Study On The Optical Nonreciprocity In Strongly Coupled Cavity QED System

The strongly coupled cavity quantum electrodynamics(QED)system is an exciting playground for a long-time interaction between atoms and photons.Benifitting from the strong coupling between atom and cavity field,numerous achievements have been realized based on the manipulation of single-quanta and the interaction between light and matter,such as controllable single photon source,nonlinear effect on the single-quanta level,precise measurement of atomic motion trajectory,atom-photon and atom-atom entangelemnt,quantum memory,quantum network interface,quantum logic gate,etc.Here in this thesis we have studied the optical nonreciprocal(ONR)based on the nonlinearity in cavity QED system.Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise.In the context of the rapid development of photonic information processing,the realization of ONR,especially nonmagnetic ONR for chip-based optical information processing,has been studied extensively.However,despite the enormous experimental progress in terms of ONR,most studies focused on the control of the light field with classic mechanisms,and these kinds of ONR cannot alleviate the stringent requirement for extremely low power in chip-based photonic information processing.By utilizing quantum nonlinearity of strong coupling cavity QED,where single atoms coupled with an asymmetric high-finesse optical microcavity,a fewphoton level non-reciprocal transmission phenomenon of the light field can be observed.With about 12 mean atoms trapped inside an optical cavity,more than 30-d B blocking ratio of reverse light field is achieved.The mechanism can be applied to optical chips as ultralow-power optical diodes by using fiber-based cavity QED systems.It has great potential in continuous variable photon information processing.More importantly,by preparing the the atoms into a biased Zeeman sub-level in cavity QED,cavity polariton as an inherently nonreciprocal qusiparticle which can be regarded as the hybrid of photon and matter has been demonstrated.This qusiparticle breaks the time reversal symmetry of system inherently,we have realized a magneto-free optical isolatior with the isolation greater than 30 d B and the non-reciprocal quantum statistics of ligth field.This reveals the inherent non-reciprocal properties of cavity polariton.Such new quasiparticle holds great potential for exploring the quantum non-reciprocity in photonics and quantum network applications,and new topological phases in many-body physics.The main contents of this thesis are as follows:1.The motivation,development and achievements of the cavity QED are introduced briefly.The motivation of our works and arrangement of this thesis are presented.2.Introducing the Jaynes-Cummings model and presenting the behavior of cavity QED in the case of no losses.Under the rotating wave approximation,by introducing the master equation and solving the steady-state solution of Heisenberg-Langevin equations,we discuss the cavity transmission of the weak excitation case.The model can be extended to N two-level atom-cavity system,and under the mean field approximation,we discuss the cavity transmission and the so-called biastability based on the Maxwell-Bloch equations.3.Giving a brief introduction of the general information of cavity QED system in our lab.The system includes ultra-high vacuum system,the magneto-optical trap,the system for atom transferring,structure of the micro-sized cavity,the frequency chain system and techniques of measurement system.4.Cavity enhanced measurement of trap frequency in an optical dipole trap.By utilizing parametric heating process we obtain the cavity transmission vs modulation frequency and extract frequencies of 2.76 ± 0.01 k Hz and 33.0 ± 0.8 Hz which correapond to the trap frequencies of radial and axial direction,respectively.By splitting atom cloud into two parts,we directly get a signal of oscillation in time scale which corresponds to the harmonic frequency of the axial oscillation.5.Realization of nonlinear optical nonreciprocity on a few-photon level based on atoms strongly coupled to an asymmetric cavity.By adopting the strong nonlinearity in this strongly coupled cavity QED system,the nonreciprocal transmission between two counterpropagating light fields with extremely low power is demonstrated.By controlling the effective atom number in the cavity,we can tune the ONR working window and the maximum blocking ratio for the reverse light which eventually reaches 30 d B.Comparing the nonlinear ONR with other conventional systems,we obtained the records of lowest working power and the highest blocking ratio.6.By preparing the the atoms into a biased Zeeman sub-level in cavity QED,we realize so-called cavity polariton as an inherently non-reciprocal qusiparticle which can be regarded as the hybrid of photon and matter.This qusiparticle breaks the time reversal symmetry of system inherently,we realize a magneto-free optical isolatior with the isolation of more than 30 d B on single-photon level and also observe the non-reciprocal quantum statistics of ligth field for the first time.