High-fidelity, multi-qubit generalized measurements with dynamic circuits

Abstract

Generalized measurements, also called positive operator-valued measures (POVMs), can offer advantages over projective measurements in various quantum information tasks. Here, we realize a generalized measurement of one and two superconducting qubits with high fidelity and in a single experimental setting. To do so, we propose a hybrid method, the "Naimark-terminated binary tree," based on a hybridization of Naimark's dilation and binary tree techniques that leverages emerging hardware capabilities for mid-circuit measurements and feed-forward control. Furthermore, we showcase a highly effective use of approximate compiling to enhance POVM fidelity in noisy conditions. We argue that our hybrid method scales better toward larger system sizes than its constituent methods and demonstrate its advantage by performing detector tomography of symmetric, informationally complete POVM (SIC-POVM). Detector fidelity is further improved through a composite error mitigation strategy that incorporates twirling and a newly devised conditional readout error mitigation. Looking forward, we expect improvements in approximate compilation and hardware noise for dynamic circuits to enable generalized measurements of larger multi-qubit POVMs on superconducting qubits.

arXiv comment15 pages, 10 figures

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Cited by in corpus (6)

• Quasi-Probabilistic Readout Correction of Mid-Circuit Measurements for Adaptive Feedback via Measurement Randomized Compiling
• Symmetry verification for noisy quantum simulations of non-Abelian lattice gauge theories
• Readout Error Mitigation for Mid-Circuit Measurements and Feedforward
• Unambiguous discrimination of general quantum operations
• Error-Tolerant Quantum State Discrimination: Optimization and Quantum Circuit Synthesis
• Feedforward suppression of readout-induced faults in quantum error correction