# Heisenberg limit

In quantum metrology, and especially interferometry, the **Heisenberg limit** is the optimal rate at which the accuracy of a measurement can scale with the energy used in the measurement. Typically, this is the measurement of a phase (applied to one arm of a beam-splitter) and the energy is given by the number of photons used in an interferometer.

Although some claim to have broken the Heisenberg limit, this reflects disagreement on the definition of the scaling resource.[1] Suitably defined, the Heisenberg limit is a consequence of the basic principles of quantum mechanics and cannot be beaten, although weak Heisenberg limit can be beaten.[2]

## References

- Giovannetti, V.; Lloyd, S.; Maccone, L. (2011). "Advances in quantum metrology".
*Nature Photonics*.**5**(4): 222. arXiv:1102.2318. Bibcode:2011NaPho...5..222G. doi:10.1038/nphoton.2011.35.; arXiv - Luis, Alfredo (2017-03-13). "Breaking the weak Heisenberg limit".
*Physical Review A*.**95**(3). doi:10.1103/PhysRevA.95.032113. ISSN 2469-9926.

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