| Due to its long lifetime and tunable interaction,Rydberg atomic system has become one of the most popular platform in quantum optics and quantum information fields.In particular,because of the strong dipole-dipole interactions between atoms,Rydberg atoms can exhibit the so-called dipole blockade effect,that is,in the certain blockade radius,only one atom can be excited to the Rydberg state,while the other excitations will be suppressed.Based on this feature,Rydberg atoms become excellent carriers for many quantum tasks such as realizing quantum logic gates,preparing quantum entangled states,and simulating quantum multibody physics.Moreover,the combination of the Rydberg atomic system with Electromagnetically induced transparency(EIT)also exhibits many special phenomena that are not available in ordinary atomic systems.For example,in the Rydberg-EIT system,the transmission of the medium will gradually increase or decrease as the change of the intensity of the probe field and the corresponding photons will exhibit the bunching or anti-bunching phenomenon,as well as realize the giant photoelectric effect.In particular,the Rydberg EIT medium exhibits a single-photon-level nonlinear effect,that is,it maintains high absorption rate for two photons and is transparent for single photon,which makes the Rydberg-EIT medium of great significance in realizing single-photon source.In this dissertation,focus on the Rydberg atomic system,we studied:(i)the phase diagrams of collective states of dimerized Rydberg atoms in two-dimensional lattices;(ii)the dynamical evolution of quantum entanglement state between two Rydberg atom pairs;(iii)the nontrivial interplay of single-photon-level light storage with distributed Rydberg excitations in Rydberg-EIT system;and(iv)the nontrivial dynamics of slowlight in all-optical transistors based on single-photon-level storage.In the third chapter,by solving the Lindblad master equation under the mean field approximation,we investigated the phase diagram and the dynamical evolution of quantum state in a dimerized two-dimensional Rydberg lattices.We found that compared to the mono-excitation atomic system,the phase diagram of the dualexcitation atomic system exhibits richer physical phenomena,for example,all uniform phases become non-uniform,with the presence of imperfect bifurcation,and furthermore,it is possible to found a tri-stable state in certain parameter range.Our results are expected to be instructive for exploring novel non-equilibrium phases in Rydberg system.At the same time,we found a dynamic irreversibility phenomenon in the adiabatic evolution of the Rydberg population,which could be a potential feature in designing new quantum devices such as quantum fuses.In the fourth chapter,we studied the dynamic evolution of quantum entanglement states between two Rydberg atomic pairs with different optical detuning by solving the Schrodinger equation.We found that by choosing certain initial state and moderate strength of interaction,the entanglement in different atomic pairs could exhibit in-phase or anti-phase dynamic behavior.Moreover,in such four-atom system,we can achieve two different types of maximum entanglement states of four particles under the optimal in-phase or anti-phase condition.To take the relevant dissipation processes into account,we further solved the Lindblad master equation and found that the dissipation only changes the steady-state values of the systemic entanglement and does not influence the phenomena of in-phase or anti-phase dynamic evolution.Our result provides a new idea for realizing multi-particle entangled state and effectively controlling entanglement dynamics.In the fifth chapter,we combined Rydberg atoms with EIT,using an improved‘Super-Atom’(SA)model to explore the relationship between single-photon-level Rydberg atomic excitation and single-photon-level storage in optical storage process by numerically solving atomic equations,super-atom equations and field propagation equations.Different from previous works,we investigated the optical storage process at the single-photon-level,and took the interaction between different positions of the single photon wave packet into account.We proved that the excitation number of Rydberg states calculated from both atomic and super-atomic equations are selfconsistent and equal to the number of photons stored in the medium,which has not been mentioned neither experimentally nor theoretically before.At the same time,we also found a counterintuitive asymmetry phenomenon,that is,the spatial distribution of the gate photon in the medium will gradually shift with the increase of the probe field intensity.The asymmetry phenomenon only appears in the storage process,and it will disappear when the gate photon is retrieved at the end of the medium.In the sixth chapter,we revisited the issue of all-optical transistors by examining the slow-light transportation of a signal pulse in Rydberg-EIT medium based on the single-photon storage by solving Maxwell and Langevin equation.Different from other theoretical work,we considered the more practical situation,the gate photon that plays a control role is not a localized point or a perfect wave packet,but a real-time storage spatial distribution as dealt in Chapter 5.We found that the different spatial distribution of gate photons not only affect the shape of the signal pulse propagating in the medium,but also change the performance of the transistor.Moreover,the two-photon correlation at the end of the medium exhibits an approximately uniform anti-bunching characteristic in time.In particular,we found that by introducing single photon detuning,the gain of the transistor can be controlled.Our work not only realized the non-localized control in the transistor,but also revealed the non-trivial dynamics of the signal field propagation in the all-optical transistor. |
PDF Full Text Request