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Physical Review A

Quantum phase properties of the field in a lossless micromaser cavity

Ts. Gantsog, R. Tanaś

Published Jan 1, 1996• 15 citations
Publisher

Abstract

Phase properties of the micromaser field are studied for different initial states of the cavity field and the atom. It is shown that a multipeak phase structure develops when the cavity field is initially in a coherent state and the atoms enter the cavity in their excited state, which eventually leads to the randomization of the phase. If initially the field is thermal and the atoms entering the cavity are polarized, the steady state with a considerably well defined phase is reached, which asymptotically can be one of the cotangent states or some mixed state depending on the atom-cavity interaction time. An interesting effect of switching between the two- and three-peak phase structure caused by each subsequent atom passing the cavity has been found. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.562

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Phase properties of the micromaser field are studied for different initial states of the cavity field and the atom. It is shown that a multipeak phase structure develops when the cavity field is initially in a coherent state and the atoms enter the cavity in their excited state, which eventually leads to the randomization of the phase. If initially the field is thermal and the atoms entering the cavity are polarized, the steady state with a considerably well defined phase is reached, which asymptotically can be one of the cotangent states or some mixed state depending on the atom-cavity interaction time. An interesting effect of switching between the two- and three-peak phase structure caused by each subsequent atom passing the cavity has been found. \textcopyright{} 1996 The American Physical Society.
We present a study on the quantum statistical properties of radiation in a one-photon micromaser. In particular, the possibility of generating steady-state squeezing is investigated. The spectral properties of the radiation field in a micromaser are also studied. \n \nWe show that the steady-state squeezing can be generated in a lossless micromaser by injecting the atoms in a coherent superposition of upper and lower states. It is shown by considering initial vacuum number and thermal state of the cavity field, that for a particular choice of the interaction time field evolves to a squeezed state. Steady- state squeezing is found to be independent of the initial state of the cavity field. However, the temporal evolution of the squeezing depends on the initial state of the field. Effects of cavity losses and pump fluctuations on steady-state squeezing are also investigated. \n \nFinally, an exact analytic expression for the linewidth of a micromaser in the absence of cavity losses is obtained by evaluating the two-time correlation function. A comparison with the natural linewidth of laser shows that under certain conditions gain contribution to the linewidth is same in both the cases. We also, derive an exact expression for the phoston distribution function and show that for a particular choice of the interaction time, the number state of the field can be generated.
The micromaser possesses a variety of dynamical phase transitions parametrized by the flux of atoms and the time of flight of the atom within the cavity. We discuss how these phases may be revealed to an observer outside the cavity using the long-time correlation length in the atomic beam. Some of the phase transitions are not reflected in the average excitation level of the outgoing atom, which is the commonly used observable. The correlation length is directly related to the leading eigenvalue of the time evolution operator, which we study in order to elucidate the phase structure. We find that as a function of the time of flight the transition from the thermal to the maser phase is characterized by a sharp peak in the correlation length. For longer times of flight there is a transition to a phase where the correlation length grows exponentially with the flux. We present a detailed numerical and analytical treatment of the different phases and discuss the physics behind them. \textcopyright{} 1996 The American Physical Society.
We describe the dynamics of a micromaser pumped by atoms in superposition states and driven by a resonant coherent field. By a quantum jump approach to the master equation solution, we show how the coherences excited in the cavity mode affect the nonclassical steady-state behaviour of the system, in a way that depends on the relative phase between the polarized atoms and the driving field. Both the mean photon number and the phase of the cavity field can be controlled via the atomic transit time and pump rate, or the driving field intensity. The predicted coherence and phase competition effects can show up in the statistics of the populations of outgoing atoms.
We consider a lossless micromaser in which a monoenergetic, low-density beam of two-level atoms in a coherent superposition of their upper and lower states is injected inside a single-mode high-Q cavity. This is a realization of a harmonic oscillator driven by a quantum current. We find that under appropriate conditions the field may evolve to pure states, which we call tangent and cotangent states, even for mixed-state initial conditions. In various limits, they exhibit nonclassical properties such as sub-Poissonian photon statistics, or even more interestingly acquire the characteristics of ``macroscopic'' quantum superpositions. The conditions under which these states are reached, as well as the dynamical approach of the system to steady state, are discussed in detail.
A detailed theoretical and experimental study of the atom-field interaction starting from first principles was made possible by the realization of the single-atom micromaser. The situation is very close to the ideal case of a single two-level atom interacting with a single quantized mode of a superconducting cavity. In spite of the considerable amount of work devoted to the study of the micromaser, it still remains to be established how the system behaves under coherent pumping. We present a comprehensive study of the coherently pumped micromaser; we develop an analytic method to obtain the steady-state solution of the master equation governing the time evolution of the cavity field. We illustrate this method with a simple example and present results for the photon distribution and purity of the steady state of the coherently pumped micromaser.