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Journal of Physics Conference Series

Coherent coupling of two semiconducting flux qubits

Marcin Kurpas, Jerzy Dajka, E. Zipper

Published Mar 1, 2008• 2 citations
Publisher

Abstract

The entanglement of two distant two-level systems (qubits) built on semiconducting quantum rings is discussed. A mechanism of entangling the qubits by swapping is shown to lead to entanglement of subsystems which have never physically interacted. The numerical calculations of linear entropy beeing the entanglement measure are presented.
DOI
10.1088/1742-6596/104/1/012004

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Abstract We study the entanglement creation between two flux qubits interacting with electromagnetic field modes. No direct interaction between the qubits exists. Entanglement is reached using the entanglement swapping method by an interference measurement performed on photons. We discuss the influence of off‐resonance and multi‐photon initial states on the qubit–qubit entanglement. The presented scheme is able to drive an initially separable state of two qubits into an highly entangled state suitable for quantum information processing (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Entanglement swapping, the process to entangle two particles without coupling them in any way, is one of the most striking manifestations of the quantum-mechanical nonlocal characteristic. Besides fundamental interest, this process has applications in complex entanglement manipulation and quantum communication. Here we report a high-fidelity, unconditional entanglement swapping experiment in a superconducting circuit. The measured concurrence characterizing the qubit-qubit entanglement produced by swapping is above 0.75, confirming most of the entanglement of one qubit with its partner is deterministically transferred to another qubit that has never interacted with it. We further realize delayed-choice entanglement swapping, showing whether two qubits previously behaved as in an entangled state or as in a separable state is determined by a later choice of the type of measurement on their partners. This is the first demonstration of entanglement-separability duality in a deterministic way.