Low-Surface-Loss Quantum Devices with Recessed Transmon Electrodes
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Solution Overview
Problem
Existing quantum devices suffer from significant surface losses due to imperfections in materials like silicon and silicon dioxide proximate to the top surface of transmon elements, which limit the resonance quality factor (Q) and coherence time (T1) of qubits, hindering the development of scalable quantum computing devices.
Innovation Solution
The implementation of transmon elements with recessed electrodes and reduced dielectric layer thickness, along with rounded edges, to minimize electric field amplitudes and redistribute energy density within the dielectric layer, thereby reducing surface losses and maintaining capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If transmon elements use standard flat electrodes on thick dielectric layers, then manufacturing is simpler, but surface losses are high due to material imperfections near the top surface
Solution Approach 1:
The patent transitions from two-dimensional flat electrodes to three-dimensional recessed electrodes with rounded edges. By creating recesses in the dielectric layer and forming electrodes within these recesses, the design moves the electrode-dielectric interface away from the problematic top surface, reducing surface losses by up to three orders of magnitude while maintaining manufacturability through standard semiconductor processing techniques
Solution Approach 2:
The patent specifically employs rounded edges at the corners of recesses and curved electrode geometries instead of sharp corners. This curvature eliminates field concentration points that would otherwise create hotspots for energy loss, directly addressing the surface loss problem while the rounded features can be formed using conventional photolithography and etching processes
2Loss of energy
If dielectric layer thickness is reduced to move electrodes away from lossy surface, then surface losses decrease, but capacitance may be affected
Solution Approach 1:
The patent applies different dielectric thicknesses at different locations: thinner dielectric within recesses to reduce surface losses, and thicker dielectric in inter-qubit coupling regions to maintain appropriate capacitance values. This spatial variation of dielectric properties allows simultaneous optimization of both loss reduction and capacitance control
Solution Approach 2:
The patent systematically varies geometric parameters including recess depth (0.1-1.0 micrometers), electrode width, and dielectric thickness to optimize the balance between surface loss reduction and capacitance maintenance. These parameter adjustments are achieved through controlled fabrication processes that can precisely tune the final device characteristics
3Loss of energy
If recesses are formed in dielectric layer to reduce surface losses, then energy density is redistributed, but manufacturing precision requirements increase
Solution Approach 1:
The patent incorporates recess formation as an early step in the fabrication sequence, before electrode deposition. This preliminary creation of the recess structure using photolithography and etching allows subsequent electrode formation to proceed with standard techniques, distributing the precision requirements across multiple well-established process steps rather than requiring a single high-precision operation
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
This design achieves a substantial reduction in surface losses by up to three orders of magnitude, enhancing the resonance quality factor and coherence time of transmon elements, facilitating the development of more efficient quantum computing devices.
Implementation Method 1
Superconducting qubits are among the leading candidates for quantum computing due to their ability to be fabricated using conventional semiconductor manufacturing techniques, their scalability, and their long coherence times.
Implementation Method 2
Quantum computers utilize quantum mechanical effects to store, transport, and process information in ways that are fundamentally different from classical computers.
Data Source
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AI summary
Circuits and methods of operation that can facilitate reducing surface losses for quantum devices are provided. In one example, a quantum device can comprise a dielectric layer, a first electrode, and a second electrode. The dielectric layer can comprise a recess formed in a surface of the dielectric layer that reduces a thickness of the dielectric layer from a first thickness external to a footprint of the recess to a second thickness within the footprint of the recess. The second thickness can be less than the first thickness. The first electrode can be positioned within the footprint of the recess. The second electrode can be electrically isolated from the first electrode by the dielectric layer. The first and second electrodes can be positioned on opposing surfaces of the dielectric layer.