For example, if a photon is sent through a horizontal polarisation filter, then it does not pass through a subsequent vertical filter.

Conversely, if the second filter is positioned at a 45 degree angle to the first filter, then the photon passes the second filter with a 50 percent probability. In this case, it is pure chance whether the photon passes through or not. This is a fundamental statement of quantum mechanics.

The photon has now also lost any information about whether it was previously horizontally or vertically polarised. If it is sent through a horizontal filter again, then the probabilty that it does not pass through is once again 50 percent.