The problem transform from github discussion :
At first, thanks for the developer’s reply. However, I am afraid that the problem still exists in some cases.
for example.
I attempt to encode 2 data examples that have 3 dimensions into a quantum state. (x1=[0, 1, 1], x2 = [1, 1, 0] )
So, the resulting circuit maybe
0 IDX 1
0 XX 0
0 XID 1
In the above result, their have 2 problem >

PauliX gate can not make the superposition, so the coefficient may not reflect the probability of quantum states, namely the probability to measure the x1 as well as x2 is zero. Furthermore, we are only able to measure the result x = [1, 0, 1] which is not the original data point.

In the single data example, the PauliX may produce the suitable result (as the developer reply). For example, x = [1, 0, 0, 1] just flip bit 0 and 3, then done~
However, the double PauliX gate will produce the Identity transformation in the corresponding wire.
For more specific, suppose x1= [0, 0, 1], x2 = [0, 1, 0], x3 = [0, 1, 1]
While we encode the 3 data example, the result will be x = [0, 0, 0]…
Due to the last 2 bit transformed by PauliX twices without superposition.
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By the way, in the tfq tutorial mnist, which use the independent circuit to perform the Basis Encoding (then everything make sense like the developer’s reply – just flip bit by PauliX).
However, I found that Pennylane stack the data examples into only 1 circuit as the following blog plot!!
Any suggestion will be appreciate !!