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انجمن اپتیک و فوتونیک ایران

Influence of temperature and magnetic field on the quantum speed limit in a coupled quantum dots system

Zahra Karimi, M. Bagheri Harouni

Published Mar 15, 2015• 0 citations
OpenAlex

Abstract

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.

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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.
Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated. The excess electron spin in each quantum dot constitutes the physical system (qubit). Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field. Taking into account the spin relaxation as a non-Markovian process, the quantum speed limit and entanglement evolution are discussed. Our findings reveal that increasing the magnetic field leads to the faster quantum evolution. In addition, the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.
Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated. The physical system studied is the excess electron spin in two adjacent quantum dots. The influences of magnetic field inhomogeneity as well as spin–orbit coupling are studied. Moreover, the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process. The spin–orbit interaction provides two important features: the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.
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
We study the quantum speed limit (QSL) time of the two-qubit XYZ spin chain model with the influence of intrinsic decoherence. We show that the intrinsic decoherence can suppress the evolution of this system, no matter what initial states the two qubits start from. The investigation of entanglement reveals that quantum correlation is the physical reason for the acceleration of the system. In addition, we also demonstrate that for different initial states, external magnetic field may have opposite influence on QSL time and it mainly derives from the inhibition of entanglement as magnetic field increases.
The lower bounds of the evolution time between two distinguishable states of a system, defined as quantum speed limit time, can characterize the maximal speed of quantum computers and communication channels. We study the quantum speed limit time between the composite quantum states and their target states in the presence of nondissipative decoherence. For the initial states with maximally mixed marginals, we obtain the exact expressions of the quantum speed limit time which mainly depend on the parameters of the initial states and the decoherence channels. Furthermore, by calculating the quantum speed limit time for the time-dependent states started from a class of initial states, we discover that the quantum speed limit time gradually decreases in time, and the decay rate of the quantum speed limit time would show a sudden change at a certain critical time. Interestingly, at the same critical time, the composite system dynamics would exhibit a sudden transition from classical decoherence to quantum decoherence.
Quantum theory sets a bound on the speed of quantum evolution. The shortest time needed for a quantm system to evolve from an initial state to the target state is known as the quantum speed limit time. The study of this time in open and closed quantum systems has been the subject of much work in quantum information theory. Quantum speed limit time is inversely related to the evolution rate of a quantum process. This relation is such that the speed of evolution decreases with increasing quantum speed limit time and vice versa. In this work we study the QSL time for the case in which a qubit interacts with a quantum critical environment. We choose the environment to be an Ising spin chain in a transverse field. It is observed that for the quantum speed limit time has a direct relation with quantum coherence of the initial state of the system. We will also study the effect of perturbation coupling on quantum speed limit time. It is observed that the quantum speed limit time decreases with increasing the coupling parameter. It is also observed that the quantum speed limit time decreases with increasing the number of spin in spin chain.