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arXiv:2103.07793

Broadband Microwave Isolation with Adiabatic Mode Conversion in Coupled Superconducting Transmission Lines

Mahdi Naghiloo, Kaidong Peng, Yufeng Ye, Gregory Cunningham, Kevin P. O’Brien

Published Mar 13, 2021• 2 citations
arXivHTMLPDF

Abstract

We propose a traveling wave scheme for broadband microwave isolation using parametric mode conversion in conjunction with adiabatic phase matching technique in a pair of coupled nonlinear transmission lines. This scheme is compatible with the circuit quantum electrodynamics architecture (cQED) and provides isolation without introducing additional quantum noise. We first present the scheme in a general setting then propose an implementation with Josephson junction transmission lines. Numerical simulation shows more than 20 dB isolation over an octave bandwidth (4-8\,GHz) in a 2000 unit cell device with less than 0.05 dB insertion loss dominated by dielectric loss.

DOI
10.48550/arxiv.2103.07793

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We propose a traveling wave scheme for broadband microwave isolation using parametric mode conversion in conjunction with adiabatic phase matching technique in a pair of coupled nonlinear transmission lines. This scheme is compatible with the circuit quantum electrodynamics architecture (cQED) and provides isolation without introducing additional quantum noise. We first present the scheme in a general setting then propose an implementation with Josephson junction transmission lines. Numerical simulation shows more than 20 dB isolation over an octave bandwidth (4-8,GHz) in a 2000 unit cell device with less than 0.05 dB insertion loss dominated by dielectric loss.
Superconducting traveling-wave parametric amplifiers have emerged as highly promising devices for near-quantum-limited broadband amplification of microwave signals and are essential for high quantum-efficiency microwave readout lines. Built-in isolation, as well as gain, would address their primary limitation: lack of true directionality due to potential backward travel of electromagnetic radiation to their input port. Here, we demonstrate a Josephson-junction-based traveling-wave parametric amplifier isolator. It utilizes third-order nonlinearity for amplification and second-order nonlinearity for frequency upconversion of backward propagating modes to provide reverse isolation. These parametric processes, enhanced by a novel phase matching mechanism, exhibit gain of up to 20~dB and reverse isolation of up to 30~dB over a static 3~dB bandwidth greater than 500~MHz, while keeping near-quantum limited added noise. This demonstration of a broadband truly directional amplifier ultimately paves the way towards broadband quantum-limited microwave amplification lines without bulky magnetic isolators and with inhibited back-action.
We propose a technique to overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using "resonant phase matching," we design a compact superconducting device consisting of a transmission line with subwavelength resonant inclusions that simultaneously achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of -98 dBm. Such an amplifier is well suited to cryogenic broadband microwave measurements such as the multiplexed readout of quantum coherent circuits based on superconducting, semiconducting, or nanomechanical elements, as well as traditional astronomical detectors.
This work presents the design, fabrication strategy, and numerical modeling of niobium-based Josephson traveling-wave parametric amplifiers (JTWPAs) for quantum microwave readout. These devices are designed as nonlinear transmission lines composed of more than two thousand Josephson junction unit cells, with periodically embedded resonators enabling phase matching. The use of Nb trilayer technology (Nb/AlO[Formula: see text]/Nb) with respect to Al-based devices ensures higher junction uniformity, lower losses, and higher resilience to stray magnetic fields. We developed a multi-scale modeling framework combining harmonic balance methods and time-domain simulations of nonlinear coupled differential equations to describe wave propagation, parametric amplification, and spectral dynamics. Numerical results predict broadband gain up to 20[Formula: see text]dB over multi-GHz bandwidths. These results demonstrate the potential of Nb-based JTWPAs as scalable components for quantum applications.
Light waves do not interact in vacuum but can mix in nonlinear media. A strong pump wave can thus convert the frequency of a weaker signal, provided energy and momentum are conserved. These conditions are typically satisfied when all waves propagate with comparable phase velocity along a given axis. Here, we investigate an alternative scheme by which a microwave signal propagating along a one-dimensional Josephson metamaterial is converted into a counter-propagating wave through interaction with a slower pump. In this regime, the input wave is exponentially attenuated, enabling an on-chip microwave isolator reconfigurable into a reciprocal, tunable coupler. The device’s operating mode and working frequency can be selected in situ over a broad microwave range. We measure isolation exceeding 5 dB in the 5-8.5 GHz range and 10 dB in the 7-8.5 GHz range, with a typical 200 MHz bandwidth. Further improvements are expected through design optimization and reduced fabrication disorder, opening new possibilities for microwave routing and processing in superconducting circuits. Wave-mixing is investigated in a Josephson traveling-wave device supporting two modes of propagation. A phase-matched conversion process between counterpropagting waves is leveraged to implement a robust on-chip circulator and tunable coupler.
We develop a concept of traveling-wave Josephson parametric amplifier based on a ladder-type superconducting transmission line containing serial array of one-junctions SQUIDs. The circuit operates in a three-wave mixing mode and exploits both quadratic and cubic (Kerr) nonlinearities in the current-phase relation of the SQUIDs controlled by external magnetic flux. These two types of nonlinearities allow efficient three-wave mixing and perfect phase matching, respectively. The transmission line exhibits a power gain with exponential dependence on its length (number of cells NNN) in the widest frequency range, 0≲fs,fi≲fp0 \lesssim f_s, f_i \lesssim f_p0≲fs​,fi​≲fp​, where fsf_sfs​, fif_ifi​ and fpf_pfp​ are the signal, idler and pump frequencies, respectively, obeying relation fs+fi=fpf_s + f_i = f_pfs​+fi​=fp​. Estimation of the amplifier characteristics with typical experimental parameters, number of cells NNN = 700, length of 28 mm and pump frequency of 12.5 GHz yields a flat (-3 dB) gain of about 20 dB in the bandwidth from 3.35 GHz to 9.15 GHz and a saturation power of -90 dBm.
Detecting single-photon level signals—carriers of both classical and quantum information—is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz with sufficient dynamic range to read out 20 superconducting qubits. To achieve this performance, we introduce a subwavelength resonant phase-matching technique that enables the creation of nonlinear microwave devices with unique dispersion relations. We benchmark the amplifier with weak measurements, obtaining a high quantum efficiency of 75% (70% including noise added by amplifiers following the Josephson amplifier). With a flexible design based on compact lumped elements, this Josephson amplifier has broad applicability to microwave metrology and quantum optics.