NASA - National Aeronautics and Space Administration

Metrology is the Science of Measurement. It encompasses time/clock standards, distance measurements, orientation/navigation, electromagnetic and gravitational field detection and determination of physical constants. This research is of fundamental importance to Physics, since it involves the scrutiny of exactly how we observe and interact with Nature. But it is also of great significance for NASA, as quantum metrology has implications for improved Space Sensors and telescopes, and superior inertial navigation for Spacecraft.

Measurements of a continuous parameter are subject to error, which can fall into two categories: Accuracy and Precision. Repeated measurements that are accurate take values averaging to the true value of the parameter being measured. Precise measurements result in data with a small variance. So a measurement may be accurate but not precise, and vice versa. Some devices that exist today, e.g. Interferometers like LIGO and atomic clocks are operating at or close to the classical limits of precision. Classically what limits precision are external sources of noise like seismic, acoustic and thermal fluctuations.

However once all of these have been accommodated or suppressed one is left with an intrinsic statistical source of noise that emerges from quantum mechanics. Quantum Metrology is concerned with harnessing quantum many-body correlations and entanglement for the purposes of enhancing measurement sensitivity past the classical bounds. This classical bound is easily defined for a many-body system containing N particles: In this case the precision sensitivity (the variance on any estimate of the parameter being investigated) scales with the inverse square root of the particle number. This is exactly the precision limit resulting from making N independent single particle measurements of the parameter. So any greater sensitivity implies that the device is operating beyond this classical limit, and that the particles are behaving in a quantum-correlated fashion.

We aim to model real quantum measurement devices and to explore in a realistic setting what sort of quantum probe states of light, spin systems or atom ensembles may access this new domain of parameter super-sensitivity.

Physical Review Letters article

Metrology Related Publications