Measurements of the gravitational constant using two independent methods.

The Newtonian gravitational constant, G, is one of the most fundamental constants of nature, but we still do not have an accurate value for it. Despite two centuries of experimental effort, the value of G remains the least precisely known of the fundamental constants. A discrepancy of up to 0.05 per cent in recent determinations of G suggests that there may be undiscovered systematic errors in the various existing methods. One way to resolve this issue is to measure G using a number of methods that are unlikely to involve the same systematic effects. Here we report two independent determinations of G using torsion pendulum experiments with the time-of-swing method and the angular-acceleration-feedback method. We obtain G values of 6.674184 × 10-11 and 6.674484 × 10-11 cubic metres per kilogram per second squared, with relative standard uncertainties of 11.64 and 11.61 parts per million, respectively. These values have the smallest uncertainties reported until now, and both agree with the latest recommended value within two standard deviations.

Improvement for Testing the Gravitational Inverse-Square Law at the Submillimeter Range.

We improve the test of the gravitational inverse-square law at the submillimeter range by suppressing the vibration of the electrostatic shielding membrane to reduce the disturbance coupled from the residual surface potential. The result shows that, at a 95% confidence level, the gravitational inverse-square law holds (|α|≤1) down to a length scale λ=48 µm. This work establishes the strongest bound on the magnitude α of the Yukawa violation in the range of 40-350 µm, and improves the previous bounds by up to a factor of 3 at the length scale λ≈70 µm. Furthermore, the constraints on the power-law potentials are improved by about a factor of 2 for k=4 and 5.

New Test of the Gravitational Inverse-Square Law at the Submillimeter Range with Dual Modulation and Compensation.

By using a torsion pendulum and a rotating eightfold symmetric attractor with dual modulation of both the interested signal and the gravitational calibration signal, a new test of the gravitational inverse-square law at separations down to 295 µm is presented. A dual-compensation design by adding masses on both the pendulum and the attractor was adopted to realize a null experiment. The experimental result shows that, at a 95% confidence level, the gravitational inverse-square law holds (|α|≤1) down to a length scale λ=59 µm. This work establishes the strongest bound on the magnitude α of Yukawa-type deviations from Newtonian gravity in the range of 70-300 µm, and improves the previous bounds by up to a factor of 2 at the length scale λ≈160 µm.

A high precision surface potential imaging torsion pendulum facility to investigate physical mechanism of patch effect.

The physical mechanism of the patch effect is still an open question. Thus, a high-precision surface potential mapping facility based on a specially designed electrostatically-controlled torsion pendulum is proposed in this paper. The facility not only features high sensitivity and a two-dimensional mapping function but also adapts to various measurement requirements for centimeter-sized samples. The sensitivity of the torsion pendulum reaches about 2.0 × 10-14 N m/Hz1/2 in a frequency range of 1-8 mHz. The temporal variation of the surface potential can be detected at a level of 30 µV/Hz1/2 with a probe whose surface area is 7 mm2. The potential spatial distribution resolution comes to 0.1 mm2 at a level of 40 µV with 1 h integration time.