Superconducting resonator parametric amplifiers with intrinsic separation of pump and signal tones

Abstract Superconducting resonator parametric amplifiers achieve ultra-low-noise amplification through the nonlinear kinetic inductance of thin-film superconductors. One of the main challenges to the operation of these devices is the separation of the strong pump tone from the signal tone after amplification has been achieved. In this paper, we propose and experimentally demonstrate a pump separation method based on operating a half-wave superconducting resonator amplifier behind a cryogenic circulator. Our pump separation scheme does not involve post-amplification interference, and thereby avoids the delicate phase matching of two different pump paths. We demonstrate the scheme using two-port half-wave resonator amplifiers based on superconducting NbN thin-films. We present measurements of gain profiles and degrees of pump separation for amplifiers having different coupling quality factors. On an amplifier having a coupling quality factor of ∼2000, we measured a peak signal gain of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>15</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>dB</mml:mi> </mml:mrow> </mml:mrow> </mml:math> whilst achieving pump separation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>12</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>dB</mml:mi> </mml:mrow> </mml:mrow> </mml:math> . The amplifier was stable for continuous measurements, and the gain drift was measured to be <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>0.15</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>dB</mml:mi> </mml:mrow> </mml:mrow> </mml:math> over an hour. The same amplifier was operated at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>3.2</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> </mml:mrow> </mml:math> and achieved a peak signal gain of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>11</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>dB</mml:mi> </mml:mrow> </mml:mrow> </mml:math> whilst having a pump separation factor of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>10.5</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>dB</mml:mi> </mml:mrow> </mml:mrow> </mml:math> . The pump separation scheme, and these promising results, will advance the development of superconducting resonator amplifiers as an important technology in quantum sensing.