Experiment

Nicolas Gisin

Koen Sponselee

Five experiments are performed to characterise the time development of the chemical potential and temperature of a bimodal Bose-condensed gas. The five experiments are a stationary experiment, a slow motion experiment, a slow motion over a barrier experiment, a fast motion experiment and a fast motion over a barrier experiment. In the two slow motion experiments the atoms are moved with velocities below the critical velocity of superfluidity, while in the two fast motion experiments the atoms are moved with velocities above the critical velocity. We observed superfluidity in the slow slow motion experiments. Additional heating was observed in fast motion experiments, indicating that the system is not superfluid in this regime.\nFurthermore we find transition temperatures for the five experiments. Below this transition temperature, heating of the system occurs and above, cooling of the system occurs. For the stationary experiment, the transition temperature is found to be approximately 719 nK.

Robert P Crease

See ”The double-slit experiment“ on p15 When I asked readers earlier this year to submit candidates for the ”most beautiful experiment in physics“ (Physics World May p17), I was pleased to receive more than 200 replies. The responses covered a broad spectrum, ranging from actual experiments to thought experiments, and from proposed experiments to proofs, theorems and models. However, one experiment – the double-slit experiment with electrons – was cited more often than any other, receiving a total of 20 votes.

Gerhard Grössing

Abolfazl Soltani

In physics, whenever we cannot do an experiment for physical, technological, financial or ethical reasons, we use "thought experiment". In this letter we will prove that a thought experiment leads us only to possible results of an experiment not decisive result. To achieve a definitive results, an experiment must be done in the real world.