# Detection of a Quantum Measurement

Suppose it is known that a photon has diagonal polarisation (e.g. it has just passed through a diagonal slit), then Alice comes along and measures the photon using a horizontal/vertical polarisation basis. So, I believe there is a 50% chance she will get a horizontal result and 50% chance she will obtain a vertical result.

Now Bob comes along and also knows the particle has passed through the diagonal slit, but he is unaware that Alice has already made a measurement using a horizontal/vertical basis. Is there an experiment Bob can do to check if the particle's polarisation has been measured?

Thanks

DrChinese
Gold Member
Suppose it is known that a photon has diagonal polarisation (e.g. it has just passed through a diagonal slit), then Alice comes along and measures the photon using a horizontal/vertical polarisation basis. So, I believe there is a 50% chance she will get a horizontal result and 50% chance she will obtain a vertical result.

Now Bob comes along and also knows the particle has passed through the diagonal slit, but he is unaware that Alice has already made a measurement using a horizontal/vertical basis. Is there an experiment Bob can do to check if the particle's polarisation has been measured?

Thanks

No in this case, and also generally no.

Hello.

No in this case, and also generally no.

Measurement of Alice decreases percentage of Bob's finding diagonal polarized photon to 50%, doesn't it?