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Japanese Journal of Applied Physics

Real-Time Observation of Charge States and Energy Relaxation in a Double Quantum Dot

T. Hayashi, T. Fujisawa, Ritsuya Tomita, Y. Hirayama

Published Apr 1, 2006• 3 citations
Publisher

Abstract

We performed real-time observation of charge states in a double quantum dot (QD) by monitoring the current passing through an adjacent quantum point contact (QPC). The position of the QPC was chosen in such a way that the Coulomb coupling of the QPC to one QD is made stronger than to the other QD, so that the QPC current can clearly resolve the charge states of the double QD. With a response time of ∼200 µs, we also investigated the energy relaxation time T 1 of the double QD by applying rectangular voltage pulses to the double QD. We confirmed that T 1 can be made sufficiently longer than the response time of the QPC.

DOI
10.1143/jjap.45.3629

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We present the measurement of a hybrid double-dot qubit using a quantum point contact (QPC). To study the dynamics, we derive the rate equations of the entire system. Numerical results show that QPC current can directly reflect the evolution of the qubit. By adjusting Coulomb interaction, energy mismatch, and QPC tunneling rate, the efficiency and dephasing time can be improved. In addition, the initial state with a hybrid triplet state is superior to that with the purely triplet states on the efficiency. Moreover, the decoherence time is estimated on the magnitude of a microsecond, long enough to implement quantum operations.
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