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arXiv:1109.5734

Back-action Driven Electron Spin Singlet-Triplet Excitation in a GaAs Quantum Dot

Cao, Gang, Ming Xiao, Hai-Ou Li, Cheng Zhou, Runan Shang, Tu, Tao, Guang‐Can Guo, Guo‐Ping Guo, H. W. Jiang

Published Sep 26, 2011• 0 citations
arXivHTMLPDF

Abstract

In a single quantum dot (QD), the electrons were driven out of thermal equilibrium by the back-action from a nearby quantum point contact (QPC). We found the driving to energy excited states can be probed with the random telegraph signal (RTS) statistics, when the excited states relax slowly compared with RTS tunneling rate. We studied the last few electrons, and found back-action driven spin singlet-triplet (S-T) excitation for and only for all the even number of electrons. We developed a phenomenological model to quantitatively characterize the spin S-T excitation rate, which enabled us to evaluate the influence of back-action on spin S-T based qubit operations.

DOI
10.48550/arxiv.1109.5734

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In a single quantum dot (QD), the electrons were driven out of thermal equilibrium by the back-action from a nearby quantum point contact (QPC). We found the driving to energy excited states can be probed with the random telegraph signal (RTS) statistics, when the excited states relax slowly compared with RTS tunneling rate. We studied the last few electrons, and found back-action driven spin singlet-triplet (S-T) excitation for and only for all the even number of electrons. We developed a phenomenological model to quantitatively characterize the spin S-T excitation rate, which enabled us to evaluate the influence of back-action on spin S-T based qubit operations.
We perform real-time charge counting with a quantum point contact (QPC) for the last six electrons in a single quantum dot. At zero magnetic field, the charge-counting statistics show distinctive non-thermal-equilibrium effects for the even and odd electron numbers. A detailed study relates this difference to the excitation from the spin singlet state to triplet states driven by QPC back-action. At a finite magnetic field, spin excitations to different triplet states and Zeeman states are also observed. A master-equation model is developed to quantitatively characterize the back-action-driven spin excitation rate.
We develop a theoretical model to describe the dissipative dynamics of singlet-triplet qubits in GaAs quantum dots. Using the concurrence experimentally obtained [Shulman et al., Science 336, 202 (2012)] as a guide, we assume that each logical qubit fluctuates under the action of a random telegraph noise (RTN) that simulates the $1/{f}^{\ensuremath{\alpha}}$ noise. We also study the dynamics of concurrence as a function of the amplitude of the RTN, the correlation time of the RTN, the preparation time of states, and the two-qubit coupling. Furthermore, we show that the two-qubit coupling together with the preparation time strongly affect the entanglement dissipative dynamics and both physical quantities can be employed to enhance the entanglement between singlet-triplet qubits.
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