Final Report Summary - SISQ (Silicon Spin Quantum Bits)
Spin qubits in coupled quantum dots (QDs) are promising for future quantum information processing (QIP). A quantum bit (qubit) is the quantum mechanical analogon of a classical bit. In general, each quantum mechanical two-level system can represent a qubit. For the spin of a single charge carrier e.g. which is a natural two-level system, the basis quantum states are given by the spin-up and the spin-down state. QIP based on the spin degree of freedom requires long spin coherence times. Silicon provides an environment where spins can be controlled with minimal decoherence because of the weak hyperfine and spin-orbit interaction. So far, most experiments have focused on electron spins, but hole spins offer great potential for spin-based QIP as well. A hole-spin qubit in silicon can benefit from its finite spin-orbit coupling, because it allows efficient electric-field driven spin resonance applicable via local gate electrodes. However, it is still unclear whether the electron spin or the hole spin is most suitable as a qubit.
We have developed an ambipolar MOSFET-based device that allows the electron and the hole transport regime to be compared in one and the same nanostructure. A top gate overlaps n++ and p++ implanted regions on the source and the drain side. Depending on the applied top gate voltage VL, a two-dimensional electron or hole gas is formed at the Si/SiO2 interface. We locally control the charge density by an additional bottom gate. Non-linear transport measurements show single-charge transport through a QD created underneath the bottom gate. The same charging energy and capacitances of the last charge transition in both regimes indicate that we load the same QD with either an electron or a hole. Ambipolar QDs with single-charge occupancy can break new ground in spin-based QIP, since they have the potential to act as a qubit comparator where the suitability of electron-spin and hole-spin qubits can be evaluated in the same crystalline environment. Taking the advantages of either qubit one could think of future “quantum CMOS” technology based on ambipolar QDs.
We have developed an ambipolar MOSFET-based device that allows the electron and the hole transport regime to be compared in one and the same nanostructure. A top gate overlaps n++ and p++ implanted regions on the source and the drain side. Depending on the applied top gate voltage VL, a two-dimensional electron or hole gas is formed at the Si/SiO2 interface. We locally control the charge density by an additional bottom gate. Non-linear transport measurements show single-charge transport through a QD created underneath the bottom gate. The same charging energy and capacitances of the last charge transition in both regimes indicate that we load the same QD with either an electron or a hole. Ambipolar QDs with single-charge occupancy can break new ground in spin-based QIP, since they have the potential to act as a qubit comparator where the suitability of electron-spin and hole-spin qubits can be evaluated in the same crystalline environment. Taking the advantages of either qubit one could think of future “quantum CMOS” technology based on ambipolar QDs.