Session Z46: Broadband Parametric Amplifiers and Circulators

A multi-mode traveling-wave Josephson converter for on-chip circulation: part I

Circulators are key components of circuitQED setups. However, commercially available devices are bulky, lossy and rely on ferrite cores which cannot be integrated in superconducting devices. A reliable on-chip circulator would allow integration of amplification chains in superconducting processors, thereby boosting measurement efficiency and reducing devices footprint. Moreover, it would pave the way for the simulation of non-trivial phases of matter. Unfortunately, existing implementations of on-chip non-reciprocal components face limitations in terms of bandwidth, tunability, and isolation.

In this two-part talk, we introduce a novel method that utilizes a two-mode transmission line doped with Josephson junctions. A traveling-wave pump applied on one mode activates a directional photon conversion process on the second mode, ultimately leading to circulation within the circuit. Our approach offers the advantage of broad tunability, high isolation, and is compatible with traveling-wave amplification. In this first part, I will present the working principle of our device.   

A multi-mode traveling-wave Josephson converter for on-chip circulation: part II

Circulators are key components of circuitQED setups. However, commercially available devices are bulky, lossy and rely on ferrite cores which cannot be integrated in superconducting devices. A reliable on-chip circulator would allow integration of amplification chains in superconducting processors, thereby boosting measurement efficiency and reducing devices footprint. Moreover, it would pave the way for the simulation of non-trivial phases of matter. Unfortunately, existing implementations of on-chip non-reciprocal components face limitations in terms of bandwidth, tunability, and isolation.

In this two-part talk, we introduce a novel method that utilizes a two-mode transmission line doped with Josephson junctions. A traveling-wave pump applied on one mode activates a directional photon conversion process on the second mode, ultimately leading to circulation within the circuit. Our approach offers the advantage of broad tunability, high isolation, and is compatible with traveling-wave amplification.

In this second part, I will present the performances and limitations of our device.   

Microwave Engineering of Parametric Interactions in Superconducting Circuits

Parametric interactions are the basis for critical and emerging superconducting quantum technologies such as quantum limited amplifiers and parametric circulators. For these devices to be practical in the context of frequency multiplexed, multi-qubit readout, they must be designed to have predictable performance over a relatively wide bandwidth. To that end, we developed a description of parametric interactions–frequency conversion and amplification processes–from a microwave engineering point of view, which allows us to harness established band-pass network-synthesis methods in our circuit designs. We will review our design methodology and its relation to the usual coupled-modes approach, then present data from two classes of parametrically-pumped Josephson devices that we designed accordingly. First, a matched parametric amplifier having 500 MHz instantaneous bandwidth with 20 dB flat gain based on a 3-pole Chebyshev network, and second, a Josephson circulator with 200 MHz bandwidth and 15 dB of isolation, built with hybrid passive and parametric coupling elements with a 2-pole matching network.   

Traveling wave parametric amplifiers with inbuilt reverse isolation, Part I

Traveling wave parametric amplifiers (TWPAs) have emerged as critical tools for near-quantum-limited broadband amplification of microwave signals. Typically these amplifiers suffer from unavoidable reflections and non-zero backward emission. Thus requiring additional isolation between the device under test (DUT) and the amplifier to protect the DUT from unwanted radiations. This not only makes the measurement setup considerably bulky but also introduces additional losses before the primary amplifier, resulting in the degradation of the noise performance of the amplification chain.

We will present our efforts towards building a Josephson-junction-based TWPA that utilizes nonlinearities not only for amplification but also to upconvert backward propagating modes to a frequency band that can be easily discarded, effectively providing reverse isolation. This should help in improving the noise performance of the amplification chain while making it compact and better suited for upscaling the multiplexed measurement setups.   

Traveling wave parametric amplifiers with inbuilt reverse isolation, Part II

Traveling wave parametric amplifiers (TWPAs) have emerged as critical tools for near-quantum-limited broadband amplification of microwave signals. Typically these amplifiers suffer from unavoidable reflections and non-zero backward emission. Thus requiring additional isolation between the device under test (DUT) and the amplifier to protect the DUT from unwanted radiations. This not only makes the measurement setup considerably bulky but also introduces additional losses before the primary amplifier, resulting in the degradation of the noise performance of the amplification chain.

We will present our efforts towards building a Josephson-junction-based TWPA that utilizes nonlinearities not only for amplification but also to upconvert backward propagating modes to a frequency band that can be easily discarded, effectively providing reverse isolation. This should help in improving the noise performance of the amplification chain while making it compact and better suited for upscaling the multiplexed measurement setups.   

TWPAC - the Traveling-Wave Parametric Amplifier and Converter: design and characterization

Superconducting traveling-wave parametric amplifiers (TWPAs) have become ubiquitous in superconducting circuit readout, owing their popularity to their large bandwidth, high gain, and near-quantum-limited operation. While TWPAs are in principle directional, non-idealities lead to pump, signal and idler reflections that can substantially raise the thermal occupancy of the readout cavity. As a consequence, several stages of lossy and magnetic isolators are often placed between the qubit system and the TWPA, degrading the noise performance and inhibiting scalability. To circumvent this issue, we consider a TWPA with forward gain and backward isolation, achieved by using two parametric processes: (i) parametric amplification in the forward direction, and (ii) frequency conversion in the backward direction. In this talk we will discuss experimental progress toward the design, fabrication and basic scattering characterization of this traveling-wave parametric amplifier and converter – or TWPAC.   

Embedded Amplifier for Efficient Superconducting Qubit Readout, Part 1: Theory

High fidelity qubit readout is a cornerstone of quantum computing. In superconducting architecture, this is typically achieved by routing signals from a readout cavity to a parametric amplifier via microwave circulators. The use of these off-chip components enables the independent design and optimization of the readout cavity and parametric amplifier. However, the intrinsic losses and large magnetic fields of these circulators reduces measurement efficiency and inhibits scalability. Our strategy to circumvent this is to perform the amplification and signal routing directly on-chip, by coupling a transmon qubit to a nonreciprocal multimode parametric system. As a consequence of this, the qubit and amplifier become a single open quantum system with a large Hilbert space. In this talk, we will discuss the theoretical challenges in understanding the quantum dynamics, focusing on extracting qubit measurement and dephasing rates.   

Embedded Amplifier for Efficient Superconducting Qubit Readout, Part 2: Experiment

In a typical dispersive superconducting qubit readout, microwave circulators are placed between the readout cavity and the first parametric amplifier to avoid excess amplifier backaction on the qubit. The microwave losses intrinsic to these circulators and their associated wiring reduce measurement fidelity, scalability, and the viability of weak measurement-based feedback protocols. Recently, it was shown that directional amplifiers can circumvent the need for conventional circulators, enabling record high measurement efficiencies [1]. In this talk, we will discuss experimental progress toward directly embedding a qubit inside a directional amplifier to further increase measurement efficiency. In particular, we will focus on the characterization of a transmon qubit coupled to a multimode parametric system acting as an effective readout cavity with directional gain.

[1] F. Lecocq, L. Ranzani, G. A. Peterson, K. Cicak, X. Y. Jin, R. W. Simmonds, J. D. Teufel, and J. Aumentado, Physical Review Letters 126 (2021).   

Noise Characterization of a Floquet-Mode Josephson Traveling-Wave Parametric Amplifier

Floquet-mode Josephson traveling-wave parametric amplifiers (Floquet TWPAs) are recently proposed to suppress higher-order sideband noise dominant in conventional uniform TWPAs and achieve broadband near-ideal quantum efficiency. Here we report the noise characterization result of a low-loss, qubit-fabrication-compatible Floquet TWPA device using both the circuit-QED and the waveguide-QED (wQED) power calibration methods. We directly compare the optimized system signal-to-noise improvement of our Floquet TWPA and a conventional homogeneous TWPA in the same experimental setup.

 

*This work was funded in part by the AWS Center for Quantum Computing. This material is based upon work supported under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the U.S. Air Force.   

Demostration of an rf-SQUID based three-wave mixing traveling-wave parametric amplifier

Modern quantum experiments, which operate with microwave signals at power levels of a few fW, greatly benefit from amplification with near quantum-limited added noise. To address this demand, while also providing a large bandwidth, we realize a traveling-wave parametric amplifier (TWPA) based on an array of ~2000 rf-SQUIDs [1]. The device operates in a three-wave mixing regime, delivering gain of 18 dB over a bandwidth of ~4 GHz and exhibits a saturation power of approximately -90 dBm. We achieve phase-matching by periodic capacitance loading [2], which we optimised by time-domain circuit simulations. Our TWPA is fabricated using Nb/Al-AlOx/Nb trilayer technology. We present simulations and experimental results including noise characterization of the device.

[1] Zorin, A. B. Physical Review Applied 6.3 (2016): 034006.

[2] Gaydamachenko, V., et al. Journal of Applied Physics 132.15 (2022): 154401   

Assessing the Impact of Fabrication Variations on Josephson Travelling Wave Parametric Amplifiers

Josephson junction-based travelling wave parametric amplifiers (JTWPAs) are widely used in cQED experiments for high-fidelity readout of superconducting qubits over a large bandwidth. The bandwidth results from a transmission line configuration with thousands of Josephson junctions. However, achieving high gain in such a device necessitates multi-layer structures over a large footprint. As a result, the performance can be impacted by the non-uniformity inherent in the fabrication process.

In this work, we analyze the superconducting circuit performance in the presence of fabrication variations to predict the process constraints needed to enable the high reproducibility of micro- and nanostructured components in the JTWPA fabricated on an all-Aluminium qubit-compatible process. We show systematic improvements in device performance from the refinement of Josephson junction fabrication treatments for yield and uniformity. We compare measurements on fabricated devices and correlate the effects of mismatched cell impedance and signal reflections between cells to the parameter spread in fabrication runs. Subsequently, we model cell-to-cell variations of circuit parameters and evaluate the impact of non-uniformity on the gain, quantum efficiency, return loss, and insertion loss. Finally, we combine experimental data and simulations to obtain gain scaling from the relative standard deviation of process parameters.

 

*This work was funded in part by the AWS Center for Quantum Computing   

Embedding networks for ideal performance of a travelling-wave parametric amplifier

We investigate the required embedding networks to enable ideal performance for a high-gain travelling-wave parametric amplifier (TWPA) based on three-wave mixing (3WM). By embedding the TWPA in a network of superconducting diplexers and hybrid couplers, the amplifier can deliver a high stable gain with near-quantum-limited noise performance, with suppressed gain ripples, while eliminating the reflections of the signal, the idler and the pump as well as the transmission of all unwanted tones. We demonstrate a configuration where the amplifier can isolate. We call this technique Wideband Idler Filtering (WIF). The theory is supported by simulations that predict over 20 dB gain in the band 4-8 GHz with 10 dB isolation for a single amplifier and 30 dB isolation for two cascaded amplifiers. We demonstrate how the WIF-TWPAs can be used to construct switchable isolators with over 40 dB isolation over the full band 4-8 GHz. We also propose an alternative design where the WIF can be implemented without diplexers. Finally we show how, with small modifications, the technique can be implemented for four-wave mixing (4WM) TWPAs as well.