An overview is given on the demonstration of the electronic control of 1-qubit achieved in a solid state device. The scalability of this qubit is a prerequisite for a practical quantum computer of the future.
The proposal of quantum information processing has shown us the first serious possibility, though still limited in applications, to break away from the traditional spell that has been binding integration scale and processing power for some time. The qubit (quantum bit), the basic element of quantum information processing, consists of a quantum two-level system that can be brought to a superposition by an external mean. Among the numerous possible two-level systems, various typical microscopic two-level systems such as nuclear spins and atomic states have been utilized first to demonstrate the realization of quantum calculation. However, to realize a scaled-up version of a quantum computing system consisting of hundreds of qubits, a solid state electronics version of it is considered to be indispensable. We demonstrate the first electronic control of 1-qubit achieved in a solid state device using a submicron electron device called a single-electron box, a small conductive box connected to the outside by a tunnel junction and a gate capacitor. The scalability of such a solid state qubit is considered to be a prerequisite for a practical quantum computer of the future.
Recent advances in solid-state qubit technology are paving the way to fault-tolerant quantum computing systems. However, qubit technology is limited by qubit coherence time and the scaling of quantum processors is limited by the complexity of coupling quantum systems with a classical electronic infrastructure. Hence, the proposed approach is to use CMOS at cryogenic temperatures, in order to ensure physical proximity to the quantum bits, thus reducing thermal gradients and increasing compactness. In this thesis, several RF circuits designed using commercial CMOS technology have been shown to be working at cryogenic temperatures. Such circuits could be easily interfaced (or integrated, in the future) with a qubit processor. The performance of the circuits is comparable to the state-of-the-art systems, currently used as control units for qubits. Moreover, these circuits have a much smaller form factor and could be made to work inside a dilution refrigerator where the qubits are operational, hence providing the first demonstration of a scalable solution.
Single electron transistors (SETs) are nanoscale electrometers of unprecedented sensitivity, and as such have been proposed as readout devices in a number of quantum computer architectures. The authors show that the functionality of a standard SET can be multiplexed so as to operate as both readout device and control gate for solid-state qubit systems based on charge localization and spin-charge transduction. Such multiplexing offers new possibilities for gate density reduction in nanoscale devices, and may therefore play a role in scalable quantum computer architectures.