[en] We consider the problem of identifying the quantum spin states that are the optimal sensors of a given transformation averaged over all possible orientations of the spin system. Our geometric approach to the problem is based on a fidelity criterion and is entirely general, encompassing both unitary transformations (such as rotations and squeezing) and non-unitary transformations (such as Lorentz boosts). This formalism leads to a universality result: There exists a zero-measure subset of states that will be optimal sensors for certain transformations and the worst sensors for others, and this set does not depend on the transformation under consideration. In other words, some spin states are simply the best (or worst) sensors, regardless of what they detect.
Disciplines :
Physics
Author, co-author :
Aragón-Muñoz, Luis; Institute for Nuclear Sciences (UNAM)
Chryssomalakos, Chryssomalis; Institute for Nuclear Sciences (UNAM)
Gabriela Flores-Delgado, Ana; Institute for Nuclear Sciences (UNAM)
Martin, John ; Université de Liège - ULiège > Département de physique > Optique quantique
Serrano Ensástiga, Eduardo ; Université de Liège - ULiège > Complex and Entangled Systems from Atoms to Materials (CESAM)
ULiège - University of Liège F.R.S.-FNRS - Fonds de la Recherche Scientifique EOS - The Excellence Of Science Program
Funding number :
EOS project 40007526
Funding text :
Financial support is acknowledged, in the form of a SECIHTI (Mexico) postdoctoral fellowship (LFAM), a SECIHTI SNI assistantship (AGFD) and the SECIHTI CBF-2025-I-676 and DGAPA-PAPIIT-UNAM IN112224 projects (LFAM, CC, AGFD). ESE acknowledges support from the postdoctoral fellowship of the IPD-STEMA program of the University of Liège (Belgium). JM and ESE acknowledge the FWO and the F.R.S.-FNRS for their funding as part of the Excellence of Science program (EOS project 40007526).
