Properties and control of an hybrid qubit based on a double quantum dot.

A. Y. RAMOS, O. OSENDA

Buenos Aires

Congreso; XVIII Giambiagi Winter School: Quantum Chaos & Control; 2016

Departamento de F´ısica Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires, Argentina

Electronic spins confined in semiconductor quantum dots is considered one of themost promising alternatives as qubits. It has been thoroughly investigated whatthe typical problems associated with its implementation are. This problems includequantum operation times which ar e very short or very large, decoherence, difficultyin preparing a specific initial state, among others. A remarkable difficulty relies inthe low coupling between electronic spin and external magnetic fields applied to thequantum dot. In consequence, the operation times to generate, for instance, a logicalgate become excessively large allowing the decoherence mechanisms to deterioratethe quantum state. In order to solve this kind of problem, it has been proposedto use hybrid quantum dots, which have short operation times. In hybrid qubits,information is stored in the el ectronic spin whereas the operations on the qubitare performed through external electric fields. In this work we study the quantumdynamics of a hybrid qubit based on a double quantum dot in presence of constantexternal magnetic fields and periodic time dependent electric fields. We model thequbit as a quartic potential well and we use the effective mass approximation. Inthis work, we not only consider the usual spinorial depend ence with the magneticfield but also we include the orbital dependence. Through a oscillatory electric fieldwe control the Rabi oscillations of the qubit. We analyze the robustness of thesystem when the initial state is different from an eigenstate of the system and whenthe forcing frequency is slightly different to the resonance frequency of the system.Since the original proposal of DiVincenzo and Loss (Phys. Rev. A57, 120 (1998))to use the spin of an electron trapped in a quantum dot as qubit, a lot of workhas been done to circumvent the huge difficulties associated to the implementation.One of the major problems associated to spin qubits is the long timerequired toimplement quantum logical gates or other control operations. This is so becausethe low strength of the coupling between the spin andthe external magnetic fields