The authors observed coherent time evolution between two quantum states of a superconducting flux qubit, which consists of three Josephson junctions in a loop. They manipulated the superposition of these states by resonant microwave pulses and read out the quantum states using a superconducting quantum interference device (SQUID). The results showed high-fidelity quantum-state oscillations, with hundreds of coherent oscillations induced under strong microwave driving. The relaxation time was 900 nanoseconds, and the free-induction dephasing time was 20 nanoseconds. These findings are promising for future solid-state quantum computing. The qubit's behavior is influenced by external and internal noise, particularly flux noise, which can be reduced in future designs. The high fidelity of qubit excitation and readout, along with the potential to reduce the dephasing rate, make the superconducting flux qubit an attractive candidate for solid-state quantum computing.The authors observed coherent time evolution between two quantum states of a superconducting flux qubit, which consists of three Josephson junctions in a loop. They manipulated the superposition of these states by resonant microwave pulses and read out the quantum states using a superconducting quantum interference device (SQUID). The results showed high-fidelity quantum-state oscillations, with hundreds of coherent oscillations induced under strong microwave driving. The relaxation time was 900 nanoseconds, and the free-induction dephasing time was 20 nanoseconds. These findings are promising for future solid-state quantum computing. The qubit's behavior is influenced by external and internal noise, particularly flux noise, which can be reduced in future designs. The high fidelity of qubit excitation and readout, along with the potential to reduce the dephasing rate, make the superconducting flux qubit an attractive candidate for solid-state quantum computing.