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IEEE Transactions on Instrumentation and Measurement

A Technique to Improve Accuracy of S-Parameter Measurements of Coaxial Connectorized Devices at Cryogenic Temperatures

Manoj Stanley, Murat Celep, Asem Elarabi, Martin J. Salter, Dilbagh Singh, James Skinner, Sang-Hee Shin, Nick Ridler

Published Jan 1, 2025• 3 citations
Publisher

Abstract

Recent developments in microwave-based quantum computing technologies have motivated the need for the development of new and improved cryogenic microwave devices packaged in coaxial connectorized technology, and for their performance to be accurately characterized through S-parameter measurements made at cryogenic operating temperatures. To facilitate such accurate characterization, S-parameter measurement systems utilizing in-situ calibration techniques at cryogenic temperatures have been developed. This required use of cryogenic RF switches inside cryostats to select between calibration standards and devices to perform calibration and measurement in a single cooling cycle. However, this caused significant measurement errors due to non-identical signal paths due to differences in switch paths limiting the measurement accuracy of such measurement systems. In this work, a new technique is proposed to significantly improve the accuracy of cryogenic S-parameter measurements of coaxial connectorized devices by accounting for non-ideal effects in such switch-based cryogenic calibration units. The technique is demonstrated at room temperature (296 K) and cryogenic temperature (1.5 K) through S-parameter measurements of coaxial devices with up to two ports.

DOI
10.1109/tim.2025.3595257

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Recent developments in microwave-based quantum computing technologies have motivated the need for the development of new and improved cryogenic microwave devices packaged in coaxial connectorized technology, and for their performance to be accurately characterized through S-parameter measurements made at cryogenic operating temperatures. To facilitate such accurate characterization, S-parameter measurement systems utilizing in-situ calibration techniques at cryogenic temperatures have been developed. This required use of cryogenic RF switches inside cryostats to select between calibration standards and devices to perform calibration and measurement in a single cooling cycle. However, this caused significant measurement errors due to non-identical signal paths due to differences in switch paths limiting the measurement accuracy of such measurement systems. In this work, a new technique is proposed to significantly improve the accuracy of cryogenic S-parameter measurements of coaxial connectorized devices by accounting for non-ideal effects in such switch-based cryogenic calibration units. The technique is demonstrated at room temperature (296 K) and cryogenic temperature (1.5 K) through S-parameter measurements of coaxial devices with up to two ports.
Multi-port microwave devices operating at cryogenic temperatures are used in quantum computing to enable complex quantum operations. These components need to be precisely characterized at their operating temperature to ensure adequate overall system performance. In this work, an S-parameter measurement system to characterize the performance of coaxial connectorized microwave devices having up to four ports at temperatures of 3 K and above is presented. A four-port calibration setup is implemented at the 3 K temperature stage inside a dilution refrigerator. Measurement results for devices under test at 3 K are presented and the performance of the measurement system is evaluated.
Development of RF and microwave metrology capabilities at cryogenic temperatures is critical for the development of high-performance microwave devices to facilitate commercialization of cryogenic quantum technologies. This article presents a broadband microwave S-parameter calibration scheme suitable for cryogenic environments operating at temperatures down to tens of milli-kelvin (mK). The technique is based on a weighted multi-line thru-reflect-line (TRL) calibration approach and is demonstrated using coaxial air line calibration standards. One-and two-port microwave devices commonly used in cryogenic quantum computing applications, a cryogenic 50 Ω~\Omega Ωmatched load and a cryogenic 6 dB attenuator, were measured. The measured results at mK temperatures indicate that when combined with calibration standards of appropriate electrical length, the weighted multi-line TRL calibration scheme allows broadband frequency coverage compared to conventional TRL calibration schemes utilizing a single line standard. The mechanical and electrical properties of the line standards at mK temperatures were investigated and discussed. These findings establish the feasibility of utilizing multiple off-the-shelf coaxial air lines to enhance the frequency range of calibrations at mK temperatures.
Quantum computing technologies utilise microwave components and interfaces at cryogenic temperatures during operation. This paper describes an S-parameter measurement system to characterise coaxial microwave devices at temperatures down to tens of milli-kelvin. The measurement system is calibrated using a Thru-reflect-line technique utilising a coaxial air-dielectric transmission line as the reference impedance standard. Various coaxial microwave devices having a wide range of reflection and transmission coefficient values are measured at both room temperature and mK temperature to investigate the calibration performance and understand the various error sources in the measurements.
Accurate S-parameter characterization of coaxial microwave devices and interfaces at milli-kelvin (mK) temperatures is essential for building high performance quantum computing systems. Coaxial air-dielectric transmission lines (air lines) are used routinely as primary reference standards for S-parameter measurements at room temperature. For the first time, the feasibility of utilizing such air lines as primary reference standards at mK temperatures is investigated. However, for air lines to be used at such temperatures, they must first be characterized accurately in terms of their characteristic impedance and propagation constant. This paper describes techniques for characterizing air lines at both room temperature (taken here to be 296 K) and mK temperature (around 25 mK). The measurement results demonstrate the feasibility of using air lines as primary reference standards at mK temperatures.
To realize a quantum information processing system, it is necessary not only to increase the number of physical qubits but also to cooperatively operate a multitude of cryogenic microwave components such as cables, circulators, and amplifiers for controlling or reading them. Therefore, it is essential to develop metrological methods to precisely evaluate the microwave scattering parameters of each component at low temperatures. Here, we report a calibrated microwave measurement method for a wide temperature range of 4 K to 300 K. At each temperature, we performed a full two-port calibration, which enables us to precisely measure the scattering parameters of various cryogenic microwave components up to 26.5 GHz by using 3.5 mm connectors as the reference planes. We carefully verified the validity of the calibration impedance elements and demonstrated our method by evaluating the temperature-dependent characteristics of a coaxial cable and a circulator.
Designing large-scale superconducting quantum circuits involves complex microwave engineering to minimize loss, spurious reflections, and signal crosstalk. Essential for engineering more complex circuits is precise knowledge of devices’ microwave performance, which can be characterized by measuring its calibrated scattering parameters (S-parameters) at mK temperatures. In this work, we introduce a full 2-port calibrated S-parameter measurement setup which can characterize superconducting quantum integrated circuits and other RF integrated circuits operating at mK temperatures. The design and architecture of the measurement system consisting of in-house developed microwave calibration unit (MCU) housing the newly designed cryogenic calibration standards and the device under test (DUT) is discussed in detail. The measurement setup is then used to demonstrate the first calibrated S-parameter measurements of an in-house developed superconducting qubit integrated circuit at mK temperature.