arXiv subjects

Mohsen Sarbishaei

Publications and source records attributed to Mohsen Sarbishaei.

14 recordsLinked to original sources

arXiv2026

Hardy and Cabello Arguments in Spatial and Temporal Frauchiger-Renner Scenarios

We investigate Hardy- and Cabello-type logical structures within spatial and temporal extensions of the Frauchiger--Renner (FR) framework, embedding these constructions directly into the FR multi-observer architecture. In the spatial multi-observer scenario, both Hardy and Cabello contradictions arise, with the Cabello construction yielding the stronger violation,$$Δ_{\rm Cabello}^{\max}=0.1078$$, which exceeds the maximal Hardy probability $$P_{H}^{\max}=\frac{5\sqrt{5}-11}{2}\approx 0.09017$$. We then develop a sequential temporal FR protocol based on coherent multi-observer measurements performed on a single spin-$\tfrac12$ system. In this temporal setting, the Hardy contradiction disappears identically due to dynamical constraints imposed by sequential state updates, whereas a finite Cabello-type violation survives, $Δ_{\rm Cabello}^{\max}\approx 0.0674$. Our results establish a fundamental structural distinction between spatial entanglement and temporal multi-observer correlations in FR-type logical scenarios, and demonstrate that certain observer-independent description failures persist even without spacelike separation.

quant-ph↗

arXiv2023

Quantum theory can consistently describe the use of itself in Frauchiger-Renner's Gedankenexperiment

Theoretical physics has faced many challenges since the advent of quantum mechanics. Recently, Frauchiger and Renner have presented a no-go theorem, which makes quantum mechanics more controversial. However, from our perspective, the process of proving appears questionable. Therefore, we discuss the validity of their proof approach in this letter. Here, we propose a simple thought experiment that clarifies how correctly the attributed quantum state can be written in problems similar to Frauchiger and Renner's Gedankenexperiment. In the next step, with the help of the correct form of the quantum state, it is demonstrated that a fallacy occurred in the proof of the no-go theorem, which means it cannot be valid because of the wrong proof. Ultimately, getting help from Hardy's paradox, we investigate whether there is an approach to modify their proof in order to lend the no-go theorem validity.

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arXiv2021

Mutually unbiased measurements with arbitrary purity

Mutually unbiased measurements are a generalization of mutually unbiased bases in which the measurement operators need not to be rank one projectors. In a $d$-dimension space, the purity of measurement elements ranges from $1/d$ for the measurement operators corresponding to maximally mixed states to $1$ for the rank one projectors. In this contribution, we provide a class of MUM that encompasses the full range of purity. Similar to the MUB in which the operators corresponding to different outcomes of the same measurement commute mutually, our class of MUM possesses this sense of compatibility within each measurement. This makes the provided class more similar to the MUB, so that the main difference between them and MUB is due to the purity of the measurement operators. The spectra of these MUMs provides a way to construct a class of $d$-dimensional orthogonal matrices which leave the vector of equal components invariant. Based on this property, and by using the MUM-based entanglement witnesses, we investigate the role of purity to detect entanglement of bipartite states.

quant-ph↗

arXiv2018

Parametrization of quantum states and the quantum state discrimination problem

A discrimination problem consists of $N$ linearly independent pure quantum states $Φ=\{\ket{ϕ_i}\}$ and the corresponding occurrence probabilities $η=\{η_i\}$. To any such problem we associate, up to a permutation over the probabilities $\{η_i\}$, a unique pair of density matrices $\boldsymbol{ρ_{_{T}}}$ and $\boldsymbol{η_{p}}$ defined on the $N$-dimensional Hilbert space $\mathcal{H}_N$. The first one, $\boldsymbol{ρ_{_{T}}}$, provides a new parametrization of a generic full-rank density matrix in terms of the parameters of the discrimination problem, i.e. the mutual overlaps $γ_{ij}=\bra{ϕ_i}ϕ_j\rangle$ and the occurrence probabilities $\{η_i\}$. The second one is defined as a diagonal density matrix $\boldsymbol{η_p}$ with the diagonal entries given by the probabilities $\{η_i\}$ with the ordering induced by the permutation $p$ of the probabilities. $\boldsymbol{ρ_{_{T}}}$ and $\boldsymbol{η_{p}}$ capture information about the quantum and classical versions of the discrimination problem, respectively. In this sense, when the set $Φ$ can be discriminated unambiguously with probability one, i.e. when the states to be discriminated are mutually orthogonal and can be distinguished by a classical observer, then $\boldsymbol{ρ_{_{T}}}\rightarrow \boldsymbol{η_{p}}$. Moreover, if the set lacks its independency and cannot be discriminated anymore the distinguishability of the pair, measured by the fidelity $F(\boldsymbol{ρ_{_{T}}}, \boldsymbol{η_{p}})$, becomes minimum. This enables one to associate to each discrimination problem a measure of discriminability defined by the fidelity $F(\boldsymbol{ρ_{_{T}}}, \boldsymbol{η_{p}})$. This quantity, has the advantage of being easy to calculate and in this respect it can find useful applications in estimating the extent to which the set is discriminable.

quant-ph↗

arXiv2017

Reexamination of strong subadditivity: A quantum-correlation approach

The strong subadditivity inequality of von Neumann entropy relates the entropy of subsystems of a tripartite state $ρ_{ABC}$ to that of the composite system. Here, we define $\boldsymbol{T}^{(a)}(ρ_{ABC})$ as the extent to which $ρ_{ABC}$ fails to satisfy the strong subadditivity inequality $S(ρ_{B})+S(ρ_{C}) \le S(ρ_{AB})+S(ρ_{AC})$ with equality and investigate its properties. In particular, by introducing auxiliary subsystem $E$, we consider any purification $|ψ_{ABCE}\rangle$ of $ρ_{ABC}$ and formulate $\boldsymbol{T}^{(a)}(ρ_{ABC})$ as the extent to which the bipartite quantum correlations of $ρ_{AB}$ and $ρ_{AC}$, measured by entanglement of formation and quantum discord, change under the transformation $B\rightarrow BE$ and $C\rightarrow CE$. Invariance of quantum correlations of $ρ_{AB}$ and $ρ_{AC}$ under such transformation is shown to be a necessary and sufficient condition for vanishing $\boldsymbol{T}^{(a)}(ρ_{ABC})$. Our approach allows one to characterize, intuitively, the structure of states for which the strong subadditivity is saturated. Moreover, along with providing a conservation law for quantum correlations of states for which the strong subadditivity inequality is satisfied with equality, we find that such states coincides with those that the Koashi-Winter monogamy relation is saturated.

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arXiv2016

Comparison of quantum discord and fully entangled fraction of two classes of $d\otimes d^2$ states

The quantumness of a generic state is the resource of many applications in quantum information theory and it is interesting to survey the measures which are able to detect its trace in the properties of the state. In this work we study the quantum discord and fully entangled fraction of two classes of bipartite states and compare their behaviors. These classes are complements to the $d\otimes d$ Werner and isotropic states, in the sense that each class possesses the same purification as the corresponding complemental class of states. Our results show that maximally entangled mixed states are also maximally discordant states, leading to a generalization of the well-known fact that all maximally entangled pure states have also maximum quantum discord. Moreover, it is shown that the separability-entanglement boundary of a Werner or isotropic state is manifested as an inflection point in the diagram of quantum discord of the corresponding complemental state.

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arXiv2016

Revealing quantum correlation by negativity of the Wigner function

We analyze two two-mode continuous variable separable states with the same marginal states. We adopt the definition of classicality in the form of well-defined positive Wigner function describing the state and find that although the states possess positive local Wigner functions, they exhibit negative Wigner functions for the global states. Using the negativity of Wigner function as an indicator of nonclassicality, we show that despite these states possess different negativities of the Wigner function, they do not reveal this difference as phase space nonclassicalities such as negativity of the Mandel $Q$ parameter or quadrature squeezing. We then concentrate on quantum correlation of these states and show that quantum discord and local quantum uncertainty, as two well-defined measures of quantum correlation, manifest the difference between negativity of the Wigner functions. The non-Gaussianity of these states is also examined and show that the difference in behavior of their non-Gaussianity is the same as the difference between negativity of their Wigner functions. We also investigate the influence of correlation rank criterion and find that when the states can be produced locally from classical states, the Wigner functions can not reveal their quantum correlations.

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arXiv2015

Computable Measure of Total Quantum Correlation of Multipartite Systems

Quantum discord as a measure of the quantum correlations cannot be easily computed for most of density operators. In this paper, we present a measure of the total quantum correlations that is operationally simple and can be computed effectively for an arbitrary mixed state of a multipartite system. The measure is based on the coherence vector of the party whose quantumness is investigated as well as the correlation matrix of this part with the remainder of the system. Being able to detect the quantumness of multipartite systems, such as detecting the quantum critical points in spin chains, alongside with the computability characteristic of the measure, make it a useful indicator to be exploited in the cases which are out of the scope of the other known measures.

quant-ph↗

arXiv2014

Stable solitary waves in Super dense plasmas at external magnetic fields

Propagation of localized waves in a Fermi-Dirac distributed super dense matter at the presence of strong external magnetic fields is studied using the reductive perturbation method. Previous works indicate that localized waves break down in unmagnetized super dense hadronic matter. We have shown that stable solitons can be created in such non-relativistic fluids in the presence of an external magnetic field. Such solitary waves are governed by the Zakharov-Kuznetsov (ZK) equation. Properties of solitonic solutions are studied in media with different values of back ground mass density and strength of magnetic field.

astro-ph.HE↗

arXiv2013

Interaction of double sine-Gordon solitons with external potentials: an analytical model

Interaction of Double sine-Gordon solitons with a space dependent potential wall and also a potential well has been investigated by employing an analytical model based on the collective coordinate approach. The potential has been added to the model through a suitable nontrivial metric for the background space-time. The model is able to predict most of the features of the soliton-potential interaction. It is shown that a soliton can pass through a potential barrier if its velocity is greater than a critical velocity which is a function of soliton initial conditions and also characters of the potential. It is interesting that the solitons of the double sine-Gordon model can be trapped by a potential barrier and oscillate there. This situation is very important in applied physics. Soliton-well system has been investigated using the presented model too. Analytical results also have been compared with the results of the direct numerical solutions.

hep-th↗

arXiv2011

Measurement-induced nonlocality for an arbitrary bipartite state

Measurement-induced nonlocality is a measure of nonlocalty introduced by Luo and Fu [Phys. Rev. Lett \textbf{106}, 120401 (2011)]. In this paper, we study the problem of evaluation of Measurement-induced nonlocality (MIN) for an arbitrary $m\times n$ dimensional bipartite density matrix $ρ$ for the case where one of its reduced density matrix, $ρ^{a}$, is degenerate (the nondegenerate case was explained in the preceding reference). Suppose that, in general, $ρ^{a}$ has $d$ degenerate subspaces with dimension $m_{i} (m_{i} \leq m, i=1, 2, ..., d)$. We show that according to the degeneracy of $ρ^{a}$, if we expand $ρ$ in a suitable basis, the evaluation of MIN for an $m\times n$ dimensional state $ρ$, is degraded to finding the MIN in the $m_{i}\times n$ dimensional subspaces of state $ρ$. This method can reduce the calculations in the evaluation of MIN. Moreover, for an arbitrary $m\times n$ state $ρ$ for which $m_{i}\leq 2$, our method leads to the exact value of the MIN. Also, we obtain an upper bound for MIN which can improve the ones introduced in the above mentioned reference. In the final, we explain the evaluation of MIN for $3\times n$ dimensional states in details.

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arXiv2011

Measurable lower bounds on concurrence

We derive measurable lower bounds on concurrence of arbitrary mixed states, for both bipartite and multipartite cases. First, we construct measurable lower bonds on the purely algebraic bounds of concurrence [F. Mintert et al. (2004), Phys. Rev. lett., 92, 167902]. Then, using the fact that the sum of the square of the algebraic bounds is a lower bound of the squared concurrence, we sum over our measurable bounds to achieve a measurable lower bound on concurrence. With two typical examples, we show that our method can detect more entangled states and also can give sharper lower bonds than the similar ones.

quant-ph↗

arXiv2010

Factorization Law for Two Lower Bounds of Concurrence

We study the dynamics of two lower bounds of concurrence in bipartite quantum systems when one party goes through an arbitrary channel. We show that these lower bounds obey the factorization law similar to that of [Konrad et al., Nat. Phys. 4, 99 (2008)]. We also, discuss the application of this property, in an example.

quant-ph↗

arXiv2008

Thermal entanglement in a two-qutrit system with nonlinear coupling under nonuniform external magnetic field

We study the thermal entanglement of a 2-qutrit spin chain with nonlinear coupling in the presence of nonuniform magnetic field. Thermal entanglement of an arbitrary (finite dimensional) m-partite system vanishes at some finite threshold temperature T_s. We investigate the dependence of T_s on the system's parameters, i.e. the nonlinear coupling and the magnetic field, for this 2-qutrit system. In addition, we compare two lower bounds of I-concurrence for this system and also study its dense coding capacity as a function of system's parameters.

quant-ph↗