QFilter-II is your compact solution for advanced multi-stage low-pass filtering. It’s specifically designed to reject noise and maintain millikelvin electron temperatures across 24 signal lines. This makes it an ideal fit for your quantum electronics devices and other sensitive cryogenic circuits. Originating from extensive research at Harvard University and the University of Copenhagen, QFilter is now a trusted tool in over 100 research groups worldwide.

Advanced Filtering and Thermalization Below 1 Kelvin

At millikelvin temperatures, ensuring cold electrons in signal lines is a challenge. QFilter-II addresses this by cooling electrons and filtering out electrical noise ranging from about 65 kHz to tens of GHz. Constructed from gold-coated high-conductivity copper and mountable on your cryostat’s mixing chamber plate, it is a key component for any cryogenic setup.

24 Line Filter Configuration with Optimal Performance

Our standard configuration offers two filtering banks (low-frequency and radio frequency) with 25-pin micro-D connectors. These banks are connected in series using a shielded jumper cable. The compact, non-magnetic design allows for direct mounting on the mixing chamber plate, compatible with most fridge manufacturers such as Bluefors fridges and the Oxford Instrument Proteox shown below.

Well-Engineered Filtering Banks for Low Temperatures and High Signal Integrity

QFilter-II features two low-pass filtering banks in series: a low-frequency (65 kHz) filter with RC circuits and a high-frequency (RF, 225 MHz) filter with LC circuits. Each bank is crafted with several individually shielded filter stages. Signal lines support 150V voltages (below 4 Kelvin, max. 6mA for RC, 10mA for RF) and provide >10GΩ isolation below 4K to ground and other lines. Individual low-frequency filter lines can be shortened upon request, allowing for higher signal currents e.g. used for current biasing flux-lines.

Scalability for High Channel Demands

For systems requiring more than 24 lines, QFilters can be efficiently stacked (top image) saving space on the mixing chamber plate or connected in series (bottom image) removing the need for jumper cables. This flexibility allows for configurations like dual RC or dual RF filters, catering to diverse setup requirements.

Key Features

  • Effective Electron Temperature Cooling: Reduces electron temperature through filtering to typically 5-15 mK above the mixing chamber.
  • Advanced Low-Pass Filtering: Dual filter boards (RC and RF) with 24 channels each for strong noise rejection.
  • Effortless Integration: Easily mountable on standard mixing chamber plates of dilution refrigerators with 20 mm x 20 mm pitch.
  • Robust and Scalable Design: Sturdy build, suitable for stacking to accommodate higher channel counts.
  • Optimal Thermal and Electrical Performance: Thermal anchoring to gold-plated copper brackets and 2GΩ isolation per channel.
  • High Magnetic Field Compatibility: Non-magnetic, shielded components including titanium connectors for reliable operation in various environments.
  • Connector Compatibility: Equipped with 25-pin microD connectors used in most dilution refrigerators.
  • Compact and Space-Efficient: Dimensions of 30 mm x 47 mm x 70 mm for space-sensitive setups.
  • Versatile Configuration: Suitable for 48, 96, or more lines, with options for stacking or in-series connections.


Lowers Electron Temperature

QFilter effectively reduces electron temperatures to typically 5-15 mK above the mixing chamber, ideal for sensitive experiments.

Rejects Electronic Noise

QFilter including both low frequency and RF filters transmits below 65 kHz and attenuates from 10 MHz to 20 GHz by more than -60dB.

High Magnetic Field Resilience

Designed with non-magnetic, shielded components, QFilter excels in high magnetic fields, offering dependable performance.

Flexible and Scalable Design

Adaptable for filtering 48, 96, or more lines, QFilter’s scalable design meets the demands of growing research projects.


Customers’ Success Using QFilter

Superfluid response of an atomically thin gate-tuned van der Waals superconductor

Apr 2023

Josephson diode effect from Cooper pair momentum in a topological semimetal

Aug 2022

Isospin order in superconducting magic-angle twisted trilayer graphene

Feb 2022

Spin-orbit–driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene

Jan 2022

Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires

Sep 2020

Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

Sep 2019

Superconducting, insulating and anomalous metallic regimes in a gated two-dimensional semiconductor–superconductor array

Aug 2018

Robust anomalous metallic states and vestiges of self-duality in two-dimensional granular In-InOx composites

Mar 2021

Controlled dc Monitoring of a Superconducting Qubit

Feb 2020

Ultra-fast electronic pulse control at cryogenic temperatures

May 2019

Precision measurement of the quantized anomalous Hall resistance at zero magnetic field

Feb 2018

Spin-degeneracy breaking and parity transitions in three-terminal Josephson junctions

Jul 2023

Flip-chip-based fast inductive parity readout of a planar superconducting island

Jul 2023

Demonstration of nonlocal Josephson effect in Andreev molecules

Jun 2023

Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

May 2023

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