Abstract
We describe the Quantum Test of the Equivalence principle and Space Time (QTEST), a concept for an atom interferometry mission on the International Space Station (ISS). The primary science objective of the mission is a test of Einstein’s equivalence principle with two rubidium isotope gases at a precision of better than 10−15, a 100-fold improvement over the current limit on equivalence principle violations, and over 1,000,000 fold improvement over similar quantum experiments demonstrated in laboratories. Distinct from the classical tests is the use of quantum wave packets and their expected large spatial separation in the QTEST experiment. This dual species atom interferometer experiment will also be sensitive to time-dependent equivalence principle violations that would be signatures for ultralight dark-matter particles. In addition, QTEST will be able to perform photon recoil measurements to better than 10−11 precision. This improves upon terrestrial experiments by a factor of 100, enabling an accurate test of the standard model of particle physics and contributing to mass measurement, in the proposed new international system of units (SI), with significantly improved precision. The predicted high measurement precision of QTEST comes from the microgravity environment on ISS, offering extended free fall times in a well-controlled environment. QTEST plans to use high-flux, dual-species atom sources, and advanced cooling schemes, for N > 106 non-condensed atoms of each species at temperatures below 1 nK. Suppression of systematic errors by use of symmetric interferometer configurations and rejection of common-mode errors drives the QTEST design. It uses Bragg interferometry with a single laser beam at the ‘magic’ wavelength, where the two isotopes have the same polarizability, for mitigating sensitivities to vibrations and laser noise, imaging detection for correcting cloud initial conditions and maintaining contrast, modulation of the atomic hyperfine states for reduced sensitivity to magnetic field gradients, two source-regions for simultaneous time reversal measurements and redundancy, and modulation of the gravity vector using a rotating platform to reduce otherwise difficult systematics to below 10−16.
Highlights
Gravity is the least-tested force of nature
We have investigated QTEST, an International Space Station (ISS) mission concept that performs high precision atom interferometer experiments in the microgravity environment in space
The measurements with quantum test masses will probe the nature of gravity and quantum mechanics, and explore dark matter and quantum electrodynamics
Summary
Gravity is the least-tested force of nature. For example, even the best solar system tests (e.g., the Shapiro time delay to Cassini) reach 10-5 sensitivity in the parameterized post-Newtonian (PPN) formalism [1], while the theory of quantum electrodynamics has some of its predictions confirmed at the part-per-billion level. The lack of a large, static gravitational force in space minimizes the necessary length of the atom trajectories and, simplifies and enhances environmental isolation and control This aspect can be most appreciated by the fact that, to achieve an equivalent of 10 s total interrogation time on the ground would need over 100 m of apparatus size [13], whereas the same sensitivity in microgravity can be realized in a sensor measuring less than 1 m, planned for QTEST. This helps to suppress the sensitivity to vibrational noise, which is necessary on the ISS where the vibration environment is not the most quiet It will use two dual-species sources, enabling two dual-species atom interferometers (four AIs in total) to be interrogated simultaneously in a time-reversed configuration.
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