Catastrophic breakdown of the Caves model for quantum noise in some phase-insensitive linear amplifiers or attenuators based on atomic systems

Abstract

When considering the effect of quantum noise (QN) in a phase-insensitive linear amplifier or attenuator, it is customary to use the single channel Caves model (SC-CM). Although this model is valid in simple situations, such as the presence of a beam splitter, it is not necessarily valid when a system with many degrees of freedom is involved. In order to address this issue, we consider in this paper various atomic transitions corresponding to amplification or attenuation using the master-equation-(ME-) based approach to model the QN and to compare the results with the SC-CM. For a four-level system that consists of a transition producing a broad gain peak and a transition producing an absorption dip, which results in perfect transparency at the center, we observe a catastrophic breakdown of the SC-CM. We also show that for a general two-level atomic system, the SC-CM does not apply, except in the limiting case when only either amplification or attenuation exists. A special case where the two models predict the same result is a Λ-type three-level electromagnetically induced transparency (EIT) system in which the QN at zero detuning vanishes while the system is in the dark state. We also study an optically pumped five-level gain EIT system which has a perfect transparency dip superimposed on a gain profile, and yields the negative dispersion suitable for use in enhancing the sensitivity-bandwidth product of an interferometric gravitational wave detector. In this case, we find that, for some set of parameters, the QN is vanishingly small at the center of the dip, and the SC-CM agrees closely with the ME model. However, we also find that for some other set of parameters, the SC-SM model disagrees strongly with the ME model. All these cases illustrate a wide range of variations in the degree of disagreement between the predictions of the SC-CM and the ME approaches.

Realization of a gain with electromagnetically induced transparency system using non-degenerate Zeeman sublevels in 87Rb

“…+ -polarized and ! " -polarized optical pumping beams ensure This system can be used as the NDM in the white-light-cavity signal-recycling (WLC-SR) [8,9] interferometeric gravitational wave detector, which is shown schematically in Fig. 3.…”

“…2 The decay of the upper levels to the ground states are included using the decay rates ! m ( m = 4,5, 8,9,10,11,12,16,17 ). The time-independent Hamiltonian after the rotating wave approximation (RWA) and…”

“…Here we follow the two-photon formalism developed by Caves and Schumaker [15,16] to represent the fields as the amplitudes of the two-photon modes. In order to calculate the QN in this GEIT system accurately, the ME approach should be used [9]. However, since a total of 17 energy levels are involved, applying the full ME approach to this system is very complex.…”

“…For realizing such an NDM, we had proposed a system using five energy levels in the Mconfiguration that produces gain with electromagnetically induced transparency. The quantum noise from this configuration, which we call a GEIT system, was evaluated rigorously using the master equation (ME) approach [9] in our numerical simulation. The resulting sensitivity-bandwidth product is enhanced by a factor of ~18 [8] compared to the highest sensitivity result predicted by Bunanno and Chen [10].…”

“…For realizing such an NDM, we had proposed a system using five energy levels in the Mconfiguration that produces gain with electromagnetically induced transparency. The quantum noise from this configuration, which we call a GEIT system, was evaluated rigorously using the master equation (ME) approach [9]…”