As stated in the text, Figs. 3 and 4 (transmission versus probe laser detuning) were taken at an energy of 10 nJ in a 0.5-mm-diam beam. We should have noted that when the probe energy is increased to 150 n3 (— 10" W/cm ) the absorption cross section at the transmission maximum increases by a factor of approximately 2. At this energy density, with or without the coupling laser present, transmitted probe energy is no longer linear with incident probe energy.

Observation of Electromagnetically Induced Transparency in Collisionally Broadened Lead Vapor

The quantum theory of the spontaneous emission (SpE) in the optical microscopic cavity (microcavity) is reported we believe for the first time.1,2 The forms of the modes propagating orthogonally to the mirrors and previously studied by Ley and Loudon3 are here generalized to cover all spatial directions. Microcavity field quantization leads to the expressions of the SpE probabilities Γ||, Γ⊥ for dipoles parallel and orthogonal to the mirrors, respectively. These are computer calculated for some experimentally significant cases involving both metal and dielectric multilayer-mirror coatings.

Spontaneous emission in the optical microscopic cavity

The fundamental limit to photovoltaic efficiency is widely thought to be radiative recombination which balances radiative absorption. We here show that it is possible to break detailed balance via quantum coherence, as in the case of lasing without inversion and the photo-Carnot quantum heat engine. This yields, in principle, a quantum limit to photovoltaic operation which can exceed the classical one. The present work is in complete accord with the laws of thermodynamics.

http://absimage.aps.org/image/MAR12/MWS_MAR12-2011-003553.pdf

Quantum Photocell: Using Quantum Coherence to Reduce Radiative Recombination and Increase Efficiency

The behavior of two-dimensional (2D) atom localization is explored by monitoring the probe absorption in a microwave-driven four-level atomic medium under the action of two orthogonal standing-wave fields. Because of the position-dependent atom-field interaction, the information about the position of the atom can be obtained via the absorption measurement of the weak probe field. It is found that the localization behavior is significantly improved due to the joint quantum interference induced by the standing-wave and microwave-driven fields. Most importantly, the atom can be localized at a particular position and the maximal probability of finding the atom in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. The proposed scheme may provide a promising way to achieve high-precision and high-resolution 2D atom localization.

Proposal for efficient two-dimensional atom localization using probe absorption in a microwave-driven four-level atomic system

A scheme is proposed for two-dimensional atom localization in the subwavelength domain via controlled spontaneous emission. We consider a five-level M-type atomic system interacting with two orthogonal standing-wave laser fields and the vacuum of the radiation field. The interaction of the atom with space-dependent standing-wave fields can provide information about the position of the atom passing through, thus leading to atom localization. It is found that the localization is significantly improved due to the interference effect between the spontaneous decay channels and the dynamically induced quantum interference generated by the two standing-wave fields. By properly varying the system parameters, we can achieve high-precision and high-resolution atom localization.

Two-dimensional atom localization via spontaneous emission in a coherently driven five-level M-type atomic system

By investigating the third-order nonlinearity of a four-level ladder-type atomic system, it is found that, with spontaneously generated coherence (SGC) present, the nonlinear absorption or refraction can be significantly enhanced with vanishing linear absorption. We attribute the enhancement of nonlinearity mainly to quantum interference in the two decay pathways from the two upper closely lying levels. With a standing-wave trigger field, absorption or phase grating, which effectively diffracts a weak probe into high-order direction, can be induced by the SGC-enhanced absorptive or refractive nonlinear modulation. In contrast to the schemes for enhancing nonlinearity, no additional coupling field is required. Moreover, the present gratings result from the nonlinear modulation, which differs from the recent investigations based on linear modulation.

/pdf/electromagnetically-induced-grating-via-enhanced-nonlinear-4j61we2xo4.pdf

Electromagnetically induced grating via enhanced nonlinear modulation by spontaneously generated coherence

A scheme of two-dimensional (2D) atom localization based on the interference of double-dark resonances is proposed, in which the N-type atom interacts with two orthogonal standing-wave fields. Because of the spatial-dependent atom–field interaction, 2D atom localization can be realized via measuring the upper state population or the probe absorption. We obtain that the maximum probability of finding an atom at a particular position in a wavelength domain (λ1×λ2) is 1/2 when the atom is localized at the intersection of the antinodes of quadrants I and III of the standing-wave plane. This scheme shows more advantages than other schemes of 2D atom localization.

Two-dimensional atom localization via interacting double-dark resonances

A scheme for two-dimensional (2D) subwavelength atom localization is proposed, in which the atom is in a four-level tripod configuration and driven by two orthogonal standing-wave lasers. Because of the spatial dependence of atom-field interaction, the spontaneously emitted photon carries information about the position of the atom in standing-wave fields. We exploit this fact to 2D atom localization conditioned on the measurement of spontaneously emitted photon at a particular frequency, and obtain a high precision and resolution in the position probability distribution. Moreover, an improvement by a factor of 2 in the detecting probability of an atom can be achieved by initially preparing the atom in the coherent population trapping state. Qualitatively, the high-precision, high-resolution atom localization can be attributed to the quantum interference effect between competitive multiple spontaneous decay channels.

Two-dimensional atom localization via controlled spontaneous emission from a driven tripod system

Two-dimensional atom localization via quantum interference in a coherently driven inverted-Y system

A four-level inverted-Y scheme with an electromagnetically induced transparency (EIT) core is investigated for the enhancement of cross-Kerr effect in rubidium atoms. When detunings of the coupling and control fields are appropriately set, an enhanced EIT window is observed, and the induced phase shift of the probe field due to cross-phase modulation (XPM) is obtained by measuring the dispersive property of the probe transition. The maximal XPM phase shift is about 12° under the current experimental conditions. The experimental measurements agree well with the theoretical calculations. The enhanced XPM phase shift in such an atomic system has applications in quantum nonlinear optics and quantum information science.

Ren-Gang Wan

Papers

Electromagnetically induced grating via enhanced nonlinear modulation by spontaneously generated coherence

Two-dimensional atom localization via interacting double-dark resonances

Two-dimensional atom localization via controlled spontaneous emission from a driven tripod system

Two-dimensional atom localization via quantum interference in a coherently driven inverted-Y system

EIT-assisted large cross-Kerr nonlinearity in a four-level inverted-Y atomic system