arXiv subjects

Yahya Akbari-Kourbolagh

Publications and source records attributed to Yahya Akbari-Kourbolagh.

3 recordsLinked to original sources

arXiv2020

Quantum thermometry by single-qubit dephasing

We address the dephasing dynamics of a qubit as an effective process to estimate the temperature of its environment. Our scheme is inherently quantum, since it exploits the sensitivity of the qubit to decoherence, and does not require thermalization with the system under investigation. We optimize the quantum Fisher information with respect to the interaction time and the temperature in the case of Ohmic-like environments. We also find explicitly the qubit measurement achieving the quantum Cramer- Rao bound to precision. Our results show that the conditions for optimal estimation originate from a non-trivial interplay between the dephasing dynamics and the Ohmic structure of the environment. In general, optimal estimation is achieved neither when the qubit approaches the stationary state, nor for full dephasing.

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arXiv2017

Entanglement witnesses for families of the bound entangled three-qubit states

We construct three-qubit entanglement witnesses with relatively simple structures. Despite their simplicity, these witnesses are capable of detecting a number of bound entangled states more effectively. To illustrate this, two families of bound entangled three-qubit states, introduced by Kay [Phys. Rev. A 83, 020303 (2011)] and Kye [J. Phys. A: Math. Theor. 48, 235303 (2015)], are considered and it is shown that these witnesses are able to detect the entanglement of all states in the families.

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arXiv2015

On the entanglement of formation of two-mode Gaussian states: a compact form

We define an EPR-like uncertainty by using the Duan et al.'s inequality which gives a necessary and sufficient condition for the separability of any two-mode Gaussian state. We show that for a given amount of entanglement, the uncertainty is minimized by pure two-mode squeezed states. Using this fact, we write the optimal pure-state decomposition and derive a compact form for the entanglement of formation of two-mode Gaussian states. For illustration purposes, we consider symmetric and squeezed thermal states as special cases and evaluate their entanglement of formation explicitly. For the symmetric states, our result is in agreement with the Giedke et al.'s one. To our knowledge, our work is the first one which gives the exact entanglement of formation of two-mode squeezed thermal states explicitly.

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