Measurable Improvement in Multi-Qubit Readout Using a Kinetic Inductance Traveling Wave Parametric Amplifier

TL;DR

This paper demonstrates that integrating a kinetic inductance traveling wave parametric amplifier (KI-TWPA) with a multiplexed qubit system significantly improves readout signal-to-noise ratio and fidelity, approaching quantum-limited performance.

Contribution

The work presents the first integration of a KI-TWPA with a multiplexed qubit device, showing measurable improvements in readout fidelity and noise performance.

Findings

Maximum SNR improvement factor of 1.45 for cavities within KI-TWPA bandwidth

Readout fidelity increased from 96.2% to 97.8% with KI-TWPA

System noise below 5 quanta on-chip, with excess noise below 4 quanta for cavities inside bandwidth

Abstract

Increasing the size and complexity of quantum information systems requires highly-multiplexed readout architectures, as well as amplifier chains operating near the quantum limit (QL) of added noise. While documented prior efforts in KITWPA integration in quantum systems are scarce, in this work we demonstrate integration of a KI-TWPA with a multiplexed-qubit device. To quantify the system noise improvement we perform an ac Stark shift calibration to precisely determine noise power levels on-chip (at each cavity's reference plane) and the total system gain. We then characterize the qubit state measurement fidelity and the corresponding signal-to-noise ratio (SNR). To conduct the most faithful measurement of the benefits offered by the KI-TWPA we perform these measurements for readout chains where the high electron mobility transistor (HEMT) amplifier is the first-stage amplifier (FSA) - with none of the external hardware required to operate the KI-TWPA - and with the KI-TWPA as the FSA. While some readout cavities fall outside the KI-TWPA bandwidth, for those inside the bandwidth we demonstrate a maximum improvement in the state measurement SNR by a factor of 1.45, and increase the fidelity from 96.2% to 97.8%. These measurements demonstrate a system noise below 5 quanta referenced on-chip and we bound the KI-TWPA excess noise to be below 4 quanta for the six cavities inside its bandwidth. These results show a promising path forward for realizing quantum-limited readout chains in large qubit systems using a single parametric amplifier.