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Inverse mask design for interference lithography using automatic differentiable wave propagation
Authors:
Chuntian Cao,
Jangwoon Sung,
Jack Griffiths,
Yuan Gao,
Xi Yu,
Paul Baity,
Nikhil Tiwale,
Zhitian Shi,
Juhong Ahn,
Shinjae Yoo,
Yong S. Chu,
Chang-Yong Nam
Abstract:
Interference lithography (IL) is powerful for fabricating high-resolution periodic nanostructures, but designing masks to produce non-periodic patterns remains challenging. We introduce a gradient-based optimization framework for binary IL mask design using automatic differentiation. The forward model is implemented using the differentiable angular spectrum method (ASM). The inverse mask design is…
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Interference lithography (IL) is powerful for fabricating high-resolution periodic nanostructures, but designing masks to produce non-periodic patterns remains challenging. We introduce a gradient-based optimization framework for binary IL mask design using automatic differentiation. The forward model is implemented using the differentiable angular spectrum method (ASM). The inverse mask design is formulated as an optimization problem, where the mask logits are updated through backpropagation of the loss between the simulated field amplitude and the target pattern. We optimize a mask that reproduces a target pattern with only 0.1% isolated pixel-level defects, resolving features at half the mask pixel pitch. To scale mask optimization, we employ the shifted ASM, which partitions the mask into patches that are propagated independently and summed at the image plane. For a 3.84 mm$\times$3.84 mm mask, shifted ASM with 16 patches reduces peak GPU memory by 3.8$\times$ at only 1.3$\times$ runtime cost relative to standard ASM. With gradient checkpointing, peak memory is reduced by 7.4$\times$ at 2$\times$ runtime. Distributing across multiple GPUs further accelerates the optimization. This work establishes a physics-informed, machine learning-driven approach for IL mask design, moving a step further towards complex, non-periodic patterns. The source code is available at https://github.com/chuntian236/holography-optimization.git .
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Submitted 5 August, 2026;
originally announced August 2026.
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Characterizing Niobium Nitride Superconducting Microwave Coplanar Waveguide Resonator Array for Circuit Quantum Electrodynamics in Extreme Conditions
Authors:
Paniz Foshat,
Paul Baity,
Sergey Danilin,
Valentino Seferai,
Shima Poorgholam-Khanjari,
Hua Feng,
Oleg A. Mukhanov,
Matthew Hutchings,
Robert H. Hadfield,
Muhammad Imran,
Martin Weides,
Kaveh Delfanazari
Abstract:
The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material candidate for applications in superconducting quantum technology. However, NbN-based devices and circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplana…
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The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material candidate for applications in superconducting quantum technology. However, NbN-based devices and circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays, with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor (Qi) decreases from Qi ~ 1.07*10^6 in a high power regime (< nph > = 27000) to Qi ~ 1.36 *10^5 in single photon regime at temperature T = 100 mK. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature dependence internal quality factor and frequency tuning of the coplanar waveguide resonators to characterise the quasiparticle density of NbN. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure the resonators' resonance frequency and internal quality factor at single photon regime in response to in-plane magnetic fields B||. We verify that Qi stays well above 10^4 up to B|| = 240 mT in the photon number < nph > = 1.8 at T = 100 mK. Our results may pave the way for realising robust microwave superconducting circuits for circuit quantum electrodynamics (cQED) at high magnetic fields necessary for fault-tolerant quantum computing, and ultrasensitive quantum sensing.
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Submitted 4 June, 2023;
originally announced June 2023.
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Strong magnon-photon coupling with chip-integrated YIG in the zero-temperature limit
Authors:
Paul G. Baity,
Dmytro A. Bozhko,
Rair Macêdo,
William Smith,
Rory C. Holland,
Sergey Danilin,
Valentino Seferai,
João Barbosa,
Renju R. Peroor,
Sara Goldman,
Umberto Nasti,
Jharna Paul,
Robert H. Hadfield,
Stephen McVitie,
Martin Weides
Abstract:
The cross-integration of spin-wave and superconducting technologies is a promising method for creating novel hybrid devices for future information processing technologies to store, manipulate, or convert data in both classical and quantum regimes. Hybrid magnon-polariton systems have been widely studied using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and three-dimensional microwave p…
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The cross-integration of spin-wave and superconducting technologies is a promising method for creating novel hybrid devices for future information processing technologies to store, manipulate, or convert data in both classical and quantum regimes. Hybrid magnon-polariton systems have been widely studied using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and three-dimensional microwave photon cavities. However, limitations in YIG growth have thus far prevented its incorporation into CMOS compatible technology such as high quality factor superconducting quantum technology. To overcome this impediment, we have used Plasma Focused Ion Beam (PFIB) technology -- taking advantage of precision placement down to the micron-scale -- to integrate YIG with superconducting microwave devices. Ferromagnetic resonance has been measured at millikelvin temperatures on PFIB-processed YIG samples using planar microwave circuits. Furthermore, we demonstrate strong coupling between superconducting resonator and YIG ferromagnetic resonance modes by maintaining reasonably low loss while reducing the system down to the micron scale. This achievement of strong coupling on-chip is a crucial step toward fabrication of functional hybrid quantum devices that advantage from spin-wave and superconducting components.
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Submitted 14 June, 2021; v1 submitted 16 April, 2021;
originally announced April 2021.
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An Electromagnetic Approach to Cavity Spintronics
Authors:
Rair Macêdo,
Rory C. Holland,
Paul G. Baity,
Luke J. McLellan,
Karen L. Livesey,
Robert L. Stamps,
Martin P. Weides,
Dmytro A. Bozhko
Abstract:
The fields of cavity quantum electrodynamics and magnetism have recently merged into \textit{`cavity spintronics'}, investigating a quasiparticle that emerges from the strong coupling between standing electromagnetic waves confined in a microwave cavity resonator and the quanta of spin waves, magnons. This phenomenon is now expected to be employed in a variety of devices for applications ranging f…
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The fields of cavity quantum electrodynamics and magnetism have recently merged into \textit{`cavity spintronics'}, investigating a quasiparticle that emerges from the strong coupling between standing electromagnetic waves confined in a microwave cavity resonator and the quanta of spin waves, magnons. This phenomenon is now expected to be employed in a variety of devices for applications ranging from quantum communication to dark matter detection. To be successful, most of these applications require a vast control of the coupling strength, resulting in intensive efforts to understanding coupling by a variety of different approaches. Here, the electromagnetic properties of both resonator and magnetic samples are investigated to provide a comprehensive understanding of the coupling between these two systems. Because the coupling is a consequence of the excitation vector fields, which directly interact with magnetisation dynamics, a highly-accurate electromagnetic perturbation theory is employed which allows for predicting the resonant hybrid mode frequencies for any field configuration within the cavity resonator, without any fitting parameters. The coupling is shown to be strongly dependent not only on the excitation vector fields and sample's magnetic properties but also on the sample's shape. These findings are illustrated by applying the theoretical framework to two distinct experiments: a magnetic sphere placed in a three-dimensional resonator, and a rectangular, magnetic prism placed on a two-dimensional resonator. The theory provides comprehensive understanding of the overall behaviour of strongly coupled systems and it can be easily modified for a variety of other systems.
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Submitted 25 October, 2020; v1 submitted 22 July, 2020;
originally announced July 2020.