Asymmetric Josephson Junction Layout for Quasiparticle Error Suppression
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Solution Overview
Problem
Superconducting qubits in quantum computers are prone to correlated errors due to quasiparticle excitations caused by ionizing radiation, which challenge conventional error correction schemes and the feasibility of fault-tolerant quantum computing.
Innovation Solution
Employing asymmetric Josephson junctions with varying superconducting gap energies to block quasiparticle tunneling, where the electrode with a lower gap energy is oriented to face a larger source of quasiparticles, thereby reducing correlated errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetric Josephson junctions are used in superconducting qubits, then the device structure is simple and easy to manufacture, but correlated errors occur frequently due to quasiparticle tunneling from ionizing radiation
Solution Approach 1:
The patent applies asymmetry by creating Josephson junctions with non-uniform superconducting gap energies across the junction. Specifically, one side of the junction has a higher superconducting gap energy while the other side has a lower gap energy. This asymmetric structure prevents quasiparticle tunneling from the high-gap side to the low-gap side, thereby suppressing correlated errors while maintaining manufacturing feasibility through standard deposition techniques with varying film thicknesses.
Solution Approach 2:
The patent implements local quality by varying the superconducting gap energy at different locations within the same junction structure. The first region of the substrate has a first superconducting gap energy while the second region has a second superconducting gap energy that is less than the first. This spatial variation in gap energy creates the asymmetric junction that blocks quasiparticle tunneling pathways without requiring completely different structural components throughout the device.
2Reliability
If asymmetric Josephson junctions with varying gap energies are implemented, then quasiparticle tunneling is suppressed and correlated errors are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies parameter changes by modifying the superconducting gap energy parameter across different regions of the junction. This is achieved through controlling the thickness of superconducting film layers during deposition - thinner regions produce lower gap energies while thicker regions produce higher gap energies. By adjusting this single physical parameter (film thickness) during standard fabrication processes, the asymmetric junction is created without requiring complex additional manufacturing 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
Mitigates spatiotemporally correlated qubit errors by suppressing quasiparticle tunneling, enhancing the computational accuracy and reliability of quantum computing devices.
Implementation Method 1
The asymmetric junction operates as a Josephson junction to prevent quasiparticle tunneling related to a spatiotemporally correlated error burst at the quantum computing device
Implementation Method 2
block or reduce a first tunneling rate of quasiparticles from the second region through the barrier to the first region as compared to a second tunneling rate of quasiparticles from the first region through the barrier to the second region
Data Source
AI summary
A unit of quantum information comprises a first electrode having a first thickness and providing a first superconducting gap energy at a first region of a substrate, a second electrode a second thickness that is greater than the first thickness and providing a second superconducting gap energy at a second region of the substrate that is less than the first superconducting gap energy, a barrier that separates the first region and the second region, and an asymmetric junction at the, the asymmetric junction having a low superconducting energy gap region at the second region; and a low superconducting energy gap region at the first region. The asymmetric junction is oriented so that the second electrode is a lower gap electrode having a larger external source of quasiparticles than the first electrode that can otherwise induce correlated errors to block or reduce a first tunneling rate of quasiparticles from the second region through the barrier to the first region as compared to a second tunneling rate of quasiparticles from the first region through the barrier to the second region.