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arXiv:1510.03065 · Applied Physics Letters

Broadband parametric amplification with impedance engineering: Beyond the gain-bandwidth product

Tanay Roy, Suman Kundu, Madhavi Chand, A. M. Vadiraj, Arpit Ranadive, N. Nehra, Meghan P. Patankar, J. Aumentado, A. A. Clerk, R. Vijay

Published Dec 28, 2015• 184 citations
arXivHTMLPDF

Abstract

We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of −110 dBm and near quantum-limited noise. The results are in a good agreement with our theoretical model.

DOI
10.1063/1.4939148

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We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of −110 dBm and near quantum-limited noise. The results are in a good agreement with our theoretical model.
Quantum-limited Josephson parametric amplifiers play a pivotal role in advancing the field of circuit quantum electrodynamics by enabling the fast and high-fidelity measurement of weak microwave signals. Therefore, it is necessary to develop robust parametric amplifiers with low noise, broad bandwidth, and reduced design complexity for microwave detection. However, current broadband parametric amplifiers either have degraded noise performance or rely on complex designs. Here, we present a device based on the broadband impedance-transformed Josephson parametric amplifier that integrates a hornlike coplanar waveguide transmission line, which significantly decreases the design and fabrication complexity while keeping comparable performance. The device shows an instantaneous bandwidth of 700 (200) MHz for 15 (20) dB gain with an average input saturation power of −110 dBm and near quantum-limited added noise. The operating frequency can be tuned over 1.4 GHz using an external flux bias. We further demonstrate the negligible backaction from our device on a transmon qubit. The amplification performance and simplicity of our device promise its wide adaptation in quantum metrology, quantum communication, and quantum information processing. Published by the American Physical Society 2024
In this paper, we introduce a method of using a double-layer resist lift-off process to prepare the capacitor dielectric layer for fabricating impedance-engineered Josephson parametric amplifiers (IMPAs). Compared to prior art, this method enhances fabrication success rate and accelerates production. The IMPA we made, experimentally achieves an instantaneous bandwidth over 950 (600) MHz with a gain exceeding 10 (14) dB, along with saturation input power of −115 dBm and near quantum-limited noise. We demonstrate the negligible backaction from the IMPA on superconducting qubits, resulting in no significant degradation of the relaxation time and coherence time of the qubits. The IMPA improves the signal-to-noise ratio from 1.69 to 14.56 and enables the amplification chain to achieve high quantum efficiency with η ≈ 0.26, making it a critical necessity for large-scale quantum computation.
We describe a wide-band Josephson Parametric Amplifier (JPA) that is impedance-matched using an integrated compact superconducting transmission line transformer. The impedance transformer consists of two broadside coupled transmission lines configured in a Ruthroff topology which enables a wide matching bandwidth from 2 to 18GHz, reducing the input line impedance and the device resonance quality factor by a factor of 4. This enables gain flatness and flexibility in the choice of the amplifier’s tuning range. The amplifier has up to 20dB gain, with less than 1dB of ripple, 2-3GHz gain-bandwidth product and -126dBm input 1-dB compression point. Moreover, the device active area fits into a 1mm×1mm space, thus easing integration into large quantum systems.
We present an experimental demonstration of an impedance-engineered Josephson parametric amplifier (IEJPA) fabricated in a single-step lithography process. Impedance-engineering is implemented using a lumped-element series LC circuit. We use a simpler lithography process where the entire device—impedance transformer and Josephson parametric amplifier (JPA)—is patterned in a single electron beam lithography step, followed by a double-angle Dolan-bridge technique for Al–AlOx–Al deposition. We observe amplification with 18 dB gain over a wide 400 MHz bandwidth centered around 5.3 GHz with added noise approaching the quantum limit, and a saturation power of −114 dBm. To accurately explain our experimental results, we extend existing theories for IEJPAs to incorporate the full sine nonlinearity of both the JPA and the transformer. Our work provides a route to simpler realization of broadband JPAs and a theoretical foundation for a regime of JPA operation that has been less explored in literature.
Broadband quantum-limited amplifiers play a critical role in the single-shot readout of superconducting qubits, but a popular implementation, the traveling wave parametric amplifier, involves a complex design and fabrication process. Here, we present a simple design for a Josephson parametric amplifier, using a lumped element resonator comprising a superconducting quantum interference device whose useful bandwidth is enhanced with an on-chip impedance-matching circuit. We demonstrate a flux-coupling geometry that maximizes the coupling to the Josephson loop and minimizes spurious excitation of the amplifier resonant circuit. The amplifier, which operates in a flux-pumped mode, is demonstrated with a power gain of more than 20 dB over a bandwidth of about 300 MHz, where approximate noise measurements indicate quantum-limited performance. A procedure is given for optimizing the bandwidth for this kind of amplifier, using a linearized circuit simulation while minimizing non-linearities.
We designed and fabricated an impedance-matched Josephson parametric amplifier (JPA) working in the flux-pump mode for the broadband amplification of microwave signals. A simple fabrication method suitable for a small cleanroom was developed. We also studied the phase response, as well as the gain, as a function of signal frequency and pump power at various pump frequencies. The phase response can be explained with the behavior of the nonlinear Duffing oscillator. The observed decrease of the resonance frequency as the pump power increases, as well as the emergence of an unstable bifurcation zone, are the characteristic nonlinear behavior of the Duffing oscillator. The features of the gain profile in the stable zone can be explained with a model adapted from the theoretical model for the two-dimensional gain profile of an impedance-matched, current-pumped JPA. Over 17 dB gain with a bandwidth more than 300 MHz (centered around 6.45 GHz) was observed. Our impedance-matched JPA is used for improving the fast readout fidelity of transmon qubits.