arXiv subjects

Bahram Ahansaz

Publications and source records attributed to Bahram Ahansaz.

11 recordsLinked to original sources

arXiv2023

Selective weak measurement reveals super ergotropy

The concept of ergotropy was previously introduced as the maximum extractable work from a quantum state. Its enhancement, which is induced by quantum correlation via projective measurement, was formulated as the daemonic ergotropy. In this work, we investigate the ergotropy in the presence of quantum correlation via weak measurement because of its elegant effects on the measured system. By considering a bipartite correlated quantum system consisting of main and ancillary systems, we demonstrate that the extractable work by the non-selective weak measurement on the ancilla is always equal to the situation captured by the strong measurement. However, the selective weak measurement interestingly reveals more work than the daemonic ergotropy and the ergotropy of the total system is greater than or equal to the daemonic ergotropy. Moreover, it is shown that for Bell diagonal states, at the cost of losing quantum correlation, the total extractable and thus non-local extractable works can be increased by using measurement. Also, we find that there is no direct relationship between quantum correlation and non-local extractable work for these cases.

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arXiv2021

Quantum Steering Ellipsoid and Unruh Effect

Quantum steering is a perplexing feature at the heart of quantum mechanics that provides profound implications in understanding the nature of physical reality. On the other hand, the effect of relativistic features on quantum systems is vital in understanding the underlying foundations of physics. In this work, we study the effects of Unruh acceleration on the quantum steering of a two-qubit system. In particular, we consider the so-called quantum steering ellipsoid and the maximally-steered coherence in a non-inertial frame and find closed-form analytic expressions for the role of the Unruh acceleration in these quantities. Analyzing the conditions for the steerability of the system, we develop a geometric description for the effect of Unruh acceleration on the quantum steering of a two-qubit system.

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arXiv2020

Maximal Steered Coherence Protection by Quantum Reservoir Engineering

We show that the effects of decoherence on quantum steering ellipsoids can be controlled by a specific reservoir manipulating, in both Markovian and non-Markovian realms. Therefore, the so-called maximal steered coherence could be protected through reservoir engineering implemented by coupling auxiliary qubits to the reservoir.

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arXiv2019

Quantum speedup, non-Markovianity and formation of bound state

In this paper, we investigate the relationship between the quantum speedup, nonMarkovianity and formation of a system-environment bound state. Previous results show a monotonic relation between these three such that providing stronger bound states can lead to a higher degree of non-Markovianity, and hence to greater speed of quantum evolution. By studying dynamics of a dissipative two-level system or a V-type three-level system in the presence of similar and additional systems, we reveal that the quantum speedup is exclusively related to the formation of the system-environment bound state, while the non-Markovian effect of the system dynamics is neither necessary nor sufficient to speed up the quantum evolution. In the other hand, it is demonstrated that only the formation of the system-environment bound state plays a decisive role in the acceleration of the quantum evolution.

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arXiv2018

Protection of entanglement for a two-qutrit V-type open system on the basis of system-reservoir bound states

In this work, a mechanism for long time protection of entanglement of a two-qutrit V-type atomic system each of which interacts independently with a dissipative reservoir is investigated. It is shown that the protection process is related exclusively on the formation of bound states in the system-reservoir energy spectrum. It is demonstrated that the degree of boundedness for the system-reservoir bound states is well-controlled by entering other V-type qutrits into the reservoirs, and also through the manipulation of the spontaneously generated interference related to decay channels of the V-type atoms.

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arXiv2018

Effects of oscillatory deformations on the coherent and incoherent quantum transport

Inspired by the works of [F. Caruso, New J. Phys. 16, 055015 (2014)] and [T. Scholak et al, J. Phys. B: At. Mol. Opt. Phys. 44 184012 (2011)], which state that for a large class of complex noisy networks, the optimal efficiency of quantum transport is universally obtained by mixing coherent (Hamiltonian) and incoherent (noisy) parts where the contribution of the coherent part is strictly more than incoherent one, we examine the effect of oscillatory deformations on two simple prototypes in order to study their effects on the efficiency of coherent and incoherent energy transport. The prototypes are interchangeable to each other only by a simple phase modulation, such that the dynamics for the first type is only coherent, while for the second one the coherent evolution is completely suppressed and the evolution of the system is only incoherent (noisy). In this regard, it is shown that there exist a special deformation by which the efficiency of incoherent transport becomes better than the coherent one. This result suggests that in the noisy networks with collective harmonic motions, the optimality of transport can be occurred in such a way that the contribution of incoherent term is more than the coherent one.

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arXiv2018

Enhancement of quantum transport efficiency in a noisy spin channel

In this paper, based on the notion of pseudomode framework introduced by Garraway in [Phys. Rev. A 55, 2290 (1997)], we propose a mechanism for enhancing the efficiency of excitation energy transport in a spin channel which is in contact with a Lorentzian reservoir, through the inclusion of other similar auxiliary spin chains into the reservoir. To this aim, a Lindblad-type master equation for the dynamics of the transport process is provided on the basis of pseudomode approach. It is figured out that increasing the number of auxiliary chains in the reservoir enhances the efficiency of transport or equivalently, rises the population of the reaction center attached to the end of the channel. Moreover, it is interesting to note that the mechanism has better efficiency for the channels with longer lengths.

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arXiv2017

Well-protected quantum state transfer in a dissipative spin chain

In this work, a mechanism for improving the quantum state transfer efficiency in a spin chain, which is in contact with a dissipative structured reservoir, is investigated. The efficiency of the method is based on the addition of similar non-interacting auxiliary chains into the reservoir. In this regard, we obtain the exact solution for the master equation of the spin chain in the presence of dissipation. It is found out that entering more auxiliary chains into the reservoir causes, in general, the better improvement of the fidelity of state transfer along the mentioned chain. Furthermore, it is reveal that the protocol has better efficiency for a chain with longer length. Therefore, by this method, quantum state transfer along a linear chain with an arbitrary number of qubits, can be well-protected against the dissipative noises.

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arXiv2017

Quantum coherence and entanglement preservation in Markovian and non-Markovian dynamics via additional qubits

In this paper, we investigate preservation of quantum coherence of a single-qubit interacting with a zero-temperature thermal reservoir through the addition of noninteracting qubits in the reservoir. Moreover, we extend this scheme to preserve quantum entanglement between two and three distant qubits, each of which interacts with a dissipative reservoir independently. At the long time limit, we obtained analytical expressions for the coherence measure and the concurrence of two and three qubits in terms of the number of additional qubits. It is observed that, by increasing the number of additional qubits in each reservoir, the initial coherence and the respective entanglements are completely protected in both Markovian and non-Markovian regimes. Interestingly, the protection of entanglements occurs even under the individually different behaviors of the reservoirs.

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arXiv2016

Enhancing quantum state transfer efficiency in binary-tree spin networks by partially collapsing measurements

In this work, quantum state transfer (QST) over binary-tree spin networks is studied by using advantages of partially collapsing measurements. To this aim, we perform initially a weak measurement (WM) on central qubit of the binary-tree network, which encoding the state of concern and after time evolution of the whole system, a quantum measurement reversal (QMR) on the destined qubit is performed. By taking the optimal value of the QMR, it is shown that the QST can be improved considerably by controlling the WM strength and by choosing it close enough to 1, near-perfect QST can be achieved. We also show that how entanglement distribution quality over the binary-tree spin network can be obviously improved by using this approach.

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arXiv2015

Dephasing-assisted selective incoherent quantum transport

Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photo-systems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate a situation that in the absence of dephasing noises the coherent evolution of the system has no role in the energy transport in the network. Therefore, incoherent evolution via application of dephasing noises throughout a selected path of the network leads to transfer the excitation completely to a desired reaction center.

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