arXiv subjects

Ilia D. Lazarev

Publications and source records attributed to Ilia D. Lazarev.

5 recordsLinked to original sources

arXiv2026

Macroscopic entanglement distribution with atomic ensembles

The distribution of entanglement is a crucial task for quantum communication towards realizing a globe-spanning quantum internet. Recently a protocol for deterministic long-distance distribution of macroscopic entanglement over a network of ensembles of qubits was introduced [Adv. Quantum Technol. 2025, 8, 2400524]. It was shown that this protocol allows for the propagation of macroscopic amounts of entanglement with a protocol complexity that is independent on the ensemble size. However, questions remained on whether the scheme is viable, particularly for a large particle number, which is the case for realistic atomic ensembles. Here we develop improved numerical techniques that allow calculation of realistic ensemble sizes up to 10^6 with a negligible loss of accuracy. We find that moderate dephasing leaves the entanglement largely intact at the magic times, whereas stronger noise monotonically suppresses the entanglement. Our results demonstrate that the protocol retains its functionality towards the macroscopic regime and provides quantitative benchmarks for its robustness under a realistic level of decoherence.

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arXiv2025

Hybrid quantum-classical unsupervised data clustering based on the self-organizing feature map

Unsupervised machine learning is one of the main techniques employed in artificial intelligence. We introduce an algorithm for quantum-assisted unsupervised data clustering using the self-organizing feature map, a type of artificial neural network. The complexity of our algorithm scales as O(LN), in comparison to the classical case which scales as O(LMN), where N is the number of samples, M is the number of randomly sampled cluster vectors, and L is the number of the shifts of cluster vectors. We perform a proof-of-concept demonstration of one of the central components on the IBM quantum computer and show that it allows us to reduce the number of calculations in the number of clusters. Our algorithm exhibits exponential decrease in the errors of the distance matrix with the number of runs of the algorithm.

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arXiv2024

Quantum repeater protocol for deterministic distribution of macroscopic entanglement

Distributing long-distance entanglement is a fundamental goal that is necessary for a variety of tasks such as quantum communication, distributed quantum computing, and quantum metrology. Currently quantum repeater schemes typically aim to distribute one ebit at a time, the equivalent of one Bell pair's worth of entanglement. Here we present a method to distribute a macroscopic amount of entanglement across long-distances using a number of operations that scales only linearly with the chain length. The scheme involves ensembles of qubits and entangling them with an $S^z S^z$ interaction, which can be realized using atomic gas ensembles coupled by a shared optical mode. Using only local measurements on the intermediate ensembles, this leaves the ensembles at the ends of the chain entangled. We show that there are particular ``magic'' interaction times that allow for distribution of entanglement with perfect fidelity, with no degradation with chain length. The scheme is deterministic, such that with suitable local conditional unitary corrections, the same entangled state can always be prepared with good approximation.

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arXiv2024

Some Aspects of Remote State Restoring in State Transfer Governed by XXZ-Hamiltonian

We consider the remote state restoring and perfect transfer of the zero-order coherence matrix (PTZ) in a spin system governed by the XXZ-Hamiltonian conserving the excitation number. The restoring tool is represented by several nonzero Larmor frequencies in the Hamiltonian. To simplify the analysis we use two approximating models including either step-wise or pulse-type time-dependence of the Larmor frequencies. Restoring in spin chains with up to 20 nodes is studied. Studying PTZ, we consider the zigzag and rectangular configurations and optimize the transfer of the 0-order coherence matrix using geometrical parameters of the communication line as well as the special unitary transformation of the extended receiver. Overall observation is that XXZ-chains require longer time for state transfer than XX-chains, which is confirmed by the analytical study of the evolution under the nearest-neighbor approximation. We demonstrate the exponential increase of the state-transfer time with the spin chain length.

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arXiv2020

Many-spin entanglement in multiple quantum NMR with a dipolar ordered initial state

Multiple quantum (MQ) NMR with a dipolar ordered initial state opens new possibilities for the exploration of many-spin entanglement. In this paper, we investigate many-spin entanglement in a gas of spin-carrying molecules (atoms) in nanocavities in the conditions of MQ NMR with a dipolar ordered initial state. The second moment of the distribution of the intensities of MQ NMR coherences, which provides a lower bound on the quantum Fisher information, is used for an estimate of the number of the entangled spins. Many-spin entanglement is investigated at different temperatures and different numbers of spins.

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