Hello, thank you for your swift response!

In my scenario, **I am dealing with ancillary qubits followed by system qubits (i.e. ancilla is placed at the top or starting of the circuit and then system qubits).** To clarify, I am attempting to calculate the probability of the bit strings for all system qubits, excluding the ancillary ones. For instance, the list provided represents the desired basis states for which I want to calculate the probabilities. Itâs worth noting that my code is designed to be generalized, accommodating cases where the total qubits may vary, such as having 9 qubits with 4 ancilla and 5 system qubits.

As a follow-up question, the `state_vector()`

function currently returns the state vector for all 12 qubits in the circuit. However, my expectation is to obtain the state vector specifically for the system qubits. This will allow me to calculate the probabilities of all basis states for the system qubits, as illustrated in the code snippet provided.

```
system qubits: 8
ancilla qubits: 4
total qubits: 12
['00000000', '10000000', '01000000', '11000000', '00100000', '10100000', '01100000', '11100000', '00010000', '10010000', '01010000', '11010000', '00110000', '10110000', '01110000', '11110000', '00001000', '10001000', '01001000', '11001000', '00101000', '10101000', '01101000', '11101000', '00011000', '10011000', '01011000', '11011000', '00111000', '10111000', '01111000', '11111000', '00000100', '10000100', '01000100', '11000100', '00100100', '10100100', '01100100', '11100100', '00010100', '10010100', '01010100', '11010100', '00110100', '10110100', '01110100', '11110100', '00001100', '10001100', '01001100', '11001100', '00101100', '10101100', '01101100', '11101100', '00011100', '10011100', '01011100', '11011100', '00111100', '10111100', '01111100', '11111100', '00000010', '10000010', '01000010', '11000010', '00100010', '10100010', '01100010', '11100010', '00010010', '10010010', '01010010', '11010010', '00110010', '10110010', '01110010', '11110010', '00001010', '10001010', '01001010', '11001010', '00101010', '10101010', '01101010', '11101010', '00011010', '10011010', '01011010', '11011010', '00111010', '10111010', '01111010', '11111010', '00000110', '10000110', '01000110', '11000110', '00100110', '10100110', '01100110', '11100110', '00010110', '10010110', '01010110', '11010110', '00110110', '10110110', '01110110', '11110110', '00001110', '10001110', '01001110', '11001110', '00101110', '10101110', '01101110', '11101110', '00011110', '10011110', '01011110', '11011110', '00111110', '10111110', '01111110', '11111110', '00000001', '10000001', '01000001', '11000001', '00100001', '10100001', '01100001', '11100001', '00010001', '10010001', '01010001', '11010001', '00110001', '10110001', '01110001', '11110001', '00001001', '10001001', '01001001', '11001001', '00101001', '10101001', '01101001', '11101001', '00011001', '10011001', '01011001', '11011001', '00111001', '10111001', '01111001', '11111001', '00000101', '10000101', '01000101', '11000101', '00100101', '10100101', '01100101', '11100101', '00010101', '10010101', '01010101', '11010101', '00110101', '10110101', '01110101', '11110101', '00001101', '10001101', '01001101', '11001101', '00101101', '10101101', '01101101', '11101101', '00011101', '10011101', '01011101', '11011101', '00111101', '10111101', '01111101', '11111101', '00000011', '10000011', '01000011', '11000011', '00100011', '10100011', '01100011', '11100011', '00010011', '10010011', '01010011', '11010011', '00110011', '10110011', '01110011', '11110011', '00001011', '10001011', '01001011', '11001011', '00101011', '10101011', '01101011', '11101011', '00011011', '10011011', '01011011', '11011011', '00111011', '10111011', '01111011', '11111011', '00000111', '10000111', '01000111', '11000111', '00100111', '10100111', '01100111', '11100111', '00010111', '10010111', '01010111', '11010111', '00110111', '10110111', '01110111', '11110111', '00001111', '10001111', '01001111', '11001111', '00101111', '10101111', '01101111', '11101111', '00011111', '10011111', '01011111', '11011111', '00111111', '10111111', '01111111', '11111111']
```