The custom operator allows the user to use popular operators or custom operators to change the state of the qubit.
The panel has a 2x2 matrix input to allow the user to enter an operator manually, or populate it using the popular quantum operators on the right. When the operator is input, the user can have the operator act on the qubits by hitting either the "Apply To Visible Qubits" button or by clicking on the "Apply To All Qubits" button. The buttons will apply the operator on each qubit individually. Clicking on the button multiple times will cause the operator to act on the qubits multiple times. Some operators are Hermitian (X, Y, Z, H for example) and if applied twice will return the qubit to its original state after using the operator twice.
As seen in the image above, the custom operator allows the user to populate the X, Y, Z, H, S or T operator. Clicking on these buttons will cause the operator values to be filled into the 2x2 matrix.
Clicking on the rotation buttons Rx(θ), Ry(θ), or Rz(θ) will prompt the user to enter the angle (in degrees) to rotate the qubit around the applicable axis. Once the angle is entered, the operator values will be populated.
The operator values can be set manually. They must form a unitary operator. If the values do not create a unitary operator, then the user will get an error when applying the operator to the qubits. The individual values must be a decimal number.