Superradiance: An essay on the theory of collective spontaneous emission

DICKE’S SUPERRADIANCE IN ASTROPHYSICS. II. THE OH 1612 MHz LINE

“…In this section we use the formalism developed in Gross & Haroche (1982) to describe the behavior of a superradiant system. Since, as will be seen in Section 4, the realization of a superradiance small sample is unlikely to take place in the CSEs of evolved stars for the collisional timescales previously calculated (see Paper I), we focus our analysis on the case of a large sample.…”

“…In order to do so, we first discuss the necessary conditions for superradiance in Section 2, and narrow down our focus to the 1612 MHz line interacting with OH molecules in the outer regions of the circumstellar envelope (CSE) of highly evolved stars. In Section 3, we investigate the likelihood that these conditions can be met in these regions using the Heisenberg approach, with a method of analysis that is an electric dipolar version of the magnetic dipole study found in Paper I and is similar to earlier analyses found in the physics literature (Gross & Haroche 1982;Benedict et al 1996). In Section 4 we discuss our numerical results on the characteristics of a potential OH 1612 MHz coherent system, with an application to previous observations performed on the U Orionis Mira star (Jewell et al 1981) and the IRAS 18276-1431 preplanetary nebula (Wolak et al 2014).…”

Coherent Rabi Dynamics of a Superradiant Spin Ensemble in a Microwave Cavity

“…For this phenomenon he coined the term superradiance and showed that the atom ensemble can behave as a large collective pseudospin. Superradiant emission has been observed in numerous physical systems [2][3][4][5][6][7][8][9][10]. These collective effects are particularly prominent when the coupling between the spin ensemble and the radiation field (g ffiffiffiffi N p for N spins individually coupled with strength g) is larger than any of the losses in the system (κ þ γ, where κ is the radiative loss rate and γ is the spin dephasing rate).…”

“…These collective effects are particularly prominent when the coupling between the spin ensemble and the radiation field (g ffiffiffiffi N p for N spins individually coupled with strength g) is larger than any of the losses in the system (κ þ γ, where κ is the radiative loss rate and γ is the spin dephasing rate). This strong-coupling regime (g ffiffiffiffi N p ≫ κ þ γ) has been extensively studied in both theory and experiment [11][12][13][14], but clearly resolved dynamics of these collective effects are generally lacking in large ensembles due to strong dephasing (short T Ã 2 ¼ 1=γ) [2,15,16]. Here, we demonstrate the dynamics of a strongly coupled ensemble of phosphorus donor spins in highly isotopically enriched 28 Si with both a long dephasing time [17,18] and uniform coupling to the radiation field (due to the use of a 3D microwave cavity), as shown schematically in Fig.…”

Spinor Condensates and Light Scattering from Bose-Einstein Condensates

“…The amplification of this "Coherence brightened laser" is provided by electronic coherence: "The memory of the previously emitted electromagnetic field is burned into the radiating system rather than being sent back into the radiating system by the use of mirrors [49]." The key feature of superradiance (or superfluorescence) [54][55][56][57][58] is that spontaneous emission is not a single-atom process, but a collective process of all atoms, leaving the atoms in a coherent superposition of ground and excited states [59]. The condensate at rest "pumped" by the off-resonant laser corresponds to the electronically excited state in the Dicke case.…”