Matter-wave Tests of the Gravitational Redshift in Space

A recent measurement of the gravitational redshift was based on interference of matter waves. Operation in microgravity can improve it by a factor of $10^5$ and, in some models, even $10^{10}$.Comment: Talk given at the Fifth Meeting on CPT and Lorentz Symmetry, at Indiana University, Bloomington, IN. Corrected problem with Figur

Force-Free Gravitational Redshift: Proposed Gravitational Aharonov-Bohm experiment

We propose a feasible laboratory interferometry experiment with matter waves in a gravitational potential caused by a pair of artificial field-generating masses. It will demonstrate that the presence of these masses (and, for moving atoms, time dilation) induces a phase shift, even if it does not cause any classical force. The phase shift is identical to that produced by the gravitational redshift (or time dilation) of clocks ticking at the atom's Compton frequency. In analogy to the Aharonov-Bohm effect in electromagnetism, the quantum mechanical phase is a function of the gravitational potential and not the classical forces.Comment: Updated to published versio

Precision tests of General Relativity with Matter Waves

We review the physics of atoms and clocks in weakly curved spacetime, and how each may be used to test the Einstein Equivalence Principle (EEP) in the context of the minimal Standard Model Extension (mSME). We find that conventional clocks and matter-wave interferometers are sensitive to the same kinds of EEP-violating physics. We show that the analogy between matter-waves and clocks remains true for systems beyond the semiclassical limit. We quantitatively compare the experimentally observable signals for EEP violation in matter-wave experiments. We find that comparisons of $^{6}$Li and $^{7}$Li are particularly sensitive to such anomalies. Tests involving unstable isotopes, for which matter-wave interferometers are well suited, may further improve the sensitivity of EEP tests.Comment: Conference Proceedings for talk given in January, 2011 at the Winter Colloquium on the Physics of Quantum Electronics. Submitted to the Journal of Modern Optic

Particle-Accelerator Constraints on Isotropic Modifications of the Speed of Light

The absence of vacuum Cherenkov radiation for 104.5 GeV electrons and positrons at LEP combined with the observed stability of 300 GeV photons at the Tevatron constrains deviations of the speed of light relative to the maximal attainable speed of electrons. Within the Standard-Model Extension (SME), the limit $-5.8\times10^{-12} \leq \tilde{\kappa}_{\rm tr}-{4/3}c_e^{00} \leq 1.2\times10^{-11}$ is extracted, which sharpens previous bounds by more than 3 orders of magnitude. The potential for further refinements of this limit with terrestrial experiments and astrophysical observations is discussed.Physic

Improved Constraints on Isotropic Shift and Anisotropies of the Speed of Light using Rotating Cryogenic Sapphire Oscillators

We demonstrate that Michelson-Morley tests, which detect direction-dependent anisotropies in the speed of light, can also be used to place limits upon isotropic deviations of the vacuum speed of light from $c$, as described by the photon sector Standard Model Extension (SME) parameter $\tilde{\kappa}_{tr}$. A shift in the speed of light that is isotropic in one inertial frame implies anisotropic shifts in others. Using observer Lorentz covariance, we derive the time-dependent variations in the relative resonance frequencies of a pair of electromagnetic resonators that would be generated by such a shift in the rest frame of the Sun. A new analysis of a recent experimental test of relativity using this result constrains $\tilde{\kappa}_{tr}$ with a precision of $7.4\times10^{-9}$. This represents the first constraint on $\tilde{\kappa}_{tr}$ by a Michelson-Morley experiment and the first analysis of a single experiment to simultaneously set limits on all nine non-birefringent terms in the photon sector of the SME

Gravitational Redshift, Equivalence Principle, and Matter Waves

We review matter wave and clock comparison tests of the gravitational redshift. To elucidate their relationship to tests of the universality of free fall (UFF), we define scenarios wherein redshift violations are coupled to violations of UFF ("type II"), or independent of UFF violations ("type III"), respectively. Clock comparisons and atom interferometers are sensitive to similar effects in type II and precisely the same effects in type III scenarios, although type III violations remain poorly constrained. Finally, we describe the "Geodesic Explorer," a conceptual spaceborne atom interferometer that will test the gravitational redshift with an accuracy 5 orders of magnitude better than current terrestrial redshift experiments for type II scenarios and 12 orders of magnitude better for type III.Comment: Work in progress. 11 page