arXiv subjects

Utkarsh Mishra

Publications and source records attributed to Utkarsh Mishra.

26 records · Page 2Linked to original sources

arXiv2016

Constructive Interference Between Disordered Couplings Enhances Multiparty Entanglement in Quantum Heisenberg Spin Glass Models

Disordered systems form one of the centrestages of research in many body sciences and lead to a plethora of interesting phenomena and applications. A paradigmatic disordered system consists of an one-dimensional array of quantum spin-1/2 particles, governed by the Heisenberg spin glass Hamiltonian with natural or engineered quenched disordered couplings in an external magnetic field. These systems allow disorder-induced enhancement for bipartite and multipartite observables. Here we show that simultaneous application of independent quenched disorders results in disorder-induced enhancement, while the same is absent with individual application of the same disorders. We term the phenomenon as constructive interference and the corresponding parameter stretches as the Venus regions. Interestingly, it has only been observed for multiparty entanglement and is absent for the single- and two-party physical quantities.

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arXiv2015

Survival of time-evolved correlations depends on whether quenching is across critical point in XY spin chain

The time-dynamics of quantum correlations in the quantum transverse anisotropic XY spin chain of infinite length is studied at zero as well as finite temperatures. The evolution occurs due to the instantaneous quenching of the coupling constant between the nearest-neighbor spins of the model, which is either performed within the same phase or across the quantum phase transition point connecting the order-disorder phases of the model. We characterize the time-evolved quantum correlations, entanglement and quantum discord, which exhibit varying behavior depending on the initial state and the quenching scheme. We show that the system is endowed with enhanced bipartite quantum correlations compared to that of the initial state, when quenched from ordered to the deep disordered phase. However, bipartite quantum correlations are almost washed out when the system is quenched from disordered to the ordered phase with the initial state being at the zero-temperature. Moreover, we identify the condition for the occurrence of enhanced bipartite correlations when the system is quenched within the same phase. Finally, we investigate the bipartite quantum correlations when the initial state is a thermal equilibrium state with finite temperature which reveals the effects of thermal fluctuation on the phenomena observed at zero-temperature.

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arXiv2015

Time dynamics of multiparty quantum correlations indicate energy transfer route in light-harvesting complexes

The time-evolution of multiparty quantum correlations as quantified by monogamy scores and bipartition collections of quantum correlations is investigated for light-harvesting complexes modeled by the fully connected and the Fenna-Mathews-Olson (FMO) networks. The dynamics consists of a coherent term as well as dissipative, dephasing, and sink operator terms. The multiparty quantum correlation reveals important information regarding the sharability of quantum correlations in the networks, which allow us to categorize the network sites into three distinct groups in the FMO complex and to predict the structural geometry of the complex. In particular, we show that the relative values of the ingredients of multiparty quantum correlation measures in the time dynamics clearly indicate the primary route of energy transfer from the antenna to the bacterial reaction center in the FMO complex.

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arXiv2014

Benford's law gives better scale exponents in phase transitions of quantum XY models

Benford's law is an empirical law predicting the distribution of the first significant digits of numbers obtained from natural phenomena and mathematical tables. It has been found to be applicable for numbers coming from a plethora of sources, varying from seismographic, biological, financial, to astronomical. We apply this law to analyze the data obtained from physical many-body systems described by the one-dimensional anisotropic quantum XY models in a transverse magnetic field. We detect the zero-temperature quantum phase transition and find that our method gives better finite-size scaling exponents for the critical point than many other known scaling exponents using measurable quantities like magnetization, entanglement, and quantum discord. We extend our analysis to the same system but at finite temperature and find that it also detects the finite temperature phase transition in the model. Moreover, we compare the Benford distribution analysis with the same obtained from the uniform and Poisson distributions. The analysis is furthermore important in that the high-precision detection of the cooperative physical phenomena is possible even from low-precision experimental data.

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arXiv2014

Enhancing robustness of multiparty quantum correlations using weak measurement

Multipartite quantum correlations are important resources for the development of quantum information and computation protocols. However, the resourcefulness of multipartite quantum correlations in practical settings is limited by its fragility under decoherence due to environmental interactions. Though there exist protocols to protect bipartite entanglement under decoherence, the implementation of such protocols for multipartite quantum correlations has not been sufficiently explored. Here, we study the effect of local amplitude damping channel on the generalized Greenberger-Horne-Zeilinger state, and use a protocol of optimal reversal quantum weak measurement to protect the multipartite quantum correlations. We observe that the weak measurement reversal protocol enhances the robustness of multipartite quantum correlations. Further it increases the critical damping value that corresponds to entanglement sudden death. To emphasize the efficacy of the technique in protection of multipartite quantum correlation, we investigate two proximately related quantum communication tasks, namely, quantum teleportation in a one sender, many receivers setting and multiparty quantum information splitting, through a local amplitude damping channel. We observe an increase in the average fidelity of both the quantum communication tasks under the weak measurement reversal protocol. The method may prove beneficial, for combating external interactions, in other quantum information tasks using multipartite resources.

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arXiv2014

Local Decoherence-free Macroscopic Quantum states

We identify a class of quantum states, each consisting of a microscopic and a macroscopic section, that are effectively decoherence-free when each particle is locally passed through a quantum channel. In particular, and in contrast to other macroscopic quantum states like the Greenberger-Horne-Zeilinger state, the content of entanglement and other quantum correlations in the microscopic to macroscopic partition of this class of states is independent of the number of particles in their macroscopic sectors, when all the particles suffer passage through local amplitude and phase damping channels. Decay of quantum correlations -- entanglement as well as quantum discord -- of this class of states in the microscopic to macroscopic partition is also much lower in the case of all the local quantum channels, as compared to the other macroscopic superposition states. The macroscopic sections of the states are formed, in each case, by using a Dicke state and an orthogonal product state, which are macroscopically distinct in terms of markedly different amounts of violation of Bell inequality.

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arXiv2013

Tuning interaction strength leads to ergodic-nonergodic transition of quantum correlations in anisotropic Heisenberg spin model

We investigate the time dynamics of quantum correlations of the anisotropic Heisenberg model in a time-dependent magnetic field, in one-dimensional, ladder, and two-dimensional lattices. We find that quantum correlation measures in the entanglement-separability paradigm are ergodic in these systems irrespective of system parameters. However, information-theoretic quantum correlation measures can also be nonergodic, and exhibit a transition from nonergodic to ergodic behavior with the change of interaction strength in the direction of the magnetic field. We also observe that the transition point changes drastically as we go from one-dimensional and ladder lattices to the two-dimensional one.

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arXiv2012

Macroscopic Schrödinger Cat Resistant to Particle Loss and Local Decoherence

The Schrödinger cat state plays a crucial role in quantum theory, and has important fundamental as well as technological implications, ranging from quantum measurement theory to quantum computers. The power of the potential implications of the cat state lies in the quantum coherence, as measured by the degree of entanglement, between its microscopic and macroscopic sectors. We show that in contrast to other cat states, it is possible to choose the states of the macroscopic sector in a way that the resulting cat state, which we term as the W-cat state, has quantum coherence that is resistant to the twin effects of environmental noise -- local decoherence on all the particles and loss of a finite fraction of its particles. The states of the macroscopic sector of the W-cat state are macroscopically distinct in terms of their violation of Bell inequality.

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