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Abstract: Quantum devices in general are limited by noise in detection and measurements greatly. One such device is the cavity-embedded Cooper Pair Transistor (cCPT), which can be used as an electrometer. To make the cCPT operate at its resonant frequency, we use a feedback loop to minimize the difference between the cavity’s resonant frequency and the drive frequency, i.e. the error frequency, at a minimum. To improve the feedback loop, we need a better estimate of the actual state of the error frequency that is not corrupted by process and measurement noise, so that we can apply a control law that is more proportional to the “true” state of the system. A Kalman filter does exactly this; by calculating a weighted average of the best estimate of the previous measurement of the system and the measured value of the current state, it provides an improved estimate of the “true” state. The error signal being our state, we model our feedback loop to first order as a damped-driven harmonic oscillator. Then, by selecting an optimal gain value that minimizes the error between the estimated state and the actual measurement, we can find the “true” error signal. This calculation is implemented by inserting an FPGA board in the feedback loop. By determining the true state of the error signal and applying proportional integral control techniques, we anticipate a significant reduction in the noise within the system. Therefore, this project focuses on implementing a filter based on state-estimation that eventually improves the feedback control techniques in a quantum-limited electrometer, which represents a promising avenue for enhancing the precision of quantum measurements.

Advisor: Professor Alexander Rimberg

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Meeting ID: 952 1016 7250
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