Semiconductor quantum dot qubits
- PDF / 725,018 Bytes
- 8 Pages / 585 x 783 pts Page_size
- 68 Downloads / 278 Views
Introduction The goal of developing a large-scale quantum information processor has attracted much interest and activity over the past decade, not just because quantum information processors have the potential to efficiently solve problems that are not tractable using classical computers,1 but also because substantial fundamental physics and materials science questions must be understood in order to fabricate such a device. To understand how large a quantum computer needs to be in order for it to be potentially much more powerful than a classical one, it is useful to compare the number of quantities needed to describe a physical state classically and quantum-mechanically.2 For a system with M classical degrees of freedom, the size of the quantum mechanical description grows exponentially with M. A quantum computer with N qubits has the potential to outperform a current classical computer with M transistors only when N > log2M. For M = 109, typical of a personal computer, one needs N > 30. Therefore, the current state of the art of 15 qubits achieved in ion traps,3 though extremely impressive, does not yet improve upon classical computers from a purely computational point of view. Practically useful quantum computational devices will require at least hundreds and probably thousands of qubits.4 Therefore, a feasible path to scalability is an important criterion for the development of quantum information processing devices. In 1998, Loss and DiVincenzo proposed to use electron spins in quantum dots formed in quantum wells as qubits, through
the use of electrostatic fields generated by surface gates.5 Constructing qubits using such electrically gated quantum dots has attracted substantial interest and effort, both theoretical6–11 and experimental.12–17 While fabrication of gated quantum dots with few-electron occupancy is demanding, this strategy has the important advantage that the metal top gates that are used to define the quantum dots can also be used to perform the necessary manipulations.18 Control of the interactions between dots is possible simply by changing voltages on the electrostatic gates and is greatly facilitated by the relatively large spatial extent of electron wave functions in semiconductor dots. Because of the similarities with classical electronics, it is plausible that both scale-up and integration with classical electronics will be feasible. However, first it is necessary to construct the basic building blocks of a quantum computer: controllable single qubits and high-fidelity two-qubit gates. Quantum dot-based single qubits have been demonstrated in both III–V and Group IV materials systems,12,15,17,19,20 while two-qubit gates have been demonstrated in gallium arsenide devices.16,21 However, further improvements to the fidelity of both the single and two-qubit gates are required to achieve the performance necessary for implementation of a scalable quantum processor.4 This article discusses the materials science and engineering underlying the development of quantum dot qubits. The main focus is on q
Data Loading...
