Quantum-beat laser

Chapter 4. Quantum correlations in four-wave mixing and quantum- beat lasers... 

Quantum-beat lasers are a particular form of correlated spontaneous emission lasers (CEL s) [43-49]. Quantum-beat is formed by creating coherence between near degenerate atomic states, either excited states or ground states. In particular, a beam of three-level atoms in Vee configuration emit photons into two modes. The atomic upper levels are initially prepared in a coherent superposition or are coupled by a coherent field [13-17]. The fluetuations of the relative phase and the relative amplitude drop to the vacuum levels. In addition to this, as a different form, correlated spontaneous emission can be formed by creating eoherenee between a pair of states between which lasing transitions occm. One such example is a two-photon CEL [13-17] with a beam of three-level atoms in cascade configuration. The top and bottom states are initially prepared in a coherent superposition state. It was predicted that the phase noise is reduced by 50% below the vacuum noise level. 

A quantum-beat laser can be initialized by using lasing without population inversion. The mechanism for lasing without inversion essentially is CPT/EIT absorption is reduced while stimulated emission remains unaffected [50-56]. At the same time, the coherence leads to noise squeezing [57-61]. The fluctuations of the laser intensity are suppressed up to or more than 50% below the shot noise. We also note that noise squeezing is possible even when neither initial coherence nor external coherent driving is used. This is caused by dynamic noise reduction... 

It is convenient to use a collective mode approach [47] to describe the quantum-beat lasers or CEL s. The collective modes are defined as... 

Figure 11 A quantum-beat laser scheme with dynamical noise reduction. Quantum-beat is created by using a microwave field to couple the two closely spaced states 1> and 2). Atoms are pumped incoherently from the ground state 0> to the top state 3) with rate A, emit photons into two lasing modes (ai 2) on the 11,2)- 3> transitions, and then return to the ground state at rate 72.

A quantum-beat laser with external coherent driving [67,78]. Shown in Fig. 13 is a pumping and coupling scheme. The atoms are pumped from the ground state 10 ) to the excited states (/=1,2) to provide necessary population for the laser gain. An external coherent field of circular frequency coq is applied to the 2 )- 3 ) transitions to create atomic coherence, by which the system can operate without population inversion. Atoms emit photons into the laser modes o of circular frequencies a 12. In the dynamics, the atoms recycle throngh the snccessive channels... 

X. M. Hu and J. S. Peng. Dynamic quantum noise reduction in a A quantum-beat laser. Optics Communications 1998 Aug 15 154(1-3) 152-159. 

Shahid Qamar, Fazal Ghafoor, Mark Hillery, M. Suhail Zubairy. Quantum beat laser as a source of entangled radiation. Physical Revew A 2008 Jun 16 77(6) 062308(7). 

Xiang-ming Hu and Jin-hua Zou. Quantum-beat lasers as bright sources of entangled sub-Poissonian light. Physical Revew A 2008 Sep 15 78(4) 045801(4). 

Xiaoxia Li and Xiangming Hu. Tripartite entanglement in quantum-beat lasers. Physical Revew A 2009 Jun 1 80(2) 023815(8). 

M.O. Scully, S.-Y. Zhu, A. Gavridiles Degenerate quantum-beat laser Lasing without inversion and inversion without lasing. Phys. Rev. Lett. 62, 2813 (1989)... 

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