Efficient direct quantum state tomography using fan-out gates

Quantum State Tomography provides complete information about a quantum system but becomes impractical for large systems due to its exponential resource requirements. Direct measurement offers an efficient alternative by extracting wavefunction information without extensive post-processing. While early implementations relied on weak measurements, strong-measurement strategies have recently shown superior accuracy and scalability. In this work, we introduce Direct Quantum State Tomography (DQST), a strong-measurement protocol that reconstructs the full density matrix through a single-depth fanout coupling between a meter qubit and system qubits, followed by measurements in the X and Y basis. DQST requires only 2ⁿ⁺¹−1 circuits to reconstruct an n-qubit state, achieving a substantial reduction compared to conventional QST. Experiments on IBM quantum hardware demonstrate reconstruction of four-qubit states with fidelities above 97%. Moreover, DQST enables single-circuit estimation of GHZ-state fidelity, allowing direct verification of genuine multipartite entanglement for up to 20 qubits.