Abstract
Quantum metrology studies the use of entanglement and other quantum resources to improve precision measurement. An interferometer using N independent particles to measure a parameter χ can achieve at best the “standard quantum limit” (SQL) of sensitivity δ χ ∝ N−1/2. The same interferometer using N entangled particles can achieve in principle the “Heisenberg limit” δ χ ∝ N−1, using exotic states, e.g., NooN states. Recent theoretical work argues that interactions among particles may be a valuable resource for quantum metrology, allowing scaling beyond the Heisenberg limit [1].Specifically, a k-particle interaction will produce sensitivity δ χ ∝ N−k with appropriate entangled states and δ χ ∝ N−(k−1/2) even without entanglement [2]. Here we demonstrate this “super-Heisenberg” scaling in a nonlinear, non-destructive [3-4] measurement of the magnetisation of an atomic ensemble.
© 2011 IEEE
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