Microwave Amplifiers Research Articles

Reflection-enhanced gain in traveling-wave parametric amplifiers

The operating principle of traveling-wave parametric amplifiers is typically understood in terms of the standard coupled mode theory, which describes the evolution of forward propagating waves without any reflections, i.e. for perfect impedance matching. However, in practice, superconducting microwave amplifiers are unmatched nonlinear finite-length devices, where the reflecting waves undergo complex parametric processes, not described by the standard coupled mode theory. Here, we present an analytical solution for the TWPA gain, which includes the interaction of reflected waves. These reflections result in corrections to the well-known results of the standard coupled mode theory, which are obtained for both 3-wave and 4-wave mixing processes. Due to these reflections, gain is enhanced and unwanted nonlinear phase modulations are suppressed. Predictions of the model are experimentally demonstrated on two types of unmatched TWPA, based on coplanar waveguides with a central wire consisting of i) a high kinetic inductance superconductor, and ii) an array of 2000 Josephson junctions.

Gain of a High-Impedance Cavity Coupled to Strongly Driven Semiconductor Quantum Dots

The architecture of artificial atoms coupled to superconducting cavities allows the study of light-matter interactions and intriguing phenomena such as cavity gain implying photon generation. Here, we integrate a high-impedance cavity with a double quantum dot (DQD) in GaAs/(Al,Ga)As heterostructures, achieving a considerable DQD-cavity coupling strength and a relatively small cavity decay rate. By applying a strong drive to the DQD, we realize a population inversion and observe the cavity amplitude gain in multiple regions in the measured Landau-Zener-St\"uckelberg-Majorana interference pattern. We further systematically investigate the dependence of cavity gain on the driving frequency and tunnel coupling strength of the DQD. The results show that the cavity gain is tunable, with a maximum value of approximately $1.16$ in the measured range. Our experimental results are in good agreement with theoretical simulations and may provide an opportunity to implement on-chip microwave sources or microwave amplifiers in a controllable way.

Fiber-Coupled Diamond Magnetometry with an Unshielded Sensitivity of 30pT/Hz

Ensembles of nitrogen-vacancy centers (NVCs) in diamond can be employed for sensitive magnetometry. In this work, we present a fiber-coupled NVC magnetometer with an unshielded sensitivity of $(30\ifmmode\pm\else\textpm\fi{}10)\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in a (10--500)-Hz frequency range. This sensitivity is enabled by a relatively high green-to-red photon conversion efficiency, the use of a [100] bias-field alignment, microwave and lock-in amplifier (LIA) parameter optimization, as well as a balanced hyperfine-excitation scheme. Furthermore, a silicon carbide ($\mathrm{SiC}$) heat spreader is used for microwave delivery, alongside low-strain 1-${\mathrm{mm}}^{3}{\phantom{\rule{0.2em}{0ex}}}^{12}$$\mathrm{C}$ diamonds, one of which is placed in a second magnetically insensitive fluorescence-collecting sensor head for common-mode noise cancellation. The magnetometer is capable of detecting signals from sources such as a vacuum pump up to 2 m away, with some orientation dependence but no complete dead zones, demonstrating its potential for use in remote-sensing applications.

On the stability & phase locking to a system reference of an optoelectronic oscillator with large delay

Delay line oscillators based on photonic components, offer the potential for realization of phase noise levels up to 3 orders of magnitude lower than achievable by conventional microwave sources. Fibreoptic-based delay lines can realize the large delay required for low phase noise systems whilst simultaneously achieving insertion loss levels that can be compensated with available microwave and photonic amplification technologies. Multimode operation is an artefact of the delay line oscillator and introduces modulational instability into phase-locked control loops. An optoelectronic oscillator (OEO) with large delay under proportional integral control by a phase-locked loop (PLL) is modelled, providing the first report of the location of all the infinity of poles of the PLL-OEO system function. The first experimental observation of giant phase modulated oscillation of a free OEO and spontaneous giant phase modulated oscillation of a PLL-OEO are also reported and explained respectively as a source and manifestation of modulational instability. Nevertheless, the analysis and experimental observations, including a prototype 10 GHz PLL-OEO phase noise spectral density achieving - 80dBc/Hz {text{at}} 10 Hz and - 145dBc/Hz {text{at}} 10 kHz, demonstrate that stable phase lock operation and optimum phase noise performance is achievable provided full account of the multimode nature of the OEO is taken in the phase lock analysis.

In situ amplification of spin echoes within a kinetic inductance parametric amplifier.

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 × 107 spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of [Formula: see text] for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions.

Characterization of a low-noise superconductor–insulator–superconductor-based microwave amplifier with local oscillator phase-adjusting architecture

This paper describes a low-noise microwave amplifier based on up- and down-frequency-conversion processes in quasiparticle superconductor–insulator–superconductor (SIS) tunnel junctions. The SIS amplifier was configured with two SIS frequency-converter modules and a cryogenic millimeter-wave isolator inserted between them. Moreover, a local oscillator (LO) using millimeter-wave attenuators and a phase shifter was considered. This setup allowed the control of individual LO power and differential phase in these SIS frequency converters to optimize the amplifier performance. The SIS amplifier showed noise temperatures as low as 11 K and a 6–8 dB gain from nearly DC to 5 GHz. The attained microwave performance is promising for obtaining large-format arrays, such as multibeam heterodyne receivers. Moreover, this two-frequency-converter concept based on SIS junctions might enable microwave applications, such as wideband non-reciprocal circuits in isolators, gyrators, and circulators, which are essential devices in the quantum computing and radio astronomy fields.

Pulsed microwave photonic vector network analyzer based on direct sampling.

Pulsed VNAs enabling large dynamic measurement at a low pulse duty cycle are necessary for the characterization of active devices due to the overheating damage risk under continuous wave stimulation. In this paper, we proposed a pulsed microwave photonic vector network analyzer (p-MPVNA) based on direct sampling. With the broad system bandwidth of the p-MPVNA and undersampling technique, pulsed signals are received thru asynchronous wideband detection, and pulsed S-parameters are calculated thru vector superposition. In asynchronous wideband detection, the continuous spectrum of the pulsed signal is discretized into multiple frequency components. A low repetition rate optical pulse train undersamples the pulsed signal, and the discretized frequency components are aliased. The frequency components in the main lobe including most energy of the pulse signal are vector superimposed to calculate the pulsed S-parameter. The proposed p-MPVNA has a dynamic range decreases rate of 10log(duty cycle) when pulse duty cycle is below 10% , which is much slower than that of 20log(duty cycle) for classical narrowband detection. An experimental p-MPVNA is established for validation. A 6 to 18 GHz microwave amplifier is measured with continuous and pulsed power supply and the measured gain curves are consistent with the results from a commercial VNA. The system dynamic range decrease with pulse duty cycle is verified by the pulsed S-parameter measurement of a 10 GHz low pass filter under continuous and pulsed stimulation.

Наведенный нелинейный сдвиг частоты активного кольцевого резонатора на магнонном кристалле

The nonlinear shift of the resonant frequencies of a microwave active ring resonator (ARR) induced by a pump wave has been studied for the first time. The resonator was designed according to the scheme in the form of a closed ring containing a spin-wave delay line made on the basis of a one-dimensional magnonic crystal, as well as a microwave amplifier in a feedback circuit. It is shown, that with an increase in the power of the pumping wave, the shift of the resonant frequencies of the ARR increases in different ways depending on the position of the pumping frequency. The maximum induced nonlinear frequency shift is observed if the pumping frequency is at the minimum of the ARR transmission coefficient. A model describing the studied effect is developed.

Maser polarization simulation in the circumstellar envelope of an evolving star

An important phenomenon in a pulsing AGB (Asymptotic Giant Branch) star is the variability of its circumstellar envelope. The study of stimulated radiation called SiO maser (microwave amplification by stimulated emission of radiation) in the inner edge of the envelope shows fluctuations in polarization during the stellar pulsation period which is caused by the unstable magnetic field around the AGB star and needs to be investigated in order to understand it. We simulate the maser signal and polarization by using a computer code to describe the circumstellar envelope of the AGB star for comparison with the observations. The methods, i) Generate the energy transition of the stimulation matrix ii) Simulate the first stimulation from an electric field background iii) Convert the radiation to the frequency domain by using Fourier transform iv) Simulate the observation by amplifying radiation along a line of sight within the medium toward an observation position. At this stage, we set the tubular maser cloud with a constant magnetic field strength toward the observer. The program can simulate the maser signal and polarization, brighter when stimulating with a longer medium; the simulated polarization agrees well with expectations for this magnetic field orientation. Further works need to be carried out by testing this program with many cases to explain the obtained data from actual observations.

Characterization of Traveling-Wave Josephson Parametric Amplifiers at T = 0.3 K

The growing interest in quantum technologies, from fundamental physics experiments to quantum computing, demands for extremely performing electronics only adding the minimum amount of noise admitted by quantum mechanics to the input signal (i.e., quantum-limited electronics). Superconducting microwave amplifiers, due to their dissipationless nature, exhibit outstanding performances in terms of noise (quantum limited), and gain. However, bandwidth and saturation power still show space for substantial improvement. Within the DARTWARS <xref ref-type="fn" rid="fn1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">¹</xref> <fn id="fn1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><label>¹</label> DARTWARS (Detector Array Readout with Traveling Wave AmplifieRS), funded by Italian National Nuclear Institute (INFN), is a quantum technologies project targeted at the development of wideband superconducting amplifiers with noise at the quantum limit and the implementation of a quantum-limited readout in different types of superconducting detectors and qubit. </fn> collaboration, we are developing state-of-the-art microwave superconducting amplifiers based on Josephson junction arrays and on distributed kinetic inductance transmission lines. Here we report the realization of a setup for the characterization of the performances of Josephson traveling-wave parametric amplifiers at a temperature of 300 mK. Although in the final experimental setup, these amplifiers will operate at a base temperature of about 20 mK, their characterization at 300 mK allows to evidence the main aspects of their performances, but the ultimate noise level. This represents a quick and relatively inexpensive way to test these superconductive devices that can be of help to improve their design and fabrication.

Non-reciprocal acoustoelectric microwave amplifiers with net gain and low noise in continuous operation

Piezoelectric acoustic devices that are integrated with semiconductors can leverage the acoustoelectric effect, allowing functionalities such as gain and isolation to be achieved in the acoustic domain. This could lead to performance improvements and miniaturization of radio-frequency electronic systems. However, acoustoelectric amplifiers that offer a large acoustic gain with low power consumption and noise figure at microwave frequencies in continuous operation have not yet been developed. Here we report non-reciprocal acoustoelectric amplifiers that are based on a three-layer heterostructure consisting of an indium gallium arsenide (In0.53Ga0.47As) semiconducting film, a lithium niobate (LiNbO3) piezoelectric film, and a silicon substrate. The heterostructure can continuously generate 28.0 dB of acoustic gain (4.0 dB net radio-frequency gain) for 1 GHz phonons with an acoustic noise figure of 2.8 dB, while dissipating 40.5 mW of d.c. power. We also create a device with an acoustic gain of 37.0 dB (11.3 dB net gain) at 1 GHz with 19.6 mW of d.c. power dissipation and a non-reciprocal transmission of over 55 dB.

Cylindrical Dielectric Resonator as Dielectric Matching on Microwave Amplifier for the Unconditionally Stable and Conditionally Stable Transistor at 5 GHz Frequency

Stability and matching techniques on microwave amplifier have been an important consideration to maintain their required performances, but typically its frequency dependent. Thus, a frequency variable mechanism is required. The dielectric matching employing the stability and matching techniques on microwave amplifier with cylindrical dielectric resonator has been investigated and realized. The cylindrical dielectric resonator (CDR) with parallel microstrip lines is proposed at 5 GHz frequency for unconditionally stable and conditionally stable transistor as dielectric matching. Hence, the proposed dielectric resonator with +2 mm spacing and 155˚ of curved configuration indicated the best performances for preliminary study. The result improves the performance of the parallel inhomogeneous CDR by 9.77%. Subsequently, the homogeneous CDR is also successfully working as the variable frequency mechanism for unconditionally stable and conditionally stable transistor at 5 GHz frequency in maintaining their stability performances.

Diamond-based microwave quantum amplifier

Amplification of weak microwave signals with minimal added noise is of importance to science and technology. Artificial quantum systems, based on superconducting circuits, can now amplify and detect even single microwave photons. However, this requires operating at millikelvin temperatures. Natural quantum systems can also be used for low-noise microwave amplification using stimulated emission effects; however, they generate a higher noise, especially when operating above ~1 K.Here, we demonstrate the use of electron spins in diamond as a quantum microwave amplifier operating with quantum-limited internal noise, even above liquid nitrogen temperatures. We report on the amplifier's design, gain, bandwidth, saturation power, and noise. This capability can lead the way to previously unavailable quantum science, engineering, and physics applications.

X- and Q-band EPR with cryogenic amplifiers independent of sample temperature

Inspired by the success of NMR cryoprobes, we recently reported a leap in X-band EPR sensitivity by equipping an ordinary EPR probehead with a cryogenic low-noise microwave amplifier placed closed to the sample in the same cryostat [Šimėnas et al. J. Magn. Reson.322, 106876 (2021)]. Here, we explore, theoretically and experimentally, a more general approach, where the amplifier temperature is independent of the sample temperature. This approach brings a number of important advantages, enabling sensitivity improvement irrespective of sample temperature, as well as making it more practical to combine with ENDOR and Q-band resonators, where space in the sample cryostat is often limited. Our experimental realisation places the cryogenic preamplifier within an external closed-cycle cryostat, and we show CW and pulsed EPR and ENDOR sensitivity improvements at both X- and Q-bands with negligible dependence on sample temperature. The cryoprobe delivers signal-to-noise ratio enhancements that reduce the equivalent pulsed EPR measurement time by 16× at X-band and close to 5× at Q-band. Using the theoretical framework we discuss further improvements of this approach which could be used to achieve even greater sensitivity.

Analysis of Conditional Stability and Unconditional Stability and Instability for Microwave 3-Ports

A full and rigorous treatment of conditional and unconditional stability and instability for an active 3-port microwave circuit, represented at a given frequency by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters, is carried out. By terminating a given port with a variable termination one may study at the input and the output of the resulting 2-port circuit the occurrence of unconditional stability and instability, as well as of special cases of conditional stability, defined as reactive unconditional stability or instability. Such conditions are especially relevant in microwave oscillator design and were exhaustively identified for the first time and treated in previous analysis by the authors. Drawing from its conclusions, one obtains in the plane of the variable termination and with a simple algorithm, a single parametric representation, providing at once, in a closed and direct form, the entire collection of boundaries of the regions, wherein the listed conditions occur at ports of the resulting 2-port circuit. Guidelines for the design of microwave amplifiers and oscillators, both in series and shunt configuration, are sketched. Numerical examples, validated by simulations, are also presented.

Advanced Theoretical Models for Broadband Klystron Development

Broadband klystrons (BBKs) offer the potential of both high power and broad-bandwidth performance as microwave amplifiers. Staggered tuned bunching circuit and filter-loaded output cavity are the mainstream techniques adopted for developing such devices. However, in the design and optimization stage, the accurate and fast theoretical models are still missing before final particle-in-cell (PIC) simulations are conducted. In this article, the small-signal theory of klystron has been derived from accurate large-signal models used in KlyC, where complex mode field distribution, relativistic effects, mode coupling, and precise space charge model are fully considered in the final analytic formulas compared with existing simplified models. Furthermore, mode coupling theory with partially beam-loading conditions has been developed in KlyC to analyze the filter-loaded output cavity and overall klystron performance in the large-signal domain. An example of the retrofit design of 100-kW five-cavity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band klystron is then presented to demonstrate the advanced design methodology based on the above fast theoretical models. The 3-D PIC simulation finally verifies this BBK design, showing −1-dB bandwidth of 200 MHz is attainable with output power over 100 kW, where the maximum discrepancy between theoretical models and PIC is within 2% in the whole bandwidth.

On radiation dynamics in plasma relativistic microwave amplifier at the edge of electron beam pulse

We consider dynamics of radiation of a plasma microwave amplifier on a surface wave at the leading edge of the relativistic electron beam pulse. It has been shown that depending on the electron density of the plasma, different modes of operation of the amplifier are possible. At low plasma density, there is an early activation of the amplifier with large gain at the leading edge of the electron beam pulse and a significant decrease in the amplification of the signal when the electron energy reaches a plateau. With a higher plasma density, a later activation takes place with an almost constant output amplitude. The effect of ponderomotive force on plasmas was discussed.

Quantum-noise-limited microwave amplification using a graphene Josephson junction.

Josephson junctions (JJs) and their tunable properties, including their nonlinearities, play an important role in superconducting qubits and amplifiers. JJs together with the circuit quantum electrodynamics architecture form many key components of quantum information processing1. In quantum circuits, low-noise amplification of feeble microwave signals is essential, and Josephson parametric amplifiers (JPAs)2 are the widely used devices. The existing JPAs are based on Al-AlOx-Al tunnel junctions realized in a superconducting quantum interference device geometry, where magnetic flux is the knob for tuning the frequency. Recent experimental realizations of two-dimensional (2D) van der Waals JJs3-5 provide an opportunity to implement various circuit quantum electrodynamics devices6-8 with the added advantage of tuning the junction properties and the operating point using a gate potential. While other components of a possible 2D van der Waals circuit quantum electrodynamics architecture have been demonstrated, a quantum-noise-limited amplifier, an essential component, has not been realized, to the best of our knowledge. Here we implement a quantum-noise-limited JPA using a graphene JJ, that has a linear resonance gate tunability of 3.5 GHz. We report 24 dB amplification with 10 MHz bandwidth and -130 dBm saturation power, a performance on par with the best single-junction JPAs2,9. Importantly, our gate-tunable JPA works in the quantum-limited noise regime, which makes it an attractive option for highly sensitive signal processing. Our work has implications for novel bolometers; the low heat capacity of graphene together with JJ nonlinearity can result in an extremely sensitive microwave bolometer embedded inside a quantum-noise-limited amplifier. In general, this work will open up the exploration of scalable device architectures of 2D van der Waals materials by integrating a sensor with the quantum amplifier.

Characterization of Novel ALD Process for the Synthesis of CaO for 12CaO·7Al2O3 electride Applications

In this work we report on a novel CaO ALD process development with a little used solid ALD precursor for Calcium. This forms part of a larger effort to synthesize 12CaO·7Al2O3 [C12A7], which is a new electronic oxide compound with very low work function and applications potentials in displays and Field-Emission (FE) Cathodes. Currently there are no existing thin film technologies for the conformal deposition of C12A7 electride films on complex device surfaces with nanoscale precision. Use of ALD to obtain precise nanoscale interleaving of CaO and Al2O3 layers over Micro-Hollow Cathode Discharge devices MHCD or FE devices allows conversion to correct alloying of C12A7 in the desired nano-layers. Success in reproducibly obtaining these layers will significantly benefit applications using cathodes, such as light sources, nano-sat thrusters, vacuum electronics and small-format microwave amplifiers. For the final C12A7 film, the challenge is to develop two ALD processes for two binary films in this case CaO and Al2O3 which must be synthesized as alternating nanolaminates in the correct stoichiometric ratio and are subsequently reacted under high temperature annealing. Since ALD of Al2O3 is already a well-known established ALD process, we had to focus on developing an ALD process for CaO. For this study we decided to utilize the relatively novel solid ALD precursor Bis(N,N-di-iso-propylformamidinato)calcium(II) dimer [Ca(famd)2], which is a low vapor pressure solid Ca amidinate precursor and which has to be reacted with ozone or DI H2O vapors. The chemical structure of the Calcium precursor is shown schematically in Fig. 1. The Al2O3 binary compound will be synthesized with trimethylaluminum (TMA) and DI water vapor. The low vapor pressure of Ca amidinate precursor Ca(famd)2 in solid form constitutes a major technical challenge and cannot be reacted by ALD in vapor draw mode but necessitated as new hardware a 150mL booster bubbler with dip tube for bubbling the molten precursor and the installation of a Low Vapor Pressure Delivery (LVPD) kit with bypass. For this presentation we will report the physical characterization of the ALD CaO film with FE-SEM surface morphology studies, SEM EDS elemental analysis of the final composition, X-ray diffraction XRD analysis and atomic force microscopy AFM. Fig. 1: Schematic of chemical structure of the novel solid ALD Ca amidinate precursor Bis(N,N-di-iso-propylformamidinato)calcium(II) dimer [Ca(famd)2] Figure 1

Reflections on the Life of Oleg A. Tretyakov [In Memoriam

Dr. Oleg Alexandrovich Tretyakov, 83, passed away on Tuesday, 25 January 2022, in Istanbul, Turkey, after a short battle with lung cancer. He was an outstanding expert in electrodynamics and radiophysics. He was the chair of Commission B of the International Union of Radio Science (URSI) Committee of Ukraine since 1993, a Member of IEEE, and a professor emeritus of the Department of Theoretical Radiophysics, V.N. Karazin Kharkiv National University (KhNU), Ukraine. He had experience in solving diffraction problems by mathematically rigorous methods, wave scattering from rough surfaces, and wave propagation in random media, linear and nonlinear phenomena, and dynamic chaos in microwave oscillators and amplifiers. With him, we lost an internationally well-known and highly regarded leading figure in electromagnetic theory. His intellect, integrity, humor, professionalism, and humanity will be greatly missed.