Southwest Quantum Information and Technology

State Preparation Fidelities for Dicke States

Presenting Author: Shamminuj Aktar, New Mexico State University
Contributing Author(s): Andreas Bärtschi, Abdel-Hameed A. Badawy, Stephan Eidenbenz

Estimating the fidelity of highly entangled states on NISQ devices is an important benchmarking task. We present a divide-and-conquer approach to deterministically prepare Dicke states (equal-weight superpositions of all n-qubit states with Hamming Weight k) and measure their experimental state preparation fidelity on superconducting devices with LNN and ion-trap devices with all-to-all connectivity: (i) We design linear-depth Dicke state preparation circuits which first divide the Hamming weight between blocks of n/2 qubits, and then conquer those blocks with improved versions of Dicke state unitaries [arXiv:1904.07358], including versions for both LNN and all-to-all connectivity. (ii) Experimental evaluation up to n=6 on IBMQ Sydney and Montreal devices using 3^n state tomography settings gives significantly higher state fidelity compared to previous results [arXiv:2007.01681,1807.05572], due to more efficient circuits, measurement error mitigation, and hardware improvement. (iii) Further, we use techniques to give lower bounds for state preparation fidelities using only 3 measurement settings [arXiv:quant-ph/0606023]. These bounds have so far not been tight enough to provide reasonable estimations for larger states on NISQ devices, including (ii). 15 years after the technique's introduction, we report meaningful lower bounds for the state preparation fidelity of all Dicke States up to n=10 on the Quantinuum H1 system. (ii): arXiv:2112.12435 (iii): work in progress

Read this article online: https://ieeexplore.ieee.org/document/9774323

(Session 9a : Friday from 5:45 pm - 6:15 pm)