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Josephsonin parametrivahvistimen kehittäminen keskitetyillä elementeillä alle 1 GHz:n taajuuksia varten

Räisänen, Ilmo

Published May 12, 2015• 0 citations
OpenAlex

Abstract

It is important to measure temperature fast and accurately in many experiments in low-temperature physics and nanophysics. The accuracy of the measurement is compromised by noise. A Josephson parametric amplifier (JPA) can provide us with low-noise amplification in the microwave frequency range (300 MHz - 30 GHz) for, e.g., radio frequency thermometry and radiation detection. This Master's thesis presents a lumped element JPA made in collaboration by Aalto University and VTT and reports its refection coefficient, gain, bandwidth, 1 dB compression point, noise temperature and quality factors. Experimental results are compared with nonlinear circuit simulations done with APLAC, which gives us information about component properties for fabrication of a new device. Reflection coefficient measurement gives us the resonance frequency (642.0 MHz) and the bifurcation frequency (640.2 MHz) of the JPA. Gain measurement reveals the maximal gain (26.2 dB), the optimal operating frequency (641.3 MHz) and the optimal pump power (-96 dBm). The gain-bandwidth product is simulated as a function of coupling capacitance and pump power and it is observed to be lower than what theory suggests. The noise temperature of the JPA is measured to be between 1 K and 4 K in thefrequency range 639.25 MHz ... 640.45 MHz according to both the Y-factor method and the signal-to-noise ratio (SNR) method, but according to the SNR method the noise temperature is roughly 50 % lower than according to the Y-factor method. When the pump generator is off, the noise temperature of the system is between 25 K and 80 K in the frequency range 639.15 MHz ... 640.30 MHz according to the SNR method.

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It is important to measure temperature fast and accurately in many experiments in low-temperature physics and nanophysics. The accuracy of the measurement is compromised by noise. A Josephson parametric amplifier (JPA) can provide us with low-noise amplification in the microwave frequency range (300 MHz - 30 GHz) for, e.g., radio frequency thermometry and radiation detection. This Master's thesis presents a lumped element JPA made in collaboration by Aalto University and VTT and reports its refection coefficient, gain, bandwidth, 1 dB compression point, noise temperature and quality factors. Experimental results are compared with nonlinear circuit simulations done with APLAC, which gives us information about component properties for fabrication of a new device. Reflection coefficient measurement gives us the resonance frequency (642.0 MHz) and the bifurcation frequency (640.2 MHz) of the JPA. Gain measurement reveals the maximal gain (26.2 dB), the optimal operating frequency (641.3 MHz) and the optimal pump power (-96 dBm). The gain-bandwidth product is simulated as a function of coupling capacitance and pump power and it is observed to be lower than what theory suggests. The noise temperature of the JPA is measured to be between 1 K and 4 K in thefrequency range 639.25 MHz ... 640.45 MHz according to both the Y-factor method and the signal-to-noise ratio (SNR) method, but according to the SNR method the noise temperature is roughly 50 % lower than according to the Y-factor method. When the pump generator is off, the noise temperature of the system is between 25 K and 80 K in the frequency range 639.15 MHz ... 640.30 MHz according to the SNR method.
Cryogenic, ultralow-noise microwave amplification is critical in superconducting qubit readout, microwave detection, and space technology. Josephson parametric amplifiers (JPAs) are widely used in microwave amplification. Parametric amplification occurs because a nonlinear element and a strong pump enable frequency mixing. The core component of a JPA is a Josephson junction, which acts as a nonlinear inductor and is formed by a thin layer of insulator or normal metal sandwiched between two superconductors. However, gate-controlled Josephson field-effect transistors (JoFETs) have been less studied in this context. In particular, graphene-based JoFETs have shown promising results in terms of scalability and electrostatic control, which could provide an alternative to magnetic field control. The aim of this thesis is to study graphene-based JoFETs as a nonlinear element in superconducting parametric amplifiers. The study was carried out as a literature review and circuit-level simulations using Keysight Advanced Design System (ADS) software. At first, an LC resonator-based JPA was implemented, in which the nonlinear element was a Verilog-A model of a nonlinear Josephson inductance. Harmonic balance (HB) simulation was performed to study the bandwidth, and gain as a function of signal frequency and the dependence on pump power. It showed that parametric gain occurs only when the pump is on. 30 dB gain and 290 MHz bandwidth were achieved. As the gain increased, the bandwidth became narrower. Finally, a gate-pumped JPA using a JoFET was simulated. The JoFET was implemented using a Verilog-A model, which was based on measurements by VTT of their graphene JoFETs. HB simulations showed the electrostatic control of the gate-pumped JPA and gain-bandwidth trade-off typical of JPAs. 15–35 dB gain and 150 MHz bandwidth were obtained, and the resonance frequency could be adjusted with the DC gate voltage. Overall, the observed behavior corresponds well with the reported results for JPAs and fabricated JoFET JPAs. These findings suggest that graphene JoFETs enable parametric gain that can be controlled electrostatically. Although their noise levels may not meet the requirements of quantum computers, they could be useful in other demanding applications, such as space technology.
Josephson parametric amplification is a tool of paramount importance in circuit-QED especially for the quantum-noise-limited single-shot read-out of superconducting qubits. We developed a Josephson parametric amplifier (JPA) based on a lumped-element LC resonator, in which the inductance L is composed by a geometric inductance and an array of 4 superconducting quantum interference devices (SQUIDs). We characterized the main figures of merit of the device, obtaining a −3 dB bandwidth BW = 15 MHz for a gain G = 21 dB and a 1 dB compression point P1dB = −115 dBm. The obtained results are promising for the future use of such JPA as the first stage of amplification for single-shot readout of superconducting qubits.
We designed and fabricated an impedance-matched Josephson parametric amplifier (JPA) working in the flux-pump mode for the broadband amplification of microwave signals. A simple fabrication method suitable for a small cleanroom was developed. We also studied the phase response, as well as the gain, as a function of signal frequency and pump power at various pump frequencies. The phase response can be explained with the behavior of the nonlinear Duffing oscillator. The observed decrease of the resonance frequency as the pump power increases, as well as the emergence of an unstable bifurcation zone, are the characteristic nonlinear behavior of the Duffing oscillator. The features of the gain profile in the stable zone can be explained with a model adapted from the theoretical model for the two-dimensional gain profile of an impedance-matched, current-pumped JPA. Over 17 dB gain with a bandwidth more than 300 MHz (centered around 6.45 GHz) was observed. Our impedance-matched JPA is used for improving the fast readout fidelity of transmon qubits.
Many experiments operating at millikelvin temperatures with signal frequencies in the microwave regime are beginning to incorporate Josephson Parametric Amplifiers (JPA) as their first amplification stage.While there are implementations for a wideband frequency response with a minimal need for tuning, designs using resonant structures with small numbers of Josephson elements still achieve the best noise performance.In a typical measurement scheme involving a JPA, one needs to control the resonance frequency, pump frequency and pump power to achieve the desired amplification and noise properties.In this work, we propose a straightforward approach for operating JPAs with the help of a look-up table (LUT) and online fine-tuning.Using the proposed approach, we demonstrate the operation of a flux-driven JPA with 20 dB gain around 5.9 GHz, covering approximately 100 MHz with 20 kHz tuning steps.The proposed methodology was successfully used in the context of a haloscope axion experiment.
Abstract We design a sub-gigahertz Josephson parametric amplifier for the readout of nanoscale calorimeters which consist of normal-metal–superconductor heterostructures. We characterize the amplifier performance at two operating points, 605 and 655 MHz, corresponding to reproducible local frequency maxima with respect to the applied magnetic flux. At the 655 MHz operating point, the device displays its maximum small-signal gain of 32 dB and gain-bandwidth product of 2 π × 3.3 MHz . The gain remains above 20 dB for incident powers up to −119 dBm. The added noise of the amplifier, determined by the hot/cold source method, assumes a minimum value of 0.2 K.