Experimental investigation of geometric quantum speed limits in an open quantum system

• Published in: Communications physics Vol. 7; no. 1; pp. 142 - 8
• Main Authors: Pires, Diego Paiva, deAzevedo, Eduardo R., Soares-Pinto, Diogo O., Brito, Frederico, Filgueiras, Jefferson G.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02.05.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/483/1255; 639/766/483/481; Chloroform; Evolution; Fisher information; Lower bounds; NMR; Nuclear magnetic resonance; Open systems; Physics; Physics and Astronomy; Quantum theory; Qubits (quantum computing); Speed limits; System dynamics; Tightness
• ISSN: 2399-3650; 2399-3650
• DOI: 10.1038/s42005-024-01634-5

The quantum speed limit (QSL) is a fundamental lower bound on the evolution time for quantum systems, and its tightness has been observed to be dependent on the properties of the physical process. However, experimental studies exploring the QSL in open quantum systems are still missing. Here, we studied geometric quantum speed limits of a qubit subject to decoherence in an ensemble of chloroform molecules in a Nuclear Magnetic Resonance experiment. We controlled the system-reservoir interaction and the spin relaxation rates by adding a paramagnetic salt, allowing the observation of both Markovian and non-Markovian open system dynamics for the qubit. We used two distinguishability measures of quantum states to assess the speed of the qubit evolution: the quantum Fisher information (QFI) and Wigner-Yanase skew information (WY). For non-Markovianity and low salt concentrations, we found crossovers between QSLs related to those metrics. The WY metric sets the tighter QSL for high concentrations and Markovian dynamics. We also show that QSLs are sensitive even to small fluctuations in spin magnetization. Quantum Speed Limit (QSL) is a lower bound on the time evolution for quantum systems. Still, experimental studies for open systems are few due to the lack of control over their environment’s interaction. The authors control the qubitreservoir interaction in an ensemble of chloroform molecules, observing crossovers between different QSLs.