Journal of Optics B Quantum and Semiclassical Optics
Statistical properties of macroscopic laser fields after coherent interaction with an atomic vapour
Carlos L. Garrido Alzar, Luciano Soares da Cruz, J. G. Aguirre Gómez, M. Martinelli, Marcelo França Santos, D. Felinto, Paulo Valente, H. Failache, A. Lezama, P. Nussenzveig
We present a series of experiments measuring intensity fluctuations and correlations of laser beams after propagation through an atomic vapour at room temperature in situations where coherent effects play a major role. In particular, we investigate these properties in the condition of electromagnetically induced transparency (EIT) in three-level lambda systems and in degenerate two-level systems. In a similar way, we also study the Hanle-EIT effect and electromagnetically induced absorption (EIA) in degenerate two-level systems. These results show the great influence of coherent interaction with the atomic system over the noise properties of the macroscopic laser fields, and indicate new sensitive ways of probing an atomic sample.
We present a series of experiments measuring intensity fluctuations and correlations of laser beams after propagation through an atomic vapour at room temperature in situations where coherent effects play a major role. In particular, we investigate these properties in the condition of electromagnetically induced transparency (EIT) in three-level lambda systems and in degenerate two-level systems. In a similar way, we also study the Hanle-EIT effect and electromagnetically induced absorption (EIA) in degenerate two-level systems. These results show the great influence of coherent interaction with the atomic system over the noise properties of the macroscopic laser fields, and indicate new sensitive ways of probing an atomic sample.
The quantum fluctuations of optical beams are highly correlated in electromagnetically induced transparency (EIT). The intensity fluctuations are enhanced by conversion of phase noise to intensity noise in atomic vapour. We have studied spectra of intensity fluctuations in dense rubidium vapour for different laser beam powers. Observed excess noise spectrum is broader than EIT window at the same optical power. Both spectral widths are proportional to the laser beam intensity. By using signal subtraction scheme we can reduce amplitude of the fluctuations to close the photonic short noise level. This result confirms the high degrees of intensity correlations and can be used to improve quality of optical atomic clocks.
Rydberg atoms, with large principal quantum number n, have been widely investigated in recent years due to their peculiar properties, such as big sizes, long lifetimes and strong interactions with fields and other Rydberg atoms. Rydberg atoms are very sensitive to external fields due to their large polarizabilities scaling as n7.These make Rydberg atoms an ideal candidate for the quantum information, the many-body interaction, etc.In this work, we investigate the Rydberg atoms using electromagneticlly induced transparency (EIT) in a ladder three-level system. The EIT is a quantum interference effect between two excitation path-ways driven by two laser fields. The main idea is performed in a room temperature cesium vapor cell, where the probe laser frequency is modulated. The ground state (6P1/2), excited state (6P3/2), and Rydberg state (nS1/2) constitute a Rydberg three-level system, in which the probe laser is fixed to the 6S1/2 (F = 4)6P3/2 (F = 5) transition by saturated absorption spectrum technique, whereas the coupling laser is scanned across the 6P3/249S1/2 transition. We detect the demodulated EIT signal with the lock-in amplifier (SR830). The modulated EIT signal shows a two-peak structure. The measured spacing between two peaks increases with the frequency detuning, caused by the modulation amplitude, and half the spacing between the peak-to-peak is nearly 1.67 times the modulation amplitude of the probe laser; the measured result shows that the splitting is independent of the modulation frequency. The experimental results are in agreement with the theoretical calculations. The results in our work can be used for real-time monitoring of the laser-line profiles and the fluctuation of laser frequency.
Due to interaction with the vacuum of the radiation field, a K-type atomic system with near-degenerate excited and ground levels, which is driven by two strong coherent fields and two weak probe fields, has additional coherence terms — the vacuum-induced coherence (VIC) terms. In this paper, we find that, if the interference is optimized, the two-photon absorption properties of this atom system can be significantly modified and electromagnetically-induced transparency (EIT) is dependent on this interference. Furthermore, we find that in all the cases the coherence can suppress or enhance the partial two-photon transparency, while the complete transparency window is still strictly preserved, which means that it cannot be affected by the VIC. Another important result is the finding of the crucial role played by the relative phase between the probe and coupling fields: the relative height of absorption peaks can be modulated by the relative phase. The physical interpretation of the phenomena has been given.
The appearance of quantum interference in the microscopic world is one of the deepest mysteries at the very root of quantum mechanics. When light interacts with atoms, it can induce transitions by way of distinct but indistinguishable pathways and yield unexpected and often counter-intuitive results. Electromagnetically Induced Transparency (EIT), Coherent Population Trapping (CPT), and Lasing Without Inversion (LWI) are modern examples of phenomena where the traditional rules that govern absorption and dispersion undergo major revisions. Spectacular consequences of this new state of affairs include the ability of a light beam to propagate through a normally absorbing medium with little or no absorption, or to undergo amplification even if the active medium is not prepared in a state of population inversion. Light signals have been shown to travel with strongly subluminal group velocities of only a handful of meters per second and, even, to propagate at speed greater than the ordinary speed of light, but without violation of causality or of the established rules that control the transfer of optical information through space. Three-level atoms can interact with two coherent electromagnetic fields according to three different systems, known as Cascade, Lambda and Vee systems. The propagation of a weak probe field can be deeply affected by the presence of a second stronger beam, the so-called coupling field. Transparency windows, splitting of emission and absorption lines and enormously enhanced dispersion have been documented in numerous experiments. In this thesis we explore the physical origin of the transparency induced in these systems by the simultaneous interplay of the coupling and probe fields. We focus our attention on the Cascade system and study its two configurations, Cascade-EIT and Cascade-AT. We develop a variety of complementary approaches for the description of these two configurations, some semiclassical and others fully quantum mechanical. We prove the existence of quantum interference in Electromagnetically Induced Transparency and also the surprising absence of interference in a closely related phenomenon, known as the Autler-Townes effect. Finally we complement the traditional machinery of theoretical quantum optics with techniques borrowed from quantum scattering theory, and offer what we believe is the most convincing physical evidence for the appearance, or for the absence, of quantum interference effects.
We report a detailed investigation on the properties of intensity correlation spectra for laser beams interacting with cold atoms under the condition of electromagnetically induced transparency (EIT). We describe the transition of their intensity fluctuations from correlation to anticorrelation as the mean intensity of the fields increases. Such a transition occurs for laser frequencies around the EIT resonance, which is characterized by a correlation peak. The transition point between correlation and anticorrelation is independent of power broadening and provides directly the ground-state coherence time. We introduce a method to extract in real time the correlation spectra of the system. The experiments were done in two distinct magneto-optical traps, one for cesium and the other for rubidium atoms, employing different detection schemes. A simplified theory is introduced assuming three-level atoms in $\ensuremath{\Lambda}$ configuration interacting with a laser with stochastic phase fluctuations, providing a good agreement with the experimental observations.
This thesis presents work on experiments performed using electromagnetically induced transparency (EIT) in Rubidium vapour cells. Starting with a simple three-level Λ-system, extra complexity is introduced by adding an additional control beam. This makes the switching from narrow transmitting resonances to absorbing resonances possible. Rydberg EIT is then introduced and is used to shown how the switching of such resonances using external electric fields in possible. The work then progresses towards the use of thin vapour cells to overcome the limitations of conventional systems. In the transition to thin vapour cells, the role of dipole interactions in Rydberg atoms motivates the idea of an atomic quantum dot. The Kerr effect is then characterised and used to perform phase modulation in a gas. The Rydberg state itself is then phase modulated and this is shown to give rise to frequency sidebands which offer a promising way of determining dc electric fields.