Development And Application Of High Speed Homodyne Detector

Ever since the 20^th century,quantum mechanics has been found and developed rapidly,the human understanding of the micro-physical world has also been continuously strength.There is a basic principle in quantum mechanics:any measurement to a quantum state will bring irreversible effects,the quantum state itself will collapse to one of its eigenstate.Besides,a quantum state can't be cloned,so measuring a quantum state is quite a difficult task.But things get better when considering laser,because light from a laser source is considered to be coherent state,which means the quantum states of laser are totally same regardless of time varying.So laser is an ideal source by providing countless identical quantum states,and we can take a measurement on each of these quantum states to get full information about the quantum state.This technology about measuring quantum state in quantum optics is well known as quantum state tomography.In this article,we will present a kind of widely used quantum detector to make a quantum state tomography:balanced homodyne detector.The first quantum state tomography based on Homodyne detector was implemented successfully in 1993,after which,the Homodyne detector was widely used in various field in quantum optics.One can obtain the quadrature operator measurement value by a single homodyne detection,and after amounts of homodyne detection,one can get the probability distribution of quadrature measurement.The full information about the quantum state is got by scanning the relative phase of the signal from 0 to ?,and finally we can get the quasi-probability distribution which is well known as the wigner function.Here we present the detailed steps of building a homodyne detector from scratch,including picking a pair of photodiodes which response most likely and designing detector circuit and the PCB layout.The two aspect above is the most important thing of building a well-worked homodyne detector.We also introduced two standards which indicating the performance of a homodyne detector:the common mode rejection ratio?CMRR?and the shot-noise limit.Finally,we introduced an experimental testbed to make a test on our homodyne detector.we got a CMRR of 55dB and good shot-noise limit performance.