Joint measurement using a spatio-temporal mode sorter

Determine whether an equivalent Helstrom-optimal joint measurement for multiparameter incoherent imaging can be implemented using a spatio-temporal mode sorter that groups individual photons distributed across multiple temporal modes into a single temporal mode.

Background

The paper proposes two asymptotically Helstrom-optimal joint-detection receivers for estimating emitter brightnesses. One relies on transduction into quantum memories and quantum computation, while the other uses optomechanical bosonic ancillas cooled near their motional ground state.

Both proposed implementations require substantial quantum resources. The authors therefore leave unresolved whether a mode-sorting architecture alone could realize an equivalent joint measurement, which would substantially improve the experimental feasibility of collective measurements across multiple temporal copies.

References

First, while we articulate two protocols for realizing optimal joint measurements predicated on the use of quantum resources (i.e. atomic quantum memories or optomechanical membranes cooled to the motional ground state), it is unknown whether an equivalent measurement can be implemented simply using a spatio-temporal mode sorter that groups individual photons spread across multiple temporal modes into a single temporal mode .

— Attaining Fundamental Limits of Multiparameter Incoherent Optical Imaging Using Joint-Detection Quantum Measurements  (2608.19524 - Deshler et al., 20 Aug 2026) in Conclusion, paragraph beginning “Several open questions remain”