Dr Ali Raza Mirza


Postdoctoral Research Fellow in Open Quantum Systems
PhD in Theoretical Physics

Academic and research departments

School of Mathematics and Physics.

About

Research

Research interests

Research projects

Publications

Ali Raza Mirza, Muhammad Zia, and Adam Zaman Chaudhry (2021) Master equation incorporating the system-environment correlations present in the joint equilibrium state

We present a general master equation, correct to second order in the system-environment coupling strength, that takes into account the initial system-environment correlations. We assume that the system and its environment are in a joint thermal equilibrium state, and thereafter, a unitary operation is performed to prepare the desired initial system state, with the system Hamiltonian possibly changing thereafter as well. We show that the effect of the initial correlations shows up in the second-order master equation as an additional term, similar in form to the usual second-order term describing relaxation and decoherence in quantum systems. We apply this master equation to a generalization of the paradigmatic spin-boson model, namely, a collection of two-level systems interacting with a common environment of harmonic oscillators, as well as a collection of two-level systems interacting with a common spin environment. We demonstrate that, in general, the initial system-environment correlations need to be accounted for in order to accurately obtain the system dynamics.

Ali Raza Mirza, Mah Noor Jamil, Adam Zaman Chaudhry (2023) The role of initial system-environment correlations with a spin environment

Open quantum systems are a subject of immense interest as their understanding is crucial in the implementation of modern quantum technologies. In the study of their dynamics, the role of the initial system-environment correlations is commonly ignored. In this work, to gain insights into the role of these correlations, we solve an exactly solvable model of a single two-level system interacting with a spin environment, with the initial system state prepared by a suitable unitary operation. By solving the dynamics exactly for arbitrary system-environment coupling strength while taking into account the initial system-environment correlations, we show that the effect of the initial correlations is, in general, very significant and non-trivial. To further highlight the importance of the initial system-environment correlations, we also extend our study to investigate the dynamics of the entanglement between two two-level systems interacting with a common spin environment

Ali Raza Mirza, Adam Zaman Chaudhry (2023) Improving the estimation of the environment parameters via a two-qubit scheme

We demonstrate how using two qubits can drastically improve the estimation of environment parameters as compared to using only a single qubit. The two qubits are coupled to a common harmonic oscillator environment, and the properties of the environment are imprinted upon the dynamics of the two qubits. The reduced density matrix of only one of these qubits contains a decoherence factor as well as an additional factor taking into account the indirect interaction induced between the qubits due to the interaction with their common environment. This additional factor can drastically improve the estimation of the environment parameters, as quantified by the quantum Fisher information. In particular, we investigate the estimation of the cutoff frequency, the coupling strength, and the temperature using our two-qubit scheme as compared to simply using a single qubit. For super-Ohmic environments in particular, one can improve the precision of the estimates by orders of magnitude.