arXiv subjects

Pritam Halder

Publications and source records attributed to Pritam Halder.

22 records · Page 2Linked to original sources

arXiv2022

Circulating Genuine Multiparty Entanglement in Quantum Network

We propose a deterministic scheme of generating genuine multiparty entangled states in quantum networks of arbitrary size having various geometric structures -- we refer to it as entanglement circulation. The procedure involves optimization over a set of two-qubit arbitrary unitary operators and the entanglement of the initial resource state. We report that the set of unitary operators that maximize the genuine multipartite entanglement quantified via generalized geometric measure (GGM) is not unique. We prove that the GGM of the resulting state of arbitrary qubits coincides with the minimum GGM of the initial resource states. By fixing the output state as the six-qubit one, we find the optimal way to create such states according to the available resource. Moreover, we show that the method proposed here can be implemented by using logic gates, or by using the time dynamics of realizable spin Hamiltonians. In case of an ordered system, GGM varies periodically with time while the evolution via disordered models lead to a low but constant multipartite entanglement in outputs at a critical time, which decreases exponentially with the increase of the strength of the disorder.

quant-ph↗

arXiv2022

Manifestation of Rank-Tuned Weak Measurements Towards Featured State Generation

We propose that an unsharp measurement-based process to generate genuine multipartite entanglement from an entangled initial state with a fewer number of qubits can be classified in two ways -- biased and unbiased inflation protocols. In the biased case, genuine multipartite entanglement (GME) of the resulting state obtained after a single measurement outcome is optimized, thereby creating a possibility of states with high GME while in the unbiased case, average GME is optimized over all possible outcomes. Interestingly, we show that the set of two-qubit unsharp measurements can generate multipartite states having different features according to GME measure, generalized geometric measure, the monogamy-based entanglement measure, tangle and robustness against particle loss quantified via persistency depending on the rank of the unsharp measurement operators. Specifically, in the process of producing three-qubit pure states, we prove that rank-$2$ measurements can create only Greenberger Horne Zeilinger (GHZ)-class states while only W-class states are produced with rank-$4$ measurements although rank-$3$ measurements are capable to generate both. In the case of multipartite states with an arbitrary number of qubits, we report that the average content of genuine multipartite entanglement increases with the decrease of the rank in the measurement operators although the persistency decreases with the rank, both in the biased as well as unbiased protocols.

quant-ph↗

arXiv2022

Limits of network nonlocality probed by time-like separated observers

In an entanglement swapping scenario, if two sources sharing entangled states between three parties are independent, local correlations lead to a different kind of inequalities than the standard Bell inequalities, known as network local models. A highly demanding task is to find out a way to involve many players nontrivially in a quantum network since measurements, in general, disturb the system. To this end, we consider here a novel way of sharing network nonlocality when two observers initially share close to a maximally entangled states. We report that by employing unsharp measurements performed by one of the observers, six pairs can sequentially demonstrate the violation of bilocal correlations while a maximum of two pairs of observers can exhibit bi-nonlocality when both the observers perform unsharp measurements. We also find the critical noise involved in unsharp measurements in each round to illustrate the bi-nonlocality for a fixed shared entangled state as a resource. We also establish a connection between entanglement content of the shared state, quantified via von-Neumann entropy of the local density matrix for pure states and entanglement of formation for Werner states, and the maximum number of rounds showing violation of bilocal correlations. By reducing entanglement content in the elements of the joint measurement by the third party, we observe that the maximum number reduces to two sequential sharing of bi-nonlocality even for the maximally entangled state when the settings at each side are taken to be three and fixed.

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arXiv2021

Measurement-based Multipartite Entanglement Inflation

Generating entanglement between more parties is one of the central tasks and challenges in the backdrop of building quantum technologies. Here we propose a measurement-based protocol for producing multipartite entangled states which can be later fed into some network for realizing suitable quantum protocols. We consider weak entangling measurement on two parties as the basic unit of operation to create entanglement between more parties starting from an entangled state with a lesser number of parties and auxiliary systems in the form of a single-qubit or entangled state itself. We call the introduced expansion procedure, "multipartite entanglement inflation". In the context of inflating bipartite entanglement to more number of parties, surprisingly, maximally entangled states as inputs turn out to be worse than that of the non-maximally entangled states, Haar uniformly generated pure states having a moderate amount of entanglement and the Werner state with a certain threshold noise. We also report that the average multipartite entanglement created from the initial Greenberger Horne Zeilinger- and the W- class states are almost same. Interestingly, we also observe that for Haar uniformly generated pure states, unentangled auxiliary systems are sometimes more advantageous than the protocol with multiple copies of the initial entangled states.

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