In the IBM Q Experience, which is IBM's cloud-based quantum computing platform, you can specify the qubits you want to use by utilizing the "Qubit Operations" available in their programming interface. Here's a general outline of the process:
Choose the backend: First, select the quantum computer or simulator you want to use from the available options provided by IBM Q. The backends can be physical quantum devices or simulators that mimic quantum behavior.
Define quantum circuits: Use a quantum circuit framework such as Qiskit (IBM's open-source quantum programming framework) to define your quantum circuits. A quantum circuit is a sequence of quantum gates that operate on qubits to perform computations. You can specify the number of qubits you want to use in your circuit.
Specify qubit operations: Within your quantum circuit, you can specify operations on specific qubits. Qubits are typically labeled or indexed, and you can refer to them by their index or label in your circuit definition. For example, if you want to apply a gate operation to the qubit with index 0, you can include that operation in your circuit definition.
Execute the circuit: Once you have defined your quantum circuit, you can submit it for execution on the chosen backend. If the backend is a simulator, the circuit will be executed on a classical computer that emulates quantum behavior. If the backend is a physical quantum device, the circuit will be sent to the device for execution.
It's important to note that the specific details of how you specify qubits may depend on the quantum programming framework or platform you are using. Different frameworks may have different conventions for specifying qubits and operations. However, the general concept remains the same: you define your quantum circuit and specify operations on the desired qubits within that circuit.