Efficient Circuit-Based Quantum State Tomography via Sparse Entry Optimization

Abstract: We propose an efficient circuit-based quantum state tomography (QST) scheme to reconstruct $n$-qubit states with $k$ nonzero entries using measurements of $|\psi\rangle$ and $U_1|\psi\rangle, \dots, U_{2m}|\psi\rangle$, where $m \le k$. Each $U_j$ involves CNOT gates followed by a single-qubit gate, either Hadamard $H$ or $HD$, where $D = {\rm diag}(1,i)$, targeting a specific qubit. We provide an upper limit on the number of CNOT gates based on the nonzero entries' positions in $|\psi\rangle$. This approach, applied to both state and process tomography, was tested using the Qiskit simulator.