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Applied Physics Letters

An on-chip compact Chebyshev filter for semiconductor quantum dots in cQED architecture

Ze-Cheng Wei, Song-Yan Deng, Zi-Qing Huang, Yuan Kang, Zong-Hu Li, Yong-Qiang Xu, Ranran Cai, Bao‐Chuan Wang, Hai-Ou Li, Gang Cao, Guo‐Ping Guo

Published Mar 1, 2025• 0 citations
Publisher

Abstract

Circuit quantum electrodynamics (cQED) architecture enables long-range qubit coupling and nondemolition readout, with a key requirement of a small resonator photon leakage rate, κ. Several types of low-pass on-chip LC filter designs have been proposed to mitigate κ. However, the non-flat frequency response in the passband introduces waveform distortion, which may degrade qubit performance. In this work, we develop an on-chip compact Chebyshev filter for semiconductor quantum dots in cQED architecture. It exhibits a flat passband up to a 2 GHz cutoff frequency with microwave attenuation <−30 dB at 7 GHz, without observing the sign of damping oscillations induced by waveform distortion. We also analyze the integration of the filter with the cQED architecture and demonstrate that microwave attenuation meets the need for integration. The developed Chebyshev filter paves the way for the precise control of semiconductor quantum dots in cQED architecture with a low photon leakage rate.

DOI
10.1063/5.0256274

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Circuit quantum electrodynamics (cQED) architecture enables long-range qubit coupling and nondemolition readout, with a key requirement of a small resonator photon leakage rate, κ. Several types of low-pass on-chip LC filter designs have been proposed to mitigate κ. However, the non-flat frequency response in the passband introduces waveform distortion, which may degrade qubit performance. In this work, we develop an on-chip compact Chebyshev filter for semiconductor quantum dots in cQED architecture. It exhibits a flat passband up to a 2 GHz cutoff frequency with microwave attenuation <−30 dB at 7 GHz, without observing the sign of damping oscillations induced by waveform distortion. We also analyze the integration of the filter with the cQED architecture and demonstrate that microwave attenuation meets the need for integration. The developed Chebyshev filter paves the way for the precise control of semiconductor quantum dots in cQED architecture with a low photon leakage rate.
We develop an engineered microwave environment for coupling high Q superconducting resonators to quantum dots using a multilayer fabrication stack for dot control wiring. Analytical and numerical models are presented, which show that high resonator quality factors can be attained by either minimizing the parasitic coupling capacitance to the leads or creating a low effective environmental impedance at the cavity frequency. We implement the later approach by fabricating low characteristic impedance (Zg≈10 Ω) microstrips on-chip for the dot bias wiring and show resonator quality factors of 8140 that can be attained without the addition of explicit filtering. Using this approach, we demonstrate single electron occupation in double and triple dots detected via dipole or quadrupole coupling to a superconducting resonator. Additionally, by using multilayer fabrication, we are able to improve ground plane integrity and keep microwave crosstalk below −20 dB out to 18 GHz while maintaining high wire density, which will be necessary for future circuit quantum electrodynamics quantum dot processors.
Circuit quantum electrodynamics (QED) employs superconducting microwave resonators as quantum buses. In circuit QED with semiconductor quantum-dot-based qubits, increasing the resonator impedance is desirable as it enhances the coupling to the typically small charge dipole moment of these qubits. However, the gate electrodes necessary to form quantum dots in the vicinity of a resonator inadvertently lead to a parasitic port through which microwave photons can leak, thereby reducing the quality factor of the resonator. This is particularly the case for high-impedance resonators, as the ratio of their total capacitance over the parasitic port capacitance is smaller, leading to larger microwave leakage than for 50-x resonators. Here, we introduce an implementation of on-chip filters to suppress the microwave leakage. The filters comprise a high-kinetic-inductance nanowire inductor and a thin-film capacitor. The filter has a small footprint and can be placed close to the resonator, confining microwaves to a small area of the chip. The inductance and capacitance of the filter elements can be varied over a wider range of values than their typical spiral inductor and interdigitated capacitor counterparts. We demonstrate that the total linewidth of a 6.4 GHz and approximately 3-kx resonator can be improved down to 540 kHz using these filters.
Circuit quantum electrodynamics with qubits based on semiconductor quantum dots can enable long-range two-qubit gates between distant spins, or improve gate-based charge sensing for readout. Compared to conventional resonators, high-impedance resonators improve the coupling to the qubits, but their losses to the quantum dot's leads are also larger. This study implements on-chip filtering using high-kinetic-inductance nanowires and thin-film capacitors to mitigate this source of losses. These filters are very compact and easily extended to a large number of leads, all while preserving state-of-the-art resonator quality factors.
Semiconductor quantum dots in silicon demonstrate exceptionally long spin lifetimes as qubits and are therefore promising candidates for quantum information processing. However, control and readout techniques for these devices have thus far employed low frequency electrons, in contrast to high speed temperature readout techniques used in other qubit architectures, and coupling between multiple quantum dot qubits has not been satisfactorily addressed.This dissertation presents the design and characterization of a semiconductor charge qubit based on double quantum dot in silicon with an integrated microwave resonator for control and readout. The 6 GHz resonator is designed to achieve strong coupling with the quantum dot qubit, allowing the use of circuit QED control and readout techniques which have not previously been applicable to semiconductor qubits. To achieve this coupling, this document demonstrates successful operation of a novel silicon double quantum dot design with a single active metallic layer and a coplanar stripline resonator with a bias tee for dc excitation.Experiments presented here demonstrate quantum localization and measurement of both electrons on the quantum dot and photons in the resonator. Further, it is shown that the resonator-qubit coupling in these devices is sufficient to reach the strong coupling regime of circuit QED. The details of a measurement setup capable of performing simultaneous low noise measurements of the resonator and quantum dot structure are also presented here.The ultimate aim of this research is to integrate the long coherence times observed in electron spins in silicon with the sophisticated readout architectures available in circuit QED based quantum information systems. This would allow superconducting qubits to be coupled directly to semiconductor qubits to create hybrid quantum systems with separate quantum memory and processing components.
Maturing hybrid circuit quantum electrodynamics architectures composed of semiconductor quantum dots and on-chip microwave resonators promise an effective approach for quantum nondemolition readouts in semiconductor systems. Here, we study quantum coherence in a semiconductor charge qubit coupled with a high-impedance resonator. The qubit is controlled by a periodic pulse sequence, and a dispersive measurement is performed by measuring the time-averaged resonator response. From the Rabi oscillation and Ramsey fringe measurements, the coherence time of the charge qubit is determined as T2, Rabi ≈2.7 ns and T2, Ramsey ≈3.5 ns. Compared with the time-resolved (pulsed) measurement, this time-averaged dispersive measurement process eliminates the limitation caused by the resonator response time, enabling a high repetition rate of the pulse sequence in the experiments.
Semiconductor quantum dot spin qubits, which employ radio frequency (RF) techniques for manipulation and readout, present a compelling pathway toward scalable quantum computation. We introduce a robust, miniaturized, and modular RF package designed for high-fidelity, low-crosstalk control of quantum dot qubit systems. This design integrates a master board with an interchangeable daughterboard for rapid sample exchange. Its compact footprint (28 × 50 × 12 mm3) is compatible with standard dilution refrigerator stages. The module provides 48 low-pass-filtered DC bias lines, 28 of which support combined RF/DC operation for qubit control. Dedicated RF lines include eight microwave channels with a DC to 6 GHz bandwidth and 20 DC pulse gate lines with a −3 dB cutoff at 3 GHz. A significant feature of this design is the suppression of crosstalk between adjacent microwave lines to <−30 dB (or less than 0.1% signal leakage) from DC to 6 GHz. This is achieved using optimized alternating ground planes and fencing vias. The module directly supports baseband control strategies, thereby mitigating gigahertz-frequency heating effects in high-density qubit arrays.