State Tomography of a Chain of Qubits Embedded in a Spin Field-Effect Transistor via Repeated Spin-Blockade Measurements on the Edge Qubit

TL;DR

This paper demonstrates that full quantum state tomography of a chain of qubits embedded in a spin FET is feasible using repeated measurements on only the edge qubit, leveraging entangling dynamics.

Contribution

It introduces a method for state tomography of multiple qubits with limited measurement access, utilizing entanglement and repeated measurements, including a detailed scheme for two-qubit systems.

Findings

State tomography is possible with only edge qubit measurements.

A specific recipe for two-qubit tomography is provided.

The impact of measurement imperfections is analyzed.

Abstract

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.