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IEEE Transactions on Applied Superconductivity

A superconducting microwave switch

G.D. Poulin, Frank A. Hegmann, Jean Lachapelle, Steven H. Moffat, J. S. Prestón

Published Jun 1, 1995• 5 citations
Publisher

Abstract

We describe a superconducting microwave switch. The switch comprises a tapering microwave transmission line which can he switched from a very low loss ON state to a high impedance OFF state with a DC voltage applied to the transmission line through a bias-tee. Switching is essentially thermal in nature, occurring due to the formation of a 'hot spot' in the transmission line. Thermal runaway is avoided through the use of voltage rather than current biasing. Once switched, the transmission line attenuates the applied microwave signal. An isolation of 20 dB is readily achievable. The intrinsic response time of the hot spot to applied microwave fields was estimated to be approximately 1 /spl mu/s by measuring the frequency dependence of the transmitted signal.>

DOI
10.1109/77.403234

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We describe a superconducting microwave switch. The switch comprises a tapering microwave transmission line which can he switched from a very low loss ON state to a high impedance OFF state with a DC voltage applied to the transmission line through a bias-tee. Switching is essentially thermal in nature, occurring due to the formation of a 'hot spot' in the transmission line. Thermal runaway is avoided through the use of voltage rather than current biasing. Once switched, the transmission line attenuates the applied microwave signal. An isolation of 20 dB is readily achievable. The intrinsic response time of the hot spot to applied microwave fields was estimated to be approximately 1 /spl mu/s by measuring the frequency dependence of the transmitted signal.>
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Since superconducting quantum computers use microwave signals to control and readout their qubits, microwave transmission lines and circuits that can be used under cryogenic conditions are required. For microwave transmission lines, thermal insulation is essential to enhance wiring density and to prevent parasitic heating that can lead to increased computational errors. Thus, here we design and characterize a scalable, thermally insulated microwave transmission line. The transmission line designed for superconducting qubit readout at 5 GHz band achieves both thermal insulation and low loss, by employing resonator-based impedance matching in a microstripline structure. A flexible cable including eight planar transmission lines was designed, fabricated and characterized using S-parameter measurement, demonstrating low crosstalk below 40dB and signal attenuation of -23.5±0.07dB; this coincides with electromagnetic simulations. These microwave properties remained stable across a wide temperature range from room temperature down to 4 K, including steep gradients. The integration of chip attenuators further reduces thermal noise and protects sensitive cryogenic components. Our approach offers a promising solution for compact, high-density microwave wiring using flat cables under thermal gradients, necessary for large scale quantum computing.
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