Preparation of metrological states in dipolar-interacting spin systems

• Published in: npj quantum information Vol. 8; no. 1; pp. 150 - 7
• Main Authors: Zheng, Tian-Xing, Li, Anran, Rosen, Jude, Zhou, Sisi, Koppenhöfer, Martin, Ma, Ziqi, Chong, Frederic T., Clerk, Aashish A., Jiang, Liang, Maurer, Peter C.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.12.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/483/1255; 639/766/483/640; Algorithms; Classical and Quantum Gravitation; Normal distribution; Optimization techniques; Parameter estimation; Physics; Physics and Astronomy; Quantum Computing; Quantum Field Theories; Quantum Information Technology; Quantum Physics; Relativity Theory; Spintronics; String Theory
• ISSN: 2056-6387; 2056-6387
• DOI: 10.1038/s41534-022-00667-4

Spin systems are an attractive candidate for quantum-enhanced metrology. Here we develop a variational method to generate metrological states in small dipolar-interacting spin ensembles with limited qubit control. For both regular and disordered spatial spin configurations the generated states enable sensing beyond the standard quantum limit (SQL) and, for small spin numbers, approach the Heisenberg limit (HL). Depending on the circuit depth and the level of readout noise, the resulting states resemble Greenberger-Horne-Zeilinger (GHZ) states or Spin Squeezed States (SSS). Sensing beyond the SQL holds in the presence of finite spin polarization and a non-Markovian noise environment. The developed black-box optimization techniques for small spin numbers ( N  ≤ 10) are directly applicable to diamond-based nanoscale field sensing, where the sensor size limits N and conventional squeezing approaches fail.