Quantum dots Recent advances in materials science have made possible the fabrication of small conducting devices in semiconductor materials known as quantum dots, where from few up to several thousand electrons are confined to a region whose linear size is between nanometres to a few microns. The size and shape of these structures and therefore the number of electrons they contain, can be precisely controlled. Because the electronic motion is restricted in all three dimensions, a quantum dot is sometimes refered to as a zero-dimensional system. The transport properties of a quantum dot can be measured by coupling it to leads and passing current through the dot, conductance through a quantum dot is characterized by quantum coherence. A non-zero addition energy when adding an additional electron into the dot can lead to a charge blockade for tunneling of electrons on and off the dot, this addition energy includes charging energy which is from Coulomb repulsion of the electrons already in the dot and level quantization energy which is the single-particle energy level differences of the dot. This phenomenon is called as Coulomb blocakade, it can be removed by changing the gate voltage. Since they were first produced about a decade ago, quantum dots have become a powerful tool for investigating the physics of small, coherent quantum systems. The ability to control their shape, size, number of electrons, and coupling strength has made them particularly attractive for experimental studies and applications, they have been transformed from laboratory curiosities to the building blocks for a future computer industry. We investigate occupation number of electrons inside two level single dot in presence of magnetic field by using exact diagonalization method.
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