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Practical Microwave Amplifiers with Superconductors

Practical Microwave Amplifiers with Superconductors. Lafe Spietz Leonardo Ranzani Minhyea Lee Kent Irwin Norm Bergren Jos é Aumentado. Outline. Motivation The NIST DC-SQUID microwave amp Parametric amplifiers. Motivation.

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Practical Microwave Amplifiers with Superconductors

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  1. Practical Microwave Amplifiers with Superconductors Lafe Spietz Leonardo Ranzani Minhyea Lee Kent Irwin Norm Bergren José Aumentado

  2. Outline • Motivation • The NIST DC-SQUID microwave amp • Parametric amplifiers

  3. Motivation • Some qubit readouts are limited by amplifier • Improve the amplifer, improve the readout • Present state of the are amplifiers are transistor amplifiers which must be separated from the experiment • SQUIDs provide lower noise and can be closer to experiment than transistor amplfiers

  4. What is Noise Temperature*? Temperature of matched load which doubles noise at output *for T>>hf/k

  5. Better Amplifiers Provide Orders of Magnitude Speedup: • Dicke Radiometer Formula: • Thus • 40x lower TN gives 1600x speedup in measurement times! Comes from Poisson statistics!

  6. Microwave Quantum Circuits semiconductor amplifier superconductor amplifier

  7. Quantum Noise of a Resistor 7 GHz  170 mK n = ½Coth(hf/2kT)

  8. Quantum Limits to Amplifiers I f(t) = A Cos(wt + f) f(t) = X Cos(wt) + Y Sin(wt) Phase quadratures are conjugate variables, subject to an uncertainty principle DX·DY ≥½

  9. Quantum Limits to Amplifiers II Amplified coherent state Coherent state Quantum limit Noise above quantum limit

  10. Present Commercial State of the Art Semiconducting Amplifier:HEMT Amps from Weinreb Group • 0.1-14 GHz • 35 dB gain • TN = 1.5-3 K (5- 40 photons added) • $5000 each • Typical system noise ~10-20 K

  11. DC Squids: Flux to Voltage Amplifier ∂V/∂F gives gainFrom power coupled to flux

  12. Statement of the Problem:DC Squids in the Microwave(Nomenclature Disaster) Stray capacitances shunt incoming microwave signal making it difficult to couple power in:

  13. Our Approach • Shrink the physical size of the SQUID until it can be treated as a lumped element component • Model and experimentally characterize input and output impedance • Design input and output impedance transformers • Design box/board infrastructure to make a usable “product” which can be easily disseminated

  14. NIST SQUID design • Kent Iriwin’s octopole gradiometer squid design

  15. Assembly Line Constructionand Interchangeable Parts

  16. Assembly Line Constructionand Interchangeable Parts

  17. Impedance Measurementand Matching • Measure S parameters at harmonics of a quarter wave resonator to learn about input impedance V(x) V(x)

  18. Chip Layout of Quarter Wave 8 mm

  19. Multiple Harmonics 3f0 =5.04 GHz f0 =1.68 GHz

  20. Impedance Measurement >95% power coupling to 0.18 W source

  21. Impedance Model • With physically small squids, we treat them as lumped elements with minimal stray reactances *

  22. Measured Real[Zin]

  23. Voltage [mV]

  24. Voltage [mV]

  25. Transfer Function

  26. Gain and Noise Measurement (or shot noise source)

  27. Typical Gain Curves

  28. Broadband Gain 1 GHz

  29. Noise Temperature

  30. Noise Temperature

  31. Gain Map (5.4 GHz)

  32. Gain Scan Zoom

  33. Extreme Zoom Steep Ridge

  34. Drift Test:Gain Dependence on Flux

  35. Overnight Gain Drift

  36. Dynamic Range

  37. Parametric Amplification Vary some parameter of an oscillator to pump energy into or out of the system

  38. Josephson Parametric Amplifiers pump signal • Use the nonlinearity of JJ circuits to modify some resonant frequency in a microwave circuit • No quantum limit • Usually reflection amplifiers • Can create “squeezed states” of microwave radiation

  39. Josephson Parametric Amplifiers Driven by needs of QC community • Lehnert et al. at JILA (beat quantum limit in a practical experiment!) • Nakamura et al. at NEC • Aumentado et al. at NIST • Devoret et al. at Yale • Siddiqi et al. at Berkeley • Etc. Rapidly growing field!

  40. Amplification: The Dream

  41. Amplifier Technologies

  42. SNR Improvement: Before 20 hours No SQUID

  43. SNR Improvement: After 5 hours SQUID amp

  44. END

  45. Imaginary Component of Input Impedance

  46. DC IV Characteristics

  47. Output Matching 170 pH 700 pH 4 pF 0.9 pF

  48. Summary • Measured input impedance at a range of microwave frequencies • Demonstrated minimal stray reactance • Demonstrated useful gains and bandwidths in 4-8 GHz frequency range • Constructed system for easy production and deployment of SQUID amplifiers • Demonstrated extreme stability of SQUIDs over hours of measurement time

  49. Future Work • Improve ultra-broadband design • Build amplifiers at several more frequencies • Understand and improve noise • Measure shot noise with amplifiers • Distribute amplifiers to collaborators

  50. Output Matching

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