Editing Bell test (section)

=== A typical CH74 (single-channel) experiment ===
[[File:Single-channel Bell test.svg|300px|thumb|right|'''Setup for a "single-channel" Bell test'''<br>The source S produces pairs of "photons", sent in opposite directions. Each photon encounters a single channel (e.g. "pile of plates") polariser whose orientation can be set by the experimenter. Emerging signals are detected and coincidences counted by the coincidence monitor CM.]]

Prior to 1982 all actual Bell tests used "single-channel" polarisers and variations on an inequality designed for this setup. The latter is described in Clauser, Horne, Shimony and Holt's much-cited 1969 article as being the one suitable for practical use.<ref name="Clauser-1969"/> As with the CHSH test, there are four subexperiments in which each polariser takes one of two possible settings, but in addition there are other subexperiments in which one or other polariser or both are absent. Counts are taken as before and used to estimate the test statistic.

{{NumBlk|:|<math>S = \frac{N(a, b) - N(a, b') + N(a', b) + N(a', b') - N(a', \infty) - N(\infty, b)}{N(\infty, \infty)},</math>|{{EquationRef|3}}}}

where the symbol ∞ indicates absence of a polariser.

If ''S'' exceeds 0 then the experiment is declared to have infringed the CH inequality and hence to have refuted local hidden-variables. This inequality is known as CH inequality instead of CHSH as it was also derived in a 1974 article by Clauser and Horne more rigorously and under weaker assumptions.<ref name="Clauser-1974">{{cite journal |author1=J.F. Clauser |author2=M.A. Horne |year=1974 |title=Experimental consequences of objective local theories |journal=Phys. Rev. D |volume=10 |issue=2 |pages=526–35 |doi=10.1103/PhysRevD.10.526|bibcode = 1974PhRvD..10..526C}}</ref>