Coherent control of AC Stark allowed transition in Λ system

Abstract

We show that quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index may occur on electric-dipole forbidden transitions. Gain/dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and probe fields. Unlike allowed transitions, gain/absorption behavior of forbidden transitions exhibit antisymmetric feature on the Rabi sidebands. Absorption/gain spectra possess extremely narrow sub-natural resonances.PACS numbers: 42.50. Gy, 42.62.Fi, 32.70.Jz Quantum-interference-related phenomena, such as electromagnetically induced transparency (EIT), lasing without inversion (LWI) etc., are based on the interference between two independent quantum channels [1, 2,3,4,5,6,7,8,9,10]. Traditional treatment of such phenomena typically involves a three level scheme and two coherent fields, a strong driving field and a weak probe one, applied to two dipole-allowed transitions, followed by measurement of the absorption and the dispersion of the probe transition.In this Letter we show that dipole-forbidden transitions can also exhibit amplification, enhanced dispersion and other coherent phenomena. The electric field component of the driving laser field breaks the space spherical symmetry and renders the parity not well defined, as in dc Strark effect. In other words, the presence of a strong driving field exerts ac Strark effect and thus breaks the spherical symmetry of the system and creates an infinite ladder of dressed states [11,12]. An interesting signature of the forbidden transitions is the antisymmetric character of the gain and dispersion on the Rabi sidebands. We found that gain and dispersion properties of such transitions are phase sensitive as they strongly depend upon the relative phase between the driving and probe fields. Our results open a perspective for new type of phase sensitive spectroscopy in a wide spectral range.We consider a tree level scheme in Λ-configuration shown in Fig. 1. A strong driving field with Rabi frequency Ω L exp(iϕ L ) and a weak probe field with Rabi frequency Ω P exp(iϕ P ) are applied to atomic transitions |b → |c and |a → |c , respectively. Note that the phases ϕ L and ϕ P are introduced explicitly in the driving and the probe fields, respectively.Due to selection rules the transition |a → |b is dipoleforbidden by parity which is well defined in the absence of the laser fields. However, the parity becomes ill defined due to the presence of the ac electric fields of the two impinging lasers. These fields break the space symmetry and mix states of different parity. Hence the originally * Electronic address: quant@bgu.ac.il † Electronic address: shuker@bgu.ac.il forbidden transition becomes undefined. In this sense it becomes dynamically allowed. We call such dynamically allowed transitions ac-Stark allowed (ACSA) transitions. In other words the interaction with two coherent fields, at least one of which is strong, creates an infinite ladder of dressed ...

Counterintuitive Gaussian pulse sequence in three-level ladder scheme

“…Quantum interferences, LWI and absorption with inversion were studied in a variety of schemes [2][3][4][5][6][7][8].…”