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The Newtonian gravitational constant G has proved to be one of the most difficult constants to measure in physics. The improvement of measuring G with the atomic interferometry method is significantly limited by the positioning accuracy of the atom clouds and source masses, and the measurement accuracy of the atomic velocity. In this article, we propose an idea for designing the source masses to determine G with atom interferometry, in which a nearly uniform gravitational field in the motion region of the atom clouds is constructed. This design can greatly reduce the influence of the uncertainty of the atomic initial position and velocity on the precision of G measurement, since these atomic initial conditions affect the interferometer phase shift by coupling themselves with the gravitational gradient. Finally, we present a scheme for measuring G with a relative standard uncertainty of 27 parts per million.

We construct a quasi-inertial reference system for the atom interferometer in terms of the light-field compensation, which is equivalent to the establishment of a quantum drag-free system. The compensation considered in our approach involves feedbacks of both classical and quantum nature. As a result, it may significantly reduce the dependence of the interferometric phase shift on the atomic initial position and velocity. As the error bound for gravity experiments originates primarily from the uncertainties in the initial conditions, the proposed quasi-inertial reference system might lead to substantial improvement in this regard. To be specific, the refined process introduced in the present study gives rise to the possibility of the measurement of the Newtonian gravitational constant G beyond the precision level of 10−6, as well as the test of the weak equivalence principle beyond 10−14. Moreover, when compared with the conventional quasi-inertial reference based on macroscopic objects, additional quantum feedback plays an essential role concerning both theoretical rigor and practical performance enhancement. We further explore the possibility of implementing the proposed quasi-inertial reference system in ongoing experimental developments.

We report a molecular dynamics study of structural and transport properties of liquid nickel under high pressures. Pressure dependencies of pair distribution function and pair correlation entropy along the melting line indicate that the configuration change along melting lines decreases with increasing pressure. The calculated diffusion coefficients and viscosity by using entropy-scaling laws with modified parameters and ideal parameters are compared with those extracted from mean-square displacement or the Stokes–Einstein relation. The results suggest that the entropy-scaling laws hold well for liquid nickel under high-pressure conditions, and the diffusion coefficients and viscosity increase moderately with pressure along melting lines.