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Russian Microelectronics

Generation of Nonmaximally Entangled States between BECs with Quantum Optimal Control Methods

I. D. Lazarev, Alexey N. Pyrkov

Published Dec 1, 2023• 0 citations
Publisher

Abstract

In the last decade, different theoretical methods for entanglement generation between distant BEC qubits (macroscopic cold atomic ensembles) were proposed. However, experimental realization of such states is still challenging beside some special cases. The most theoretically investigated entangled states between macroscopic BECs are nonmaximally entangled states obtained with $$SzSz$$ entangling Hamiltonian. With the use of such states, the protocols for quantum teleportation, remote state preporation and many others were developed for macroscopic qubits on the basis of BECs. Here we show that it is possible to obtain such states with the use of the bosonic analog of $$XY$$ Hamiltonian and the methods of quantum optimal control. We compare performance of this scheme in the meaning of fidelity and entanglement for different drift and control Hamiltonians. We use the well-established QuTip open python library for all calculations.

DOI
10.1134/s1063739723600553

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We present a general approach to measurement-based quantum feedback that employs proportional and quantum state--(PaQS-) based feedback components to obtain locally optimal protocols. To demonstrate the power of the method, we first show that it reproduces many known feedback protocols and then apply it to generation of multipartite entanglement with an emphasis on remote entanglement, which requires spatially local feedback Hamiltonians. The symmetry of both measurement and feedback operators is found to be essential for construction of effective protocols. We show that under perfect measurement efficiency, entangled states can be reached with fidelity approaching unity under non-Markovian feedback control protocols, while Markovian protocols resulting from optimizing the feedback unitaries on ensemble-averaged states still yield fidelities above 94%. Application of the PaQS approach to generation of NNN-qubit WWW, general Dicke, and Greenberger-Horne-Zeilinger states shows that such entangled states can be efficiently generated with high fidelity, for up to N=100N=100N=100 in some cases.
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