Amplitude Noise Cancellation of Microwave Tones

TL;DR

This paper introduces a feedback cancellation technique using FPGA to significantly reduce amplitude noise in microwave tones, improving sensitivity and reducing heating in quantum and sensing systems.

Contribution

The paper presents a novel FPGA-based feedback method for amplitude noise cancellation in microwave generators, effective where phase noise cancellation fails.

Findings

Achieved 13 dB noise power reduction at 2 MHz offset

Reduced cavity heating rate by a factor of 3.5

Lowered minimum oscillator occupation by a factor of 2

Abstract

Carrier noise in coherent tones limits sensitivity and causes heating in many experimental systems, such as force sensors, time-keeping, and studies of macroscopic quantum phenomena. Much progress has been made to reduce carrier noise using phase noise cancellation techniques, however, in systems where amplitude noise dominates, these methods are ineffective. Here, we present a technique to reduce amplitude noise from microwave generators using feedback cancellation. The method uses a field-programmable gate array (FPGA) to reproduce noise with a tunable gain and time delay, resulting in destructive interference when combined with the original tone. The FPGA additionally allows for tuning of the frequency offset and bandwidth in which the noise is canceled. By employing the cancellation we observe 13 dB of noise power reduction at a 2 MHz offset from a 4 GHz microwave tone, lowering the total noise to the phase noise level. To verify its applicability we utilize the setup in a microwave optomechanics experiment to investigate the effect of generator noise on the sideband cooling of a 0.5 mm silicon nitride membrane resonator. We observe that with our technique the rate of externally induced cavity heating is reduced by a factor of 3.5 and the minimum oscillator occupation is lowered by a factor of 2. This method broadens the field of noise cancellation techniques, where amplitude noise is becoming an increasingly important consideration in microwave systems as phase noise performances improve over time.