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arXiv:2202.13944 · Physical review. B./Physical review. B

Coherence limitations in the optical control of the singlet-triplet qubit in a quantum dot molecule

Karol Kawa, T. Kühn, Paweł Machnikowski

Published Sep 26, 2022• 2 citations
arXivHTMLPDF

Abstract

We analyze the optically driven dynamics of a qubit implemented on a singlet-triplet subspace of two-electron states in a self-assembled quantum dot molecule. We study two possible control schemes based on the coupling to an excited (four-particle) state either by two spectrally separated laser pulses or by a single spectrally broad pulse. We quantitatively characterize the imperfections of the qubit operation resulting from nonadiabatic evolution and from limited spectral selectivity in a real system, as compared to the ideal adiabatic Raman transfer of occupation in the $\mathrm{\ensuremath{\Lambda}}$ system. Next, we study the effects of decoherence induced by the coupling to the phonons of the surrounding crystal lattice and by radiative recombination. As a result, we are able to identify the optimization trade-offs between different sources of errors and indicate the most favorable conditions for quantum control of the singlet-triplet qubit in the two optical control schemes.

DOI
10.1103/physrevb.106.125308

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We propose two schemes to coherently transfer arbitrary quantum states of the two-electron singlet-triplet qubit across a chain of three quantum dots. The schemes are based on electrical control over the detuning energy of the quantum dots. The first is a pulse-gated scheme, requiring dc pulses and engineering of inter- and intradot Coulomb energies. The second scheme is based on the adiabatic theorem, requiring time-dependent control of the detuning energy through avoided crossings at a rate that the system remains in the ground state. We simulate the transfer fidelity using typical experimental parameters for silicon quantum dots. Our results give state transfer fidelities between 94.394.3%<\mathcal{F}<99.5%94.3 at sub-ns gate times for the pulse-gated scheme and between 75.475.4%<\mathcal{F}<99.0%75.4 at tens of ns for the adiabatic scheme. Taking into account dephasing from charge noise, we obtain state transfer fidelities between 94.094.0%<\mathcal{F}<99.2%94.0 for the pulse-gated scheme and between 64.964.9%<\mathcal{F}<93.6%64.9 for the adiabatic scheme.
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