Study On The Dissipative Coupling Induced Phonon Lasing And Dark Mode In Non-Hermitian Multimode Cavity Optomechanics

Cavity optomechanics explores the interaction between light and mechanical resonators,using optical resonant cavities and radiation pressure to realize precise control and measurement of the mechanical oscillator motions.This research area can be applied to a wide range of applications,such as microwave-to-optics conversion and ultrasensitive detection.Compared with the common optomechanical system,which consists of a single-cavity field and single-mechanical oscillator,multi-mode systems have a higher degree of freedom for manipulation and,therefore,a greater advantage in the study of macroscopic quantum coherence and entanglement.This has become a hot research topic in recent years and has achieved breakthroughs in non-equilibrium thermodynamics and nonreciprocal transport.The study of optomechanical interaction in multi-mode systems also provides experimental tools for realizing more complex quantum manipulation of macroscopic systems.Non-Hermitian systems exchange energy with the environment,and the study of non-Hermitian physics can deepen the knowledge of open systems.In particular,after the introduction of the concept of Parity-Time(PT)symmetry,a system constructed by coherent coupling and exhibiting this symmetry exists a symmetry-broken phase.At the boundary of this phase,exceptional point(EP)has many peculiar properties,can realize lossless propagation,and has vital application prospects in highly sensitive sensing,topological energy transfer,and so on.In comparison,the anti-PT symmetric system constructed by dissipative coupling also has the EP,can realize refractionless propagation,and has a different mechanism of exchanging energy with the environment,which is of great significance for analyzing the interaction between open systems and the environment.Explore non-Hermitian optomechanics,the peculiar phenomenon at the EP opens up new perspectives for optomechanical interaction and provides ideas for new applications.Realizing phonon transport between oscillators via optical fields is vital for phonon-based information processing,and the ground state cooling of degenerate oscillators caused by dissipative coupling is also an urgent problem to be solved for the construction of multi-dimensional macroscopic quantum systems.In this work,a cavity optomechanical platform with two mechanical oscillators and two cavity fields is experimentally constructed,which satisfies the resolved sideband condition.Purely dissipative couplings between two spatially separated mechanical oscillators are realized by using optomechanical couplings,and a non-Hermitian multimode cavity optomechanical system satisfying the anti-PT symmetry is constructed.Special multimode phonon lasing and dark mode clock synchronization are studied in the symmetry-broken regime,and a method to cool two degenerate oscillators below the dark mode cooling limit by dual-mode cavity field is proposed.The results of this thesis are as follows:1.Multimode phonon laser induced by dissipative couplingThis study provides a new mechanism for the generation of phonon lasers.Phonon lasers,the counterparts of photonic lasers,have been extensively studied in many systems,but most of them are generated via coherent pumping and dissipation is not conducive to the coherent amplification of phonons.In the experiment,by precisely controlling the dissipation of two mechanical oscillators and the intensity modulation of the driving field,pure dissipative coupling between two mechanical oscillators was generated through the optomechanical interaction.After the EP,a multimode phonon laser was generated,which had three distinct phases of oscillation compared to conventional phonon lasers.This work opens a new avenue for the study of phonon lasers in non-Hermitian open systems.2.Clock synchronization induced by dissipative couplingThis study reveals a mechanism for achieving clock synchronization through dissipative coupling.Oscillator is a type of clock that performs Brownian motion with a fixed frequency and random phase,and clock synchronization lies at the core of timekeeping.By precisely controlling the intensity of the dissipative coupling strength,leading to a dark mode phenomenon between two near-degenerate phonon modes,after the EP,symmetry-breaking leads to spontaneous clock synchronization.The impact of the phase and intensity of the optomechanical coupling is also found.Achieving clock synchronization through optomechanical interaction is also instructive for improving accuracy in the fields of communication as well as localization in classical or quantum domains.3.Cooling limit of dissipative coupling-induced dark mode and its breakthroughThis study provides a method to break the dark mode cooling limit and realize the simultaneous cooling of two degenerate mechanical oscillators.Cooling mechanical oscillators to their ground state is a necessary foundation for realizing macroscopic quantum behavior.However,the dissipative coupling causes two near-degenerate mechanical oscillators to form a dark mode which is decoupled from the cavity field,blocking the cooling progress and making it difficult to approach its ground state.In the experiment,a cavity optomechanical system containing two cavity fields was set up,and a dissipative channel was constructed through the addition of a red-detuned laser field,allowing for the simultaneous cooling of two degenerate mechanical oscillators caused by the dissipative coupling and thus realizing the break of the dark mode cooling limit.Meanwhile,the theoretical simulation proved that the two near-degenerate mechanical oscillators can be cooled to the ground state at low temperatures with this method.This thesis carries out the study of dissipative coupling-induced phonon lasing as well as dark mode effects based on a non-Hermitian multi-mode cavity optomechanical system that contains dual-mode cavity fields,which expands the degrees of freedom of the existing experimental systems in the research field,demonstrates that the dissipation can be a favorable resource for manipulating the interactions in the open systems,improves the knowledge and understanding of the interactions between the non-Hermitian system and the environment,and provides new schemes for realizing the non-Hermitian devices.Meanwhile,the proposed dual-mode cavity fields cooling scheme provides a basis for realizing macroscopic quantum systems in more dimensions as well as quantum manipulation.