Innovative laser technology: a novel quantum cavity model for superradiance emission

Quantum optics is a complex field where theoretical and experimental physicists collaborate to achieve breakthroughs in explaining subatomic level phenomena.

Recently, Farokh Mivehvar from the University of Innsbruck used the most comprehensive model in quantum optics, the Dicke model, to study the interaction between two groups of atoms in a quantized field. This new study makes it possible to observe superradiance states and paves the way for high-performance superradiance lasers.

In 1954, Dick first proposed the concept of superradiance, which describes the collective emission of light by a large group of atoms. Dick's model involves a system consisting of N two-level atoms, all of which are initially in excited states. When an atom spontaneously emits photons, it triggers a cascade effect, causing all N atoms to decay and emit photons simultaneously.

Dicke proposed that by limiting these atoms to a small portion of the wavelength, the emitted photons will be the same, leading to constructive interference and generating an electromagnetic field with amplitude proportional to N and energy density proportional to N2. This behavior is in stark contrast to the independent decay of N isolated atoms, where light emission is incoherent and energy density is linearly proportional to N.
In 1973, Hepp and Lieb discovered a unique steady-state superradiance form, in which a group of atoms interact with the quantized mode of the cavity. They studied the thermal equilibrium characteristics of this interaction and used the Dicke model as a framework.

They revealed a continuous phase transition between two states: normal state and superradiance state. In the normal phase, the number of photons does not increase with the number of atoms, while in the superradiative phase, n is proportional to N.
Quantum materials are complex quantum multibody systems composed of multiple atomic species. Their low-energy behavior typically involves complex interactions of multiple degrees of freedom, such as charge, spin, orbit, and lattice.

When exploring modifications to the emergent properties of quantum materials, an alternative approach has emerged, which is to replace classical laser fields with quantum mechanical photon modes confined within the cavity
In traditional cavity quantum electrodynamics, the focus is on the interaction between one or more emitters and the clear field modes of the cavity. When a single dipole transition of the emitter is strongly coupled with the cavity, this interaction becomes particularly noteworthy, characterized by frequency ω。 This situation can be effectively described using a simple two-level model, where the interaction between light and matter is quantified by a single coupling strength g.

The field of cavity quantum materials is still in its early stages, attracting researchers from different communities, including quantum materials science and quantum multibody physics. Cavity quantum materials are expected to serve as photon platforms and can be integrated into photon based quantum technologies.

The inherent strong electronic interactions in quantum materials can promote efficient photon interactions in two-photon quantum gates and generate non classical optical states.

The Dicke model has effectively utilized cavity assisted two-photon Raman transitions, where both boson and fermion atoms are in low atomic momentum or hyperfine states. Researchers are also enthusiastic about implementing Dicke type models and exploring superradiance in waveguide QED configurations and cavity quantum materials.

The attenuation rate of a single transmitter is influenced by its surrounding radiation environment, which is a key concept of cavity QED. By using high reflective mirrors to restrict individual optical modes, the cavity QED creates a local reservoir for the transmitter, thereby enhancing its attenuation in the cavity.

In the context of "waveguide QED", atoms are connected to the optical modes of propagation, and the concept of one-dimensional bath becomes relevant.

The environment also shapes a collective decay of excited emitters. Dick superradiance is an example of this phenomenon: a completely inverted set of emitters synchronizes their decay, resulting in the emission of a brief and intense photon pulse.

Inspired by the latest developments in quantum gas cavity QED, theoretical physicist Farokh Mivehvar from the University of Innsbruck introduced a new variant of the Dicke model. This method is called the "non-standard Dick model", which involves coupling two independent spin 1/2 atomic ensembles to a single cavity mode, each with different coupling strengths.

Then, the research focuses on specific scenarios with opposite coupling strengths, equivalent to having equal coupling strengths under unitary transformations. This configuration leads to various interesting phenomena, mainly attributed to the conservation of total spin in each set.

The semi classical method reveals the existence of multiple steady-state phases, especially the bistable superradiance state. In this bistable region, there is a ± xFo-SR state, where the total spins of two atomic ensembles are arranged in the same x-direction, whether positive or negative. Observing other superradiance phases, characterized by the total spin of two ensembles pointing in opposite x-directions.

Mivehvar also determined the initial states in the system's multiple steady states, and the subsequent non-equilibrium dynamics diverged from these states to any steady state. The system does not evolve towards a constant state, but transitions to a non-stationary state characterized by vibration paths. This phenomenon is related to the existence of competitive fixed points. The complete quantum mechanical calculations also verified the coexistence of ± xFo SR and ± xFi SR states.

When two coupling strengths λ Time 1 and λ 2. The difference is that the Hamiltonian is no longer simply mapped to the standard Dicke model. Therefore, the system exhibits a wider range of steady-state and non-stationary phenomena. This is due to the conservation of total spin in each ensemble, which promotes physical exploration beyond the range of symmetric Dirk subspaces.

In general, where λ 1 is not equal to ± λ 2. With the interaction of different symmetric sectors, the dynamics of the system become more complex and diverse. This complexity may lead to different critical behaviors and the emergence of multiple critical points within the system.

Understanding these multi critical points is crucial for advancing our understanding of complex superradiative emission phenomena in quantum cavity models. The proposed model can be easily implemented in state-of-the-art experiments, providing a new approach for studying various non-equilibrium magnetic ordering and dynamic phenomena in cavity QED experimental devices.

Source: Laser Net