In the quantum metrology problem, one wishes to use a quantum resource to measure an signal with known structure but unknown strength. Quantum metrology does not require the full power of quantum computation, and might serve as an early use-case for quantum technologies.
The quantum resource in quantum metrology are probe states. Probe states are unfortunately fragile, and need to be designed to be robust against errors. Surprisingly, entanglement in a probe state, while necessary for quantum metrology, is not sufficient to allow robust metrology. The search for robust probe states is non-trivial, and symmetric probe states are good candidates.
Eventually quantum metrology will integrate with quantum error correction, to allow measurements to attain their maximum precision, namely via fault tolerant quantum metrology.
2019 Robust quantum metrology with explicit symmetric states [Metrology/QEC/PI code]
Y. Ouyang, Nathan Shettell, Damian Markham http://arxiv.org/abs/1908.02378