Which of the following gates when applied twice brings the system back to itsoriginal state?

The gate that brings the system back to its original state when applied twice is the NOT gate (also known as a Pauli-X gate in quantum computing).

Here's why:

1. The NOT gate flips the state of a system. If the system is in state 0, the NOT gate changes it to state 1. If the system is in state 1, the NOT gate changes it to state 0.

2. If you apply the NOT gate twice, it will flip the state of the system twice. So, if the system starts in state 0, the first NOT gate changes it to state 1, and the second NOT gate changes it back to state 0. Similarly, if the system starts in state 1, the first NOT gate changes it to state 0, and the second NOT gate changes it back to state 1.

So, no matter what state the system starts in, applying the NOT gate twice will always bring it back to its original state.

The gate that brings the system back to its original state when applied twice is the NOT gate (also known as a Pauli-X gate in quantum computing).

Here's why:

1. The NOT gate flips the state of a system. If the system is in state 0, the NOT gate changes it to state 1. If the system is in state 1, the NOT gate changes it to state 0.

2. If you apply the NOT gate a second time, it will flip the state back to its original value. If the system was originally in state 0, two applications of the NOT gate will leave it in state 0 (because 0 flips to 1 and then back to 0). Similarly, if the system was originally in state 1, two applications of the NOT gate will leave it in state 1 (because 1 flips to 0 and then back to 1).

So, the NOT gate is the gate that, when applied twice, brings the system back to its original state.