Observation of coherent population trapping in a V-type two-electron system

Alok K Singh,Vasant Natarajan

doi:10.1088/1367-2630/17/3/033044

Abstract

We observe coherent population trapping (CPT) in a two-electron atom—174Yb—using the transition. CPT is not possible for such a transition according to one-electron theory because the magnetic sublevels form a V-type system, but in a two-electron atom like Yb, the interaction of the electrons transforms the level structure into a Λ-type system, which allows the formation of a dark state and hence the observation of CPT. Since the two levels involved are degenerate, we use a magnetic field to lift the degeneracy. The single fluorescence dip then splits into five dips—the central unshifted one corresponds to coherent population oscillation, while the outer four are due to CPT. The linewidth of the CPT resonance is about 300 kHz and is limited by the natural linewidth of the excited state, which is to be expected because the excited state is involved in the formation of the dark state.

Highlights

Coherent population trapping (CPT) is a widely studied phenomenon since its first observation in 1976 [1], because of its potential applications in fields like atomic clocks [2], electromagnetically induced transparency (EIT) [3], lasing without inversion [4], stopping and storing of light pulses [5], optical memory and quantum computing [6], precise magnetometry based on the nonlinear Faraday effect [7], and so on.As the name implies, CPT is a phenomenon in which the atomic population is driven into a dark non-absorbing state in the presence of two coherent laser beams— usually called the pump and the probe
In order to verify that the shifted peaks are CPT like, we have studied the separation of the peaks as a function of the applied magnetic field
CPT is not possible for such a transition according to one-electron theory because the V-type system does not allow the formation of a longlived dark state

Summary

INTRODUCTION

Coherent population trapping (CPT) is a widely studied phenomenon since its first observation in 1976 [1], because of its potential applications in fields like atomic clocks [2], electromagnetically induced transparency (EIT) [3], lasing without inversion [4], stopping and storing of light pulses [5], optical memory and quantum computing [6], precise magnetometry based on the nonlinear Faraday effect [7], and so on. CPT requires such a dark state to be formed, which happens in Λ-type three-level systems where there are two long-lived lower levels. Many CPT experiments have been done in degenerate two-level systems, where the magnetic sublevels of the levels involved form the required Λ-type system. One way to separate the two effects is to use a magnetic field This will cause the CPT resonances to shift, while the CPO resonance will not. The observed linewidth is about 300 kHz, limited by the 185 kHz natural linewidth of the excited 3P1 state, which is expected because the dark state involves the upper state This linewidth is larger than what is seen in normal CPT resonances of one-electron atoms with Λ-type level structure, where the dark state involves two lower levels and is extremely narrow

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSION