Coherent Manipulation Of Fast, Slow And Stationary Light In Ultra-cold Atomic Media

In the future, the realization of quantum internet requires that people shoulduse accurate means to control the dynamic propagation of optical pulses, toeffectively store optical information in quantized media, and apply noveltechniques to coherently control optical data. The quantum interference effectbetween light and matter provides powerful tools to achieve this goal. Inparticular, electromagnetically induced transparency (EIT) technique has beenwidely and successfully used in the field of quantum information.This thesis reviews the atomic coherence effects and focuses on thedevelopments and frontiers of EIT-based light storage techniques and researcheson optical precursors. On this basis, we investigate the dynamic evolution andcoherent control of weak optical signals with information in ultra-cold EIT atomicmedia. Our work includes the coherent generation and manipulation of slowoptical beating signals, stationary light pulse pairs, and fast optical precursorsused for marking the slow pulse in the regime of EIT.I. Dynamic generation of robust and controlled beating signals in anasymmetric procedure of light storage and retrievalWe investigate the generation of beating signals from a quantum probe fieldbased on an asymmetric procedure of light storage and retrieval in a sample oftripod-type cold atoms under EIT condition. In this scheme, when we modulatetwo classical coupling fields with equal detunings in the storage stage, a quantumprobe field first slowly enters the atomic sample and then transform into two spincoherence wave-packets. In the retrieval stage, we turn on two classical coupling fields with opposite detunings and then retrieve the probe field withbeating signals. Through theoretical analysis, the beating signals rely on thealternative constructive and destructive interference between two opticalcomponents characterized by different time-dependent phases. The generation ofthis interesting phenomenon can be well understood in the terms of dark-statepolaritons (DSPs). In addition, the beat frequency and locations of peaks aredetermined by the detunings difference and the relative phase of two couplingfields. We also analyze the potential applications of the beating signals in fastlimited measurement of magnetic field amplitudes and atomic transitionfrequencies.II. Generating and manipulating beating signals by a microwave field infour-level cold atomsWe propose an efficient scheme for the dynamic generation andmanipulation of beating signals in a sample of cold atoms driven into thefour-level quasi-Λ configuration. This scheme relies on a procedure of lightstorage and retrieval controlled by a classical coupling field with a microwavefield introduced only in the retrieval stage. One quantum probe field, incidentupon this atomic sample, is transformed first into a collective excitation of atomicspin coherence and then into two optical components characterized by differenttime-dependent phases. Consequently the retrieved quantum probe field exhibits aseries of maxima and minima (beating signals) in intensity due to the alternativeconstructive and destructive interference. This interesting phenomenon involvesin fact the coherent conversion between single-mode and two-mode DSPs. Thebeating frequency, contrast, and phase can be easily controlled by modulating themicrowave intensity, detuning, and turn-on time. We also find that little energyloss is additionally introduced when beating signals are generated by applying themicrowave field in the light retrieval stage. If the incident probe field is a squared pulse, the output probe field will have three separate parts exhibiting oscillatingintensities, among which the former two are fast optical precursors originatingfrom the sudden rising and falling edges while the last one is slow beating signalsgenerated from the central main part. This scheme can be explored to measure themicrowave intensity with high-precision beating signalsIII. Coherent generation and dynamic manipulation of double stationarylight pulses in a five-level double-tripod system of cold atomsWe study a five-level double-tripod system of cold atoms for efficientlymanipulating the dynamic propagation and evolution of a quantum probe field bymodulating four classical control fields. A pair of two-color stationary light pulses(SLPs) can be generated either at the same time or with a suitable time delay. Ournumerical results show that the two-color double SLPs are mutually coupledthrough two wave packets of atomic spin coherence. Each SLP is contributed by apair of mutually coupled DSPs with opposite velocities and equal strengths so thatno one can conquer the other to move in its own direction. The pair of stationarylight pulses can be released either from the sample entrance and exitsynchronously or just from the sample exit with a controlled time delay. Inaddition, the two-color stationary light pulses are immune to the fast decayoriginating from the higher-order Fourier components of atomic spin and opticalcoherence, and may exhibit the quantum limited beating signals with theircharacteristic frequency determined by detunings of the four classical controlfields.IV. Marking slow light signals with fast optical precursors in the regime ofelectromagnetically induced transparencyWe propose four schemes for marking a desired slow light signal in asequence of optical pulses with fast optical precursors in a quantum delay ormemory medium of cold atoms under the EIT condition. The first three schemes are accomplished in a model of generic-type system without applying thedisturbing field. In the first scheme, we dope a special half-Gaussian wave-patternpulse into the pulse sequence. The target output signal with oscillating peaks ishighlighted by a fast optical precursor generated from the rising edge of theincident half-Gaussian pulse. In the second scheme, we modulate a Gaussian-likepulse with a sudden falling edge. The corresponding precursors will interfere withthe output slow main pulse and a few oscillating peaks can be generated. In thethird scheme, we use the precursors from the sudden rising or falling edge of thenext pulse after the target pulse to generate the oscillating peaks. However, in thefourth scheme of an N-type system, a square-modulated disturbing field isintroduced to couple the-type system and another atomic level. Only its opticalprecursors can propagate through the medium but the main pulse will be absorbed.The slow target signal pulses under EIT can be marked for that the opticalprecursors add their intensities and generate oscillating peaks. Through thesemarking schemes above, we can achieve to mark a particular pulse of an opticalsequence immediately as required. These marking schemes may have potentialapplications in optical communication and fast information processing.