First detection of collective oscillations of a stored deuteron beam with an amplitude close to the quantum limit

TL;DR

This paper reports the first detection of collective betatron oscillations in a stored deuteron beam with amplitudes near the quantum limit, demonstrating potential for ultra-precise beam control relevant to electric dipole moment experiments.

Contribution

It introduces a method to detect extremely small beam oscillations close to the quantum limit and analyzes their implications for quantum mechanics and precision measurements.

Findings

Detection of oscillations down to 1 micrometer amplitude.

Amplitudes of individual particle oscillations are within a factor of 10 of the Heisenberg limit.

The smallest Lorentz force measured is 10 attoNewtons.

Abstract

We investigated coherent betatron oscillations of a deuteron beam in the storage ring COSY, excited by a detuned radio-frequency Wien filter. The beam oscillations were detected by conventional beam position monitors. With the currently available apparatus, we show that oscillation amplitudes down to \SI{1}{\micro \meter} can be detected. The interpretation of the response of the stored beam to the detuned radio-frequency Wien filter is based on simulations of the beam evolution in the lattice of the ring and realistic time-dependent 3D field maps of the Wien filter. Future measurements of the electric dipole moment of protons will, however, require control of the relative position of counter-propagating beams in the sub-picometer range. Since here the stored beam can be considered as a rarefied gas of uncorrelated particles, we moreover demonstrate that the amplitudes of the zero-point (ground state) betatron oscillations of individual particles are only a factor of about 10 larger than the Heisenberg uncertainty limit. As a consequence of this, we conclude that quantum mechanics does not preclude the control of the beam centroids to sub-picometer accuracy. The smallest Lorentz force exerted on a single particle that we have been able to determine is \SI{10}{aN}.