THE QFILTER - A compact high-performance low-pass filter

Ensure mK electron temperature in quantum electronic devices with the QFilter low-pass filter

The QFilter is a compact multi-stage low-pass filter which rejects noise and to ensure mil­likelvin electron temperature in up to 48 signal lines going to your quantum electronics devices and other sensitive cryogenic and low-temperature electronic circuits. It is the result of several years of development at Harvard University and the University of Copenhagen on achieving the lowest possible noise and electron temperature in quantum circuits. The standard QFilter contains two low-pass filter banks, one with RC circuits and one with LC circuits, but other combinations can also be supplied.

What is a cryogenic low pass filter and what it’s used for?

An electrical low-pass filter rejects or dampens high frequencies in the signal lines passing through. RC low-pass filters dampen the high-frequency signals (converting them to heat) whereas LC filters (hence pi filters) reject the high frequencies.

SUMMARY – QFilter features and design

  • One audio frequency (RC) and one radio frequency (RF) filter board with 24 low-pass channels each.
  • Designed for easy mounting on the mixing chamber plate of common dilution refrigerators.
  • Sturdy design makes it possible to stack multiple filters for higher channel counts.
  • Signal lines are thermally anchored to non-magnetic gold-plated copper brackets.
  • Compatible with low temperatures and high magnetic fields.
  • Non-magnetic shielded 25-pin microD connectors, female input, male output.
  • Pinout compatible with Cinch connectors used in most dilution refrigerators.
  • Optimal performance is achieved by connecting the RC and RF lines in series using an optional jumper cable.
  • QFilters can be stacked or mated in-series to save space or cables respectively.
  • Compact size of 30 mm x 47 mm x 70 mm.

Radio frequency low-pass filter bank (RF)

  • Three reflective 7-pole Pi filter stages, individually shielded
  • Attenuates above 225 MHz (80 MHz in previous generations)
  • Total resistance (room temp.): 2.0±0.5 Ω
  • Isolation to ground and other channels > 2 GΩ (room temp.)
QFilters mounted with the optional 6-inch jumper cable connecting the 24-channel RC and RF filter banks in series.

QFilters mounted with the optional jumper cable connecting the 24-channel RC and RF filter banks in series.

Low-frequency low-pass filter bank (RC)

  • One reflective 7-pole Pi and two dissipative RC filter stages, individually shielded
  • Attenuates from 65 kHz or lower
  • Total resistance (room temp.): 1700±10 Ω
  • Isolation to the ground and other channels > 2 GΩ (room temp.)

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