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Journal of Optics B Quantum and Semiclassical Optics

The role of pump phase fluctuations in a micromaser

I Ashraf, Mansoora Majeed, B Akbar

Published Mar 16, 2001• 0 citations
Publisher

Abstract

We have studied the effect of pump phase fluctuations on steady-state squeezing in a one-photon micromaser for the case of both high- and low (finite)- Q cavities. Our system involves the preparation of a gain medium (atoms) in a partial coherent superposition of states, due to the finite linewidth of the pump field, before injecting them into the microwave cavity. We have found that even in the presence of a finite value of pump phase fluctuations we obtain 40% squeezing for high Q , which reduces to 25% for finite Q . In the absence of pump phase fluctuations we obtain 55% squeezing, in agreement with the previous work.

DOI
10.1088/1464-4266/3/2/306

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We have studied the effect of pump phase fluctuations on steady-state squeezing in a one-photon micromaser for the case of both high- and low (finite)- Q cavities. Our system involves the preparation of a gain medium (atoms) in a partial coherent superposition of states, due to the finite linewidth of the pump field, before injecting them into the microwave cavity. We have found that even in the presence of a finite value of pump phase fluctuations we obtain 40% squeezing for high Q , which reduces to 25% for finite Q . In the absence of pump phase fluctuations we obtain 55% squeezing, in agreement with the previous work.
The fundamental source of noise in laser and optical amplifier is spontaneous emission. However, it is possible to reduce this noise by preparing the gain medium (atoms) in coherent superposition of states. There are essentially two schemes for generating atomic coherence in optical amplifiers. \n \nFirst scheme involves the preparation of atoms in a coherent superposition of states before injecting them inside the cavity. In the other scheme atoms (initially pumped incoherently) are continuously driven by an external pump field inside the cavity. Almost all the studies concerning the quenching of spontaneous emission noise in optical amplifiers, based on the notion of atomic coherent superposition, ignore the finite bandwidth of the field that is responsible for generating coherence. In this dissertation, we have examined the effect of the finite bandwidth associated with the phase fluctuations of the driving field on a number of noise quenching schemes. \n \nIt is known that coherent preparation of atoms can, under certain conditions, lead to noise-free amplification and almost 50 percent phase squeezing in a two-photon correlated emission laser. We study the effect of phase fluctuations in the injected atoms on the phase noise of the field in these systems. We discuss the conditions under which squeezing is preserved in the two-photon linear amplifiers. We also show that, even for very large phase fluctuations in the injected atoms, almost 50 percent phase squeezing can be achieved. The corresponding gain is however significantly reduced. \n \nWe also study a system of phase-sensitive amplifier where atoms are prepared in a coherent superposition of states by a strong classical field. We study the role of pump phase fluctuations associated with the finite linewidth on the quantum statistical properties of the radiation field. A study of output field characteristics reveals that the presence of a weak pump field gives rise to equal variances in both the field quadratures which are independent of linewidth. On the other hand, the presence of strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations
We consider a phase-sensitive amplifier that consists of a system of three-level atoms in a cascade configuration that is prepared in a coherent superposition of upper and lower states by a strong classical field. We have studied the role of pump phase fluctuations associated with the finite linewidth on the quantum-statistical properties of the radiation field. A study of the output field characteristics reveals that the presence of a very weak pump field gives rise to equal variances in both field quadratures which are independent of linewidth. On the other hand, the presence of a strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations.
We study the steady-state operation and noise properties of a laser (or maser) exhibiting phase locking when an ordinary vacuum is replaced by a squeezed vacuum. Such a phase-sensitive laser can be realized by preparing the active medium initially in a coherent superposition of levels involved in the laser transition. We develop a general formalism to treat number-phase fluctuations and quadrature fluctuations. When applied to a one-photon laser with injected atomic coherence, we find that not only is a complete quenching of the (spontaneous-emission) quantum noise possible, but the field can actually be in a squeezed state. The variance in either amplitude or phase quadrature can be below the vacuum noise level by a factor of 2 (50%) at the expense of enhanced fluctuations in the other quadrature.
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.