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Science

Fermionic Bell-State Analyzer for Spin Qubits

Hans‐Andreas Engel, Daniel Loss

Published Jul 22, 2005• 101 citations
Publisher

Abstract

We propose a protocol and physical implementation for partial Bell-state measurements of Fermionic qubits, allowing for deterministic quantum computing in solid-state systems without the need for two-qubit gates. Our scheme consists of two spin qubits in a double quantum dot where the two dots have different Zeeman splittings and resonant tunneling between the dots is only allowed when the spins are antiparallel. This converts spin parity into charge information by means of a projective measurement and can be implemented with established technologies. This measurement-based qubit scheme greatly simplifies the experimental realization of scalable quantum computers in electronic nanostructures.

DOI
10.1126/science.1113203

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We propose a scheme for full Bell state measurement of spin qubits in a double quantum dot. Our scheme consists of Pauli spin-blockade measurements and biaxial electron-spin resonance. In order to eliminate the average of the Zeeman fields, the double quantum dot is designed so that the Land\'e ggg-factors of first and second dots satisfy ${g}_{1}=\ensuremath{-}{g}_{2}$ with the use of ggg-factor engineering. Thus, we can swap one of the three spin-triplet states for the spin-singlet state without disturbing the other states. Our study shows that the sequential spin-to-charge conversions enable us to implement the full Bell state measurement of electron-spin qubits.
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We propose a scheme to implement fermionic quantum SWAP and Fredkin gates for spin qubits with the aid of charge detection. The scheme is deterministic without the need of qubit–qubit interaction, and the proposed setups consist of simple polarizing beam splitters, single-spin rotations, and charge detectors. Compared with linear optics quantum computation, this charge-measurement-based qubit scheme greatly enhances the success probability for im- plementing quantum SWAP and Fredkin gates and greatly simplifies the experimental realization of scalable quantum computers with noninteracting electrons.
We proposed a possible protocol for Bell state measurements of spin qubits in a double quantum dot (QD). Our scheme consists of Pauli spin blockade measurements and biaxial electron spin resonance. It is assumed that the two QDs here are designed so that the Land? g-factors satisfy g1 = ?g2 with the use of g-factor engineering. The opposite sign of the g-factors cancel the average of the Zeeman fields on the two QDs, and enable us to swap three spin-triplet states for a spin-singlet state sequentially. We showed that it is possible to implement the full Bell state measurement by the sequential spin-to-charge conversions in the QD-based spin qubits.
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