Research On Nonlinear Su(1,1) Interferometer Using Four-wave Mixing Process Based On Rubidium Atomic Ensembles

With the development of science and technology,higher measurement sensitivity of the mea-suring device is always pursued by scientists.Quantum metrology exploits the quantum properties of the quantum system which makes it possible to have better measurement precision compared with the classical system and even break the quantum limits.Recently,nonlinear SU(1,1)inter-ferometer based on the four-wave mixing(FWM)process in hot rubidium atomic vapor cell has been realized by our group[Appl.Phys.Lett.99,011110(2011)].Some classical and quantum properties of the nonlinear SU(1,1)interferometer has been experimentally researched,such as the visibility dependence of the interference[Appl.Phys.Lett.102,011130(2013)]and the quantum enhancement of the signal-noise-ratio[Nature Communications 5,3049(2014)]of the nonlinear SU(1,1)interferometer.In this thesis,we will further investigate the quantum properties of the nonlinear SU(1,1)interferometer.There are four main parts included in this thesis:(1).With direct intensity detection,we theoretically study phase sensitivity enhancement of the nonlinear SU(1,1)interferometer and compare it with the one of Mach-Zehnder(MZ)interfer-ometer.Different detection schemes are studied and we find that the best phase sensitivity of the nonlinear SU(1,1)interferometer is better than the one of MZ interferometer.And the nonlinear SU(1,1)interferometer can also break the standard quantum limit(SQL).(2).Quantum-noise cancellation(QNC)is an effective method to control the noise of the quantum system,which reduces or even eliminates the noise of the quantum systems by utilizing destruc-tive interference in the quantum system.However,QNC can be extremely dependent on the losses inside the system.In this part,we experimentally and theoretically study how the losses can affect the QNC in the nonlinear SU(1,1)interferometer.We find that losses in the different arms inside the nonlinear SU(1,1)interferometer can have different effect on the QNC in the output fields from the nonlinear SU(1,1)interferometer.And the QNC in the nonlinear SU(1,1)interferometer can almost be insensitive to the losses in some cases.Our findings may find its potential applications in the quantum noise control.(3).In this part,a maximal joint quadrature squeezing of-6.8 ±0.4 dB is experimentally obtained by a scheme of cascaded FWM processes which gives a strong proof about the inseparability or entanglement between the twin beams output from the system.Here joint quadrature is the differ-ence between the two quadratures of the twin beams output from the cascaded FWM processes.This result is enhanced by about 3.1 dB compared with the one of the single FWM process.We also study the gain dependence of the entanglement enhancement in this cascaded system.A the-oretical prediction with the consideration of losses is also studied and a good agreement in the low-gain regime can be found between the experimental results and theoretical predictions.The scheme of cascaded FWM processes,which can be used to manipulate the entanglement resource,may find its applications in continuous-variable quantum communication protocols.(4).A new nonlinear Sagnac interferometer(NSI)is proposed by replacing the beam-splitter in the traditional Sagnac interferometer(TSI)with a FWM process.Such a NSI has better angular velocity sensitivity than the one of the TSI.The Standard Quantum Limit can be beaten and the Heisenberg Limit can even be reached for the ideal case by the NSI.We study the effect of the losses on the angular velocity sensitivity of the NSI and find that the optimal angular velocity,where the best angular velocity sensitivity can be obtained,of the NSI may be dependent on the losses inside the interferometer.Such a NSI has its advantages compared with the TSI and may find its potential applications in quantum metrology.(5).FWM process can be treated as a nonlinear beam-splitter(BS).In this section,based on the FWM and BS,two theoretical modal to generate the triple quantum correlated beams are discussed,which are respectively FWM+FWM and FWM+BS.By investigating the pairwise cor-relations of the generated triple beams,a repulsion effect phenomena can be found for the modal of FWM+FWM.Our results presented here pave the way for the manipulation of the quantum correlation in quantum networks.