Abstract
We present a theoretical model and experimental characterization of a microwave kinetic inductance traveling-wave amplifier (KIT), whose noise performance, measured by a shot-noise tunnel junction (SNTJ), approaches the quantum limit. Biased with a dc current, the KIT operates in a three-wave mixing fashion, thereby reducing by several orders of magnitude the power of the microwave pump tone and associated parasitic heating compared to conventional four-wave mixing KIT devices. It consists of a 50 Ohms artificial transmission line whose dispersion allows for a controlled amplification bandwidth. We measure $16.5^{+1}_{-1.3}$ dB of gain across a 2 GHz bandwidth with an input 1 dB compression power of -63 dBm, in qualitative agreement with theory. Using a theoretical framework that accounts for the SNTJ-generated noise entering both the signal and idler ports of the KIT, we measure the system-added noise of an amplification chain that integrates the KIT as the first amplifier. This system-added noise, $3.1\pm0.6$ quanta (equivalent to $0.66\pm0.15$ K) between 3.5 and 5.5 GHz, is the one that a device replacing the SNTJ in that chain would see. This KIT is therefore suitable to read large arrays of microwave kinetic inductance detectors and promising for multiplexed superconducting qubit readout.
Highlights
Is it possible to build a quantum-limited microwave amplifier with enough gain, bandwidth and power handling to simultaneously read thousands of frequencymultiplexed superconducting resonators, like those in qubit systems or microwave kinetic inductance detectors (MKIDs)? When designed with resonant structures, Josephson-junction-based parametric amplifiers have demonstrated high gain and quantum-limited performances [1,2,3,4,5,6,7]
The kinetic inductance traveling-wave (KIT) amplifier we present in this article is a step toward a practical, quantum-limited amplifier, whose bandwidth and power handling are compatible with high channel-count applications
To quote the true system-added noise of the chain, i.e., the one that a device replacing the shot-noise tunnel junction (SNTJ) in that chain would see, we develop a novel theoretical framework that accounts for the SNTJgenerated noise illuminating both the signal and idler ports of the KIT amplifier
Summary
Is it possible to build a quantum-limited microwave amplifier with enough gain, bandwidth and power handling to simultaneously read thousands of frequencymultiplexed superconducting resonators, like those in qubit systems or microwave kinetic inductance detectors (MKIDs)? When designed with resonant structures, Josephson-junction-based parametric amplifiers have demonstrated high gain and quantum-limited performances [1,2,3,4,5,6,7]. In the hunt for exoplanets, cameras with tens of thousands of MKID pixels are being built [23], and proposals to search for very light warm dark matter necessitate the use of a great number of MKID pixels [24, 25] All these applications are either already limited by amplifier noise, or would greatly benefit from wideband, high gain, high power handling, quantum-limited amplifiers. Operating in a 3WM fashion, and fabricated out of a single layer of NbTiN, it consists of a weakly dispersive artificial transmission line [26,27], for which we control the phase-matched bandwidth with dispersion engineering This limits spurious parametric conversion processes that otherwise degrade the power handling and noise performance. It is the first time that the broadband noise properties of a KIT amplifier are fully characterized rigorously
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