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EP-4740717-A2 - MICROWAVE FILTERS WITH SUPERCONDUCTOR-INSULATOR TRANSITION MATERIALS

EP4740717A2EP 4740717 A2EP4740717 A2EP 4740717A2EP-4740717-A2

Abstract

A microwave filter includes a superconductor-to-insulator transition (SIT) layer including a material exhibiting a superconductor-to-insulator transition associated with a superconducting gap frequency. For signals transmitting through the layer, the microwave filter is a low-pass filter in which twice the superconducting gap frequency is a cutoff frequency.

Inventors

  • STERLING, George Earl Grant
  • HAMILTON, MICHAEL C.
  • IOFFE, Lev
  • NEILL, CHARLES
  • SACEPE, Benjamin Pierre Alexis

Assignees

  • Google LLC

Dates

Publication Date
20260513
Application Date
20240815

Claims (20)

  1. 1. A microwave filter comprising: a superconductor-to-insulator transition (SIT) layer comprising a material exhibiting a superconductor-to-insulator transition associated with a superconducting gap frequency, wherein, for signals transmitting through the layer, the microwave filter is a low-pass filter in which twice the superconducting gap frequency is a cutoff frequency.
  2. 2. The micro wave filter of claim 1, wherein the SIT layer comprises a nitride alloy, niobium silicon, molybdenum germanium, molybdenum carbide, molybdenum rhenium, indium oxide, granular aluminum, or a cuprate superconductor.
  3. 3. The microwave filter of claim 2, wherein the SIT layer comprises Nb- Si i-v with x between 0. 15 and 0.25.
  4. 4. The microwave filter of any one of the preceding claims, wherein the SIT layer exhibits a sheet resistance between 100 and 2 k at a temperature less than 10 mK and for a frequency above twice the superconducting gap frequency.
  5. 5. The micro wave filter of any one of the preceding claims, wherein the SIT layer exhibits a resistance per millimeter of at least 660 Q/mm at a temperature less than 10 mK and for a frequency of 10 GHz.
  6. 6. The microwave filter of any one of the preceding claims, wherein twice the superconducting gap frequency of the layer is between 8 GHz and 50 GHz.
  7. 7. The microwave filter of any one of the preceding claims, wherein the microwave filter is a microstrip, a stnpline, or a coplanar waveguide.
  8. 8. The microwave filter of any one of the preceding claims, wherein the SIT layer is arranged in a shape such that the microwave filter behaves as a notch filter that attenuates signal components having a frequency within a predefined frequency range.
  9. 9. The microwave filter of claim 8, wherein the shape comprises at least one of a spurline geometry or a stub geometry.
  10. 10. The microwave filter of claim 8 or claim 9, wherein the predefined frequency range overlaps a frequency range of 8 GHz to 10 GHz.
  11. 11. The microwave filter of any one of the preceding claims, wherein the microwave filter is a cable.
  12. 12. The microwave filter of any one of the preceding claims, comprising a dielectric layer in which the SIT layer is embedded.
  13. 13. The microwave filter of claim 12, comprising: a first superconductor layer on a first side of the dielectric layer, and a second superconductor layer on a second side of the dielectric layer, the second side opposite the first side.
  14. 14. The microwave filter of claim 12 or claim 13, wherein the dielectric layer comprises a polyimide.
  15. 15. The microwave filter of claim 14, comprising a voltage source coupled to the first superconductor layer, the voltage source configured to apply a voltage to the first superconductor layer to provide an electric field across the SIT layer between the first superconductor layer and the second superconductor layer.
  16. 16. The microwave filter of any one of the preceding claims, comprising: a dielectric layer; and a superconductor layer, wherein the SIT layer is on a first side of the dielectric layer, and wherein the superconductor layer is on a second side of the dielectric layer, the second side opposite the first side.
  17. 17. The microwave filter of any one of the preceding claims, comprising: a substrate on which the SIT layer is disposed; a first superconductor layer disposed on the substrate, the first superconductor layer extending adjacent to a first side of the SIT layer; and a second superconductor layer disposed on the substrate, the second superconductor layer extending adjacent to a second side of the SIT layer, the second side opposite the first side.
  18. 18. The microwave filter of claim 17, wherein the SIT layer and the first and second superconductor layers are disposed on a first surface of the substrate, and wherein the microwave filter comprises: a third superconductor layer disposed on a second surface of the substrate opposite the first surface.
  19. 19. The microwave filter of any one of the preceding claims, comprising: a magnetic field source arranged to apply a magnetic field to the SIT layer; and a controller coupled to the magnetic field source, the controller configured to provide signals to the magnetic field source to adjust a magnitude of the magnetic field.
  20. 20. The microwave filter of claim 19, wherein the magnetic field source comprises a trace arranged adjacent to the SIT layer, and wherein the controller is configured to adjust a current through the trace to adjust the magnitude of the magnetic field.

Description

MICROWAVE FILTERS WITH SUPERCONDUCTOR-INSULATOR TRANSITION MATERIALS CROSS- REFERENCE FIELD OF THE DISCLOSURE [001] This application claims priority to U.S. Provisional Patent Application No. 63/533,094 filed August 16, 2023, the disclosure of which is hereby incorporated by reference in its entirety. FIELD OF THE DISCLOSURE [002] The present disclosure relates to filters, such as microwave filters. BACKGROUND [003] High-energy photons (e.g., > 20 GHz to THz) can deteriorate qubit performance. Accordingly, signals associated with quantum computation (e.g., qubit control or readout signals) can be filtered to remove high-energy signal components. SUMMARY [004] Some aspects of this disclosure relate to a microwave filter. The microwave filter includes a superconductor-to-insulator transition (SIT) layer including a material exhibiting a superconductor-to-insulator transition associated with a superconducting gap frequency. For signals transmitting through the layer, the microwave filter is a low-pass filter in which twice the superconducting gap frequency is a cutoff frequency. [005] This and other microwave filters described herein can have one or more of at least the following characteristics. [006] In some implementations, the SIT layer includes a nitride alloy, niobium silicon, molybdenum germanium, molybdenum carbide, molybdenum rhenium, indium oxide, granular aluminum, or a cuprate superconductor. [007] In some implementations, the SIT layer includes NtySi i -x with x between 0.15 and 0.25. [008] In some implementations, the SIT layer exhibits a sheet resistance between 100 Q and 2 kQ at a temperature less than 10 mK and for a frequency above twice the superconducting gap frequency. [009] In some implementations, the SIT layer exhibits a resistance per millimeter of at least 660 Q/mm at a temperature less than 10 mK and for a frequency of 10 GHz. [010] In some implementations, twice the superconducting gap frequency of the layer is between 8 GHz and 50 GHz. [OH] In some implementations, the microwave filter is a microstrip, a stripline, or a coplanar waveguide. [012] In some implementations, the SIT layer is arranged in a shape such that the microwave filter behaves as a notch filter that attenuates signal components having a frequency within a predefined frequency range. [013] In some implementations, the shape includes at least one of a spurline geometry or a stub geometry. [014] In some implementations, the predefined frequency range overlaps a frequency range of 8 GHz to 10 GHz. [015] In some implementations, the microwave filter is a cable. [016] In some implementations, the microwave filter includes a dielectric layer in which the SIT layer is embedded. [017] In some implementations, the microwave filter includes a first superconductor layer on a first side of the dielectric layer, and a second superconductor layer on a second side of the dielectric layer, the second side opposite the first side. [018] In some implementations, the dielectric layer includes a polyimide. [019] In some implementations, the microwave filter includes a voltage source coupled to the first superconductor layer, the voltage source configured to apply a voltage to the first superconductor layer to provide an electric field across the SIT layer between the first superconductor layer and the second superconductor layer. [020] In some implementations, the microwave filter includes a dielectric layer; and a superconductor layer. The SIT layer is on a first side of the dielectric layer, and the superconductor layer is on a second side of the dielectric layer, the second side opposite the first side. [021] In some implementations, the microwave filter includes a substrate on which the SIT layer is disposed; a first superconductor layer disposed on the substrate, the first superconductor layer extending adjacent to a first side of the SIT layer; and a second superconductor layer disposed on the substrate. The second superconductor layer extends adjacent to a second side of the SIT layer, the second side opposite the first side. [022] In some implementations, the SIT layer and the first and second superconductor layers are disposed on a first surface of the substrate, and the microwave filter includes a third superconductor layer disposed on a second surface of the substrate opposite the first surface. [023] In some implementations, the microwave filter includes a magnetic field source arranged to apply a magnetic field to the SIT layer; and a controller coupled to the magnetic field source, the controller configured to provide signals to the magnetic field source to adjust a magnitude of the magnetic field. [024] In some implementations, the magnetic field source includes a trace arranged adjacent to the SIT layer, and the controller is configured to adjust a current through the trace to adjust the magnitude of the magnetic field. [025] In some implementations, the microwave filter includes a controller configured to apply a