(a) and (b): Schematic picture of the chirality of the quantum Hall edge states around a single antidot when the number of PNJs (N) is (a) even and (b) odd. The present study has established that the conductance is essentially different between the two cases, namely the parity effect. (c) Optical image of the device. The inset shows that this device has a single open window (an antidot) shown by the white curves. We tuned the top gate voltages of these two top gate electrodes, marked as a and b, in order to experimentally realize the cases with N = 0, 1, 2, and 3