# Pulse Width Modulation method for quantum control design. (arXiv:1712.02211v1 [quant-ph])

Illuminated by the Pulse Width Modulation (PWM) technology in classical

control engineering, we propose the PWM approximation which transforms

continuous and bang-bang control into each other. This method works by

squeezing the approximation error into high-frequency components above a

prescribed cutoff frequency $\Omega$, which can be tailored by modulating the

switch time of the bang-bang control. Because the quantum dynamics under

bang-bang control can be efficiently calculated, PWM allows us to speed up

quantum control design particularly in large dimensional systems with small

number of control variables. Moreover, PWM paves the way to implement various

bang-bang control protocols in the literature with an arbitrary waveform, which

is more desirable in laboratory.