Atomic interferometry with the micromaser

Magnetic induction tomography of structural defects with alkali-metal spin maser

Implementation of an alkali-metal spin maser in magnetic induction tomography is explored. While the spin maser vastly improves the detection speed and solves the problem of imperfect bias magnetic field stabilization in non-destructive testing, it provides only partial information about the spatial extent of the defect. We demonstrate two ways in which the whole image of the defect can be reconstructed and experimentally demonstrate that the amplitude of the spin maser signal can be used as an indicator of defect depth. Additionally, the spatial extent of the imaging of the defect is increased by the application of a spin maser operating at two frequencies. A significant benefit of operating in the spin maser mode is that the system follows any fluctuations in the Larmor frequency due to changes in the bias magnetic field strength. This removes the need for active stabilization of the bias magnetic field, greatly reducing the complexity of the system.

Preparing Fock states in the micromaser

In this paper we give a survey of our experiments performed with the micromaser on the generation of Fock states. Three methods can be used for this purpose: the trapping states leading to Fock states in a continuous wave operation; state reduction of a pulsed pumping beam and finally using a pulsed pumping beam to produce Fock states on demand where trapping states stabilize the photon number. The latter method is discussed in detail by means of Monte Carlo simulations of the maser system. The results of the simulations are presented in a video.

Preparing pure photon number states of the radiation field

The quantum mechanical description of a radiation field is based on states that are characterized by the number of photons in a particular mode; the most basic quantum states are those with fixed photon number, usually referred to as number (or Fock) states. Although Fock states of vibrational motion can be observed readily in ion traps, number states of the radiation field are very fragile and difficult to produce and maintain. Single photons in multi-mode fields have been generated using the technique of photon pairs. But in order to generate these states in a cavity, the mode in question must have minimal losses; moreover, additional sources of photon number fluctuations, such as the thermal field, must be eliminated. Here we observe the build-up of number states in a high-Q cavity, by investigating the interaction dynamics of a probe atom with the field. We employ a dynamical method of number state preparation that involves state reduction of highly excited atoms in a cavity, with a photon lifetime as high as 0.2 seconds. (This set-up is usually known as the one-atom maser or 'micromaser'.) Pure states containing up to two photons are measured unambiguously.