Superluminal Pulse Propagation in a One-sided Nanomechanical Cavity System

We investigate the propagation of a pulse field in an optomechanical system. We examine the question of advance of the pulse under the conditions of electromagnetically induced transparency in the mechanical system contained in a high quality cavity. We show that the group delay can be controlled by the power of the coupling field. The time delay is negative which corresponds to superluminal light when there is a strong coupling between the nano-oscillator and the cavity.Comment: 10 pages, 4 figures, accepted by Acta Physica Polonica

Effect of Dimple Potential on Ultraslow Light in a Bose-Einstein Condensate

We investigate the propagation of ultraslow optical pulse in atomic Bose-Einstein condensate in a harmonic trap decorated with a dimple potential. The role of dimple potential on the group velocity and time delay is studied. Since we consider the interatomic scattering interactions nonlinear Schrodinger equation or Gross-Pitaevskii equation is used in order to get the density profile of the atomic system. We find large group delays of order 1 msec in an atomic Bose-Einstein condensate in a harmonic trap with a deep dimple potential.Comment: 4 pages, 2 figure

Control of Optical Dynamic Memory Capacity of an Atomic Bose-Einstein Condensate

Light storage in an atomic Bose-Einstein condensate is one of the most practical usage of these coherent atom-optical systems. In order to make them even more practical, it is necessary to enhance our ability to inject multiple pulses into the condensate. In this paper, we report that dispersion of pulses injected into the condensate can be compensated by optical nonlinearity. In addition, we will present a brief review of our earlier results in which enhancement of light storage capacity is accomplished by utilizing multi-mode light propagation or choosing an optimal set of experimental parameters.Comment: 4 figures, 11 page

Enhancing capacity of optical information storage in a Bose-Einstein condensate

Bose-Einstein condensates (BECs) have potential to be used in attractive applications. In particular, they have been thought to be suitable for being quantum optical dynamic memories to store coherent quantum optical information. In order to assess and enhance practical value of this proposal, we have performed various realistic examinations using detailed numerical and analytical methods. Firstly, propagation of short pulses of widths in microsecond to nanosecond range through the BEC has been considered. In this part, the influence of dispersion on the temporal characteristics and on the coherent optical information storage capacity is discussed. By modeling ultra-slow short pulses in the condensate under electromagnetically induced transparency (EIT) conditions, taking into account pulse broadening, we have determined optimum optical information storage capacity. Secondly, we have investigated conditions limiting the optimum number of optical modes that can be supported by an atomic BEC. In this part, in addition to EIT, a refractive index enhancement scheme was also considered, as it allows for accommodating many numbers  of modes in the condensate. Furthermore, we have shown that multi-mode pulses, though less in number can also be realized at the cost of tolerable absorption in the case of EIT scheme. Secondly, we determine the number of optical modes supported by a wave guide in which refractive index enhancement is produced by an atomic BEC. Some analytical approximations have been made neglecting the spatial inhomogeneity. More accurate results have been obtained using a numerical model where the spatial inhomogeneity is taken into account. In the refractive index enhancement model, the predictions of (WKB) theory have been compared with those of fully numerical simulations. In this study, we investigate potential of atomic Bose-Einstein condensates as dynamic memory devices for coherent optical information processing. Specifically, the number of ultra-slow pulses that can be simultaneously present within the storage time in the condensate has been analyzed. By modeling short pulse propagation through the condensate, taking into account high-order dispersive properties, constraints on the information storage capacity has been discussed. The roles of temperature, spatial inhomogeneity, the interatomic interactions and the coupling laser on the pulse shape have been pointed out. For a restricted set of parameters, it has been found that coherent optical information storage capacity would be optimized. Coherent optical information storage capacity of an atomic Bose-Einstein condensate is examined. Theory of slow light propagation in atomic clouds is generalized to short pulse regime by taking into account group velocity dispersion. It is shown that the number of stored pulses in the condensate can be optimized for a particular coupling laser power, temperature and interatomic interaction strength. Analytical results are derived for semi-ideal model of the condensate using effective uniform density zone approximation. Detailed numerical simulations are also performed. It is found that axial density profile of the condensate protects the pulse against the group velocity dispersion. We examine the conditions determining the number of optical modes that can be supported by an atomic Bose-Einstein condensate. We show that under the conditions of refractive index enhancement via quantum coherence, it is possible to control the number of modes by means of experimentally accessible parameters including trap size, temperature, condensate number density and scattering lengths. Analytical results for the single and two-mode conditions are found. In order to slow down the group velocity we use electromagnetically induced transparency and find detuning parameter corresponding to number of modes. Results of numerical simulations are compared with analytical  calculations of the propagation constants for a parabolic-refractive index profile. Furthermore, taking into account finite radial size of the condensate, multi-mode light propagation in atomic Bose-Einstein condensate is investigated. The number of modes that can be supported by a condensate is found. Single mode condition is determined as a function of experimentally accessible parameters including trap size, temperature, condensate number density and scattering length. Quantum coherent atom-light interaction schemes are proposed for enhancing multi-mode light propagation effects. Keywords: Optical memories, Coherent optical effects, Pulse shaping, and Bose-Einstein condensate.Bose-Einstein yoğuşuk maddesini uyumlu optik bilgi işlemleri için dinamik hafıza aleti olarak araştırdık. Özellikle, yoğuşuk maddede depolama zamanı içinde çok yavaş optik darbeler  (vurumlar) analiz edildi. Yüksek dereceden dağınım özelliklerini hesaba katarak yoğuşuk maddede optik darbelerin ilerlemesini modelledik. Bu çalışmada atomik sistemin konuma bağlı olarak değişen yoğunluğu, sıcaklık ve atomik çarpışmaların şiddetine göre değişen yoğunluk profili de dikkate alındı. Yapılan analitik hesaplar ile kısa darbenin genişlemesini sıcaklığa, konuma ve atomik çarpışmalara göre analiz ettik. Bir optik darbe yoğuşuk madde içinde rezonans frekansında elektromanyetik olarak indüklenmiş saydamlık etkisi ile çok yavaş ilerletilebilir. Hızı son derece yavaş olduğundan sistem, optik bilgiyi saklama için kullanılabilir. Sınırlı parametreler için eşevreli optik bilgi hafıza kapasitesi bulundu. Ek olarak, radyal yöndeki yoğunluk profilini dikkate alan ve fiber optikte eğimli indeks fiber profili adı ile bilinen model ile  yoğuşuk maddenin kırılma indisini modelledik. Yoğunlaşmış maddenin taşıyabileceği mod sayısını analitik olarak irdeledik. Ayrıca optik vurumların Bose-Einstein yoğuşuk maddesinde ilerlemesinde üç boyutlu etkileri ve optik modların sayısındaki bağ koşulları incelendi. Kırılma indisinin arttırılması durumunda  daha çok optik modun Bose-Einstein yoğuşuk maddesinde taşınabileceğini gösterdik. Mod sayısının sıcaklığa bağlı değişimini inceledik. Kuvantum eşevrelik sayesinde, deneysel parametreleri kullanarak mod sayısının kontrol edilebileceğini gösterdik. Ayrıca tek ve çok mod koşulları analitik olarak bulundu. Analitik sonuçlar, sayısal sonuçlarla karşılaştırıldı. Anahtar Kelimeler: Optik hafıza, eşevreli optik etkiler, darbe şekli, Bose-Einstein yoğuşması