Quantum Enhanced Interferometer With Loss Tolerance

Optical interferometers have became the most sensitive phase sensors in the world,the ever-changing technology makes optical measurement no longer limited to technical noise,and is replaced by the random distribution of photon,called shot noise.In recent years,quantum effects have been introduced to various precision devices,breaking the limit of human measurement and bring the precision to a new level.Quantum squeezing and entanglement can be used to engineer the distribution of photons to reduce the noise of optical field,which is a very effective way to improve the precision of interferometer.This article mainly uses the quantum squeezed source generated by four-wave mixing process in thermal rubidium atomic ensemble under the background of quantum metrology to improve the sensitivity of classic devices.This article will mainly introduce the following aspects of work:1.We demonstrated a four-wave mixing process with three-dimensional configuration in thermal⁸⁵Rb atomic ensemble.The non-degenerate four-wave mixing structure has been widely used in thermal atomic ensemble early,which has two collinear pump light with degenerate frequency,resulting in frequency non-degenerate twin beams.Frequency non-degenerate twin beams are difficult to achieve optical interference on traditional linear optical beam splitter,which limits the practical application of such type quantum light source.By reversing the energy level structure of the early non-degenerate four-wave mixing,the frequency of two pumps become non-degenerate with non-collinear directions,thus achieving the generation of frequency degenerate two-mode squeezed light.Four-wave mixing with three-dimensional structure have four optical field with different directions and controllable frequency,which give us more freedom to control two-mode squeezed light at the output.Finally,we use the frequency degenerate two-mode squeezed light achieving a photon correlation interferometer with PA+BS structure.2.We have demonstrated the signal and noise measurement of all-optical SU?1,1?in-terferometer at the same frequency band.All-optical SU?1,1?interferometer is a nonlinear interferometer,whose structure is similar to the traditional Mach-Zehnder interferome-ter,but its components for beam splitting and recombination are replaced by four-wave mixing based on optical parametric amplifier.Profit from the characteristics of photon correlation,the output of signal field is noiselessly amplified compare to the classical interferometer,and the sensitivity of phase measurement is improved under the same phase-sensitive light intensity.We built a phase locking system for a nonlinear interfer-ometer to achieve measurement of signal and noise at the same frequency band.The relationship between phase sensitivity and light intensity was studied in detail,and 3.2dB improvement in phase sensitivity relative to the linear interferometer under the same conditions was observed.This detection systems,for the first time,realized the direct measurement of weak signals by this type photon correlated interferometer system.3.We demonstrated a high absolute sensitive measurement with quantum enhance-ment and loss tolerance based on SU?1,1?interferometry.Early people have experimen-tally achieved SU?1,1?type interferometer with quantum enhancement,however,it is extremely difficult to generate a large amount of quantum light field since the phase-sensitive light field is generated from quantum light source.Therefore,it is difficult to realize a nonlinear interferometer with high phase-sensitive light intensity.When both input ports of the photon correlated interferometer are vacuum fields,it can also be re-garded as a squeezed source.Similar to the traditional quantum squeezed light source,which is used to reduce the optical noise of system and improve the phase sensitivity.We use this quantum source to engineer the photon distribution of the linear system,and increase the phase sensitivity of the linear system by noiseless signal amplification.We embedded a Mach-Zehnder interferometer at one arm of the quantum source.The high-intensity signal is encoded in the quantum source through the linear interferome-ter,so as to achieve the noiseless amplification of signal from the linear interferometer.This scheme overcomes the problem of low phase-sensitive photons in the nonlinear in-terferometer due to the phase-sensitive light field generated by the quantum light source.Combining the benefits of the linear interferometer's high phase-sensitive light intensity and the nonlinear interferometer's quantum boost,our phase-sensitive light intensity has been improved by nearly 100 times relative to the previous work,and the signal-to-noise ratio has been improved 2.2dB compared to the classic interferometer under the same conditions,realizing the phase measurement with high absolute sensitivity with quantum enhancement.Since we often suffer a large amount of detection loss at the operation of interferometer in practice.Thanks to the noiseless signal amplification,our system is not sensitive to detection loss,which is of great significance for the practical application of the interferometer.4.We theoretically demonstrated the arbitrary distribution of quantum resources based on SU?1,1?interference on two orthogonal components.Quantum light source can be used to improve the distribution of light field in classic optical instruments,thereby enhancing the measurement sensitivity.Optical interferometers can be used to sense various physical quantities.The two most common quantities are amplitude and phase.In the classical interferometer with quantum enhancement,both the quantum field and the classical field can be regarded as a kind of resource.Reasonable allocation of resources will help us optimize the measurement accuracy of the physical quantity we want to know.We theoretically analyzed various types of quantum enhanced interferometers,such as a linear interferometer without noise amplification.We have discussed in detail the optimization of parameters by assigning simultaneous measurements of quantum source phase and amplitude.Or devote all quantum sources into phase or amplitude to achieve optimal phase or amplitude sensitivity.