Trapping Loss Spectroscopy Based On Rydberg Atoms In Cold Atoms

Rydberg atoms have large orbital radius,strong polarizabilities and long lifetimes,which are the atoms in highly excited states.And the energy level intervals of Rydberg states contain the frequency range of microwave and terahertz wave bands.Therefore,they have becoming attractive competitors for microwave and terahertz wave quantum sensors.Next,the measurement of weak electrostatic field can be realized by measuring the frequency shift of Rydberg atomic levels based on the AC Stark effect.On the other hand,because the binding abilities of Rydberg atoms to the outermost electrons are extremely weak,they can be used to study spontaneous generation and recombination effects of the plasma.In recent years,major breakthroughs of cooling and trapping atoms through lasers have promoted the generation and development of Rydberg atoms in cold atoms.Because of excitation blocking effects caused by their strong interactions,they have important advantages in the application of quantum storage and quantum computing.And they have been applied in quantum information processing and quantum nonlinear optics.In this paper,we study excitation saturation effect based on Rydberg atoms in cold atoms,which lays the foundation for the measurement of weak microwave electric field.The paper is mainly divided into the following four parts:The first part describes the special properties of Rydberg atoms and their applications in microwave electromagnetic field measurement,terahertz field imaging,quantum computing and quantum nonlinear optics.Next,the progress of cooling and trapping atoms by lasers is introduced,which contributes to the generation and development of Rydberg atoms in cold atoms.The strength of resonance dipole-dipole interaction between Rydberg atoms scales with n⁴.The strength of van der Waals interaction between Rydberg atoms scales with n¹¹.These two strong interactions block the transition of adjacent atoms to Rydberg states.This effect can be applied to quantum logical gates.The second part mainly introduces the theoretical model of ladder-type three-level atomic system.Firstly,the total Hamiltonian is divided into free atom Hamiltonian and interaction Hamiltonian.The interaction Hamiltonian is obtained by rotating wave approximation and dipole approximation,and then the total system Hamiltonian is obtained.After that,the Hamiltonian under Schrodinger's representation is transformed into rotating wave representation by unitary operator.The total Hamiltonian under rotating wave representation is substituted into the evolution equation of density matrix with time to obtain the optical Bloch equation of the system.Then numerical solution is obtained by using programming.The third part mainly introduces magneto-optical trap system and detection system of Rydberg atoms in cold atoms.The vacuum system that reduces collision between atoms,the optical systems of trapping laser and repumping laser,the optical system of absorbing laser based on ultra-stable cavity system,the 509nm exciting laser frequency stabilization system based on Rydberg atoms,the quadrupole magnetic field that provides magnetic field gradient,the compensating magnetic field that compensates the geomagnetic field and surrounding stray magnetic field,and the timing control system of the experiment are introduced in detail.Finally,the experimental detection device of trapping loss Spectroscopy is introduced.In the fourth part,the beam qualities,frequencies and powers of trapping and repumping laser are first optimized.And then the current values of compensating magnetic field and quadrupole magnetic field are optimized by absorbing imaging.The optimized atomic fluorescence is close to three times that before.We measured atomic Doppler cooling temperature by absorbing imaging to be about 186?K.And the optimal polarization gradient cooling temperature is about 12?K.The experimental parameters are substituted into the numerical solution of theoretical model in Chapter 2.The theoretical simulation results are in good agreement with experimental results.After measuring a series of atomic density gradient results,we obtain the Rydberg excitation saturation results at different atomic densities.Innovations of this paper:First,using the quantum coherence effect of electromagnetic induced transparent spectroscopy to realize non-modulation frequency locking of 509nm laser.Considering the richness of Rydberg atomic energy levels,the electromagnetic induced transparent spectroscopy of ladder-type three-level system can realize the sub-natural line wide frequency locking in wide frequency band.Second,the non-destructive detection of Rydberg atoms in cold atoms is realized by trapping loss spectroscopy.And the high sensitive loss spectroscopy of Rydberg atoms is obtained by trapping laser modulation and demodulation technology.Third,by adjusting the frequency and power of trapping laser,the saturation effect of Rydberg excitation under different ground state atomic densities is studied.