We propose a technique to phase-match Josephson-junction traveling wave parametric amplifiers to achieve high gain over a broad bandwidth for applications such as the multiplexed readout of quantum coherent circuits.
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.
In order to build a large-scale quantum computer, one of the requirements is high-fidelity
multiplexed qubit readout, which in turn relies on the use of ultralow-noise
amplifiers. While Josephson Parametric Amplifiers (JPAs), using a cavity with
few Josephson junctions, have shown promising results for single qubit readout,
they have limitations such as low saturation power and a gain-bandwidth product
restriction. This makes them less suited for frequency multiplexed qubit readout. A
current-pumped Josephson Travelling-Wave Parametric Amplifier (JTWPA), using
4-wave mixing in a lumped-element transmission line, features both high saturation
power as well as no restriction on large bandwidth and high gain. This is possible
due to multiple junctions and the lack of a cavity. However, also this current pumped
JTWPA has an inherent problem, namely phase mismatch between the pump and
the signal. This prevents exponential gain. In this thesis, a current pumped JTWPA
using the resonant phase matching (RPM) technique to reduce the phase mismatch
problem is studied and characterised. The JTWPA shows high gain, high saturation
power and a large signal-to-noise ratio improvement. The JTWPA is also used for
qubit readout, for which it clearly improves the readout fidelity.
High gain and large bandwidth of traveling-wave parametric amplifier exploiting the nonlinearity of Josephson Junctions can be achieved by fulfilling the so-called phase-matching condition. This condition is usually addressed by placing resonant structures along the waveguide or by periodic modulations of its parameters, creating gaps in the waveguide’s dispersion. Here, we propose to employ the Josephson junctions, which constitute the centerline of the amplifier, as resonant elements for phase matching. By numerical simulations in JoSIM (and WRspice) software, we show that Josephson plasma oscillations can be utilized to create wave vector mismatch sufficient for phase matching as well as to prevent the conversion of the pump energy to higher harmonics. The proposed traveling wave parametric amplifier design has a gain of 15 dB and a 3 GHz bandwidth, which is comparable to the state-of-the-art TWPAs.