Tunable quantum Matter for Precision Measurements

Wave phenomena are well known from everyday experience. Water waves surely belong to the most striking and most impressive waves. Light propagates as a wave, and in particular the light of a laser shows a pronounced wave character. This results in interference fringes in an interference experiment and allows diverse technical applications, e.g. for the precise measurement of distances by means of an interferometer. We learn from physics that particles, for example atoms, are also capable of showing their wavelike nature. This property is very pronounced for such atoms which, inside a Bose-Einstein condensate (BEC), are part of a macroscopic, i.e. directly observable matter wave. In analogy to photons, the light particles of a laser, these atoms are synchronized, and it is possible to build an interferometer in which, in contrast to light waves, matter waves are made to overlap and interfere. The realization the first BEC has recently been recognized by awarding the Nobel Prize in physics for the year 2001, and the first matter wave interferometers on the basis of a BEC have been demonstrated. Nevertheless, a small but important difference exists between a light interferometer and a matter wave interferometer: Atoms, in contrast to photons, are capable of direct interaction. For atoms this leads for example to the formation of molecules. This is an important process, but for a matter wave interferometer it is an undesirable side effect. In Innsbruck at the Institute for Experimental Physics in the group of Prof. R. Grimm we have recently been able to achieve a breakthrough by creating the first BEC of Cesium atoms. Cesium atoms, that is to say, have under certain circumstances the peculiar property that they do not interact with each other. More precisely, it is possible to tune the strength of the interaction, and in particular it is possible to tune it to zero. We have been able to demonstrate this property in first experiments. Thus, Cesium atoms in a BEC are ideal candidates for a matter wave interferometer. We therefore propose to build such an interferometer. What would one be able to measure? It turns out that the fine structure constant a, one of the fundamental constants of nature, could be measured very precisely with such an interferometer. An exact determination of a and comparison of the result with measurements from high energy physics should therefore allow a better test of the fundamental physical theories. In addition, we propose to place a Cesium BEC with its strange interaction properties into a lattice of light. This would allow the preparation of so-called non-classical states of the matter wave. These states promise new possibilities; in particular the precision of the interferometer could be enhanced. Other diverse applications could be found, as suggested in Innsbruck by Prof. P. Zoller and collaborators at the Institute for Theoretical Physics, in the specific realization of molecular states and in the implementation of quantum gates, the elementary building blocks of a quantum computer.

Wave phenomena are well known from everyday experience. Water waves surely belong to the most striking and most impressive waves. Light propagates as a wave, and in particular the light of a laser shows a pronounced wave character. This results in interference fringes in an interference experiment and allows diverse technical applications, e.g. for the precise measurement of distances by means of an interferometer. We learn from physics that particles, for example atoms, are also capable of showing their wavelike nature. This property is very pronounced for such atoms which, inside a Bose-Einstein condensate (BEC), are part of a macroscopic, i.e. directly observable matter wave. In analogy to photons, the light particles of a laser, these atoms are synchronized, and it is possible to build an interferometer in which, in contrast to light waves, matter waves are made to overlap and interfere. The realization the first BEC has recently been recognized by awarding the Nobel Prize in physics for the year 2001, and the first matter wave interferometers on the basis of a BEC have been demonstrated. Nevertheless, a small but important difference exists between a light interferometer and a matter wave interferometer: Atoms, in contrast to photons, are capable of direct interaction. For atoms this leads for example to the formation of molecules. This is an important process, but for a matter wave interferometer it is an undesirable side effect. In Innsbruck at the Institute for Experimental Physics in the group of Prof. R. Grimm we have recently been able to achieve a breakthrough by creating the first BEC of Cesium atoms. Cesium atoms, that is to say, have under certain circumstances the peculiar property that they do not interact with each other. More precisely, it is possible to tune the strength of the interaction, and in particular it is possible to tune it to zero. We have been able to demonstrate this property in first experiments. Thus, Cesium atoms in a BEC are ideal candidates for a matter wave interferometer. We therefore propose to build such an interferometer. What would one be able to measure? It turns out that the fine structure constant a, one of the fundamental constants of nature, could be measured very precisely with such an interferometer. An exact determination of a and comparison of the result with measurements from high energy physics should therefore allow a better test of the fundamental physical theories. In addition, we propose to place a Cesium BEC with its strange interaction properties into a lattice of light. This would allow the preparation of so-called non-classical states of the matter wave. These states promise new possibilities; in particular the precision of the interferometer could be enhanced. Other diverse applications could be found, as suggested in Innsbruck by Prof. P. Zoller and collaborators at the Institute for Theoretical Physics, in the specific realization of molecular states and in the implementation of quantum gates, the elementary building blocks of a quantum computer.