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arXiv:1805.07307 · Superconductor Science and Technology

A flux-driven Josephson parametric amplifier for sub-GHz frequencies fabricated with side-wall passivated spacer junction technology

Slawomir Simbierowicz, Visa Vesterinen, Leif Grönberg, Janne Lehtinen, Mika Prunnila, Juha Hassel

Published Jul 20, 2018• 16 citations
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Abstract

Abstract We present experimental results for a Josephson parametric amplifier tailored for readout of ultra-sensitive thermal microwave detectors. In particular, we discuss the impact of fabrication details on the performance. We show that the small volume of deposited dielectric materials enabled by the side-wall passivated spacer niobium junction technology leads to robust operation across a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier has gain in excess of 20 dB in three-wave mixing and its center frequency is tunable between 540–640 MHz. At 600 MHz, the amplifier adds 105 mK ±9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device.

DOI
10.1088/1361-6668/aad4f2

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•Jan 1, 2024•0 citations
Abstract We present experimental results for a Josephson parametric amplifier tailored for readout of ultra-sensitive thermal microwave detectors. In particular, we discuss the impact of fabrication details on the performance. We show that the small volume of deposited dielectric materials enabled by the side-wall passivated spacer niobium junction technology leads to robust operation across a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier has gain in excess of 20 dB in three-wave mixing and its center frequency is tunable between 540–640 MHz. At 600 MHz, the amplifier adds 105 mK ±9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device.
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.
We observe parametric amplification of electromagnetic (EM) waves produced by a flux-flow oscillator made of YBa2Cu3O7−δ Josephson junctions arrays coupled to the resonant modes of a millimeter wave Fabry–Pérot resonator at a pump frequency fP = 45 GHz. For temperatures in the range (30–45) K, the frequency fS of the EM signal to be amplified could be tuned continuously in the range (1–25) GHz by an applied B-field induced flux Φ with a one-flux-quantum Φ0 periodicity. Consequently, we measured a significant parametric gain that is almost frequency independent, with a maximum of (8–10.4) dB reached at 40 K. For temperatures in the range (14–30) K, the magnetic field tunability of fS is gradually suppressed to a minimum of (1–5) GHz range where a parametric gain between 5 and 6 dB was measured. With an appropriate adjustment of design/fabrication parameters, our results suggest that the development of tunable MW generators/detectors as well as parametric amplifiers made of high transition temperature superconductors and operating in a wide range of temperatures (10 mK–77 K) is a reasonable and appealing possibility.
We present a structure and a fabrication method for superconducting tunnel junctions down to the dimensions of 200 nm using i-line UV lithography. The key element is a sidewall-passivating spacer structure (SWAPS) which is shaped for smooth crossline contacting and low parasitic capacitance. The SWAPS structure enables formation of junctions with dimensions at or below the lithography-limited linewidth. An additional benefit is avoiding the excessive use of amorphous dielectric materials which is favorable in sub-Kelvin microwave applications often plagued by nonlinear and lossy dielectrics. We apply the structure to niobium trilayer junctions, and provide characterization results yielding evidence on wafer-scale scalability, and critical current density tuning in the range of 0.1–3.0 kA cm −2 . We discuss the applicability of the junction process in the context of different applications, such as SQUID magnetometers and Josephson parametric amplifiers.
We present the results of an experimental effort to generate squeezed microwave radiation using the phase-sensitive gain of a Josephson parametric amplifier. To facilitate the interpretation of the experimental results, we first present a discussion of the theory of microwave squeezing via Josephson parametric amplifiers. This is followed by a detailed description of the device fabricated for our experiment. Experimental results are then presented for the device used in both the doubly degenerate or four-photon mode and for the degenerate or three-photon mode. We have observed parametric deamplification of signals by more than 8 dB. We have demonstrated squeezing of 4.2-K thermal noise. When operated at 0.1 K, the amplifier exhibits an excess noise of 0.28 K when referred to the input. This is smaller than the vacuum fluctuation noise level \ensuremath{\Elzxh}\ensuremath{\omega}/2k=0.47 K. The amplifier is thus quieter than a linear phase-insensitive amplifier in principle can be.
In this paper, we report a flux-driven Josephson parametric amplifier (JPA) fabricated using the Nb/AlOx/Nb Josephson junction process. The JPA consists of a parallel-plate type coupling capacitor and quarter-wavelength resonator terminated with a DC-SQUID. We adopt a simple process using well-established Nb trilayer technology. The overall configuration time of the Nb-based JPA can be shortened by measuring resonant frequency and its bias dependence in liquid helium. Amplification of the pre-tested device was demonstrated, showing a gain of 20 dB in a −3 dB bandwidth of 17 MHz in a 10 mK dilution fridge.
Recent progress in physics has increased the necessity for ultra-low noise amplifiers capable of operating at the quantum limit performance. These amplifiers are essential to enhance astronomical detection, dark-matter search, and qubit readout in quantum computing, among other applications. Superconducting Josephson junction Travelling Wave Parametric Amplifiers (JTWPAs) operated in the microwave range, have demonstrated high gain over several gigahertz (GHz) bandwidth, with quantum-limited noise performance and minimal heat dissipation. These excellent properties make JTWPAs an ideal solution for ultra-low noise amplification. This thesis delves into the design, fabrication and characterisation of JTWPAs operated in the microwave (1-16 GHz) and the W-band (70-115GHz) regimes. A generalised coupled-mode equations (CME) framework describing JTWPAs based on Josephson junctions and DC superconducting quantum interference devices (SQUIDs) is introduced. This framework can be combined with electromagnetic (EM) simulation softwares to model the JTWPAs, facilitating their design. It is therefore used to model two microwave JTWPA designs, using parallel plate capacitors (PPCs) and interdigitated capacitors (IDCs). The fabrication and characterisation of both designs are presented, and possible fabrication and design issues are carefully discussed. Despite these issues, we observed broadband gain in the JTWPA with PPCs, achieving > 20 dB gain at several frequency points, and a measured P1dB = −95.8dBm when operated at 17.3 dB. The RF properties of a 500-junction Josephson array are also presented in this manuscript. The device creates a Fabry-Perot cavity, leading to non-travelling wave parametric effects, such as narrow-band gain. We also observed indications of efficient phase-sensitive amplification. The thesis is concluded with the first — to the best of our knowledge — experimental attempt to extend the operational frequency of a JTWPA to the W-band. The novel design, fabrication techniques and characterisation of the W-band JTWPA are discussed in detail in this manuscript, leading to promising results suggesting that JTWPA could operate at high frequencies.