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European Microwave Conference (EuMC)

Design of Microwave Calibration Standards for Characterising S-Parameters of Quantum Integrated Circuits at Millikelvin Temperatures

Manoj Stanley, Sebastian E. de Graaf, T. Lindström, Martin J. Salter, James Skinner, Nick Ridler

Published Apr 4, 2022• 2 citations
Publisher

Abstract

In the field of quantum information science, superconducting quantum integrated circuits are operated at millikelvin temperatures inside dilution refrigerators. The microwave performance of such non-connectorised devices can be characterised by measuring their calibrated S-parameters. The design of high-quality microwave standards is essential to achieve accurate calibration. In this work we describe the architecture of a full 2-port S-parameter measurement set-up for use at millikelvin temperatures along with the microwave calibration unit. The design of the standards for use in the calibration unit at millikelvin temperatures is described and verified using electromagnetic simulation and measurements. The suitability of the standards is verified by characterising a commercial attenuator as a test device.

DOI
10.23919/eumc50147.2022.9784174

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In the field of quantum information science, superconducting quantum integrated circuits are operated at millikelvin temperatures inside dilution refrigerators. The microwave performance of such non-connectorised devices can be characterised by measuring their calibrated S-parameters. The design of high-quality microwave standards is essential to achieve accurate calibration. In this work we describe the architecture of a full 2-port S-parameter measurement set-up for use at millikelvin temperatures along with the microwave calibration unit. The design of the standards for use in the calibration unit at millikelvin temperatures is described and verified using electromagnetic simulation and measurements. The suitability of the standards is verified by characterising a commercial attenuator as a test device.
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.
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.
Abstract Quantum computers based on solid state qubits have been a subject of rapid development in recent years. In current noisy intermediate-scale quantum technology, each quantum device is controlled and characterised through a dedicated signal line between room temperature and base temperature of a dilution refrigerator. This approach is not scalable and is currently limiting the development of large-scale quantum system integration and quantum device characterisation. Here we demonstrate a custom designed cryo-CMOS multiplexer operating at 32 mK. The multiplexer exhibits excellent microwave properties up to 10 GHz at room and millikelvin temperatures. We have increased the characterisation throughput with the multiplexer by measuring four high-quality factor superconducting resonators using a single input and output line in a dilution refrigerator. Our work lays the foundation for large-scale microwave quantum device characterisation and has the perspective to address the wiring problem of future large-scale quantum computers.
Abstract Superconducting circuit testing and materials loss characterization requires robust and reliable methods for the extraction of internal and coupling quality factors of microwave resonators. A common method, imposed by limitations on the device design or experimental configuration, is the single-port reflection geometry, i.e. reflection-mode. However, impedance mismatches in cryogenic systems must be accounted for through calibration of the measurement chain while it is at low temperatures. In this paper, we demonstrate a data-based, single-port calibration using commercial microwave standards and a vector network analyzer with samples at millikelvin temperature in a dilution refrigerator, making this method useful for measurements of quantum phenomena. Finally, we cross reference our data-based, single-port calibration and reflection measurement with over-coupled 2D- and 3D-resonators against well established two-port techniques corroborating the validity of our method.
Cryogenic microwave circuit design is required for the development of future quantum systems. Discrete components can be used to design compact attenuators, matching networks or filters to verify circuit designs for later integration. However, precise passive component characterization is necessary for microwave circuit design, but has not yet been performed in the millikelvin (mK) range. This work presents for the first time a cryogenic model parameter estimation of passive surface-mounted device (SMD) components for microwave circuit design down to 50 mK and up to 8 GHz. The model parameters of an inductor, a capacitor and two resistors have been derived down to 50 mK. Measurement data were de-embedded using coplanar waveguide (CPWG) TRL calibration standards. It is shown that at 50 mK, the characteristic capacitance and inductance of the investigated components change by only 6 % respectively 2.5 % and that the inductor resistance at 50 mK is reduced by 80 % compared to room temperature, proving its suitability for microwave circuit design at mK temperatures. In contrast, the resistance value of the investigated thick film resistors increases by 20 %.