Spin Qubit Coupling via Self-Aligned Back Gate
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Solution Overview
Problem
Existing quantum devices with spin qubits lack modulable quantum coupling, preventing effective communication and operation as multiple qubits, due to fixed quantum coupling and potential misalignment issues leading to parasitic capacitances and asymmetry.
Innovation Solution
A quantum device with adjustable tunnel barriers between qubit confinement regions, controlled by a doped region in the support layer, allowing for modulated coupling without superimposed gates, thus minimizing capacitive coupling and ensuring self-alignment of rear control gates with front gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If superimposed gates are used to control coupling between qubits, then coupling control is achieved, but strong capacitive coupling is generated between the gates
Solution Approach 1:
The invention transitions from a planar gate configuration to a three-dimensional structure by placing the rear control gate in the support layer beneath the buried dielectric layer, while front gates remain in the semiconductor layer. This vertical separation in different layers eliminates strong capacitive coupling while maintaining coupling control capability through the tunnel barrier modulation.
Solution Approach 2:
The buried dielectric layer acts as an intermediary between the rear control gate in the support layer and the front gates in the semiconductor layer. This dielectric medium provides electrical insulation that prevents direct capacitive coupling between the gates, while still allowing the rear gate to modulate the tunnel barrier height through field effect.
2Ease of operation
If conventional gate structures are used, then qubit control is possible, but misalignment and parasitic capacitances occur
Solution Approach 1:
The rear control gate structure is designed to be self-aligned with the front gates through the semiconductor portion geometry. The doped region in the support layer is positioned to align automatically with the tunnel barrier region during fabrication, eliminating the need for complex alignment procedures and reducing parasitic capacitances from misalignment.
Solution Approach 2:
The support layer and buried dielectric layer are prepared in advance before introducing the front gates and tunnel barrier. This preliminary structuring establishes the rear control gate position and geometry beforehand, ensuring proper alignment when the tunnel barrier is formed, and preventing misalignment issues during subsequent fabrication steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables flexible and efficient communication between qubits by adjusting the tunnel barrier, reducing parasitic capacitances and asymmetry, allowing for reliable operation as multiple qubits with improved performance.
Implementation Method 1
The coupling between the qubit confinement regions is adjustable thanks to a tunnel barrier formed by the coupling region, the level of this tunnel barrier being adjustable as a function of the electric potential applied to the doped region of the support layer which acts by field effect on the level of this tunnel barrier
Data Source
Figure 1A~1B
Figure 2A~3B
Figure 4A~5A
AI summary
Spin qubit quantum device (100), comprising: - a portion of semiconductor (104) disposed on a buried dielectric layer (106) of a semiconductor-on-insulator substrate also comprising a support layer (102) of semiconductor, in which distinct first parts (108a, 108b) each form a confinement region of one of the qubits and are separated from each other by a second part (116) forming a coupling region between the confinement regions of the qubits; - front gates (110) each at least partially covering one of the first parts of the portion of semiconductor; and in which the support layer includes a doped region (118) a portion of which is disposed vertically above the second part of the portion of semiconductor and is self-aligned with respect to the front gates, and forms a back gate for controlling the coupling between the confinement regions of the qubits.