Abstract
We calculate the charge susceptibility and the linear and differential conductances of a double quantum dot coupled to two metallic reservoirs both at equilibrium and when the system is driven away from equilibrium. This work is motivated by recent progress in the realization of solid state spin qubits. The calculations are performed by using the Keldysh nonequilibrium Green function technique. In the noninteracting case, we give the analytical expression for the electrical current and deduce from there the linear conductance as a function of the gate voltages applied to the dots, leading to a characteristic charge stability diagram. We determine the charge susceptibility which also exhibits peaks as a function of gate voltages. We show how the study can be extended to the case of an interacting quantum dot.
Highlights
The basic idea is to manipulate the spin encoded in the first of the quantum dots by means of various dc or ac external fields, use the quantum exchange interdot coupling to carry out two-qubit operations, and readout the information on the spin encoded in the second quantum dot
It has been possible to establish the charge stability diagram of these systems in which the Coulomb oscillations of conductance observed in a single quantum dot are changed into a characteristic honeycomb structure as a function of the gate voltages applied to each dot.[8,9]
We propose in this paper to develop a study of the double quantum dot in the framework of the Keldysh nonequilibrium Green function technique (NEGF) following the same strategy as we developed[16,17]
Summary
The idea introduced two decades ago of a quantum computer based on solid state spin qubits[1] has led to an intensive effort in the realization of spin qubits on the basis of double quantum dots.[2,3,4] The basic idea is to manipulate the spin encoded in the first of the quantum dots by means of various dc or ac external fields, use the quantum exchange interdot coupling to carry out two-qubit operations, and readout the information on the spin encoded in the second quantum dot. We propose in this paper to develop a study of the double quantum dot in the framework of the Keldysh nonequilibrium Green function technique (NEGF) following the same strategy as we developed[16,17]. Before for a single quantum dot, i.e. by starting from the noninteracting case and incorporating interactions by using the Keldysh NEGF technique. We present here the method and the results obtained in the case of a noninteracting double quantum dot. Since we are considering the noninteracting case in the absence of dot Coulomb interaction, all the results obtained in this paper are spin independent as though we were working with a spinless quantum dot system.
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