Two-wavelength-difference measurement of gravitationally induced quantum interference phases

Abstract

One of the significant successes in the field of neutron interferometry has been the experimental observation of the phase shift of a neutron de Broglie wave due to the action of the Earth's gravitational field. Past experiments have clearly demonstrated the effect and verified the quantum-mechanical equivalence of gravitational and inertial masses to a precision of about 1%. In this experiment the gravitationally induced phase shift of the neutron is measured with a statistical uncertainty of order 1 part in 1000 in two different interferometers. Nearly harmonic pairs of neutron wavelengths are used to measure and compensate for effects due to the distortion of the interferometer as it is tilted about the incident beam direction. A discrepancy between the theoretically predicted and experimentally measured values of the phase shift due to gravity is observed at the 1% level. Extensions to the theoretical description of the shape of a neutron interferogram as a function of tilt in a gravitational field are discussed and compared with experiment. ͓S1050-2947͑97͒04109-7͔PACS number͑s͒: 03.30.ϩp, 03.65.

Test of some fundamental principles in physics via quantum interference with neutrons and photons

“…Finally, the discrepancy between theory an experiment [77,119] that the COW presents nowadays cannot be solved by the inclusion of torsion, as we have shown. Other effects, for instance, the consequence of the rotation of the Earth upon the interference pattern [92,156], the influence of gravity on the beam splitter [157], or the possible dependence of the dynamical diffraction on the bending and strains in the interferometer, do not provide a complete answer to this discrepancy [77].…”

“…We have already mentioned that the theoretical prediction possesses a discrepancy on the order of one percent in the phase shift [77]. Additionally, a sufficiently (for our purposes) stringent experimental bound reads [122] and, hence (employing the typical experimental values [38,77]) and denoting by Γ the contribution to this discrepancy, we deduce…”

“…For the case of the Earth, whose radius and mass will be denoted by R and M, respectively, the aforementioned restriction entails ∆x ≥ R R M (here we use geometrized units, in which length and mass have the same units [58]). In the weak-field limit M R < 1, and in consequence ∆x ≥ R. The introduction of this condition would imply the breakdown of the semiclassical approximation, the one is always present as a condition in COW [38,77]. In other words, the use of COW experiments to detect elements of the gravitational field with an invariant geometrical meaning requires two initial premises: (i) The validity of the semiclassical approximation, this fact means that the size of the wave packet has to be smaller than the region in which the gravitational potential has a noticeable change [33]; (ii) A wave packet larger than the region in which the flatness theorem is valid [58], this means that the wave packet has to be larger than the region in which the gravitational field has a considerable change.…”

“…Several models can be proposed in this direction, and among them we may find some which take into account variables usually neglected. For instance, this discrepancy could be a direct consequence of the way in which dynamical diffraction interacts with bending and strains in the interferometer [77].…”

“…Nevertheless, a careful analysis of this case shows that does not appear explicitly, and hence the interpretation of this experiment as a test of gravity in the quantum domain seems to be a little bit feeble. The COW proposal has been repeated in a series of experiments which showed an outstanding sophistication of the involved technology [75,76,77].…”