05, 2016
[contd]
The entanglement happens after the dual slit barrier; first interference (dual slits), then entanglement (βBBO) and separation of the entangled pairs (GT), then erasure (or not) on one of the entangled pair, and interference (or not) on the other.

So I'm not sure what you said is quite accurate; the photons are emitted then entangled then measured. It's not a single step operation.

If there's a cart-before-the-horse aspect to causality, it seems to me that the wave mechanics aspect is the horse and the particle of information is the cart. It's a faster horse than light [entanglement is], obviously, regardless of any physical carts and their placement. Isn't it?
Some current experiments seem to show that superposition is resolved for the entangled partner at minimum superluminally. When I get to your other post I'll expand on this much more.
Protoplasmix
5 / 5 (3) Jun 05, 2016
Thanks for the extra effort explaining DCQE, Da Schneibe, but for me it still leaves the choice of interpreting it as "all the interference effects give the photons a predisposed trajectory" or "detecting a photon affects what already occurred at a different detector."

Regarding the physical materials (slits, crystal, prism, beam splitters, mirrors and detectors) consider that for something which can propagate >>c, the locations of atoms and electrons are known (or experienced) exceedingly precisely (the experiment becomes mostly empty space) and their corresponding particle momentum is therefore off the charts to such an extent that there's no obvious effect from the interaction with the pilot wave, other than to predispose the photons being emitted to only those paths allowed by the interference effects.
Da Schneib
3.4 / 5 (5) Jun 05, 2016
Save your fingers and call me "Schneib" if you like.

Thanks for the extra effort explaining DCQE, Da Schneibe, but for me it still leaves the choice of interpreting it as "all the interference effects give the photons a predisposed trajectory" or "detecting a photon affects what already occurred at a different detector."
Yep. It doesn't follow classical logic, specifically classical causality.

Let's suppose we set up the eraser/noneraser part (the beam splitters and four idler detectors in the idler path) with mirrors instead of the first two beamsplitters, with mechanical actuators so we can flip them from "erase" to "don't erase." (The third beamsplitter is the eraser, so the mirrors each flip between their detector and the beam splitter.)

Now, first we try it with the idler path shorter than the signal path.

What do we see? Simple: flip the mirrors to erase, we see a pure interference pattern. Flip them to don't erase and we don't.
[contd]
Da Schneib
3.4 / 5 (5) Jun 05, 2016
[contd]
At least so one would presume.

But now let's make the idler path longer than the signal path. And let's flip the mirrors while the experiment is running.

When does the interference flip to noninterference?

I'll let you think about that a while. I have the rest of your post and will respond later, but hey, King of Thrones is on and the first three scenes have been compelling to say the least. More later.
Protoplasmix
4 / 5 (4) Jun 06, 2016
Schneib, sorry about the e.
When does the interference flip to noninterference?
Changing the geometry while the experiment is running sounds like a good idea, if (and only if) the timing of the change occurs after the signal photon reaches D0 but before the idler photon reaches the changed geometry. If the pilot wave interpretation is correct then the pattern recorded at D0 (clump or interference) should correlate with the initial state (before the change). If the "changing history from future events" interpretation is correct then the pattern at D0 should correlate with the changed state. Note that changing the state after the idler photon has been either transmitted or reflected should have no effect, and that changing the state before the signal photon reaches D0 still allows the pilot wave interpretation.
Hyperfuzzy
1 / 5 (2) Jun 06, 2016
I don't buy any of it!
Da Schneib
3 / 5 (4) Jun 07, 2016
@Proto, part of the point here is that we think interference should be plainly visible at the signal analysis area if the idler path is shorter and the idler photons all go by the eraser path, but we're not sure what should happen if the idler path is longer than the signal path, and especially not sure when the signal should stop showing interference if we flip the mirrors when the idler path is longer than the signal path.

I don't know whether the experiment has been performed in this way or not; I do know that Jack Cramer (the guy responsible for turning Wheeler-Feynman absorber theory into the Transactional Interpretation, up at UW in Seattle) wanted to string fiber optics down one tunnel of LIGO to make a really long signal path, and as far as I know never actually got to do it.

[contd]
Da Schneib
3.4 / 5 (5) Jun 07, 2016
[contd]
It would be interesting if there was no interference visible when the idler path was shorter and the idlers all going to the eraser; it would be more interesting if there was interference visible no matter what the relative lengths of the signal and idler paths were; and it would be most interesting (after checking for interference) to check when the interference stops compared to when the mirrors in the idler path are flipped, if the idler path were longer.

In short, this would be interesting no matter what happened.
Protoplasmix
4 / 5 (4) Jun 07, 2016
In short, this would be interesting no matter what happened.
I think so too. And if the path length for the idler photons could be increased to several hundred milliseconds then it would be easy to accomplish using (for example) this solid state mirror: http://www.kentop...ror.html
Protoplasmix
5 / 5 (3) Jun 07, 2016
I don't buy any of it!
That's the first post from you I've seen that I can understand, perhaps a diagram of the Kim et al. experiment would be helpful – see Fig. 2 here. Da Schneib suggested replacing BS_a and BS_b with mirrors to provide a forced change of state in the delayed choice as the experiment is in progress.

@Da Schneib, note that it would be possible to have D0 trigger the mirror's change of state to test a range of delay times for the state change. If it's some kind of pilot wave, the interference pattern will correlate with when the idler photons were detected at D3 or D4 (as the geometric predisposition was for D1 or D2) and vice versa, which is the opposite of the original experiment. And if it turns out the same as the original experiment then it's not a pilot wave (at least how I've applied it).
Hyperfuzzy
1 / 5 (1) Jun 07, 2016
I don't buy any of it!
That's the first post from you I've seen that I can understand, perhaps a diagram of the Kim et al. experiment would be helpful – see Fig. 2 https://en.wikipe..._choice. Da Schneib suggested replacing BS_a and BS_b with mirrors to provide a forced change of state in the delayed choice as the experiment is in progress.

@Da Schneib, note that it would be possible to have D0 trigger the mirror's change of state to test a range of delay times for the state change. If it's some kind of pilot wave, the interference pattern will correlate with when the idler photons were detected at D3 or D4 (as the geometric predisposition was for D1 or D2) and vice versa, which is the opposite of the original experiment. And if it turns out the same as the original experiment then it's not a pilot wave (at least how I've applied it).

OK, define a 4D point, let time be redefined by setting lambda nu = 1.
Protoplasmix
5 / 5 (2) Jun 07, 2016
late edit, to clarify the "vice versa," the clumped particle-like pattern without interference will correlate with the idler photons detected by D1 or D2 (as the geometric predisposition would have been for the photons to end up at D3 or D4).
Da Schneib
5 / 5 (2) Jun 08, 2016
The real key here (if we want to fully automate the experiment) is detecting interference at D0, and making it a better detector than the one originally used in this experiment. This will require three conditions:
1. A sensitive fast detector across the entire (or a large portion of the) field over which the signal beams disperse.
2. A processing device capable of detecting interference fringes.
3. Enough delay between the signal and idler detection areas to allow the processing to complete before the idlers are erased or not-erased and detected.

1 is easily accommodated by modern CCD sensor arrays available for astrophysics. 2 is relatively simple to implement; edge detection and an algorithm to analyze the distribution of edges across the field of view of the sensor; X number of edges across the field within X' of one another and it signals a detection. This can easily be implemented with a dedicated microcontroller and appropriate programming.
[contd]
Da Schneib
5 / 5 (2) Jun 08, 2016
[contd]
3 is easily implemented using fiber-optic cables in the idler path; if the signal path is appropriately configured a short run can be shorter than the signal path to ensure that we see interference when the idlers are erased and not when they are not, as classically expected, and a long enough run to ensure that we know the exact timing when the mirrors are flipped.

We don't really care about coincidence; in this configuration the results are all-or-nothing, either we see interference or we don't, either we erase all the idlers or we don't. All we care about is whether we can see interference when the idler path is shorter than the signal path and the mirrors are in erase configuration (and not when they are in not erase configuration), and when the interference disappears relative to when the mirrors are flipped when the idler path is longer than the signal path.
[contd]
Da Schneib
5 / 5 (2) Jun 08, 2016
[contd]
Thus all we need to know is whether idlers are being detected at D1/D2 or D3/D4; we will not be examining single arrivals, but timing a change of state from all D1/D2 to all D3/D4.

This is a reasonably easy experiment to set up, though perhaps a bit expensive (those astronomical CCD sensors are very pricey) and requiring some knowledge of programming (edge detection and spatial analysis). On the scale of many scientific experiments it seems like a fairly small endeavor. I'm surprised no one has done it yet.
Protoplasmix
5 / 5 (2) Jun 09, 2016
On the scale of many scientific experiments it seems like a fairly small endeavor. I'm surprised no one has done it yet.
Same here, the Kim et al. paper has been cited 159 times, I'll try to do some checking as time permits.

This one was mentioned on the Wiki page for DCQE – A quantum delayed choice experiment which is based on a quantum controlled beam-splitter for the delayed choice portion, where it's stated in the abstract, "We observe strong Bell inequality violations, thus showing that no model in which the photon knows in advance what type of experiment it will be confronted by, hence behaving either as a particle or as wave, can account for the experimental data." I don't see how that rules out a model that would violate the inequalities, though...
Da Schneib
5 / 5 (1) Jun 09, 2016
For a little history be sure to check the paper in which Scully originally proposes the experiment; you'll note Scully is also on the list in the Kim paper as well (if it's the paper I think it is).
Da Schneib
5 / 5 (1) Jun 09, 2016
No, that's not the paper I was thinking of, and it's not the Kim et al paper either. I'll hunt up the Kim et al paper and the Scully paper shortly.

Meanwhile, we need to be very clear what a "Bell inequality violation" is. Classical phenomena obey Bell's inequality; a violation of Bell's inequality means that entanglement, a non-classical quantum effect, has been observed.
Da Schneib
5 / 5 (1) Jun 09, 2016
More on Bell inequality violation:

Let's suppose that we generate two electrons entangled in the spin parameter, in opposing sense (easy to do since interactions that generate two photons from a spin-0 state must inherently have spins of +1 and -1 in order to preserve conservation of angular momentum). Then if we measure their spins (polarization) in two analyzers that are parallel, we should always get +1 for one of them and -1 for the other. If we use two analyzers that are at 45° (π/4 radians) then by Malus' law, we should see cos(45°)² = 0.5 correlation; that is, half of the photons should pass the two analyzers, and half should only pass one. If we see more then Bell's inequality is violated. In fact, what we see is the quantum mechanical prediction: 1/√2 = 0.707 correlation, which is a violation of the Bell inequality. This is what is being confirmed in so-called "Bell test" experiments.

This is a vast oversimplification since I have hand-waved at the QM prediction.
Da Schneib
5 / 5 (1) Jun 09, 2016
Kim et al. (2000): https://arxiv.org.../9903047
The original Scully/Druhl (1982) paper (unfortunately not open access): http://journals.a....25.2208
Phys1
5 / 5 (2) Jun 09, 2016
@Da Schneib
Since you seem to know a lot about this subject, how does the ensemble interpretation of Ballentine deal with DCQE ?
Da Schneib
5 / 5 (1) Jun 09, 2016
@Phys1, that's one interpretation I don't know; actually thank you for introducing me to it. I'd have to study it more to figure it out. But I'll take a hack at it.

First of all, it seems to me that it would not be permissible under that interpretation to speak of individual photons' behavior in it, or of entanglement of individual idler and signal photons. One could only speak statistically of how an ensemble of photons would behave in it. Thus one would have the ensembles of interfering and non-interfering signal photons and the ensembles of erased and non-erased idler photons. The entanglements therefore would be between the interfering signal ensemble and the erased idler ensemble in the first case, and between the non-interfering signal ensemble and the non-erased idler ensemble in the second case.

I think on considering it that's logically consistent, and may be a sufficient answer to your question. But you must judge.
Da Schneib
5 / 5 (1) Jun 09, 2016
Having looked at the ensemble interpretation, I find it very interesting; also, I think my statements above are correct, but not necessarily a complete description of it. It strictly obeys the Born Rule, which is a requirement for all interpretations; it leaves room for a superposed state, and avoids trying to define that state other than probabilistically (like I said, it strictly obeys the Born Rule). I'm not sure though that it gives any clearer a view of individual particle interactions than other interpretations; and I think both TI and CHI do, and they both obey the Born Rule strictly as well.

As I said very interesting; thanks again.
Hyperfuzzy
not rated yet Jun 09, 2016
Having looked at the ensemble interpretation, I find it very interesting; also, I think my statements above are correct, but not necessarily a complete description of it. It strictly obeys the Born Rule, which is a requirement for all interpretations; it leaves room for a superposed state, and avoids trying to define that state other than probabilistically (like I said, it strictly obeys the Born Rule). I'm not sure though that it gives any clearer a view of individual particle interactions than other interpretations; and I think both TI and CHI do, and they both obey the Born Rule strictly as well.

As I said very interesting; thanks again.

OK, intelligent ignorance.
Protoplasmix
5 / 5 (1) Jun 10, 2016
This is a vast oversimplification since I have hand-waved at the QM prediction.
I appreciate the effort, thanks Schneib. I was also just reading the Wiki page on Bell's theorem and now I appreciate (and better understand) the term "locality" – it's short for "local relativistic causality." So basically if something is considered non-local then it's a faster-than-light phenomenon. Also, if the pilot waves [hidden variables] propagate [communicate] faster than light then it's easy [apparently] to violate the Bell inequality.

I'm feeling superdetermined to try some mirror flipping. :)

@!where's that keychain laser pointer? /mumbles
Protoplasmix
5 / 5 (1) Jun 10, 2016
OK, intelligent ignorance
To erase, or not erase. That is the question, after a suitable delay.
Protoplasmix
5 / 5 (1) Jun 10, 2016
OK, intelligent ignorance
To erase, or not erase. That is the question, after a suitable delay.
Also, if it's done, when tis done, then it's best it's done within a few nanoseconds. Wot fuzzy, wot?
Hyperfuzzy
not rated yet Jun 12, 2016
OK, intelligent ignorance
To erase, or not erase. That is the question, after a suitable delay.
Also, if it's done, when tis done, then it's best it's done within a few nanoseconds. Wot fuzzy, wot?

Only require two spherical objects, the E Field of (+ Proton, - Electron at r and r as 4D, get it. Use as many as you please, moving only the centers and updating the field relative to the center of each source, at the speed of light, apply any external field if you desire, or more p&e's, nothing else. Prefer not to add an imaginary solid sphere with unknown properties, only the field. Move the centers of the spherical, ever existing fields. OK make up a stupid argument to support anything else, i.e. the imagination, anything other than reality. So what's the point, delete!?
Hyperfuzzy
not rated yet Jun 12, 2016
In other words, the above describes what? A stupid observation based upon absolute ignorance?

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