Birth and Early Growth of Entanglement by sd Exchange with Gate-Voltage-Controllable Destiny

Abstract: We investigate bipartite entanglement between two distant parties, \textit{A} and \textit{B}, comprising local magnetic impurities (or qudits) induced by the quench through \textit{sd} exchange in a field-effect-transistor geometry. A wave-function-based time-dependent formalism is employed by including non-dissipative responses that allow for the control of entanglement via gate voltages. Our study focuses on the birth and early growth of entanglement, by introducing environment support states that render site- and layer-resolved logarithmic negativity (LN) and mutual information (MI). In the minimal set, where party \textit{A} (\textit{B}) consists of a qubit, we identify entanglement sudden deaths (ESDs), which are explained by a visualization picture analyzing the density matrix. Vibrating electron currents facilitate the birth of entanglement, while they are not required for its growth and subsistence. The LN emerges near the edge layers in \textit{A} and \textit{B}, while MI shows up outside these two parties within the spacing layer. The MI is born earlier than the LN. When a gate voltage large enough to disjoint part of the system is applied within the spacing region, it partially suppresses the entanglement, quantified by the LN. This suppression does not appear immediately after the presence of the disjoint voltage. Applying this disjoint voltage to the site(s) hosting the qudit(s) helps prevent the site- and layer-resolved LN from encountering ESDs. The local impurities in parties \textit{A} and \textit{B} are initially of opposite spin directions in an unentangled state, as can be prepared by two of our proposed protocols. However, the features described above do not depend on the chosen protocols.