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Physical Review A

Phase diffusion, entangled states, and quantum measurements in the micromaser

Christian Wagner, Robert J. Brecha, Axel Schenzle, H. Walther

Published Jun 1, 1993• 47 citations
Publisher

Abstract

In this paper we show how different measurement schemes for a micromaser system may be used to investigate different aspects of the maser dynamics. The features which are investigated include a measurement of the phase diffusion in steady-state, transient states with several orders of coherence, and an interesting connection to questions of the Einstein-Podolsky-Rosen paradox. In addition, it is shown rigorously that different measurement schemes acting only on the atomic part of the system after the cavity have no influence on the ensemble properties of the cavity field.

DOI
10.1103/physreva.47.5068

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In this paper we show how different measurement schemes for a micromaser system may be used to investigate different aspects of the maser dynamics. The features which are investigated include a measurement of the phase diffusion in steady-state, transient states with several orders of coherence, and an interesting connection to questions of the Einstein-Podolsky-Rosen paradox. In addition, it is shown rigorously that different measurement schemes acting only on the atomic part of the system after the cavity have no influence on the ensemble properties of the cavity field.
We propose a method to investigate the phase dynamics of the radiation field of a micromaser in steady-state operation. The phase-diffusion information is deduced from the population statistics of the atoms leaving a classical coherent field placed after the micromaser cavity. By using the classical coherent field, one gains an additional degree of freedom which allows one to probe the polarization component of the atomic dipole which is directly correlated to the cavity-field amplitude. As an illustration we present the results of a computer experiment, modeling the complete dynamics of the proposed experiment.
We propose a realistic scheme for measuring the micromaser linewidth by monitoring the phase diffusion dynamics of the cavity field. Our strategy consists of exciting an initial coherent state with the same photon number distribution as the micromaser steady-state field, singling out a purely diffusive process in the system dynamics. After the injection of a counterfield, measurements of the population statistics of a probe atom allow us to derive the micromaser linewidth in all ranges of the relevant parameters, establishing experimentally the distinctive features of the micromaser spectrum due to the discreteness of the electromagnetic field.
We discuss a scheme to relate the phase diffusion dynamics of the micromaser field to the measured atomic population statistics. This can allow us to measure the linewidth of the micromaser spectrum and to solve a relevant decoherence problem in cavity quantum electrodynamics. The main steps are (i) a suitable preparation of the cavity field state to generate coherences, (ii) the transfer of information on the dynamics of field coherences to probe atoms by the action of an external resonant coherent field and (iii) the derivation of the phase diffusion rate, hence the micromaser linewidth, from the measured population statistics of the probe atoms. The method can be applied even in the presence of trapping states, where peculiar linewidth oscillations are expected for increasing pump rate, due to the quantum nature of the micromaser field.
We show how our recently proposed scheme for the measurement of the micromaser linewidth, which relates the phase diffusion dynamics of the cavity field to the population statistics of probe atoms, can be applied in the presence of trapping states, where the phase diffusion approximation does not strictly hold. This should allow the observation of the peculiar linewidth oscillations versus atomic pumping which are expected in this regime, and whose origin lies in the quantum nature of the cavity field.
The widely discussed applications in quantum information and quantum cryptography require radiation sources capable of producing a fixed number of photons. This paper reviews the work performed in our laboratory using the one-atom maser or micromaser to produce these fields on demand. In order to achieve this goal the maser is operating under the condition of the so-called trapping states. In this situation the field of the micromaser stabilises to a photon number state. Recently, we have also succeeded in determining the Wigner function of a single-photon state. Presently measurements of the phase diffusion of the one-atom maser field are underway, whereby the case will be studied in detail when the field approaches a number state. The measurements will also give information on the decoherence of the maser field.