arXiv subjects

Sovik Roy

Publications and source records attributed to Sovik Roy.

At least 19 recordsLinked to original sources

arXiv2026

Near perfect noisy quantum teleportation by one-sided environment engineering

Achieving near-unity fidelity of Quantum Teleportation (QT) in a noisy environment is an essential requirement for its real-world applications. Towards this goal, we devise a distinctive protocol based on the timing of the sender Alice's Bell-basis measurement, synchronous with the suitably engineered structure of noise in the receiver Bob's wing, without requiring any knowledge or manipulation of Alice's local noise. For this purpose, to finally obtain the teleported states by performing the required unitary operations, Bob has to retain his qubits for only two particular Bell-basis outcomes communicated by Alice, whose corresponding reduced states have no dependence on the noise parameters in Alice's wing. Such postselection is crucial for enhancing the fidelity of the teleported state towards its ideal limit, while ensuring its full independence of Alice's noise. We formulate the specifics of our protocol in terms of a generic two-level quantum system, subjected to a general non-Markovian spin-boson model for dephasing noise. The proposed scheme is illustrated by using any pure maximally/non-maximally entangled state as well as a Werner-type mixed state as resource. In particular, using resource states having small values of entanglement measure, we show that the high fidelity of QT is achievable in the presence of noise. Further, using our scheme, considering even the local regime of Werner states, wherein the Bell-CHSH inequalities are not violated, we show that the QT fidelity in the presence of noise can be appreciably high.

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arXiv2026

Phase-sensitive framed-ribbon representation of single-qubit Pauli measurements in linear cluster states

We provide a geometric classification of single-qubit projective measurements on one-dimensional linear cluster states within a topological framework. Establishing an explicit correspondence between local measurements and surgery operations on an associated link model, we represent the cluster state as a linear Hopf chain. Computational-basis (Z) measurements act as topological severance for bulk qubits and boundary pruning for end qubits. Transverse-basis (X) measurements remove the measured qubit and stratify the remaining state into a superposition of two disjoint but classically correlated segments. In contrast, lateral-basis (Y) measurements preserve a single continuous spliced chain while generating complex phase factors absent from unframed link descriptions. Although the unframed linking structure already distinguishes X- and Y-basis measurement outcomes geometrically, it cannot differentiate the two possible outcomes within a fixed basis. To resolve this ambiguity, we introduce a framed ribbon representation in which quantum phases are encoded as geometric twists, with chiral plus/minus 90 deg twists representing the phases plus/minus i. The resulting framework provides a phase-sensitive, outcome-resolved geometric description of single-shot Pauli measurements on linear cluster states. The twist angles are geometric labels determined by measurement outcomes and associated by-product operators rather than topological invariants, whereas the underlying linking pattern remains a genuine topological datum. The analysis is restricted to single-shot single-qubit Pauli measurements on one-dimensional cluster states; sequential measurements and classical feedforward are left as open problems.

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arXiv2026

Basis-Independent Coherence Dynamics of Tripartite States under Pure Dephasing

Quantum coherence is a fundamental quantum resource whose preservation under environmental interactions is essential for quantum information processing. While most studies have focused on basis-dependent coherence measures, the dynamics of intrinsic coherence quantified by basis-independent measures remain largely unexplored. In this work, we investigate the dynamics of basis-independent quantum coherence for several representative tripartite pure and mixed states subjected to local and common dephasing environments in both Markovian and non-Markovian regimes. We show that Markovian local dephasing leads to state-dependent coherence degradation, whereas collective dephasing significantly enhances coherence preservation through decoherence-free sectors. More importantly, non-Markovian environments give rise to nearly frozen coherence dynamics for both pure and mixed states, demonstrating the remarkable robustness of intrinsic coherence against dephasing environment. A comparison with the measure of relative entropy of coherence reveals that basis-independent coherence measure exhibits substantially greater resilience and qualitatively different dynamical behaviour than its basis-dependent counterpart. These results provide new insights into the preservation of intrinsic multipartite coherence in open quantum systems and highlight basis-independent coherence as a robust quantum resource for realistic noisy quantum technologies.

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arXiv2026

Resilience of Quantum Teleportation Fidelity for Bipartite Mixed States near Schwarzschild and Dilaton Black Holes

We investigate the robustness of quantum teleportation in the presence of strong gravitational fields by analysing bipartite mixed states derived from tripartite GHZ and W-class states near black hole event horizons. Considering a scenario where two observers approach the horizon of either a Schwarzschild or a Garfinkle Horowitz Strominger (GHS) Dilaton black hole while a third remains in flat space, we quantify the teleportation fidelity of the resulting bipartite channels after tracing out one party. Through the quantization of Dirac fields and Bogoliubov transformations, we compute the teleportation fidelity under the influence of Hawking radiation and spacetime curvature. Our results show that while entanglement degrades, teleportation fidelity remains above the classical threshold of $f>\frac{2}{3}$ for channels derived from W-class states, but not for GHZ-derived states. This indicates that quantum teleportation can remain feasible near black holes provided the initial entangled state retains useful bipartite entanglement.

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arXiv2026

Quantum Teleportation of a Single Qutrit using Two-Qutrit Entangled States

We demonstrate quantum teleportation of a qutrit system using a complete set of two-qutrit entangled states obtained from the representation theory of the SU(3) group. All measurement gates essential for end-to-end teleportation are systematically evaluated, and these are found to be non-unitary. Our approach extends Bennett's teleportation protocol to the qutrit system with minimal modifications, preserving operational simplicity and underscoring the necessity of non-unitary measurement operators in high-dimensional systems.

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arXiv2026

Coherence thermometry using multipartite quantum systems

Accurate temperature measurement at the quantum scale is becoming increasingly important for emerging quantum technologies, motivating the development of quantum thermometry based on quantum resources. In this work, we investigate how finite environmental temperature influences the coherence dynamics of multipartite quantum systems and examine whether quantum coherence can serve as a temperature sensitive observable. We consider a tripartite spin-boson model interacting with finite temperature dephasing environments under two physically distinct reservoir configurations, namely local and common environments. The dynamics of representative tripartite pure and mixed states are quantified using the relative entropy of coherence. Our results show that local dephasing produces a universal monotonic decay of coherence, with increasing temperature accelerating decoherence for all states. In contrast, common dephasing generates a markedly state dependent thermal response. Under common dephasing, the $\vert GHZ \rangle$ and $\vert Star\rangle$ states undergo complete coherence loss, the $\vert W\rangle$ state exhibits temperature independent stationary coherence, and the $\vert W\overline{W}\rangle$ state retains finite residual coherence at long times. Similar state dependent behaviour is also observed for mixed states. These results demonstrate that the thermal susceptibility of quantum coherence is governed jointly by the environmental configuration and the internal architecture of the multipartite quantum state. Furthermore, we establish a direct coherence temperature correspondence through representative thermometry tables, providing a \textit{proof-of-principle} foundation for coherence based quantum thermometry.

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arXiv2026

Geometry versus excitation sector in the decoherence of asymmetric $N$-qubit $W$ states

We investigate how network geometry and excitation sector separately control pairwise entanglement decay in asymmetric multipartite $W$ states. To disentangle these effects, we introduce an analytically tractable $N$-qubit generalization of the asymmetric Lohmayer geometry and its complementary-excitation partner, yielding inequivalent vertex-base (VB) and base-base (BB) pair classes that can be compared directly with symmetric $W$-state references. We derive closed-form concurrence dynamics under representative one-sided noise models and find that, within either excitation sector, the VB concurrence has exactly the same noise dependence as the corresponding symmetric reference, preserving a noise-independent proportional advantage wherever both remain entangled. The amplitude-damping reordering previously identified for the three-qubit Lohmayer state is therefore a cross-sector effect rather than an intrinsic fragility of the VB geometry. In contrast, the BB pair exhibits a genuine same-sector structural fragility, with lower entanglement-sudden-death thresholds than the VB pair under depolarizing noise and, in the $(N-1)$-excitation sector, under amplitude damping. The results establish network geometry, excitation sector, and noise symmetry as distinct ingredients governing pairwise entanglement robustness in asymmetric quantum networks.

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arXiv2026

Knot your average qutrit: Measurement-induced entanglement splitting and the cabling dictionary for GHZ and W States

Multipartite entanglement is conventionally classified by state families viz. family of GHZ and W class of states, with each family expected to behave differently under measurement. We show that, at least for the question of how entanglement splits after a single-particle measurement, this is not the division that matters for qutrits. Extending the Aravind's correspondence (which models entanglement as topological linking, and projective measurement as physically cutting a ring from an interlinked configuration\cite{aravind1997}) from qubits to qutrits, we derive the complete measurement-induced entanglement splitting of the GHZ type qutrit state i.e |GHZ_3> and of the full family of symmetric W class qutrit states, six two same - one different states i.e |{W_{p,p,q}^{sym}}> and one all - different state i.e. |W_{0,1,2}>, under both the computational basis (CB) and the mutually unbiased bases (MUBs), obtaining exact eigenvalues and Schmidt ranks for every outcome in every case. We see that the |W_{0,1,2}> state behaves similarly as |GHZ_3> state, a single, outcome-independent residual rank in each basis, while the |{W_{p,p,q}^{sym}> states alone show probability-weighted, outcome-dependent behaviour. The relevant structural line is therefore repeated-index versus all-different-index bag structure, not GHZ class versus $W$ class. We express this classification using a \textit{two-strand cabling} extension of Aravind's \textit{ring-and-link} picture. This is needed because the qutrit residual Schmidt rank (R) takes three values, R belonging to {1,2,3}, rather than the qubit binary (i.e. R belonging to {1,2}). We are explicit throughout that this cabling dictionary is a labeling convention built to reproduce an independently computed Schmidt rank, not a topological invariant derived from the link diagrams themselves, and we discuss what would be needed to close that gap

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arXiv2026

Interplay between teleportation fidelity and basis-independent coherence in maximally sliced states under decoherence

The influence of environmental decoherence on quantum teleportation is investigated by considering the three-qubit Maximally Sliced (MS) state as the shared entangled resource. Using the Kraus operator formalism, analytical expressions are derived for the teleportation fidelity under amplitude damping and phase damping channels. The corresponding basis-independent coherence is obtained, establishing explicit analytical relations between coherence and teleportation fidelity under both decoherence mechanisms. The results are further expressed in terms of the Coffman-Kundu-Wootters (CKW) three-tangle, thereby connecting genuine tripartite entanglement with teleportation performance. The analysis reveals distinct effects of the two noise channels: amplitude damping introduces a state-dependent threshold for achieving quantum teleportation, whereas phase damping preserves the quantum advantage until complete dephasing. These results provide a unified analytical framework for understanding the interplay among multipartite entanglement, quantum coherence and teleportation in noisy three-qubit MS states.

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arXiv2026

Quantum Information Processing: A brief overview on Quantum Teleportation

Quantum Information Processing (QIP) exploits the principles of quantum mechanics to perform information storage, communication, and computation in ways that are fundamentally impossible within classical frameworks. This article presents a pedagogical overview of the mathematical foundations of quantum information theory, including qubits, Hilbert spaces, linear operators, quantum measurements, tensor products, density operators, and quantum entanglement. Building upon these concepts, we provide a detailed introduction to quantum teleportation, one of the most remarkable protocols in quantum communication. The discussion covers the no cloning theorem, the original teleportation protocol by Bennett et al., experimental realisations of quantum teleportation, and extensions involving probabilistic and multiqubit teleportation schemes. Particular emphasis is placed on the role of entanglement as a communication resource, together with the study of teleportation channels based on bipartite and multipartite quantum states. Various quantitative measures of entanglement, including concurrence, negativity, entanglement of formation, and relative entropy of entanglement, are reviewed alongside teleportation fidelity as a performance metric. Furthermore, the interplay between Bell nonlocality, mixed state entanglement, and teleportation efficiency is examined, followed by a survey of advanced developments such as controlled teleportation, bidirectional teleportation, cluster state teleportation, and recent advances in the Quantum 2.0 era. This review aims to provide students, researchers, and engineers with a coherent introduction to the theoretical foundations and practical significance of quantum teleportation in emerging quantum technologies.

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arXiv2026

Super-Link Fragility in Asymmetric W-Class States under Quantum Noise

The asymmetric three-qubit W-class state $|\overline{W_3^L}\rangle$ defines an isosceles entanglement-network geometry, (a) two vertex-base (VB) links form stronger bipartite connections, (b) while the base-base (BB) link is weaker. This suggests that concentrating entanglement into a super-link may be advantageous for quantum-network tasks. Here, we show that this intuition is incomplete. We analytically compare the bipartite concurrence dynamics of the symmetric |W> state and the asymmetric $|\overline{W_3^L}\rangle$ state, which differ both in entanglement-network geometry and excitation sector under standard noise models. In the absence of noise, the concurrence hierarchy is $C_{VB} > C_W > C_{BB}$. Under phase damping, this hierarchy is preserved for all noise strengths and no entanglement sudden death occurs. Under amplitude damping, however, the hierarchy is reordered. The symmetric |W> state becomes the most robust, while the base-base concurrence of $|\overline{W_3^L}\rangle$ vanishes at the finite threshold of parameter $γ$. We term this reordering as the \textit{Super-Link Fragility Effect}. The same structural asymmetry that produces a stronger vertex-base link also makes it more vulnerable to energy dissipation when coupled with multi-excitation amplitudes. Under depolarization, the asymmetry advantage is erased, with $C_W$ and $C_{VB}$ sharing the same sudden-death threshold for some value of the parameter p, while $C_{BB}$ disappears earlier at some other value of the parameter p. The generalized amplitude damping channel continuously connects the damping-dominated regime to the pure-excitation limit, where the initial hierarchy is restored. These results show that entanglement robustness in $W$-class resources is controlled not by initial concurrence alone, but by the joint structure of entanglement-network geometry, excitation sector, and noise symmetry.

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arXiv2026

Entanglement, Coherence, and Recursive Linking in Dicke states : A Topological Perspective

This work investigates the topological structure of multipartite entanglement in symmetric Dicke states $|D_n^{(k)}\rangle$. By viewing qubits as topological loops, we establish a direct correspondence between the recursive measurement dynamics of Dicke states and the stability of $n$-Hopf links. We utilize the Schmidt rank to quantify bipartite entanglement resilience and introduce the $l_1$-norm of quantum coherence as a measure of link fluidity. We demonstrate that unlike fragile states such as $ \left| GHZ \right \rangle$ (analogous to Borromean rings), Dicke states exhibit a robust, self-similar topology where local measurements preserve the global linking structure through non-vanishing residual coherence.

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arXiv2025

Teleporting single qutrit using symmetric-anti symmetric two-qutrit basis states as quantum channels

This work presents a deterministic scheme for the teleportation of a single qutrit state, held by the sender Alice, using maximally entangled two-qutrit states as resource channels. These states have been constructed from symmetric and anti-symmetric bases by Leslie, Devin and Lynn (LDL). Leveraging the higher information capacity of qutrits compared to qubits, we employ these nine distinct two-qutrit entangled channels by LDL, for our protocol. For each channel, explicit unitary operations at the receiver Bob's end are derived, ensuring perfect recovery of the unknown qutrit state, initially in possesion of the sender Alice, after the sender performs joint measurements on her qutrits and communicates the outcomes through a classical channel. The proposed framework confirms teleportation with unit fidelity, thereby extending conventional teleportation schemes beyond qubits into higher-dimensional systems. This not only enriches the available toolkit for quantum communication but also highlights the utility of structured entangled states in advancing quantum information processing. The results open new avenues for secure and efficient quantum networks, higher-dimensional cryptographic schemes, and the design of novel quantum algorithms, while laying the groundwork for experimental realizations of deterministic qutrit teleportation.

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arXiv2025

Symmetric and asymmetric tripartite states under the lens of entanglement splitting and topological linking

This work establishes a direct operational connection between the entanglement structures of specific three-qubit states (i.e. multipartite entanglement) and their corresponding topological links. We investigate the symmetric $\wwbar$ state and the asymmetric $\starstate$ state through local projective measurements on individual qubits. The post measurement states are analyzed via their Schmidt rank to characterize residual bipartite entanglement. For the symmetric $\wwbar$ state, measurement of any qubit consistently results in a non-maximally entangled post-measurement state (Schmidt rank 2), analogous to the behavior of a \textit{3-Hopf link} structure, where cutting any ring leaves the remaining two nontrivially linked. On the other hand, the $\starstate$ state exhibits a context-dependent fragility. Its behavior predominantly mirrors that of a \textit{3-link chain}, where severing the central qubit decouples the system, while cutting an outer qubit often preserves a residual link. Crucially, for specific measurement outcomes, the $\starstate$ state also exhibits the defining property of the \textit{Borromean rings}, where the loss of one qubit completely disentangles the remaining two. This analysis provides a concrete interpretation of topological linking structures as a resource for characterizing distributed entanglement and its resilience under local measurement operations, revealing that a single quantum state can contextually embody multiple distinct topological analogues.

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arXiv2025

Non-maximally entangled mixed states of X and non-X types as teleportation channels

Mixed spin-1/2 states violating Bell-CHSH inequality is useful for teleportation. There exist states which do not violate Bell-inequality but is still useful as teleportation channels. Maximally entangled mixed states of Munro class and Ishizaka-Hiroshima class are such types which although satisfy Bell-CHSH inequality, yet can perform better as teleportation channels for a given degree of mixedness\cite{adhikari2010}. In this work we construct class of mixed states of non-maximally entangled types whose efficacy as teleportation channels have been studied. For certain range of state parameters, these non-maximally entangled mixed states performs better as quantum teleportation channels than certain maximally entangled mixed states (such as Werner state). These constructed states, though entangled, satisfy Bell-CHSH inequality implying further that violation of local inequalities may not be good indicators of their ability to complete quantum processing tasks such as teleportation.

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arXiv2025

Exploring quantum properties of bipartite mixed states under coherent and incoherent basis

Quantum coherence and quantum entanglement are two different manifestations of the superposition principle. In this article we show that the right choice of basis to be used to estimate coherence is the separable basis. The quantum coherence estimated using the Bell basis does not represent the coherence in the system, since there is a coherence in the system due to the choice of the basis states. We first compute the entanglement and quantum coherence in the two qubit mixed states prepared using the Bell states and one of the states from the computational basis. The quantum coherence is estimated using the l1-norm of coherence, the entanglement is measured using the concurrence and the mixedness is measured using the linear entropy. Then we estimate these quantities in the Bell basis and establish that coherence should be measured only in separable basis, whereas entanglement and mixedness can be measured in any basis. We then calculate the teleportation fidelity of these mixed states and find the regions where the states have a fidelity greater than the classical teleportation fidelity. We also examine the violation of the Bell-CHSH inequality to verify the quantum nonlocal correlations in the system. The estimation of the above mentioned quantum correlations, teleportation fidelity and the verification of Bell-CHSH inequality is also done for bipartite states obtained from the tripartite systems by the tracing out of one of their qubits. We find that for some of these states teleportation is possible even when the Bell-CHSH inequality is not violated, signifying that nonlocality is not a necessary condition for quantum teleportation.

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arXiv2025

Unitary and non-unitary operators leverage perfect and imperfect single qutrit teleportation

Teleportation, a novel scheme, initially posited by Bennett \textit{et.al}, has been studied here in the context of sending a single qutrit from Alice to Bob using two qutrit entangled channels as resources. In this paper we have considered two special two qutrit entangled states, which belong to $SU(3)$ group, as useful resources for teleportation. For the successful teleportation, these entangled states have been chosen as quantum channels shared between Alice and Bob. Another entangled basis of two qutrit states have been used as auxiliary states, which would help Alice to manipulate with her channel so that the single qutrit she holds can be successfully teleported to Bob. Bob's choices of measurement operators influence the retrieval of Alice's single qutrit.

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arXiv2025

Teleportation of unknown qubit via Star type tripartite states

Eylee Jung \textit{et.al}\cite{jung2008} had conjectured that $P_{max}=\frac{1}{2}$ is a necessary and sufficient condition for the perfect two-party teleportation and consequently the Groverian measure of entanglement for the entanglement resource must be $\frac{1}{\sqrt{2}}$. It is also known that prototype $W$ state is not useful for standard teleportation. Agrawal and Pati\cite{pati2006} have successfully executed perfect (standard) teleportation with non-prototype $W$ state. Aligned with Pati's protocol\cite{pati2006} we have considered here $Star$ type tripartite states and have shown that perfect teleportation is suitable with such states. Moreover, we have taken the linear superposition of non-prototype $W$ state and its spin-flipped version and shown that it belongs to $Star$ class. Also, standard teleportation is possible with these states. It is observed that genuine tripartite entanglement is not necessary requirement for a state to be used as a channel for successful standard teleportation. We have also shown that these $Star$ class states are $P_{max}=\frac{1}{4}$ states and their Groverian entanglement is $\frac{\sqrt{3}}{2}$, thus concluding that Jung conjecture is not a necessary condition.

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