Fig. 4: Local Measurement Strategies for the 2-LUI-RE Protocol.
From: Informationally complete distributed metrology without a shared reference frame
a Direct Computational Basis Measurement (DM). Each qudit is measured directly in the computational basis. This strategy suffers an exponential loss of information. b Local SWAP Test (LST). An ancillary qubit is introduced at each site to perform a controlled-SWAP operation between the two copies. c Local Bell-state Measurement (LBM). For qubit systems (d = 2), the local SWAP test is operationally equivalent to a Bell-state measurement. This is implemented efficiently using a CNOT gate and a Hadamard gate at each site, followed by Z-basis measurements. LST and LBM constitute optimal measurement strategies.
