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Chinese Physics Letters

Testing the Universality of Free Fall by Comparing the Atoms in Different Hyperfine States with Bragg Diffraction*

Ke Zhang, Min-Kang Zhou, Yuan Sheng Cheng, Lele Chen, Qin Luo, Wenjie Xu, Lushuai Cao, Xiao‐Chun Duan, Zhong-Kun Hu

Published Apr 1, 2020• 30 citations
Publisher

Abstract

We perform a precision atom interferometry experiment to test the universality of free fall. Our experiment employs the Bragg atom interferometer with 87Rb atoms either in hyperfine state F = 1 , m F = 0 or F = 2 , m F = 0 , and the wave packets in these two states are diffracted by one pair of Bragg beams alternatively, which is helpful for suppressing common-mode systematic errors. We obtain an Eötvös ratio η 1 − 2 = 0.9 ± 2.7 × 10 − 10 , and set a new record on the precision with improvement of nearly 5 times. This measurement also provides constraint on the difference of the diagonal terms of the mass-energy operator.

DOI
10.1088/0256-307x/37/4/043701

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We perform a precision atom interferometry experiment to test the universality of free fall. Our experiment employs the Bragg atom interferometer with 87Rb atoms either in hyperfine state F = 1 , m F = 0 or F = 2 , m F = 0 , and the wave packets in these two states are diffracted by one pair of Bragg beams alternatively, which is helpful for suppressing common-mode systematic errors. We obtain an Eötvös ratio η 1 − 2 = 0.9 ± 2.7 × 10 − 10 , and set a new record on the precision with improvement of nearly 5 times. This measurement also provides constraint on the difference of the diagonal terms of the mass-energy operator.
Testing the Universality of Free Fall at 10−10{10^{ - 10}}10−10 level by Comparing the Atoms in Different Hyperfine States with Bragg Diffraction
We have performed a precision atomic interferometry experiment on testing the universality of free fall (UFF) considering atoms' spin degree of freedom. Our experiment employs the Bragg atom interferometer with 87^{87}87Rb atoms either in hyperfine state $\left| {F = 1,{m_F} = 0} \right\rangle $ or $\left| {F = 2,{m_F} = 0} \right\rangle ,andthewavepacketsinthesetwostatesarediffractedinonepairofBraggbeamsalternatively,whichcanhelpsuppressthecommon−modesystematicerrors.WehaveobtainedanE, and the wave packets in these two states are diffracted in one pair of Bragg beams alternatively, which can help suppress the common-mode systematic errors. We have obtained an E,andthewavepacketsinthesetwostatesarediffractedinonepairofBraggbeamsalternatively,whichcanhelpsuppressthecommon−modesystematicerrors.WehaveobtainedanE\rm{\ddot{o}}tvtvtv\rm{\ddot{o}}$s ratio η=(0.9±2.7)×10−10η= \left( { 0.9 \pm 2.7} \right) \times {10^{ - 10}}η=(0.9±2.7)×10−10, and set a new record on the precision with a nearly 5 times improvement. Our experiment gives stronger restrictions on the possible UFF breaking mechanism.
Quantum Tests of the Universality of Free FallIn the process of formulating a "theory of everything" that aims to provide a self-contained model of modern physics by unifying all four fundamental interactions, two theoretical frameworks have yielded important contributions: quantum mechanics, which can explain the nature of physics at the most microscopic length scales such as the origin of spectra of electrons bound in atomic systems, and Einstein's general relativity, that conveys our understanding of gravity over the largest distances across the universe.Although no theory of "quantum gravity", that is consistent over all energy scales, exists to date, certain modifications may enable a reconciliation of quantum mechanics and general relativity.These approaches allow for violations of the universality of free fall (UFF), that among Lorentz invariance and local position invariance constitute Einstein's equivalence principle.The UFF states that all bodies, located at the same space-time point, experience the same acceleration in a gravitational field independently of their composition.Because of its central role in modern physics the UFF has been tested extensively in many experiments, most of which utilized classical test masses.Quantum mechanical tests of the UFF differ from classical ones in various aspects such as the coherence length and spin polarization of the test masses.In this thesis, the first inertial-sensitive matter wave interferometer comparing the free fall of two different elements, 87 Rb and 39 K, was realized.This quantum test of the UFF yielded an Eötvös ratio 𝜂 Rb,K = (0.3 ± 5.4) × 10 -7 , and was limited by statistical uncertainty.In this work, an existing apparatus for rubidium interferometry was extended to the use of potassium and the first inertial-sensitive potassium matter wave interferometer with a resolution to gravitational acceleration of 𝜎 K = 3 × 10 -6 m/s 2 after 4096 s integration has been demonstrated.A description of the experiment including the technical realization and the techniques used is provided.Specifically, the challenges imposed by the use of potassium, which in comparison to rubidium has a smaller mass and lower hyperfine energy splitting, are examined.The thesis furthermore discusses an assessment of the systematic effects influencing the dual species measurement and presents future strategies to further improve the performance of the apparatus.As a preliminary result, it was possible to improve the potassium short-term sensitivity to gravitational acceleration to 𝜎 K = 2.1 × 10 -5 m/s 2 / √ Hz.The results of this thesis pave the way for exciting future experiments to be performed in large-scale apparatuses and in space.
We use a dual-species atom interferometer with 2 s of free-fall time to measure the relative acceleration between 85Rb and 87Rb wave packets in the Earth's gravitational field. Systematic errors arising from kinematic differences between the isotopes are suppressed by calibrating the angles and frequencies of the interferometry beams. We find an Eötvös parameter of [1.6 +/- 1.8 (stat) +/- 3.4 (syst)] x 10^-12, consistent with zero violation of the equivalence principle. With a resolution of up to 1.4 x 10^-11 g per shot, we demonstrate the highest sensitivity to the Eötvös parameter of any laboratory experiment.
We demonstrate how simultaneously operated 39K–87Rb interferometers exhibiting a high level of correlation can be used to make competitive tests of the university of free fall. This work provides an overview of our experimental apparatus and data analysis procedure, including a detailed study of systematic effects. With a total interrogation time of 2T=40 ms in a compact apparatus, we reach a statistical uncertainty on the measurement of the Eötvös parameter of 7.8×10−8 after 2.4×104 s of integration. The main limitations of our measurements arise from a combination of wavefront aberrations, the quadratic Zeeman effect in 39K, parasitic interferometers in 87Rb, and the velocity sensitivity of our detection system. These systematic errors limit the accuracy of our measurement to η=0.9(1.6)×10−6. We discuss prospects for improvements using ultracold atoms at extended interrogation times.
We report a test of the universality of free fall by comparing the gravity acceleration of the ^{87}Rb atoms in m_{F}=+1 versus those in m_{F}=-1, of which the corresponding spin orientations are opposite. A Mach-Zehnder-type atom interferometer is exploited to alternately measure the free fall acceleration of the atoms in these two magnetic sublevels, and the resultant Eötvös ratio is η_{S}=(0.2±1.2)×10^{-7}. This also gives an upper limit of 5.4×10^{-6} m^{-2} for a possible gradient field of the spacetime torsion. The interferometer using atoms in m_{F}=±1 is highly sensitive to the magnetic field inhomogeneity. A double differential measurement method is developed to alleviate the inhomogeneity influence, of which the effectiveness is validated by a magnetic field modulating experiment.