Absorptive filters for quantum circuits: Efficient fabrication and cryogenic power handling

Paquette, Alexandre; Griesmar, J.; Lavoie, Gabriel; Albert, Romain; Blanchet, Florian; Grimm, Alexander; Ulrich, Martel,; Hofheinz, M.

doi:10.1063/5.0114887

Cited by 3 publications

(2 citation statements)

References 21 publications

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“…1d shows a SEM picture of one of the Nb-Al-AlOx-Nb junctions of the SQUID. The flux line is low-pass filtered at dilution temperature with a homemade Eccosorb filter [26]. A DC voltage bias is applied to the SQUID via a 5 Ω/1 MΩ voltage divider with heavy low-pass filtering [27].…”

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Microwave photon-number amplification

Albert¹,

Griesmar²,

Blanchet³

et al. 2023

Preprint

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So far, quantum-limited power meters are not available in the microwave domain, hindering measurement of photon number in itinerant quantum states. On the one hand, single photon detectors [1-6] accurately detect single photons, but saturate as soon as two photons arrive simultaneously. On the other hand, more linear watt meters, such as bolometers [7][8][9], are too noisy to accurately detect single microwave photons. Linear amplifiers [10][11][12] probe non-commuting observables of a signal so that they must add noise [13] and cannot be used to detect single photons, either. Here we experimentally demonstrate a microwave photon-multiplication scheme which combines the advantages of a single photon detector and a power meter by multiplying the incoming photon number by an integer factor. Our first experimental implementation achieves a n = 3-fold multiplication with 0.69 efficiency in a 116 MHz bandwidth up to a input photon rate of 400 MHz. It loses phase information but does not require any dead time or time binning. We expect an optimised device cascading such multipliers to achieve number-resolving measurement of itinerant photons with low dark count, which would offer new possibilities in a wide range of quantum sensing and quantum computing applications.

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confidence: 99%

“…The flux line for the SQUID is biased by a roomtemperature voltage source in series with a 5 kΩ resistor. It is filtered at base temperature with a custom Eccosorb filter [26] with a cut-off frequency of the order of 200 MHz.…”

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confidence: 99%

Microwave photon-number amplification

Albert¹,

Griesmar²,

Blanchet³

et al. 2023

Preprint

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Robust cryogenic matched low-pass coaxial filters for quantum computing applications

Ivanov,

Polozov,

Echeistov

et al. 2023

Applied Physics Letters

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Electromagnetic noise is one of the main external factors decreasing superconducting qubit coherence. Matched coaxial filters can prevent microwave and IR photons' negative influence on superconducting quantum circuits. In this report, we describe the design and fabrication process of matched coaxial filters for noise-sensitive measurements at millikelvin temperatures. A robust transmission coefficient and ultralow reflection loss of −20 dB in the frequency range up to 20 GHz is achieved. Fabricated low-pass filters have linear transmission and reflection characteristics with 3 dB-cutoff frequency of 1.5–2.5 GHz. A method for extracting the propagation constant and filter impedance from scattering parameter measurements is demonstrated. This method is experimentally approved on a filter with a compound of Cu powder and Stycast epoxy resin and a filter filled with ECCOSORB CR-110 epoxy resin. The proposed design and assembly technology are versatile for various compounds and provide highly repeatable geometric and microwave characteristics. Furthermore, we demonstrate that these low-pass coaxial filters can be effectively utilized to improve superconducting qubit relaxation due to suppressing standing waves originating from reflections in control coaxial cables.

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