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

We present experimental results on 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 MHz and 640 MHz. At 600 MHz, the amplifier adds 105 mK $\pm$ 9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device

Characterizing cryogenic amplifiers with a matched temperature-variable noise source

We present a cryogenic microwave noise source with a characteristic impedance of 50 $\Omega$, which can be installed in a coaxial line of a cryostat. The bath temperature of the noise source is continuously variable between 0.1 K and 5 K without causing significant back-action heating on the sample space. As a proof-of-concept experiment, we perform Y-factor measurements of an amplifier cascade that includes a traveling wave parametric amplifier and a commercial high electron mobility transistor amplifier. We observe system noise temperatures as low as $680^{+20}_{-200}$ mK at 5.7 GHz corresponding to $1.5^{+0.1}_{-0.7}$ excess photons. The system we present has immediate applications in the validation of solid-state qubit readout lines.Comment: The following article has been accepted by Review of Scientific Instruments. After it is published, it will be found at https://doi.org/10.1063/5.002895

Josephson-parametrivahvistimien materiaalien optimointia

Dark-matter particle detection and readout of quantum bits in quantum information systems call for low-noise radio-frequency amplifiers. Superconductive amplifiers such as Josephson parametric amplifiers can be used. We have built and plan to improve JPAs with a different application in mind. The aim is integration to measurement setups in nanocalorimetry and -bolometry in order to detect single microwave quanta. Such an achievement can have considerable impact in the research of small systems. Oxides act as insulators in multi-layer structures used to add capacitance in JPAs. For this reason, we characterize the loss properties of transmission line resonators covered with oxides using a cryogenic setup. Aluminium oxide is considered as a potential replacement for silicon oxide that has been believed to be the source of excess noise and the cause of low quality factors in past JPAs constructed at VTT. Notably, we prove that two-level systems play a significant part in losses in silicon oxide as well as aluminium oxide and, therefore, gain an understanding of the problems encountered previously. We determine a loss tangent of delta0 = 6-7e-3 for silicon oxide and find that resonators without added oxide exceed a high internal quality factor of 2e5 at low power. We abandon our previous Josephson junction process in favor of the cross-layer patterning (CLIP) process for improved SQUID performance, reduced flux trapping, and easier fabrication. Single junctions are measured in a four-point setup and the target of 100 A/cm2 for the critical current density is mostly reached although suppressed critical currents are observed for junctions with an in-plane cross-section smaller than 1 mum x 1 mum. We then build new JPAs and measure the current-voltage characteristics of the embedded SQUID chain. No hysteresis is observed during tuning of the resonance frequency with a magnetic field.Pimeän aineen hiukkasten havaitseminen ja kvanttibittien lukeminen kvantti-informaatiosysteemeissä vaativat matalakohinaista radiotaajuudella toimivaa vahvistinta. Suprajohtavat vahvistimet kuten Josephsonin parametriset vahvistimet (JPA) ovat näissä käyttökelpoisia. VTT:llä tehdään JPA:ita hieman toista käyttötarkoitusta varten: aiemmin niitä on jo rakennettu ja nyt niitä parannellaan aikomuksena integroida vahvistimet nanokalorimetrisiin ja -bolometrisiin mittauksiin yksittäisten fotonien havaitsemiseksi. Tällaisen onnistuessa pieniä systeemejä voitaisiin tutkia paremmin. Oksidikerroksia käytetään JPA:issa monikerrosrakenteissa kapasitanssin synnyttämiseksi, mistä syystä karakterisoimmekin oksideilla päällystettyjen transmissiolinja-tyyppisten resonaattoreiden häviöominaisuuksia kryogenisellä mittausjärjestelyllä. Harkitsemme alumiinioksidin käyttämistä JPA:issa havaittuun ylimääräiseen kohinaan ja mataliin hyvyyslukuihin. Erityisesti osoitamme kaksitasosysteemien aiheuttavan häviöitä sekä piidioksidissa että alumiinioksidissa, ja siten ymmärrämme aiemmat ongelmamme paremmin. Määritämme piidioksidin häviötangentiksi delta0 = 6-7e-3 ja saamme oksidilla päällystämättömille resonaattoreille matalan tehon hyvyysluvuksi jopa yli 2e5. Vaihdamme aiemman Josephsonin liitoksen valmistusprosessimme toiseen (CLIP) paremman SQUID-suorituskyvyn saavuttamiseksi, ehkäistäksemme vuon vangitsemista sekä valmistuksen yksinkertaistamiseksi. Mittaamme yksittäisiä liitoksia nelipistemittauksella, ja saavutamme tavoitteemme 100 A/cm2 kriittisen virran tiheydeksi useimmilla joskaan emme aivan kaikkein pienimmillä pinta-alaltaan alle 1 mum x 1 mum liitoskoilla. Lopuksi rakennamme uusia JPA:ita ja määritämme niiden SQUID-ketjujen virta-jänniteominaisuuksia. Hystereesiä ei havaita säädettäessä resonanssitaajuutta magneettikentällä

Bluefors Blog

The purpose of this application note is to demonstrate a working example of a superconducting qubit measurement in a Bluefors cryostat using the Keysight quantum control hardware. Our motivation is twofold. First, we provide pre-qualification data that the Bluefors cryostat, including filtering and wiring, can support long-lived qubits. Second, we demonstrate that the Keysight system (controlled using Labber) provides a straightforward solution to perform these characterization measurements. This document is intended as a brief guide for starting an experimental platform for testing superconducting qubits. The setup described here is an immediate jumping off point for a suite of applications including testing quantum logical gates, quantum optics with microwaves, or even using the qubit itself as a sensitive probe of local electromagnetic fields. Qubit measurements rely on high performance of both the physical sample environment and the measurement electronics. An overview of the cryogenic system is shown in Figure 1, and an overview of the integration between the electronics and cryostat (including wiring details) is shown in Figure 2