Clarification of the EPR resultset

The graph below can give some understanding in what is presented as result for a typical EPR experiment, here for spin 1/2 particles. The horizontal axis is the angle setting for the filter of Alice. Backwards is the same property for Bob (although the numbers on the axis are missing). The wave is the QM expectation of the correlation of the results obtained by the detector of Alice and those of Bob. (When analyzing a real experiment of course the results obtained by the equipment are used.)

The graph that is normally presented as result of a real experiment is the correlation projected on the slice that is indicated with the red window, thereby grouping the results for each angle difference between Alice's and Bobs polarizer (The same graph that I present in New spin-half particle EPR simulation).

An extra step of data manipulation might be to make no difference between positive and negative angle differences. This can be interpreted as mirroring one of the 'wings' of the graph so that it data covers the other 'wing'.

Finally an experimentalist might only show one S part of the cos, having a difference in angles between 0 and 90 degrees (this is enough to show the difference between the classical and the QM expectation), but might even rearrange data collected at higher angle differences, assuming these parts of the cos are symmetric.

New spin-half particle EPR simulation

In consultation with Gordon Watson I have created a new simulation (v0.9) that involves an EPR experiment using spin-half particles. The interface shows more intuitively the settings that can be used to get results for different pairs of angles for Alice's and Bob's Stern Gerlach magnet filters:

The simulation uses Visual Studio 2010 (C-sharp Express) and can be downloaded from Sourceforge at
http://sourceforge.net/projects/epr-bohm/files/SGM_Bell.zip/download
.

Documentation added

The EPR_Bohm C sharp project now contains a first version of documentation, describing the major parts of the program, and how to include a new local realistic model. The documentation can also be downloaded separately from Sourceforge.

On the fair sampling

Real EPR experiments with photons are performed using a lot of restrictions on the counting process:

• There is always a large amount of background noise (single photons, accidental doubles)
• A time windows is used: only clicks that are found on both sides (Alice and Bob) within the time window are considered to be entangled.
• Often it is the electronic logic that separates 'entangled pairs', so the 'others' don't even enter the raw data.
• Detectors mostly have low efficiency. For example in the well known Weihs experiment (1) this was 5% (Detectors have been improved since then).

Caroline Thompson has written a critical article (2) about the sample efficiency in the famous experiment of Aspect and of others. Alain Aspect had to subtract 25% of his coincidences to get his QM confirmed. Furthermore without this subtraction she shows the results follow the classical expectation. Considering all this it hardly seem fair that local realistic models should count most of the photons.

Nevertheless realistic models that allow a fraction of misses (I call them class A models*) I have found are able to produce QM like results using about 70% (3, 4) of the pairs. The Adenier model (3) is just for demonstration purposes, Ashwanden has a model based on a realistic hypothesis of the behavior of the elements involved in an EPR experiment.

Based on the description of Adenier (unfortunaly the exact details of their model is not in the article) I was able to quickly reproduce a model using 47% of the photon pairs. I have included it in the software.

1. Gregor Weihs, Thomas Jennewein, Christoph Simon, Harald Weinfurter, and Anton Zeilinger, Violation of Bell’s inequality under strict Einstein locality conditions, http://arxiv.org/abs/quant-ph/9810080
2. Caroline H Thompson, Subtraction of “accidentals” and the validity of Bell tests, http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Aquant-ph%2F9903066.
3. Testing the Fair Sampling Assumption for EPR-Bell Experiments with Polarizing Beamsplitters, Guillaume Adenier and Andrei Yu. Khrennikov, http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Aquant-ph%2F0306045. Video: http://video.google.com/videoplay?docid=-1050719353457515819#
4. Manuel Aschwanden, A classical view of quantum entanglement, http://www.iis.ee.ethz.ch/~schenk/theses/aschwanden.pdf

* Class A models normally only prove that real experiments can be explained using a LHV model. Only with high efficiency (>83 % i think) they could also disprove Bell.

Java simulation available

Chantal Roth has created a very nice Java implementation of the EPR experiment for testing purposes. In her own words:

"A simple Java simulation of a typical EPR experiment by creating "entangled" particles that are sent to two detectors A and B. After many such experiments the statistics are computed, including the CHSH value and also the correlation between the measurements at the detectors based for each angle between the filters. The GUI allows a user to enter a formula to compute the probability if a detection of a particle happens or not, which is then compiled on the fly."

The application can be downloaded at Sourceforge: https://sourceforge.net/projects/eprsimulation/

To run it, you need the Java JDK and NetBeans IDE 7. This can be downloaded in one package at: http://www.oracle.com/technetwork/java/javase/downloads/jdk-netbeans-jsp-142931.html

Rewrite of reference simulation

Recently I can enjoy some hits from an article with criticism on the work of Joy Christian from Sascha Vongehr. While it is true that the ideas of Joy contradicts mainstream physics, his arguments seems sound, but the arguments of Sascha for criticizing this work are mostly hand waving and of low scientific value.

But apart from that the challenge from Sascha (however sarcastically stated) is the same as in this blog: if a LHV model is possible, it can be demonstrated and proved by an open source program.

The reference application for these simulations, based on the work of DeRaedt, has now been completely rewritten. The classes that implements a simulation have been separated. Adding a new type of simulation can be done easily by copying a folder with classes from another simulationtype and change their implementation.

The classes mostly represents the real objects that are involved in a typical EPR experiment. A special feature in this release is the availability of a libary with classes for Geometric Algebra, as they are generated for C-sharp by Gaigen. As always, the program can be downloaded at sourceforge

What's the fuss about EPR?

What is really bugging a part of the physicists about the whole EPR-Bohr discussion? The main argument of E.P.R. was:

If, without in anyway disturbing a system, we can predict with certainty (...) the value of a physical quantity, then there exists an element of physical reality that corresponds to this physical quantity. (1)

I think the issue is in fact that Bohr and his crew (Copenhagen) have eliminated a very basic philosophy in physics: the existence of causality for all the processes in nature, that every event in nature can in principle be described as a reaction on another event.

He postulated a principle randomness in nature. So he based his QM on a number of stochastic formulas that described the quantum processes, and what is worse, postulated that these formulas where a complete description of the process, leaving out any possibility of introducing subquantum theories. It's like creating a formula for the behavior of a pile of sand being dropped from a truck and claiming there is no physics beyond to describe this process.

Because of the realm of QM being the atomic scale and beyond it is very difficult to invalidate such a position, for one needs measurements on individual particles to do that. The measuring devices themselves are gigantic compared to the particle to be measured, and mostly made of the same 'stuff' (electrons, protons, photons etc), but should not disturb the measurement.

Only the last decennia scientists are on the edge of doing this: atoms can be photographed and handled individually (2), and even individual electrons can be locked and stored for a long time (3). Atto seconds lasers are starting to reveal processes at atomic scale (4). Things that Bohr held for impossible.

When one of the premises of relativity is added, that any causal action cannot be transmitted beyond light speed, the experiments with entangled particles as discussed in this blog can play a role. That is, if these can be performed without loopholes, and if Bell is correct, these experiments prove that there are correlations between particles that cannot be explained by causality while keeping up the light speed constraint.

Even if that proves to be the case, I still think one should not give up searching for a causal explanation for these processes. It might well be nature hints us about so far unrevealed features, like (only speculating here) the existence of extra dimensions in space-time, or particles that can exceed light speed limits.

Just assuming we're on the edge of what can be revealed in QM (concerning the wave function and the Heisenberg uncertainty principle), without any proof for that, is for me a very strange position, but upheld by many physicist today.

1. Can quantum-mechanical description of physical reality be considered complete? http://membranes.nbi.dk/Kaufmann/publicationlinks/1935_EinsteinPodolskyRosen_PhysRev.pdf
2. IBM STM image gallery,  http://www.almaden.ibm.com/vis/stm/atomo.html
3. Wineland and Dehmelt 1973
4. ATTOSECOND PHYSICS: Ultrafast-laser methods reveal electrons tunneling in real time, http://www.optoiq.com/index/photonics-technologies-applications/lfw-display/lfw-article-display.articles.laser-focus-world.volume-43.issue-6.world-news.attosecond-physics-ultrafast-laser-methods-reveal-electrons-tunneling-in-real-time.html