A Torsion-Modulated Atomic Clock Comparison Unit: Differential Optical Clock Readout of a Torsion Coupling

Optical clocks now compare frequencies at levels where a new coupling, if it exists, has nowhere to hide except below the systematic floor. This paper specifies a differential comparison unit that looks for a torsion coupling in the one place it could appear cleanly: as a modulation of the frequency ratio between two clocks of different species, driven by a rotating polarised source whose torsion field at the clocks is modulated at a known frequency. With each clock at a fractional instability of 3.0e-16 per root second, the ratio instability is 4.24e-16; after 1e6 seconds it reaches 4.24e-19, and the systematic floor of 2.0e-19 corresponds, at the stated coupling, to a torsion sensitivity of 0.20 per metre. The integration time at which statistics reach the systematic floor is 13.0 days. SIMULATED, NOT MEASURED: the unit is specified and computed, not built.