We study the photon statistics of a micromaser with a nonzero thermal background for a large range of the pumping parameter \ensuremath{\theta}. The photon statistics are examined in a two-dimensional space, parametrized by \ensuremath{\theta} and k, where k is the photon number. For values of \ensuremath{\theta} which are not too large, there are prominent peaks in the photon-number distribution. The locations of these peaks are determined by well-defined structures in \ensuremath{\theta}-k space. These structures lie along curves in this space. As \ensuremath{\theta} is increased, these structures disappear and the number distribution becomes diffuse. When \ensuremath{\theta} becomes sufficiently large, however, new structures which are well localized in \ensuremath{\theta} and k appear. We call these states ``island states.'' These states exhibit a strong squeezing of the photon number and are fairly insensitive to the thermal background. Their noise increases slowly due to fluctuations of the atomic beam as long as the spread in values of the pump parameter \ensuremath{\theta} is smaller than the distance between the islands. Bistable behavior can be induced by fluctuations that overlap adjacent island states. We also present the photon statistics of a micromaser pumped by atoms in a mixture (incoherent superposition) of their upper and lower levels. It is shown that the noise in island states can be drastically reduced by an optimum amount of injected absorption. These features render these states experimentally feasible, so that they could be used for generating squeezed quantum states of the radiation field that are well localized in \ensuremath{\theta} and k.
Abstract In the photon number distribution p(θ,k) of the micromaser, distinct structures are formed by the ridges connecting the peaks in the θ-k space. We refer to these structures as phases. By a simple condition we can distinguish between "semiclassical" and "quantum" regimes of operation near and far above threshold, respectively. In the semiclassical regime, the equations of state of the phases θ= θ(k) are monotonous and coincide with the steady state solutions of the semiclassical theory. They reflect typical features of the micromaser dynamics. The transition jumps, e. g., between the phases decrease with increasing pumping parameter θ, signifying the onset of the Jaynes-Cummings collapse. On increasing 9 further, the phases first disintegrate and then restructure into new kinds of phases in the quantum regime. The equations of state are no longer monotonous. Large single peaks, the quantum island states (QIS), develop in the neighborhoods of minima. The system undergoes oscillations between two kinds of quantum island states, QIS- and QIS+ , as a function of θ. The disintegration and transformation of phases recur periodically as θ is varied, and the phases in the semiclassical region are followed by consecutive phase structures in the quantum regime. The subsequent collapses and revivals of phases are directly connected to the Jaynes-Cummings collapse and revival. The observation of these phase structures and the accompanying QIS is experimentally feasible.
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 behavior of the mean photon number, photon number variance and field squeezing is investigated for the two two-level atoms prepared in a multiatom squeezed state coupled to the vacuum or thermal field. The value of superposition angle (θ) of the atomic states is found to affect the photon number variance as well as field squeezing. The bound on the sun-Poissonian field concerning the value of θ and input mean photon number is determined. One of the field quadrature is found to exhibit permanent squeezing for the vacuum input in a small range of the value of θ. It is shown that the input thermal photons degrade the sub-Poissonian character and spontaneous squeezing. However, a considerable amount of squeezing is obtained even in the presence of thermal photons.
The statistics of the beam of excited atoms that pumps a micromaser influence the photon number distribution of the cavity field. Of the cases studied so far, regular injection statistics minimize the number fluctuations and Poisson statistics maximize them. Here we extend these studies in two directions. Previous master equations describing sub-Poissonian injection statistics were derived by using standard reservoir theory. Recently, corrections to these equations have been found that involve the commutator of the gain and loss operators. Describing the system by a discrete map, we can avoid the approximations inherent in reservoir theory. The results are compared to those of the master equation. Differences are found to be small for large photon number but increasingly important for decreasing photon number and pump beam intensity, indicating the breakdown of reservoir theory in this regime. We give an approximate expression for the photon number distribution for weak damping and discuss its connection with semiclassical theory. Finally, we generalize our treatment for super-Poissonian pump fluctuations.
A single beam of excited two-level atoms couples two micromasers in a series. It is shown that in the absence of dissipation the possible steady states of their fields are superpositions, of two-field trapping number states. Which one is realized depends upon the initial state of the fields and the interaction parameters, g'\ensuremath{\tau}' and g''\ensuremath{\tau}'', of the two cavities. A large number of these trapping states are pure quantum states, some of them showing entanglement of the two nonlocal micromaser fields of the form \ensuremath{\Vert}N,N+M〉\ifmmode\pm\else\textpm\fi{}\ensuremath{\Vert}N+M,N〉. Here, N and N+M are arbitrary trapping numbers that belong to disconnected blocks of the photon number space and M specifies the order of correlation between the fields. The time evolution of the system toward steady states is investigated numerically, mainly concentrating on the production of pure entangled trapping states of the form discussed earlier. We describe a special procedure to amplify a number state, \ensuremath{\Vert}N,N〉, into such states that is based on conditions regarding the interaction parameters. In principle, N and M can be made arbitrarily large resulting in a steady-state nonlocal quantum superposition of distinct macroscopical fields (nonlocal ``Schr\"odinger cat''). We also present a solution of the standard master equation of a damped harmonic oscillator at finite temperature and apply it to study the effect of dissipation on the production of entangled trapping states at regular and Poissonian pump statistics.It is found that although the entanglement does not survive at a steady state it can build up in the short-time transient regime when cavity losses and the number of thermal photons are not too large. In this small-loss (large
Nex) regime the quantum correlation between the micromaser fields decays into a steady-state classical superposition at a rate that depends on the cavity lifetime and the difference (or order of correlation), M, between the superposed photon numbers. In the large-loss (small
Nex) regime, however, no transient correlation can be produced and the photon statistics spreads out towards a vacuum for increasing losses. The system undergoes a transition from an uncorrelated to a correlated behavior when the pumping parametrized by
Nex exceeds the threshold between the large- and small-loss regimes. Thermal photons enhance the decay of the correlation and by coupling the disconnected blocks of the photon number space they populate the trapping number states of adjacent blocks. However, it is shown that the production of transient entanglement is not significantly affected by either thermal radiation or pumping fluctuations. The experimental realization of the entanglement of nonlocal micromaser fields employing these two-field trapping states of small photon numbers is shown to be feasible in the short-time transient regime using the presently available high-Q cavities and low temperatures, and could be possible on the macroscopic scale in the near future.
We describe the first investigation of the nonclassical radiation field of a micromaser. The maser cavity is cooled to 0.5 K to exclude thermal photons and has a quality factor 3\ifmmode\times\else\texttimes\fi{}
1010. Velocity-selected Rydberg atoms pump the maser. The photon statistics in the cavity are measured via the statistics of the atoms leaving the cavity in the lower maser level. Taking into account a detection efficiency of 10%, their fluctuations are reduced up to 40% below the Poisson level. This corresponds to photon-number fluctuations in the cavity of up to 70% below the vacuum-state limit.