Torsion balances with fibres of zero length

Highlights: • A body can be levitated such that it behaves as a classic torsion balance. • Sensitivity to seismic noise can be minimized by tuning suspension forces. • Rotational period can also be tuned independently. • These ideas have been tested with a superconducting suspension. - Abstract: Torsion balances have good immunity to tilt and low rotational stiffness. However precise control of the position of the suspended torsion 'bob' is difficult in the presence of ground vibrations and tilt and this is a limiting factor in applications where Casimir forces or putative non-Newtonian short-range forces are being measured. We describe how the desirable characteristics of torsion balances can be reproduced in a rigid body that is suspended using applied forces rather than a torsion fibre. The suspension system can then provide a more precise control of the degrees of freedom of the suspended body. We apply these ideas to a superconducting levitated torsion balance, developed by the authors, and a generic electrostatic suspension. We present results of preliminary experiments that provide support for our analyses.