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Despite being the dominant force of nature on large scales, gravity remains relatively elusive to precision laboratory experiments. Atom interferometers are powerful tools for investigating, for example, Earth’s gravity, the gravitational constant, deviations from Newtonian gravity and general relativity. However, using atoms in free fall limits measurement time to a few seconds, and much less when measuring interactions with a small source mass. Recently, interferometers with atoms suspended for 70 s in an optical-lattice mode filtered by an optical cavity have been demonstrated. However, the optical lattice must balance Earth’s gravity by applying forces that are a billionfold stronger than the putative signals, so even tiny imperfections may generate complex systematic effects. Thus, lattice interferometers have yet to be used for precision tests of gravity. Here we optimize the gravitational sensitivity of a lattice interferometer and use a system of signal inversions to suppress and quantify systematic efects. We measure the attraction of a miniature source mass to be amass = 33.3 ± 5.6stat ± 2.7syst nm s−2, consistent with Newtonian gravity, ruling out ‘screened ffth force’ theories3,15,16 over their natural parameter space. The overall accuracy of 6.2 nm s−2 surpasses by more than a factor of four the best similar measurements with atoms in free fall. Improved atom cooling and tilt-noise suppression may further increase sensitivity for investigating forces at sub-millimetre ranges, compact gravimetry, measuring the gravitational Aharonov–Bohm effect and the gravitational constant, and testing whether the gravitational field has quantum properties.
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Information content of the gravitational field of a quantum superposition
When a massive quantum body is put into a spatial superposition, it is of interest to consider the quantum aspects of the gravitational field sourced by the body. We argue that in order to understand how the body may become entangled with other massive bodies via gravitational interactions, it must be thought of as being entangled with its own Newtonian-like gravitational field. Thus, a Newtonian-like gravitational field must be capable of carrying quantum information. Our analysis supports the view that table-top experiments testing entanglement of systems interacting via gravity do probe the quantum nature of gravity, even if no “gravitons” are emitted during the experiment.
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- Award ID(s):
- 1804216
- PAR ID:
- 10169417
- Date Published:
- Journal Name:
- International Journal of Modern Physics D
- Volume:
- 28
- Issue:
- 14
- ISSN:
- 0218-2718
- Page Range / eLocation ID:
- 1943001
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract An ensemble of atoms can operate as a quantum sensor by placing atoms in a superposition of two different states. Upon measurement of the sensor, each atom is individually projected into one of the two states. Creating quantum correlations between the atoms, that is entangling them, could lead to resolutions surpassing the standard quantum limit 1–3 set by projections of individual atoms. Large amounts of entanglement 4–6 involving the internal degrees of freedom of laser-cooled atomic ensembles 4–16 have been generated in collective cavity quantum-electrodynamics systems, in which many atoms simultaneously interact with a single optical cavity mode. Here we report a matter-wave interferometer in a cavity quantum-electrodynamics system of 700 atoms that are entangled in their external degrees of freedom. In our system, each individual atom falls freely under gravity and simultaneously traverses two paths through space while entangled with the other atoms. We demonstrate both quantum non-demolition measurements and cavity-mediated spin interactions for generating squeezed momentum states with directly observed sensitivity $$3\,.\,{4}_{-0.9}^{+1.1}$$ 3 . 4 − 0.9 + 1.1 dB and $$2\,.\,{5}_{-0.6}^{+0.6}$$ 2 . 5 − 0.6 + 0.6 dB below the standard quantum limit, respectively. We successfully inject an entangled state into a Mach–Zehnder light-pulse interferometer with directly observed sensitivity $$1\,.\,{7}_{-0.5}^{+0.5}$$ 1 . 7 − 0.5 + 0.5 dB below the standard quantum limit. The combination of particle delocalization and entanglement in our approach may influence developments of enhanced inertial sensors 17,18 , searches for new physics, particles and fields 19–23 , future advanced gravitational wave detectors 24,25 and accessing beyond mean-field quantum many-body physics 26–30 .more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1142/S0218271819430016
