[Paper Review] Characterization of a flux-driven Josephson parametric amplifier with near quantum-limited added noise for axion search experiments

Çağlar Kutlu, Arjan F. van Loo+8 more|arXiv (Cornell University)|Jan 21, 2021

Dark Matter and Cosmic PhenomenaPhysics and Astronomy35 references45 citations

TL;DR

This paper demonstrates a flux-driven Josephson parametric amplifier (JPA) operating at 2.3 GHz with near-quantum-limited added noise, achieving a system noise temperature of 120 mK when cascaded with cryogenic amplifiers. The JPA enables near-quantum-limited signal detection in axion haloscope experiments, significantly improving sensitivity for dark matter searches by minimizing added noise in the detection chain.

ABSTRACT

The axion, a hypothetical elementary pseudoscalar, is expected to solve the strong CP problem of QCD and is also a promising candidate for dark matter. The most sensitive axion search experiments operate at millikelvin temperatures and hence rely on instrumentation that carries signals from a system at cryogenic temperatures to room temperature instrumentation. One of the biggest limiting factors affecting the parameter scanning speed of these detectors is the noise added by the components in the signal detection chain. Since the first amplifier in the chain limits the minimum noise, low-noise amplification is of paramount importance. This paper reports on the operation of a flux-driven Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added noise approaching the quantum limit. The JPA was employed as a first stage amplifier in an experimental setting similar to the ones used in haloscope axion detectors. By operating the JPA at a gain of 19 dB and cascading it with two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK were achieved for the whole signal detection chain.

Motivation & Objective

• To develop a low-noise microwave amplifier suitable for axion haloscope experiments operating at millikelvin temperatures.
• To minimize added noise in the signal detection chain, which limits the scanning speed of axion detectors.
• To characterize a flux-driven JPA as a first-stage amplifier with near-quantum-limited performance at 2.3 GHz.
• To achieve a system noise temperature (Tsys) as low as 190 mK in a realistic axion search setup, approaching the standard quantum limit.
• To validate the amplifier's performance in a cryogenic environment with minimal thermal and electronic noise.

Proposed method

• The JPA is based on a superconducting quantum interference device (SQUID) coupled to a λ/4 coplanar waveguide resonator, enabling frequency tuning via external magnetic flux.
• Parametric amplification is achieved through three-wave mixing (pump, signal, and idler) using a flux modulation pump tone at the SQUID loop.
• The amplifier operates in a three-stage cascade: the JPA (first stage), followed by two cryogenic HEMT amplifiers at 4 K, with noise temperature contributions modeled using the Friis formula.
• Noise temperature is measured using a noise source at 50 mK and a spectrum analyzer, with calibration performed via a microwave short to bypass the JPA.
• Theoretical modeling of noise propagation includes gain terms (GJ, Gc, GL), noise sources (Snf, Sj), and back-propagating noise, with the total output noise power derived from cascaded amplifier equations.
• The system is calibrated using a reference plane at 800 mK, and the noise temperature is extracted by fitting the measured output power to the theoretical model with Gtot and Tn as fit parameters.

Experimental results

Research questions

• RQ1 Can a flux-driven JPA achieve near-quantum-limited added noise performance at 2.3 GHz in a cryogenic environment?
• RQ2 What is the minimum achievable system noise temperature (Tsys) when using the JPA as the first amplifier in a haloscope detection chain?
• RQ3 How does the noise performance of the JPA compare to the standard quantum limit (SQL) at 2.3 GHz?
• RQ4 To what extent does the JPA’s performance degrade due to losses or non-ideal components in the signal chain?
• RQ5 Can the amplifier maintain low added noise while operating at a gain of 19 dB and enabling fast frequency scanning in axion search experiments?

Key findings

• The flux-driven JPA achieved an added noise temperature of approximately 120 mK when cascaded with two 4 K HEMT amplifiers, resulting in a total system noise temperature (Tsys) of 190 mK at a bath temperature of 50 mK.
• The measured noise temperature of 120 mK is within 10 mK of the standard quantum limit (110 mK) at 2.3 GHz, indicating near-quantum-limited performance.
• The amplifier achieved a gain of 19 dB with minimal added noise, and the noise temperature was stable across multiple measurements at 50 mK.
• The theoretical model of the cascaded system, including back-propagating noise and component losses, accurately predicted the measured output noise, validating the noise budgeting approach.
• The JPA demonstrated low sensitivity to flux noise at frequencies above 2.2 GHz, with the resonance frequency tunable from 2.18 GHz to 2.309 GHz via coil current control.
• The system achieved a noise temperature of 120 mK with a total gain of approximately 30 dB, confirming the JPA as an effective first-stage amplifier for axion haloscope experiments.