This paper reports on the observation of coherent quantum dynamics in a superconducting flux qubit, which consists of three Josephson junctions arranged in a loop. The qubit's two quantum states, which carry opposite macroscopic persistent currents, are manipulated using resonant microwave pulses. The quantum state oscillations are read out using a superconducting quantum interference device (SQUID), revealing high-fidelity oscillations. Under strong microwave driving, hundreds of coherent oscillations are induced. The qubit's relaxation time is 900 nanoseconds, and its free-induction dephasing time is 20 nanoseconds, indicating promising potential for future solid-state quantum computing. The qubit is a micron-sized superconducting ring containing billions of Cooper pairs. It can be controlled to oscillate coherently between two states, and multiple pulses can be used to create quantum operation sequences. This is of fundamental interest for studying decoherence mechanisms in macroscopic objects and for quantum computing, as these structures can be scaled up to large numbers of qubits. Superconducting circuits with mesoscopic Josephson junctions can behave according to quantum mechanics if isolated from external degrees of freedom. Quantum oscillations have been observed in Cooper pair box qubits using the charge degree of freedom. A qubit based on the phase degree of freedom in a Josephson junction has also been presented. The flux qubit is biased by magnetic flux, making it relatively insensitive to charge noise. The qubit's energy levels depend on the superconducting phase across the junctions. The qubit is initialized to the ground state by allowing it to relax. Coherent control is achieved by applying resonant microwave excitations, inducing an oscillating magnetic field through the qubit loop. The qubit state evolves driven by a time-dependent term in the Hamiltonian, similar to spin dynamics. The qubit is read out using an underdamped SQUID in direct contact with the qubit loop. The SQUID's mutual inductance enhances the qubit signal. The qubit's phase bias is shifted automatically, allowing operation near π, where the qubit is least sensitive to flux noise. The readout electronics have a limited bandwidth, so a trailing plateau is added to the current pulse to optimize the distinction of the switching probability between the two qubit states. The qubit's energy levels were examined using spectroscopic methods. Resonant absorption peaks/dips were observed when the qubit's energy separation coincided with the microwave frequency. The energy gap was estimated to be approximately 3.4 GHz. The qubit's dephasing time was measured using Ramsey interference, yielding a value of approximately 20 ns, which is much shorter than the relaxation time of approximately 900 ns. Dephasing is likely caused by variations in the qubit's energy splitting due to external or internal noise. The qubit could not be operated at the symmetry point whereThis paper reports on the observation of coherent quantum dynamics in a superconducting flux qubit, which consists of three Josephson junctions arranged in a loop. The qubit's two quantum states, which carry opposite macroscopic persistent currents, are manipulated using resonant microwave pulses. The quantum state oscillations are read out using a superconducting quantum interference device (SQUID), revealing high-fidelity oscillations. Under strong microwave driving, hundreds of coherent oscillations are induced. The qubit's relaxation time is 900 nanoseconds, and its free-induction dephasing time is 20 nanoseconds, indicating promising potential for future solid-state quantum computing. The qubit is a micron-sized superconducting ring containing billions of Cooper pairs. It can be controlled to oscillate coherently between two states, and multiple pulses can be used to create quantum operation sequences. This is of fundamental interest for studying decoherence mechanisms in macroscopic objects and for quantum computing, as these structures can be scaled up to large numbers of qubits. Superconducting circuits with mesoscopic Josephson junctions can behave according to quantum mechanics if isolated from external degrees of freedom. Quantum oscillations have been observed in Cooper pair box qubits using the charge degree of freedom. A qubit based on the phase degree of freedom in a Josephson junction has also been presented. The flux qubit is biased by magnetic flux, making it relatively insensitive to charge noise. The qubit's energy levels depend on the superconducting phase across the junctions. The qubit is initialized to the ground state by allowing it to relax. Coherent control is achieved by applying resonant microwave excitations, inducing an oscillating magnetic field through the qubit loop. The qubit state evolves driven by a time-dependent term in the Hamiltonian, similar to spin dynamics. The qubit is read out using an underdamped SQUID in direct contact with the qubit loop. The SQUID's mutual inductance enhances the qubit signal. The qubit's phase bias is shifted automatically, allowing operation near π, where the qubit is least sensitive to flux noise. The readout electronics have a limited bandwidth, so a trailing plateau is added to the current pulse to optimize the distinction of the switching probability between the two qubit states. The qubit's energy levels were examined using spectroscopic methods. Resonant absorption peaks/dips were observed when the qubit's energy separation coincided with the microwave frequency. The energy gap was estimated to be approximately 3.4 GHz. The qubit's dephasing time was measured using Ramsey interference, yielding a value of approximately 20 ns, which is much shorter than the relaxation time of approximately 900 ns. Dephasing is likely caused by variations in the qubit's energy splitting due to external or internal noise. The qubit could not be operated at the symmetry point where