Proposals of nuclear spin quantum memory in group IV elemental and II-VI semiconductors

TL;DR

This paper proposes nuclear spin quantum memory schemes in group IV and II-VI semiconductors, utilizing electron-nuclear spin interactions for long coherence times and efficient quantum state transfer.

Contribution

It introduces new protocols for quantum memory using either two-electron or single-electron systems in specific semiconductors, highlighting their advantages and practical implementations.

Findings

Protocols for quantum state transfer via magnetic/electric tuning and hyperfine interaction.

Analysis of various semiconductor systems like Si, ZnSe quantum dots, and bulk doped crystals.

Comparison of two-electron and single-electron qubit schemes.

Abstract

New schemes for the nuclear spin quantum memory are proposed based on a system composed of two electrons or one electron coupled to a single nuclear spin in isotopically purified group IV elemental and II-VI compound semiconductors. The qubit consists of the singlet state and one of the triplet states of two electrons or simply of an electron spin. These systems are free from the decoherence due to the nuclear dipole-dipole interaction and are advantageous for the long memory time. In the case of two electrons, the protocol for the quantum state transfer between the electron spin qubit and the nuclear spin qubit is based on the magnetic or electric field tuning of the singlet-triplet state crossing and on the hyperfine coupling supplemented with a well-defined scheme to initialize the nuclear spin. In the case of a single electron qubit, the quantum state transfer is driven by the hyperfine interaction itself without the need of the nuclear spin initialization. Many practical systems are considered, e.g., two electrons loaded on a Si or ZnSe quantum dot, a single electron charged state in a Si quantum dot doped with a P atom, a single electron charged $ ^{28}$Si quantum dot doped with an isotope atom of $ ^{29}$Si, and a localized electron system of Si:P and ZnSe:F in the bulk crystal. General aspects of these systems are investigated and a comparison of merits and demerits is made between the two-electron qubit and the single-electron qubit.