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IEEE Transactions on Applied Superconductivity

A Narrowband Superconducting Quadruplexer With High Isolation

Yong Heng, Xubo Guo, Bisong Cao, Bin Wei, Xiaoping Zhang, Guoyong Zhang, Xiaoke Song

Published Feb 6, 2014• 29 citations
Publisher

Abstract

A manifold-coupled microstrip superconducting quadruplexer with high isolation for S-band communications systems is presented. The problems of channel isolation and common-port impedance matching in the design of the quadruplexer are addressed and studied. An equivalent circuit model for a trial diplexer is built to analyze the isolation between two channel filters with Chebyshev responses. Analyses and simulations show that channel isolation is mainly determined by the resonators that are closest to the noncommon ports. A circuit layout is proposed for the quadruplexer to obtain high isolation. Moreover, a binary matching network is designed to minimize the undesired interactions between the four channel filters in the quadruplexer. The quadruplexer is successfully designed with the proposed methods and fabricated. The measured results show high performance and match well with the simulations.

DOI
10.1109/tasc.2014.2304886

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A manifold-coupled microstrip superconducting quadruplexer with high isolation for S-band communications systems is presented. The problems of channel isolation and common-port impedance matching in the design of the quadruplexer are addressed and studied. An equivalent circuit model for a trial diplexer is built to analyze the isolation between two channel filters with Chebyshev responses. Analyses and simulations show that channel isolation is mainly determined by the resonators that are closest to the noncommon ports. A circuit layout is proposed for the quadruplexer to obtain high isolation. Moreover, a binary matching network is designed to minimize the undesired interactions between the four channel filters in the quadruplexer. The quadruplexer is successfully designed with the proposed methods and fabricated. The measured results show high performance and match well with the simulations.
In this paper, we present a compact quint-band superconducting filter operating at 2.4, 3.5, 4.7, 5.3, and 5.9 GHz. Matching junctions with different impedance branch lines are used to connect a dual-band sub-filter with a tri-band sub-filter and to reduce the channel interactions. The quint-band filter design is divided into two sections to determine the controllable frequencies and bandwidths, while ensuring compact size and reducing design complexity. The filter is fabricated on double-sided YBCO film deposited on an MgO substrate with a size of 26 mm × 19 mm. The measured results match well with the simulations.
One of the major requirements for superconducting qubit hardware to work efficiently is high-fidelity, quantum non-demolition qubit readout. The qubits and the cavity where the qubits are placed are present in a cryogenic setup at a temperature around 10mK. To read the state of qubit at room temperature, it is necessary to amplify the weak microwave signal without adding much noise. The amplification can be done only by using quantum-limited amplifiers. One example of a superconducting quantum limited amplifier is the SNAIL parametric amplifier (SPA). SNAIL Parametric Amplifier (SPA) is a phase preserving superconducting amplifier. The amplifier has a non-linear element where the signal to be amplified interacts with a strong microwave pump at double the signal frequency. It is necessary to separate the amplified signal tone from the pump tone on the output of the device in order to protect the qubit from the strong microwave pump. In this report, we have studied how to add a diplexer to a SPA circuit to achieve this required separation between signal and pump tones. A diplexer is a device that divides the signal from a common port into different frequencies. It consists of two bandpass filters attached to the common port at one end and to the respective signal port at the other. The diplexer here directs the signal from qubit and pump tone to the amplifier which is connected to the common port. Thus, the diplexer along with a circulator is used to direct the signal from qubit to the amplifier and the amplified signal to the observer at room temperature. In this project, different diplexers with filters of different order were designed. The response (linewidth) of these diplexers was observed both in the absence and presence of the amplifier and they were compared. The report concludes by noting the difficulties in designing the perfect diplexer and presents future design methodologies to obtain a diplexer and amplifier, fulfilling the requirements- wide passband, low insertion loss at passband and high isolation between signal and pump ports.
Microwave filtering for superconducting qubits is a key element of quantum computing technology, enabling high coherence and fast state detection. This work presents the design and implementation of novel microwave Purcell filters for superconducting quantum circuits, integrated within a multilayer printed circuit board (PCB). The off-chip design removes all filter components from the qubit substrate, reducing device complexity, improving layout footprint and allowing better scalability to large qubit counts. Each embedded filter can couple up to nine readout resonators, enabling efficient multiplexed readout. Electromagnetic simulations of the filter predict a thousand-fold improvement in qubit isolation from the readout port. The design was experimentally validated under cryogenic conditions in conjunction with a 35-qubit device, demonstrating compatibility of the PCB-based filter with high-coherence superconducting qubits. The comparison of the measured qubit median T1 of 84 μμμs with the expected radiative limit from electromagnetic simulations validated the presence of Purcell filtering in the system.
The performance and scalability of superconducting quantum circuits depends critically on the microwave environment. Minimizing signal reflections and suppressing thermal noise are essential for achieving high-fidelity readout and preserving qubit coherence. A significant challenge arises from the use of conventional cryogenic components such as isolators and circulators, which exhibit nonideal out-of-band reflection characteristics. Reflections degrade impedance matching and limit the performance of broadband quantum limited amplifiers. Superconducting implementations of reflectionless microwave filters offer a promising solution to mitigate these issues. The focus of this work is the fabrication and cryogenic characterization of reflectionless filters compatible with superconducting qubit fabrication flows. Devices were implemented on high resistivity silicon substrates using aluminum ground planes, integrated nichrome resistors, and crossovers formed with SiO2 interlayer dielectric. Cryogenic measurements at 20 mK demonstrate high return loss, confirming the viability of these filters for co-fabrication with traveling-wave parametric amplifiers (TWPAs) and circuit quantum electrodynamics (cQED) architectures. The filters exhibit low insertion loss in the passband to maintain quantum measurement efficiency and provide broadband reflection suppression across frequencies relevant to superconducting qubits, offering a scalable way to manage microwave noise in superconducting quantum processors.
With increasing applications of quantum systems operating at high frequencies, the role of integrated microwave components for quantum circuits becomes more and more important. In this article, we present low-temperature superconducting bandpass-bandstop diplexers for a new generation of quantum AC-voltage standards operating at 1 GHz. Based on stringent requirements, the diplexers are designed to provide low passband loss, good stopband rejection, and otherwise a broad ideally matched spectrum with excellent spurious-free performance. A second-order 1 GHz superconducting bandpass-bandstop diplexer is fabricated and characterized for verification. To this end, a cryogenic setup and on-chip calibration standards are implemented for S-parameter measurements. The experimental results exhibit low insertion loss as low as 0.03 dB in the passband section and high rejection in the bandstop branch exceeding 43 dB. Furthermore, the diplexer features wide spurious-free response extending to more than14⋅f014 \cdot \mathrm{f}_{0}14⋅f0​and occupies a very compact area of only1.8mm×1.2mm1.8 \text{mm} \times 1.2 \text{mm}1.8mm×1.2mm.
High-Tc superconducting (HTS) receivers are promising candidates for terahertz (THz) communication applications due to their superior sensitivity and the cooling attainability with a miniature cryogenic system. Nevertheless, currently reported HTS mixers are mostly single-junction devices, and a more complicated architecture like the balanced configuration has not been investigated. This paper presents the design of a 600-GHz single-balanced HTS mixer, where detailed electromagnetic simulations are carried out to optimize the coupling efficiency and port isolation, as well as desired amplitude and phase relationship. To predict the noise and conversion performance, we present an innovative multiport network interleaving-based modeling method that enables powerful simulation verifications for single-balanced HTS Josephson mixers. Simulation results show that the presented device exhibits very good HTS mixer performance at the 600-GHz band, which validates the effectiveness of the design and the potential of the mixer for THz communication applications.