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You're touching on a very interesting point about the way Qiskit handles cll bits and how they relate to qubit states.

It's not exactly a reversal, but a change in the way we interpret the data.

Here's a breakdown:

• Classical Bits: In classical computing, bits are represented as either 0 or 1. They are ordered sequentially in a register.
• Qubits: In quantum computing, qubits can be in a superposition of both 0 and 1 simultaneously. They don't have a strict ordering like classical bits.
• Qiskit's Circuit Structure: Qiskit uses a circuit-based model for quantum computation. The circuit is built from a sequence of gates that act on qubits. The qubits are arranged in a register, and the order of the qubits in the register is important for understanding how the gates will affect them.

Now, when you input classical bit values into Qiskit to initialize qubits, you're essentially assigning those values to the qubit states. Qiskit doesn't "reverse" the order in the sense of flipping it. However, there's a subtle shift in how we interpret the bit values:

1. Classical Bit Order: You might think of the bits as being in a left-to-right order. For example, the bit string "101" would represent the bits: 1, 0, 1.
2. Qubit State Assignment: Qiskit assigns these values to the qubits starting from the least significant bit (LSB) to the most significant bit (MSB). So, using the same "101" example, the qubit register would be initialized as:
   • Qubit 0: |1>
   • Qubit 1: |0>
   • Qubit 2: |1>

Why this is important:

• Gate Application: The order of qubits in the register dictates how gates are applied. A gate acting on qubit 0 will affect the state of the least significant bit in the classical bit string representation.
• Measurement: When you measure the qubits, the resulting classical bit string will be in the same order as the qubit register (LSB to MSB).

In summary:

While Qiskit doesn't explicitly reverse the order of your classical bit input, it does use a convention where the least significant bit corresponds to the first qubit in the register. This is important for understanding how gates operate and how measurement results are interpreted.

You're right to ask about specific examples! Let's break down the string "011" using Qiskit's convention:

• Classical Bit Order: You would think of the bits as being in a left-to-right order: 0, 1, 1.
• Qubit State Assignment: Qiskit assigns the values to the qubits from LSB to MSB:
  • Qubit 0: |1> (LSB)
  • Qubit 1: |1>
  • Qubit 2: |0> (MSB)

So, the "011" string would initialize the qubits in this way.

Remember, Qiskit uses this convention for consistency. It makes it easier to understand how gates and measurements work on a circuit.