Practical design and simulation of silicon-based quantum-dot qubits

Abstract

Spins based in silicon provide one of the most promising architectures for quantum computing. Quantum dots are an inherently scalable technology. Here, we combine these two concepts into a workable design for a silicon-germanium quantum bit. The novel structure incorporates vertical and lateral tunneling, provides controlled coupling between dots, and enables single electron occupation of each dot. Precise modeling of the design elucidates its potential for scalable quantum computing. For the first time it is possible to translate the requirements of faulttolerant error correction into specific requirements for gate voltage control electronics in quantum dots. We demonstrate that these requirements are met by existing pulse generators in the kHzMHz range, but GHz operation is not yet achievable. Our calculations further pinpoint device features that enhance operation speed and robustness against leakage errors. We find that the component technologies for silicon quantum dot quantum computers are already in hand.Quantum computing offers the prospect of breaking out of the classical von Neumann paradigm that dominates present-day computation. It would enable huge speedups of certain very hard problems, notably factorization 1 . Constructing a quantum computer (QC) presents many challenges, however. Chief among these is scalability: the 10 6 qubits needed for simple applications 2 far exceed the potential of existing implementations. This requirement points strongly in the direction of Si-based electronics for QC. Silicon devices offer the advantage of long spin coherence times, fast operation, and a proven record of scalable integration.Specific Si-based qubit proposals utilize donor-bound nuclear 3,4 or electronic 5 spins as qubits. However, quantum dots can also be used to house electron spins 6-8 , and they have the advantage that the electrostatic gates controlling qubit operations are naturally aligned to each qubit. These proposals describe an intriguing possibility. Our aim here is to describe a new SiGe qubit design, and, just as importantly, to carry out detailed modeling of a specific design for the first time. Modeling provides a proof of principle, pinpoints problem areas, and suggests new directions.The fundamental goal of our design is the ability to reduce the electron occupation of an individual dot precisely to one, as in vertically coupled structures. It may be possible to use the spin of multi-electron quantum dots as qubits, but single occupation is clearly desirable. The spin state "up" = 0 or "down" = 1 , stores the quantum bit of information. At the same time, it is necessary to have tunable coupling between neighboring dots. This is achieved by controlled movement of electrons along the quantum well that contains two dots. The solution is to draw on two distinct quantum dot technologies: lateral and vertical tunneling quantum dots 9 .

Few electron limit of n-type metal oxide semiconductor single electron transistors

“…Silicon SETs based on CMOS technology represent a natural environment for realizing scalable electron spin and orbital quantum devices for quantum information processing [1] because of long coherence times [2] and scalability. The need to create a workable Hilbert space with good quantum numbers [3] at increasingly high temperatures towards room temperature operability implies the reduction of the size of the quantum dots down to the current limits of fabrication.…”

Predicting and Understanding Order of Heteroepitaxial Quantum Dots

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] SAQDs are the result of a transition from 2D growth to 3D growth in strained epitaxial films such as Si x Ge 1Àx =Si and In x Ga 1Àx As/GaAs: This process is known as Stranski-Krastanow growth or VolmerWebber growth. 3,[15][16][17] In applications, order of SAQDs is a key factor.…”

Double occupancy errors in quantum computing operations: Corrections to adiabaticity

“…2 it was proposed to use the spin of electrons residing in semiconductor quantum dots as qubits. [8][9][10][11][12][13][14][15] In this paper we revisit the quantum dynamics of gate operations between qubits of this type. Such two-qubit operations are performed by varying the amplitude of electron tunneling between the dots via external electric potentials.…”