The relative polarization of the two photons emitted when a positron annihilates at rest has been re-investigated with high precision and a different method of data analysis. An experiment using a pair of ideal polarization analyzers to measure this relative polarization would be a special case of the general class of thought experiments discussed by Einstein, Podolsky, and Rosen (EPR). EPR argued from these thought experiments that a physical system can exist in a state with definite values for two non-commuting variables. Since quantum mechanics can not describe such a state, EPR called quantum mechanics "incomplete". But EPR believed a complete theory -sometimes called a hidden variable theory- is possible. (This argument of EPR is sometimes called the Einstein-Podolsky-Rosen "paradox".) Our experimental results, together with a theorem due to Bell, provide strong evidence that a local "hidden variable" theory is not possible. The results also rule out a hypothetical modification of quantum mechanics, suggested by Bohm and Aharonov, which was motivated by the EPR thought experiments. Compton scattering was used to analyze the linear polarization. But the theorem of Bell, mentioned above, applies to relatively "ideal" polarization measurements. Therefore, it was necessary to prove the existence, and find the explicit form of the function f relating Compton and ideal linear polarization measurements. The existence of f is shown here to follow from general principles of quantum mechanics, plus parity and angular momentum conservation; the explicit form of f is deduced from the Klein-Nishina equation. Experimental evidence is cited against the argument that f may be different in a local "hidden variable" theory.

Yes / The essay revisits the puzzle of the ‘passage’ of time in relation to EPR-type measurements and asks what philosophical consequences can be drawn from them. Some argue that the lack of invariance of temporal order in the measurement of a space-like related EPR pair, under relativistic motion, casts serious doubts on the ‘reality’ of the lapse of time. Others argue that certain features of quantum mechanics establish a tensed theory of time – understood here as Possibilism or the growing block universe. The paper analyzes the employment of frame-invariant entropic clocks in a relativistic setting and argues that tenselessness does not imply timelessness. But this conclusion does not support a tensed theory of time, which requires a preferred foliation. It is argued that the only reliable inference from the EPR example and the use of entropic clocks is an inference not just to a Leibnizian order of the succession of events but a frame-invariant order according to some selected clocks.

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We report on conductance measurements in carbon nanotube based double quantum dots connected to two normal electrodes and a central superconducting finger. By operating our devices as Cooper pair beam splitters, we provide evidence for Crossed Andreev Reflection (CAR). We inject Cooper pairs in the superconducting electrode and measure the differential conductance at both left and right arm. The contacts split the device into two coupled quantum dots. Each of the quantum dots can be tuned by a lateral sidegate. If the two sidegates are tuned such that both quantum dots are at a transmission resonance, a considerable part of the injected Cooper pairs splits into different normal contacts. On the contrary, if only one of the two dots is at resonance, nearly all pairs tunnel to the same normal contact. By comparing different triple points in the double dot stability diagram, we demonstrate the contribution of split Cooper pairs to the total current. In this manner, we are able to extract a splitting efficiency of up to 50% in the resonant case. Carbon Nanotubes ensure ballistic transport and long spin-flip scattering lengths. Due to these properties they are promising candidates to investigate EPR-type correlations in solid state systems.