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A source constantly produces a stream of photons in one of the following states

$$|\varphi_1\rangle=\dfrac{1}{\sqrt2}(a|00\rangle+ b|01\rangle+c|10\rangle+d|11\rangle)$$

$$|\varphi_2\rangle=\dfrac{1}{\sqrt2}(b|00\rangle+ a|01\rangle+d|10\rangle+ c|11\rangle)$$

where $a,b,c,d$ are some (valid) scalar values **you know beforehand** and $a\ne b\ne c\ne d$.

You are only sent the first qubit and have no access to the second qubit.

How to design a measurement (on the first qubit) that allow yout to tell whether the source is producing $|\varphi_1\rangle$ or $|\varphi_2\rangle$?

Assume you can measure as many times as you want.