Probing the electric neutrality of the neutron

The charge of the neutron Summary (in English) We propose to test neutrons neutrality at small distances by a new technique using quantum interference. The idea is to explore a system consisting of a particle, the ultra-cold neutron, and a macroscopic object, a mirror-system, and its precise measurement of quantum de Broglie phases as a function of an electric field. Over the last few years, it has become possible to apply a spectroscopy technique to gravity. The method allows a precise measurement of quantum states of a neutron wave packet bouncing off a hard surface in the gravitational field of the earth. The energy eigenstates in the gravity potential can be coupled to a mechanical oscillator field. Transitions between quantum states in the gravitational field of the earth i.e. a change of the state occupation can therefore be induced similar to magnetic transitions, which occur when the oscillator frequency equals one of the Bohr frequencies of the system. As the pioneers in the field, we were able to drive resonant transitions between states 12, 13, 23, 24, 14. Within this project, we plan search for the charge of the neutron by implementing Ramseys method of separated oscillating fields to the spectroscopy of quantum states in the gravity potential. This works as a by-product of the Ramsey-technique, although until now it was considered to be impossible to use a Ramsey-technique for charge measurements, because a phase accumulation cancels by inverting the electrical field Ez. But in the presence of an electric field, the energy of quantum states in the gravity potential changes due to an additional electrostatic potential if a neutron carries a non-vanishing charge qn. Important for this method is the fact that the energy shift differs from state to state due to the properties of a Schrödinger wave packet in a linear potential. At small distances, a higher electric field than in previous measurements can be achieved. In test experiments, a gain factor of 8 for Ez has been realized.

This project has the aim to test neutrons neutrality at small distances by a new technique using quantum interference. For that purpose we have developed and explored a system consisting of a particle, the ultra-cold neutron, and a macroscopic object, a mirror-system, and its precise measurement of quantum de Broglie phases as a function of an electric field. In a previous project, we have developed a quantum technology providing highest precision through quantum interference. The new method extends the techniques of Purcel, Rabi, and Ramsey to neutron quantum states in the gravity potential of the Earth. We named the new technique Gravity Resonance Spectroscopy (GRS), in close analogy to Magnetic Resonance Spectroscopy (MRS). Here a neutron in the gravity potential of the Earth is placed on a reflecting mirror and transitions between the gravitational quantum states are performed by applying mechanical oscillations of the mirror with the proper transition frequency. In the previous project, resonant transitions between quantum states of the neutron in the gravity potential of the earth have been observed for the first time. Within this project, we have observed and carefully measured new, more energetic transitions. Next we have applied GRS to Ramseys method of separated oscillating fields for quantum states in the gravity potential above a vertical mirror. Ramseys method so far is used for example in atomic clocks to provide accurate time standards. Our Ramseys method allows in addition to the precision to use an electrode for the production of high electric fields. If the neutron had a non vanishing electric charge, the application of an electric field in our apparatus would shift the energy levels of the neutron in the gravity potential of the earth and can be detected within measuring accuracy. We are able to show that - at small distances - a substantial higher electric field than in previous measurements can be achieved. Furthermore by using ultra cold neutrons, the observation time can be increased significantly. As a by-product, the project has developed and tested a new resonance spectroscopy technique free of any kind of electromagnetic side-effect. Whilst improving the sensitivity of the techniques now available, our precision experiments were able to exclude large fractions of the parameter space for dark matter and dark energy particles, in particular the symmetron field, which has been excluded in a large fraction of the parameter space by this experiment. As regards the theoretical basis of the work, the project has addressed aspects of gravitation, which go far beyond the Einsteinian theory of gravitation.