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A Novel Method for Forming Protected Helical States in GaAs/AlGaAs heterostructures aimed for Topological Quantum Computation

Technology Number: 

1844
Summary 

An innovative technique and system for forming 1-dimensional counter-propagating electronic states with opposite spins – helical states. Such a system when coupled to a conventional superconductor is expected to form a topological superconductor hosting Majorana zero modes which can be used as topologically protected quantum bits.

Quantum computing is a technology that holds the potential to revolutionize computational power and eclipse even today’s most powerful computers. Thus, the technology holds potential for many applications such as cryptography, computational chemistry, machine learning, artificial intelligence and optimization. However, the basic building blocks of a quantum computer, the quantum bits (qubits), are fragile and prawn to errors. There is therefore a major need to develop quantum hardware that allows for complex quantum computations to be performed without errors and many platforms are being explored to achieve this.

In recent years, there has been a great interest in a novel type of qubits called topological qubits, which have a unique protection from the typical fragility of other qubit systems. Several successful experiments (mostly using semiconducting nanowires) have demonstrated initial success in forming these qubits and there are currently great effort to develop these systems. However, challenges in making reproducible and identical qubits with them and the limited fabrication methods of these systems, make scaling up very difficult.

The present technology from the group of Prof. Mordechai Heiblum at the Weizmann Institute of Science offers a novel platform that can be used to forming topological qubits. This platform utilizes 2-dimensional-electron-gas systems where rich, robust and scalable fabrication techniques, which have been developed for several decades, exist. Moreover, the system utilizes the robust and well understood edge states of the quantum Hall effect and allows for an increased flexibility in manipulation of these states in comparison to similar platform based on 1d spin-orbit based semiconductors.

Advantages


·         Robust ­– utilizes edge states of the quantum hall effect.

·         Flexibility in manipulation – 2-dimensional system compared to current 1-dimensional systems.

·         Standard materials and fabrication methods – for instance GaAs/AlGaAs heterostructures.

·         Highly controllable

·         Scalable


Technology's Essence


Topological qubits, which have sparked intensive interest in recent years are based on the engineering of an exotic state of matter called a topological superconductor. To engineer a topological superconductor, superconductivity from a conventional superconductor is induced in a so called 1-dimentional helical system - a system of two counter-propagating, 1-dimnesional states with opposite spins.

The group of Prof. Heiblum has developed a new method and a platform to engineer robust and highly controllable 1-dimnensional helical systems. The method was implemented in GaAs/AlGaAs heterostructures where the existence of well-known MBE growth techniques and well-known fabrication methods allows for a high level of control, high level of flexibility and diversity in devices’ design possibilities, and easy scale up.

The essence of the technology is the use of a carefully designed quantum well structure which hosts two sub-bands of 2D electrons; each tuned to the quantum Hall effect regime. By electrostatic gating of different areas of the structure, counter-propagating integer, as well as fractional, edge modes (belonging to Landau-levels with opposite spins) are formed – rendering the modes helical. The quantum well must be designed so that charge transfer between the two sub-bands allows for the counter propagating edge states to be formed in the interface between two gated regions.