Electromagnetic filtering is essential for the coherent control, operation and readout of superconducting quantum circuits at milliKelvin temperatures. The suppression of spurious modes around transition frequencies of a few GHz is well understood and mainly achieved by on-chip and package considerations. Noise photons of higher frequencies – beyond the pair-breaking energies – cause decoherence and require spectral engineering before reaching the packaged quantum chip. The external wires that pass into the refrigerator and go down to the quantum circuit provide a direct path for these photons. This article contains quantitative analysis and experimental data for the noise photon flux through coaxial, filtered wiring. The attenuation of the coaxial cable at room temperature and the noise photon flux estimates for typical wiring configurations are provided. Compact cryogenic microwave low-pass filters with CR-110 and Esorb-230 absorptive dielectric fillings are presented along with experimental data at room and cryogenic temperatures up to 70 GHz. Filter cut-off frequencies between 1 to 10 GHz are set by the filter length, and the roll-off is material dependent. The relative dielectric permittivity and magnetic permeability for the Esorb-230 material in the pair-breaking frequency range of 75 to 110 GHz are measured, and the filter properties in this frequency range are calculated. The estimated dramatic suppression of the noise photon flux due to the filter proves its usefulness for experiments with superconducting quantum systems.

中文翻译：

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设计用于超导量子系统的微波到红外噪声光子通量

电磁滤波对于超导量子电路在毫开尔文温度下的相干控制、操作和读出至关重要。对几 GHz 跃迁频率附近的杂散模式的抑制很容易理解，并且主要通过片上和封装考虑来实现。更高频率的噪声光子——超出对破坏的能量——会导致退相干，并且在到达封装的量子芯片之前需要进行光谱工程。进入冰箱并向下进入量子电路的外部电线为这些光子提供了直接路径。本文包含通过同轴滤波布线的噪声光子通量的定量分析和实验数据。提供了同轴电缆在室温下的衰减和典型布线配置的噪声光子通量估计值。展示了带有 CR-110 和 Esorb-230 吸收性电介质填充物的紧凑型低温微波低通滤波器以及在室温和高达 70 GHz 的低温下的实验数据。1 到 10 GHz 之间的滤波器截止频率由滤波器长度设置，并且滚降取决于材料。测量了 Esorb-230 材料在 75 至 110 GHz 的断线频率范围内的相对介电常数和磁导率，并计算了该频率范围内的滤波器特性。由于滤波器估计的噪声光子通量的显着抑制证明了它对超导量子系统实验的有用性。展示了带有 CR-110 和 Esorb-230 吸收性电介质填充物的紧凑型低温微波低通滤波器以及在室温和高达 70 GHz 的低温下的实验数据。1 到 10 GHz 之间的滤波器截止频率由滤波器长度设置，并且滚降取决于材料。测量了 Esorb-230 材料在 75 至 110 GHz 的断线频率范围内的相对介电常数和磁导率，并计算了该频率范围内的滤波器特性。由于滤波器估计的噪声光子通量的显着抑制证明了它对超导量子系统实验的有用性。展示了带有 CR-110 和 Esorb-230 吸收性电介质填充物的紧凑型低温微波低通滤波器以及在室温和高达 70 GHz 的低温下的实验数据。1 到 10 GHz 之间的滤波器截止频率由滤波器长度设置，并且滚降取决于材料。测量了 Esorb-230 材料在 75 至 110 GHz 的断线频率范围内的相对介电常数和磁导率，并计算了该频率范围内的滤波器特性。由于滤波器估计的噪声光子通量的显着抑制证明了它对超导量子系统实验的有用性。