Quantum speed limit time in a magnetic resonance

Patrice Bertet

Diego Paiva Pires, Eduardo Ribeiro DeAzevedo, Diogo O. Soares-Pinto +2 more

Abstract 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.

Niaz Ali Khan, Munsif Jan, Muzamil Shah +1 more

Soroush Haseli, Hazhir Dolatkhah, S. Salimi

Quantum theory sets a limit on the minimum time required to transform from an initial state to a target state. It is known as quantum speed limit time. quantum speed limit time can be used to determine the rate of quantum evolution for closed and open quantum systems. Given that in the real world we are dealing with open quantum systems, the study of quantum speed limit time for such systems has particular importance. In this work we consider the topological qubit realized by two Majorana modes. We consider the case in which the topological qubit is influenced by fermionic and bosonic environment. Fermionic and bosonic environments are assumed to have Ohmic-like spectral density. The quantum speed limit time is investigated for various environment with different Ohmic parameter. It is observed that for super-Ohmic environment with increasing Ohmic parameter the quantum speed limit time gradually reaches to a constant value and thus the speed of evolution reaches to a uniform value. The effects of external magnetic field on the evolution rate are also studied. It is observed that with increasing magnitude of magnetic field, the quantum speed limit time decreases

Zahra Karimi, M. Bagheri Harouni

In the present contribution, the quantum speed limit time, as a useful parameter for investigating the quantum decoherence, is studied. The influence of temperature and magnetic field on the quantum speed limit and coherence in a coupled quantum dot system is investigated. Our finding reveals that temperature decreasing will lead to quantum speed limit decrement and consequently the decoherence rate increment. In contrast to the temperature, the magnetic field impact does not follow a same scenario, whereas the role of magnetic field depends on the initial state. Depending on the initial state, the magnetic field may possess a destructive or constructive role on the quantum speed limit or the decoherence rate.

V.A. Dzhrbashyan