State Tomography of a Chain of Qubits Embedded in a Spin Field-Effect   Transistor via Repeated Spin-Blockade Measurements on the Edge Qubit
  As a possible physical realization of a quantum information processor, a system with stacked self-assembled InAs quantum dots buried in GaAs in adjacent to the channel of a spin field-effect transistor has been proposed. In this system, only one of the stacked qubits, i.e. the edge qubit (the qubit closest to the channel), is measurable via "spin-blockade measurement." It is shown that the state tomography of the whole chain of the qubits is still possible even under such a restricted accessibility. The idea is to make use of the entangling dynamics of the qubits. A recipe for the two-qubit system is explicitly constructed and the effect of an imperfect fidelity of the measurement is clarified. A general scheme for multiple qubits based on repeated measurements is also presented. 
Kazuya Yuasa, Kosuke Okano, Hiromichi Nakazato, Saori Kashiwada, Kanji   Yoh