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arXiv:1312.0427 · Physical Review A

Telegraph noise effects on two charge qubits in double quantum dots

A. Ayachi, W. Ben Chouikha, S. Jaziri, R. Bennaceur

Published Jan 27, 2014• 16 citations
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Abstract

We analyze theoretically the decoherence of two interacting electrons in a double self-assembled quantum dot due to a random telegraph noise. For this purpose we have examined the pure dephasing rate by evaluating the decoherence factor. The latter has been shown to be different from that calculated within the Gaussian approximation in the strong coupling regime. In order to determine the influence of the random telegraph noise on the entanglement of the system states, the concurrence, the populations, and the entropy are evaluated as well. Our results show that telegraph noise can severely impact the coherence of charge qubits.

DOI
10.1103/physreva.89.012330

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Quantum information and quantum computation implementation in terms of electron charges and spin has attracted tremendous attention for the development of large-scale quantum information processing [1-5]. Artificial and tunable charge qubits fabricated in a semiconductor nanostructure are suitable for the purpose, since various parameters can be controlled by external gate voltages [6,7]. The rapid control of external gate voltage in two-electron double quantum dots has been demonstrated [8,9].Entanglement has recently emerged as a significant resource in quantum information and other applications. However an important problem is to ensure the robustness of this resource; that is, the ability to maintain it against decay. Decoherence is one of the fundamental limitation in quantum information science, and the understanding and the control of its dynamics appears as a crucial issue for the development of quantum information devices.For charge qubits in quantum dots, the effects of phonons and electromagnetic and background charge fluctuations are important in the decoherence process. The effect of phonons on the dynamics of two charge qubits has been examined [10,11].In this work, we analyze the effect of telegraph noise on the dynamical of two electrons in laterally coupled quantum dots. The resulting qubit is supposed to evolve in the basis spanned by the states |0〉 and |1〉 which describe the electron localized in the left and right dot respectively. We investigate theoretically the quantum dynamics of two interacting electrons driven by an oscillatory electric field. In order to study the effect of the telegraph noise on the entanglement we adopt the concurrence.
In quantum computation, quantum coherence must be maintained during gate operation. However, in physical implementations, various couplings with the environment are unavoidable and can lead to a dephasing of a quantum bit (qubit). The background charge fluctuations are an important dephasing process, especially in a charge qubit system. We examined the dephasing rate of a qubit due to random telegraph noise. Solving stochastic differential equations, we obtained the dephasing rate of a qubit constructed of a coupled-dot system; we applied our results to the charge Josephson qubit system. We examined the dephasing rates due to two types of couplings between the coupled-dot system and the background charge, namely, fluctuation in the tunnel coupling constant and fluctuation in the asymmetric bias. For a strong-coupling condition, the dephasing rate was inversely proportional to the time constant of the telegraph noise. When there is fluctuation in the tunnel coupling constant, Gaussian decay occurs in the initial regime. We also examined the rate of dephasing due to many impurity sites. For a weak-coupling condition with fluctuation in the asymmetric bias, the obtained dephasing rate coincided with that obtained by the perturbation method using the spectral weight of a boson thermal bath, which is proportional to the inverse of the frequency.
We investigate the time evolution of a charge qubit subject to quantum telegraph noise produced by a single electronic defect level. We obtain results for the time evolution of the coherence that are strikingly different from the usual case of a harmonic-oscillator bath (Gaussian noise). When the coupling strength crosses a certain temperature-dependent threshold, we observe coherence oscillations in the strong-coupling regime. Moreover, we present the time evolution of the echo signal in a spin-echo experiment. Our analysis relies on a numerical evaluation of the exact solution for the density matrix of the qubit.
We investigate the time-evolution of a charge qubit subject to quantum telegraph noise produced by a single electronic defect level. We obtain results for the time-evolution of the coherence that are strikingly different from the usual case of a harmonic oscillator bath (Gaussian noise). When the coupling strength crosses a certain temperature-dependent threshold, we observe coherence oscillations in the strong-coupling regime. Moreover, we present the time-evolution of the echo signal in a spin-echo experiment. Our analysis relies on a numerical evaluation of the exact solution for the density matrix of the qubit.
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.