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Bell inequality violation with two remote atomic qubits
D. N. Matsukevich, P. Maunz, D. L. Moehring, S. Olmschenk, C. Monroe
TL;DR
A rigorous Bell test must close both locality and detection loopholes. This work characterizes remote Yb-ion entanglement and measures ion states after each heralded event; the measured CHSH parameter violates the Bell bound with the detection loophole closed.
Problem
A rigorous Bell test must prevent communication between qubits during measurement and prevent selective detection from mimicking a violation, requiring closure of both locality and detection loopholes.
Source: p. 1Method
The experiment uses polarization-encoded ion-photon qubits to establish and characterize remote ion entanglement, then measures the ion states after each heralded event.
Source: pp. 1, 3Results
S = 2.22 ± 0.07 violates the Bell inequality by more than three standard deviations with the detection loophole closed.
Source: p. 3Takeaways & Limitations
Remote entanglement of atomic qubits is an important step toward scalable quantum information processing and communication networks.
Source: p. 1A loophole-free test would require a much larger ion separation or shorter detection time; a realistic 50 µs detection time requires 15 km separation.
Source: p. 4
Abstract
from arXiv · showhide
We observe violation of a Bell inequality between the quantum states of two remote Yb ions separated by a distance of about one meter with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography.