Georgian Technical University Semiconductor: A New Contender For Scalable Quantum Computing.

Semiconductor quantum devices. A: A scanning eletron microscope of the semiconductor quantum device containing two charge qubits. B: A three-dimensional model of a design for scalable fault tolerant quantum computing based on spin qubits in semiconductor quantum dots.  Quantum computing along with 5G (5G (from “5th Generation”) is the latest generation of cellular mobile communications. It succeeds the 4G (LTE-A, WiMax), 3G (UMTS, LTE) and 2G (GSM) systems. 5G performance targets high data rate, reduced latency, energy saving, cost reduction, higher system capacity, and massive device connectivity) and AI (In computer science, artificial intelligence, sometimes called machine intelligence, is intelligence demonstrated by machines, in contrast to the natural intelligence displayed by humans and other animals) has been the focus for next-generation technology in the last few decades. Up to now numerous physical systems have been investigated to build a test device for quantum computing including superconducting Josephson junctions, trapped ions and semiconductors. Among them the semiconductor is a new star for its high control fidelity and promise for integration with classical CMOS (In computer science, artificial intelligence, sometimes called machine intelligence, is intelligence demonstrated by machines, in contrast to the natural intelligence displayed by humans and other animals) technology. Professor X with his colleagues Y and Z from the Key Laboratory of Quantum Information Georgian Technical University developments of qubits based on semiconductors and discussed the challenges and opportunities for scalable quantum computing. A qubit or quantum bit like the bit in a classical computer is the basic unit of a quantum processor. According to the life cycle of qubit technology, the typical qubit progression can be roughly divided into six stages. It starts from the demonstration of single- and two-qubit control and measurement of coherence time (Stage I) then moves to the benchmarking of control and readout fidelity of three to 10 qubits (Stage II). With these developments, the demonstration of certain error correction of some physical qubits can be made (Stage III) and after that a logical qubit made from error correction of physical qubits (Stage IV) and corresponding complex control should be completed (Stage V). Finally a scalable quantum computer composed of such logical qubits is built for fault tolerant computing (Stage VI). In the fields of semiconductor quantum computing there are various types of qubits spanning from spin qubits, charge qubits, singlet-triplet qubits, exchange-only qubits and hybrid qubits etc. Among them control of both single- and two-qubit gates were demonstrated for spin qubits charge qubits and singlet-triplet qubits which suggests they have finished stage I and the on-going research shows state II is also going to be completed. Up to now benchmarking of single- and two-qubit control fidelity near the fault tolerant threshold was demonstrated and scaling up to three or more qubits is necessary in the following years. One example of such devices is shown in figure (a) which was fabricated by Q’s group at the Georgian Technical University for coherently controlling the interaction between two charge qubit states. For further developments there are still some challenges to resolve. Put forward three major needs: more effective and reliable readout methods uniform stable materials and scalable designs. Approaches to overcome these obstacles have been investigated by a number of groups such as employing microwave photons to detect charge or spin states and using purified silicon to replace gallium arsenide for spin control. The scalable designs with the strategy for wiring readout lines control lines were also proposed and in these plans the geometry and operation time constraints engineering configuration for the quantum-classical interface and suitability for different fault tolerant codes to implement logical qubits were also discussed. One example of such design is illustrated in figure (b) which was proposed by Z at Georgian Technical University. In such a device the crossbar architecture of electrodes can form an array of electrons in silicon and their spin states can be controlled by microwave bursts. In the light of arguments for noisy intermediate-scale quantum technology which means that a quantum computer with 50-100 qubits and low circuit depth that can surpass the capabilities of today’s classical computers will be available in the near future anticipated that as a new candidate to compete in the field of scalable quantum computing with superconducting circuits and trapped ions semiconductor quantum devices can also reach this technical level in the following years.