Comparison of cryogenic low-pass filters

Low-temperature electronic transport measurements with high energy resolution require both effective low-pass filtering of high-frequency input noise and an optimized thermalization of the electronic system of the experiment. In recent years, elaborate filter designs have been developed for cryogenic low-level measurements, driven by the growing interest in fundamental quantum-physical phenomena at energy scales corresponding to temperatures in the few millikelvin regime. However, a single filter concept is often insufficient to thermalize the electronic system to the cryogenic bath and eliminate spurious high frequency noise. Moreover, the available concepts often provide inadequate filtering to operate at temperatures below 10 mK, which are routinely available now in dilution cryogenic systems. Herein we provide a comprehensive analysis of commonly used filter types, introduce a novel compact filter type based on ferrite compounds optimized for the frequency range above 20 GHz, and develop an improved filtering scheme providing adaptable broad-band low-pass characteristic for cryogenic low-level and quantum measurement applications at temperatures down to few millikelvin.

Switchable wiring for high-resolution electronic measurements at very low temperatures

Low-temperature transport measurements with high energy resolution require effective filtering of high-frequency input. The high dc resistance of standard RC filters results in considerable heat input and hampers measurements with high currents or voltages. We developed a wiring scheme that incorporates a commercial latching relay at very low temperature between two sets of wires. In our application one set of wires comprises a voltage divider and a high-Ohmic reference resistance at low temperature as well. The other set has low dc resistance and no voltage divider. Both sets are high frequency filtered with very robust and compact filters, though, for insuring effective damping at gigahertz frequencies. We demonstrate that with the first set, we obtain a voltage resolution of 6 microV and a current resolution of 100 pA, which is sufficient for the recording and analysis of multiparticle transport in superconducting point contacts. The second set is used for electromigration experiments on superconducting point contacts and allows application of currents up to 1 mA and voltages up to 20 V, while the sample is at 1 K. More versatile applications of the scheme are possible.