Prescription and realization of entanglement dynamics near the entanglement–unentanglement boundary

Son-Hsien Chen^1*, Seng Ghee Tan²

¹應用物理暨化學系, 臺北市立大學, 台北, Taiwan
²光電物理學系, 中國文化大學, 台北, Taiwan

* Presenter:Son-Hsien Chen, email:sonhsien@utaipei.edu.tw

The time-dependent behavior of entanglement plays a crucial role in designing quantum bit (qubit) functionalities, particularly in spintronic-based quantum devices [1-3]. We report here our recent studies on entanglement dynamics between spin qubits near the entanglement–unentanglement boundary. For both mixed and pure initial states (ISs), we identify a model-independent recipe for realizing entanglement sudden death, sudden birth, and their transitions, as shown in Fig. 1(a, top). The ISs are constructed using a penetrable entanglement switch parameter ε, whose sign reversal marks the transition between entangled and unentangled regimes [4]. To enable programmable control of the temporal entanglement trajectory [Fig. 1(a, middle)], we propose a scalable device architecture [5] utilizing Ruderman-Kittel-Kasuya-Yosida (RKKY) type superexchange coupling [Fig. 1(a, bottom)]. By introducing the exchange-time integral, the system directly maps qubit motion onto the entanglement trajectory: in-phase vibrations generate snake, bouncing, and single or multiple pulse signals of entanglement, whereas damped out-of-phase vibrations slow down temporal evolution and stabilize a steady entanglement state [Fig. 1(b)]. This RKKY-based framework provides a systematic prescription for navigating and engineering entanglement dynamics, offering promising applications in quantum computation, cryptography, and metrology.

Keywords: Entanglement, RKKY exchange, Qubit, Spintronics, Quantum computation