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arXiv:2503.11812

High-Efficiency, Low-Loss Floquet-mode Traveling Wave Parametric Amplifier

Jennifer Wang, Kaidong Peng, J.M. Knecht, Gregory Cunningham, Andres E. Lombo, Alec Yen, Daniela A. Zaidenberg, Michael Gingras, Bethany M. Niedzielski, Hannah Stickler, Katrina Sliwa, Kyle Serniak, Mollie E. Schwartz, William D. Oliver, Kevin P. O’Brien

Published Mar 14, 2025• 1 citation
arXivHTMLPDF

Abstract

Advancing fault-tolerant quantum computing and fundamental science necessitates quantum-limited amplifiers with near-ideal quantum efficiency and multiplexing capability. However, existing solutions typically achieve one at the expense of the other. In this work, we experimentally demonstrate the first Floquet-mode traveling-wave parametric amplifier (Floquet TWPA), which achieves nearly quantum-limited noise performance, minimal dissipation, and broadband operation, breaking the presumption that broadband amplifiers introduce higher noise. We achieve a system measurement efficiency of $65.1\pm5.8\%$ when measuring a superconducting qubit, which to our knowledge is the highest-reported in a superconducting qubit readout experiment utilizing phase-preserving amplifiers. Our device exhibits $>20$-dB amplification over a $3$-GHz instantaneous bandwidth, $<\!0.5\,$-dB average in-band insertion loss, and the highest reported intrinsic quantum efficiency for a TWPA of $92.1\pm7.6\%$, relative to an ideal phase-preserving amplifier. Fabricated in a superconducting qubit process, these general-purpose Floquet TWPAs are suitable for fast, high-fidelity multiplexed readout in large-scale quantum systems and future monolithic integration with quantum processors.

DOI
10.48550/arxiv.2503.11812

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Advancing fault-tolerant quantum computing and fundamental science necessitates quantum-limited amplifiers with near-ideal quantum efficiency and multiplexing capability. However, existing solutions typically achieve one at the expense of the other. In this work, we experimentally demonstrate the first Floquet-mode traveling-wave parametric amplifier (Floquet TWPA), which achieves nearly quantum-limited noise performance, minimal dissipation, and broadband operation, breaking the presumption that broadband amplifiers introduce higher noise. We achieve a system measurement efficiency of 65.1±5.8%65.1\pm5.8\%65.1±5.8% when measuring a superconducting qubit, which to our knowledge is the highest-reported in a superconducting qubit readout experiment utilizing phase-preserving amplifiers. Our device exhibits >20>20>20-dB amplification over a 333-GHz instantaneous bandwidth, < ⁣0.5 <\!0.5\,<0.5-dB average in-band insertion loss, and the highest reported intrinsic quantum efficiency for a TWPA of 92.1±7.6%92.1\pm7.6\%92.1±7.6%, relative to an ideal phase-preserving amplifier. Fabricated in a superconducting qubit process, these general-purpose Floquet TWPAs are suitable for fast, high-fidelity multiplexed readout in large-scale quantum systems and future monolithic integration with quantum processors.
Advancing error-corrected quantum computing and fundamental science necessitates quantum-limited amplifiers with near-ideal quantum efficiency and multiplexing capability. However, existing solutions achieve one at the expense of the other; for example, Josephson traveling wave parametric amplifiers (JTWPAs) are highgain, broadband, and chip-based quantum amplifiers that conventionally incur a bandwidth-noise tradeoff. When operated at 20-dB gain and instantaneous bandwidths of a few GHz, JTWPAs typically reach near-quantum limited intrinsic efficiencies of 70% - 85% relative to that of an ideal phase-preserving quantum amplifier. This is due to information leakage to the sidebands of the JTWPA, which can be recovered by adiabatically transforming the input modes to Floquet modes of the system within the device. In this thesis, we experimentally demonstrate the first Floquet-mode travelingwave parametric amplifier (Floquet TWPA). Fabricated in a superconducting qubit process, this Floquet TWPA achieves minimal dissipation, quantum-limited noise performance, and broadband operation. Our device exhibits > 20-dB amplification over a 3-GHz instantaneous bandwidth, <0.5 -dB average in-band insertion loss, and the highest-reported intrinsic quantum efficiency for a TWPA of 92.1±7.6%, relative to an ideal phase-preserving amplifier. When measuring a superconducting qubit, our Floquet TWPA enables a system measurement efficiency of 65.1 ± 5.8%, the highest-reported in a superconducting qubit readout experiment utilizing phase-preserving amplifiers to the best of our knowledge. Finally, we discuss the noise limitations of our current experimental setup, as well as impedance matching strategies that will enable us to push towards ideal JTWPA performance. These general-purpose Floquet TWPAs are suitable for fast, high-fidelity multiplexed readout in large-scale quantum systems and future monolithic integration with quantum processors.
Broadband quantum-limited amplifiers would advance applications in quantum information processing, metrology, and astronomy. However, conventional traveling-wave parametric amplifiers (TWPAs) support broadband amplification at the cost of increased added noise. In this work, we develop and apply a multi-mode, quantum input-output theory to quantitatively identify the sidebands as a primary noise mechanism in all conventional TWPAs. We then propose an adiabatic Floquet mode scheme that effectively eliminates the sideband-induced noise and subsequently overcomes the trade-off between quantum efficiency (QE) and bandwidth. We then show that a Floquet mode Josephson traveling-wave parametric amplifier implementation can simultaneously achieve >20 >20\,>20dB gain and a QE of η/ηideal>99.9%\eta/\eta_{\mathrm{ideal}}> 99.9\%η/ηideal​>99.9% of the quantum limit over more than an octave of bandwidth. Crucially, Floquet mode TWPAs also strongly suppress the nonlinear forward-backward wave coupling and are therefore genuinely directional. Floquet mode TWPAs can thus be directly integrated on-chip without isolators, making near-perfect measurement efficiency possible. The proposed Floquet scheme is also widely applicable to other platforms such as kinetic inductance traveling-wave amplifiers and optical parametric amplifiers.
Superconducting traveling-wave parametric amplifiers (TWPA) have emerged as highly versatile devices, offering broadband amplification with quantum-limited noise performance. They hold significant potential for addressing the readout bottleneck in prototype quantum computers, enabling scalability. Key challenges with this technology include achieving sufficient gain with minimal gain ripple while maintaining low noise performance. Efficient phase matching between a weak signal and a strong pump over the entire length of the TWPA is critical to overcoming these challenges. We present an experimental demonstration of the inverse Kerr phase matching technique in a TWPA, first proposed in Ref. Phys. Rev. Appl. 4, 024014. This method addresses several limitations of conventional dispersion engineering approaches of phase matching in the four-wave mixing parametric process in TWPAs. Most notably the existence of an unusable region of gain near the pump frequency which typically corresponds to the region of most optimal phase matching and maximum gain. The inverse Kerr phase matching approach, allows for greater frequency separation between the region of optimal gain and pump, \textit{in situ} tunability of the pump, minimal gain ripple, and a compact footprint which reduces losses. A TWPA employing the inverse Kerr phase matching technique experimentally demonstrated 20 dB of gain over a 3 GHz instantaneous bandwidth, with a tunable bandwidth of 8 GHz, minimal gain ripple, and near quantum-limited noise performance, with 1.5 photons of added noise.
Bringing signals from quantum to classical, from few-photon to many-photon levels for further processing, is a common challenge in rising quantum technologies. These include quantum computing, quantum communication, quantum sensing, radio astronomy, and dark matter searches, typically operating at microwave frequencies and millikelvin temperatures. Superconducting parametric amplifiers, as the first piece in the readout chain, have become a cornerstone of these technologies, since they offer unrivaled noise performance near the quantum-mechanical limit and high gain to surpass the noise of subsequent amplifiers. A notable implementation is the Josephson traveling-wave parametric amplifier (TWPA), which stands out due to its bandwidth of several Gigahertz and high saturation power, often larger than -100 dBm. These key properties come at the cost of complexity in design and fabrication: TWPA metamaterials often contain several thousands of Josephson junctions. Designing high-gain TWPAs involves three major challenges: ensuring impedance-matching, phase-matching of parametric amplification, and suppressing unwanted processes, all achievable through sub-wavelength dispersion engineering. This thesis covers the circuit design and analysis, implementation, and experimental characterization of a dispersion-engineered TWPA based on radio-frequency superconducting interference devices (rf-SQUIDs). It focuses on a detailed investigation of dispersion-engineering techniques and their effects on amplifier performance, particularly through the use of time-domain circuit simulations to analyze the multimode dynamics of the circuit. The experimentally realized device features 18 dB of gain, an instantaneous bandwidth spanning from 2.2 to 6.7 GHz, a system noise of 2.5 quanta, and a saturation power of (−86.5 ± 4.0) dBm. With these characteristics, it is suitable for frequency-multiplexed readout of detector arrays or qubits. Its high saturation power, about 10 dB higher than other reported Josephson-junction-based TWPAs, allows increasing the number of qubits per readout line, or decreasing the intermodulation between frequency-multiplexed qubits, both crucial for scaling up quantum computation.
Simultaneous ideal quantum measurements of multiple single-photon-level signals would advance applications in quantum information processing, metrology, and astronomy but require the first amplifier to be simultaneously broadband, quantum limited, and directional.However, conventional traveling-wave parametric amplifiers support broadband amplification at the cost of increased added noise and are not genuinely directional due to non-negligible nonlinear backward-wave generation.In this work, we introduce a new class of amplifiers that encode the information in the Floquet modes of the system.Such Floquetmode amplifiers prevent information leakage and overcome the trade-off between quantum efficiency (QE) and bandwidth.Crucially, Floquet-mode amplifiers strongly suppress the nonlinear forward-backward wave coupling and are therefore genuinely directional and readily integrable with qubits, clearing another major obstacle toward broadband ideal quantum measurements.Furthermore, Floquet-mode amplifiers are insensitive to out-of-band impedance mismatch, which otherwise may lead to gain ripples, parametric oscillations, and instability in conventional traveling-wave parametric amplifiers.Finally, we show that a Floquet-mode Josephson traveling-wave parametric amplifier implementation can simultaneously achieve > 20 dB gain and a QE of η/η ideal > 99.9% of the quantum limit over more than an octave of bandwidth.The proposed Floquet scheme is also widely applicable to other platforms, such as kinetic inductance traveling-wave amplifiers and optical parametric amplifiers.
Traveling-wave parametric amplifiers (TWPAs) have attracted much attention for their broadband amplification and near-quantum-limited noise performance. TWPAs are nonreciprocal by nature providing gain for forward-propagating signals and transmission line losses for backward traveling waves. This intrinsic nonreciprocity is insufficient to protect sensitive quantum devices from backaction due to noise from warmer amplification stages in practical systems, and requires the use of bulky cryogenic isolators. We present a multistage TWPA (mTWPA) that addresses this limitation by achieving passive in-band reverse isolation alongside near-quantum-limited noise performance. The multistage architecture consists of two mode conversion stages and a reflectionless high-pass filter that provides the passive isolation. Experimental measurements of a prototype mTWPA demonstrated 20 dB of forward gain across a 1.6 GHz bandwidth and greater than 35 dB of reverse isolation. Noise measurements indicate performance at 1.7 times the quantum limit. This demonstrates that the increased complexity of a multistage TWPA design does not lead to significant added noise. The designed distribution of gain across the stages is engineered to minimize internal amplifier noise at the input, and we propose further optimization strategies in redistribution of the gain between the stages. This level of isolation mitigates noise from warmer amplification stages, matching the performance of conventional isolators. The passive reverse isolation of the mTWPA, allows for the amplifier to operate in pulsed mode where the amplifier is off during qubit gate operations and is turned on during readout allowing for an isolator free scalable readout architecture.