Quantum enhanced sensing
Harnessing quantum mechanical effects is expected to provide an advantage over classical sensing technology. By entangling the center-of-mass motional state of approximately 150 ions trapped in a two-dimensional Coulomb crystal with their collective spin state, Gilmore et al. demonstrate a quantum-enhanced measurement sensitivity of displacement and electric field. Such enhanced sensitivity could, for instance, find application in probing proposed weak interactions between dark matter and normal matter, as well as enhancing gravitational wave detection.
Science, abi5226, this issue p. 673
Abstract
Fully controllable ultracold atomic systems are creating opportunities for quantum sensing, yet demonstrating a quantum advantage in useful applications by harnessing entanglement remains a challenging task. Here, we realize a many-body quantum-enhanced sensor to detect displacements and electric fields using a crystal of ~150 trapped ions. The center-of-mass vibrational mode of the crystal serves as a high-Q mechanical oscillator, and the collective electronic spin serves as the measurement device. By entangling the oscillator and collective spin and controlling the coherent dynamics via a many-body echo, a displacement is mapped into a spin rotation while avoiding quantum back-action and thermal noise. We achieve a sensitivity to displacements of 8.8 ± 0.4 decibels below the standard quantum limit and a sensitivity for measuring electric fields of 240 ± 10 nanovolts per meter in 1 second. Feasible improvements should enable the use of trapped ions in searches for dark matter.