Fig. 3
From: Experimental observation of classical analogy of topological entanglement entropy
The experimental set-up to construct and characterize the CMESs as the analogy of quantum MESs. a The overall designed classical microwave signal processing system, including transmitting and receiving dual-polarized antennas, a 2n-channel receiver array, an analog-to-digital converter (ADC) and a programmable DSP module. b An example of the work flow to construct the 4-cebit analog \(\left. {\left| {\psi _4^{{\mathrm{cl}}}} \right.} \right)\) in the DSP module. All eight signals in the channels {h1, …, v4} fed into the DSP are arranged by a digital down-converter (DDC) to have their own frequencies as planned. After a measuring process through the PROJ part followed by several mixing and filtering processes for multiplex signals, the desired signal component AΩ is selected by the FFT-based digital filter, and we collect its complex amplitude as described in Eq. (5). The red dashed box highlights a unit of the PROJ part as depicted in c, including two multiplications and an adder, which can be tuned conveniently to perform desired projective measurement settings
