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arXiv:0806.1032 · Physical Review B

State tomography of a chain of qubits embedded in a spin field-effect transistor via repeated spin-blockade measurements on the edge qubit

Kazuya Yuasa, Kosuke Okano, Hiromichi Nakazato, Saori Kashiwada, Kanji Yoh

Published Feb 23, 2009• 4 citations
arXivHTMLPDF

Abstract

As a possible physical realization of a quantum information processor, a system with stacked self-assembled InAs quantum dots buried in GaAs 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.

DOI
10.1103/physrevb.79.075318

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The theory of weak quantum measurements is developed for quantum-dot spin qubits. Building on recent experiments, we propose a control cycle to prepare, manipulate, weakly measure, and perform quantum state tomography. This is accomplished using a combination of the physics of electron spin resonance, spin blockade, and Coulomb blockade, resulting in a charge transport process. We investigate the influence of the surrounding nuclear spin environment, and find a regime where this environment significantly simplifies the dynamics of the weak-measurement process, making this theoretical proposal realistic with existing experimental technology. We further consider spin-echo refocusing to combat dephasing, as well as discuss a realization of ``quantum undemolition,'' whereby the effects of quantum state disturbance are undone.
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