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Optics Letters

Generation of macroscopic superpositions in a micromaser

John J. Slosser, Pierre Meystre, Ewan M. Wright

Published Feb 15, 1990• 78 citations
Publisher

Abstract

At low temperatures steady-state macroscopic superpositions can be generated in the field of a micromaser pumped by a stream of two-level atoms injected in a coherent superposition of their upper and lower states. The onset of these superpositions resembles a second-order phase transition, with the control parameter being the ratio of the atomic injection rate to the cavity damping rate.

DOI
10.1364/ol.15.000233

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Quantum and Semiclassical Optics Journal of the European Optical Society Part B•Jun 1, 1995•1 citation
At low temperatures steady-state macroscopic superpositions can be generated in the field of a micromaser pumped by a stream of two-level atoms injected in a coherent superposition of their upper and lower states. The onset of these superpositions resembles a second-order phase transition, with the control parameter being the ratio of the atomic injection rate to the cavity damping rate.
We study the effect of finite atomic lifetimes on a micromaser from temporal evolution. A stream of finite-lifetime two-level atoms is injected inside a cavity in a coherent superposition of their upper and lower levels. We study the effect of the atomic decay on the generation of quasipure states of the inner electromagnetic field. First, we study the stationary photon number distribution when the atoms are injected in their upper level. We compare our results with previous calculations by Zhu, Wang, and Fearn [Phys. Rev. A 44, 737 (1991)]. We find that quasinumber states can be generated for a long time, in a range of physical parameters that allows their experimental realization. Second, we investigate the effect of finite atomic lifetimes on the generation of cotangent states, and we study their squeezing properties.
This dissertation considers both a lossless and a dissipative micromaser in which a monoenergetic beam of two-level atoms in a coherent superposition of their upper and lower states is injected inside a single mode, high-Q cavity. In the lossless case, we find that under appropriate conditions a field initially in a mixed state will evolve to previously unknown pure states, which we call the tangent and cotangent states. In various limits, these states exhibit interesting properties such as sub-Poissonian photon statistics and squeezing, and most importantly they acquire the characteristics of "macroscopic" quantum superpositions. When dissipation of the cavity mode is incorporated into the model, we find that although the field no longer evolves to a pure state, the mixed steady-state field may still retain the properties of a macroscopic superposition under experimentally realizable damping rates. We then evaluate the experimental conditions necessary for the preparation and detection of such macroscopic superpositions.
We investigate the quantum dynamics of a two-photon micromaser pumped by atoms injected in the superposition state of the upper and intermediate levels. We simulate a master equation governing the system by the Monte Carlo wavefunction approach and analyse the steady-state behaviour as a function of the atomic transit time. The atomic coherence can effectively enhance the intensity and sub-Poissonian of the cavity field as compared with the atomic mixture. It is also discovered that the phase of the cavity field can be shifted by adjusting the detuning between the atom and field. This result shows that it is possible to manipulate the phase of the cavity field by detuning, due to atomic coherence.
The authors demonstrate the effect of atomic coherence on the generic example of two lossless micromasers coupled in series by a common pump beam of excited two-level atoms. The fields are studied via conditional measurements on the final state of the atoms. They consider the two simplest sequences: in the energy preserving (transferring) scheme they require each atom to be detected in its upper (lower) state. Due to the two paths that the atoms can follow to reach the same final state correlation between the two macroscopically separated fields can arise. The authors discuss a scheme which leads to the generation of entangled trapping states of the two fields of the form, mod n,n+M)+or- mod n+M,n), starting from number states mod n, n). Starting from initial coherent states arbitrary steady-state superpositions of the two fields can be generated by switching from the energy transferring to the preserving scheme at an optimum number of atoms. In the absence of dissipations, both methods can produce steady-state coherent superpositions of arbitrary number states of two macroscopically separated fields (nonlocal 'Schrodinger-cats'). A scheme is discussed where entanglement can be transferred from the fields to two atomic beams. Finally, the authors briefly discuss the effect of injected atomic coherence on lasers.