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  • Featured in Physics
  • Open Access

Entanglement-Enhanced Atomic Gravimeter

Christophe Cassens1,2,*, Bernd Meyer-Hoppe1,2, Ernst Rasel1, and Carsten Klempt1,2

  • *Contact author: Christophe.Cassens@dlr.de
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Phys. Rev. X 15, 011029 – Published 11 February, 2025

DOI: https://doi.org/10.1103/PhysRevX.15.011029

Abstract

Interferometers based on ultracold atoms enable an absolute measurement of inertial forces with unprecedented precision. However, their resolution is fundamentally restricted by quantum fluctuations. Improved resolutions with entangled or squeezed atoms were demonstrated in internal-state measurements for thermal and quantum-degenerate atoms and, recently, for momentum-state interferometers with laser-cooled atoms. Here, we present a gravimeter based on Bose-Einstein condensates with a sensitivity of −1.7−0.5+0.4  dB beyond the standard quantum limit. Interferometry with Bose-Einstein condensates combined with delta-kick collimation minimizes atom loss in and improves scalability of the interferometer to very-long-baseline atom interferometers.

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Entanglement Can Improve Precision of Gravity Measurements

Published 11 February, 2025

The first measurement of gravity using quantum mechanically entangled atoms demonstrates the potential of the approach.

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Popular Summary

Atom interferometers offer unprecedented sensitivities for the measurement of gravitational acceleration. They have already taken the leap to commercialization and are actively developed for high-sensitivity applications in fundamental science. Their resolution is generally limited by quantum fluctuations that stem from the quantum-mechanical character of the atoms. Quantum-mechanical correlations between the atoms, called entanglement, allow one to surpass these sensitivity limits. Here, we present the operation of an atom interferometer for an absolute measurement of gravitational acceleration with an entanglement-enhanced resolution.

The concept is based on atomic Bose-Einstein condensates (BECs), where the atomic ensemble is cooled close to absolute-zero temperature such that the atoms become indistinguishable, like the photons in a laser beam. The atoms of the BEC, prepared in the focus of a trapping laser beam, undergo collisions that generate entanglement. Once released from the trap, the falling BEC is split vertically and then recombined by a series of laser pulses. Meanwhile, the atoms sense the acceleration relative to the laser pulses before interfering upon recombination. The interference signal is then measured by counting the number of atoms in the two output ports. We demonstrate that the created entanglement reduces the quantum fluctuations of the interference signal, thereby achieving improved resolution in measuring the gravitational acceleration.

Because of the low temperatures and corresponding expansion velocities, our concept can be implemented in existing and planned large-scale atom interferometers, where highest sensitivities can be realized in facilities of 10  m to several kilometers in length.

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Phys. Rev. X 15, 011029– Published 11 February, 2025
  • Received 3 May 2024
  • Accepted 19 November 2024
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