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Physical Review B

Decoherence of a charge qubit embedded inside a suspended phonon cavity

Ying-Yen Liao, Y. N. Chen, W. C. Chou, Der-San Chuu

Published Jan 14, 2008• 13 citations
Publisher

Abstract

This study elucidates the theory of phonon-induced decoherence of a double dot charge qubit that is embedded inside a suspended semiconductor slab. The influences of the lattice temperature, width of the slab, and positions of the dots on the decoherence are analyzed. Numerical results indicate that the decoherence in the slab system is weaker than that in a bulk environment. In particular, the decoherence is markedly suppressed by the inhibition of the electron-phonon coupling. Such a system with low decoherence may be useful for manipulating the qubits.

DOI
10.1103/physrevb.77.033303

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This study elucidates the theory of phonon-induced decoherence of a double dot charge qubit that is embedded inside a suspended semiconductor slab. The influences of the lattice temperature, width of the slab, and positions of the dots on the decoherence are analyzed. Numerical results indicate that the decoherence in the slab system is weaker than that in a bulk environment. In particular, the decoherence is markedly suppressed by the inhibition of the electron-phonon coupling. Such a system with low decoherence may be useful for manipulating the qubits.
We investigate the decoherence of a charge qubit in a double quantum dot which is formed in a free-standing semiconductor slab. The dots are spatially arranged to align along a particular direction. Confined phonons in the slab have a remarkable influence on the dynamics of a qubit system. We show that the decoherence of such a qubit strongly depends on the positions of the dots. By varying the tunnel coupling, the decoherence differs significantly in laterally and vertically coupled quantum dots. A robust qubit is further achieved due to suppression of electron-phonon coupling. Moreover, the coherent evolution of the system is analyzed by modulating the interdot direction.
We study phonon-induced pure dephasing in a double-quantum-dot qubit that is embedded in a freestanding slab. The dispersion relations are evaluated to probe the phonon characteristics of the slab. The pure dephasing factor in the off-diagonal elements of the density matrix is calculated. Numerical results demonstrate that time evolution of this factor exhibits a nonmonotonic feature, resulting from the phonon confinement effect. Significant contribution from individual phonon mode is analyzed in detail. We also study effects of temperature and double-dot position on the pure dephasing. In particular, two remarkable oscillations are observed due to phonon van Hove singularities.
We study decoherence of a quantum dot charge qubit due to coupling to piezoelectric acoustic phonons in the Born--Markov approximation. After including appropriate form factors, we find that phonon decoherence rates are one to two orders of magnitude weaker than was previously predicted. We calculate the dependence of the QQQ factor on lattice temperature, quantum dot size, and interdot coupling. Our results suggest that mechanisms other than phonon decoherence play a more significant role in current experimental setups.
We investigate electron charge decoherence in a laterally coupled single-electron semiconductor double quantum dot through electron-phonon interaction. We analytically and numerically evaluate the relaxation and dephasing rates due to electron coupling to both acoustic and optical phonons, and explore the system parameter space in terms of interdot distance, strength of single-dot confinement, and interdot coupling strength. Our numerical results show that the electron scattering rates are strongly dependent on the strength of the electron confinement and the size of the system. In addition, although the most dominant factor that determines the charge decoherence rate is the energy splitting between the charge qubit states, the details of the double dot configuration are also very important.
We study theoretically the phonon-induced relaxation and decoherence processes in the hybrid qubit in silicon. A hybrid qubit behaves as a charge qubit when the detuning is close to zero and as a spin qubit for large detuning values. It is realized starting from an electrostatically defined double quantum dot where three electrons are confined and manipulated through only electrical tuning. By employing a three-level effective model for the qubit and describing the environment bath as a series of harmonic oscillators in the thermal equilibrium states, we extract the relaxation and decoherence times as a function of the bath spectral density and of the bath temperature using the Bloch-Redfield theory. For Si quantum dots the energy dispersion is strongly affected by the physics of the valley, i.e., the conduction band minima, so we also included the contribution of the valley excitations in our analysis. Our results offer fundamental information on the system decoherence properties when the unavoidable interaction with the environment is included and temperature effects are considered.