NMR imaging analogue of the individual qubit operations in superconducting flux-qubit chains

A solid-state quantum computer conventionally requires the control lines for each qubit to operate individually. This makes quantum circuits complicated, especially in multi-qubit systems. Here we propose a simple single-qubit operation in a superconducting flux-qubit chain without control lines in an analogy of the Nuclear Magnetic Resonance (NMR) imaging technique. A superconducting flux qubit can be regarded as an artificial atom with spin 1/2 that can be manipulated by an external magnetic field. To identify the location of each qubit in the qubit chain, a static field gradient is introduced along the qubit chain. This magnetic field gradient causes differences in the Zeeman frequencies of each separate qubit. This allows a large number of distinct qubits to be individually addressed. Single-qubit operations are then possible when the external electromagnetic frequency is adjusted to the resulting energy-level separation of the target qubit.