[Paper Review] Coherent population trapping in a dressed two-level atom via a bichromatic field

Peng Li, Qun Zhang+2 more|ArXiv.org|Aug 14, 2008

Quantum optics and atomic interactions33 references3 citations

TL;DR

This paper proposes dressed-state coherent population trapping (DSCPT) in a two-level atom driven by a strong monochromatic field and a weak bichromatic field, enabling control over dressed-state populations via quantum interference. The key result is a sharp suppression of fluorescence from an auxiliary state, demonstrating a new mechanism for manipulating atomic systems with applications in precision Rabi frequency measurement, unexpected population inversion, and lasing without inversion.

ABSTRACT

We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed as dressed-state coherent population trapping. Such effect can be viewed as a new doorknob to manipulate a two-level system via its control over dressed-state populations. Application of this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion are discussed to demonstrate such controllability.

Motivation & Objective

• To demonstrate coherent population trapping in the dressed-state basis of a two-level atom, extending conventional CPT beyond bare atomic states.
• To explore how bichromatic driving enables control over dressed-state populations through quantum interference.
• To apply DSCPT to enhance precision in Rabi frequency measurement and to reveal new mechanisms for population inversion and lasing without inversion.
• To distinguish DSCPT from existing CPT mechanisms in degenerate two-level atoms or Zeeman-sublevel systems.

Proposed method

• Model a V-type three-level atom with a strong monochromatic field driving the |2⟩–|3⟩ transition and a weak bichromatic field driving the |1⟩–|3⟩ transition.
• Use the dressed-atom picture to describe the system, identifying dressed states |S⟩ and |T⟩ as eigenstates of the strong-field-driven subsystem.
• Introduce a bichromatic field that couples the two dressed states to an auxiliary state, enabling coherent population trapping within the dressed-state manifold.
• Apply the master equation formalism to simulate the dynamics and fluorescence suppression, validating the DSCPT effect.
• Analyze the system using the rotating wave approximation and derive conditions for destructive interference between transition paths in the dressed-state basis.
• Investigate spectral signatures such as Rabi sidebands and probe gain/absorption profiles to characterize DSCPT-induced effects.

Experimental results

Research questions

• RQ1 Can coherent population trapping be realized within the dressed-state basis of a two-level atom driven by a monochromatic field?
• RQ2 How does a bichromatic field induce coherent superposition between dressed states, leading to population trapping?
• RQ3 What are the implications of DSCPT for precision measurement of the Rabi frequency?
• RQ4 Can DSCPT lead to unexpected population inversion in a driven two-level system?
• RQ5 How does DSCPT enable new regimes of lasing without inversion, both with and without hidden inversion?

Key findings

• Dressed-state coherent population trapping (DSCPT) is achieved via a bichromatic field, resulting in a sharp suppression of fluorescence from the auxiliary state, confirming the formation of a dark state in the dressed-state basis.
• The efficiency of DSCPT is limited by the spontaneous decay rate of the two-level atom, with coherence maintained as long as decoherence is slower than the driving Rabi frequency.
• DSCPT enables enhanced precision in Rabi frequency measurement by stabilizing the system in a coherent superposition of dressed states.
• The DSCPT-induced population inversion explains dynamically induced irreversibility as a limiting case of coherent control over dressed-state populations.
• DSCPT enables lasing without inversion with and without hidden inversion: gain via hidden inversion is enhanced and symmetric at resonance, while gain without hidden inversion appears at outer Rabi sidebands.
• Numerical simulations show a smooth transition between gain profiles as the degree of dressed-state coherence increases, indicating tunable amplification through coherence control.