It has been shown that control over the design of single- or multimode-transparency windows can be achieved by control-probe quantum interferometry using two delayed phase-locked ultrashort pulses. We have investigated how single- or multimode-transparency windows can be designed by eliminating the absorption to a set of odd or even vibrational levels of a molecule covered by the spectral bandwidth of the pulses. Suppression of absorption can be achieved by controlling the quantum interference of two vibrational wave packets excited by these two pulses, leading to destructive interference of transition amplitudes for one set of vibrational levels even or odd. Simuntaneously the interference becomes constructive for the other set of odd or even vibrational levels, leading to absorption to these levels. Thus, a set of transparency windows is designed in between two absorption peaks at two consecutive odd (even) vibrational levels by eliminating absorption at even (odd) vibrational levels between two absorption peaks. If the spectral bandwidth of the pulse [full width at half maximum (FWHM)] is less than the energy difference between two consecutive absorption peaks, the pulse will be transmitted without absorption through the transparency window. However, for pulses with a larger spectral bandwidth (FWHM), a set of broad transparency windows will be generated and different bands of pulse frequencies will be transmitted through these windows. We have shown that coherent control of the design of transparency windows can be achieved by controlling pulse duration, carrier frequency, delay, and the phase difference of two ultrashort pulses.
It has been shown that control over the design of single- or multimode-transparency windows can be achieved by control-probe quantum interferometry using two delayed phase-locked ultrashort pulses. We have investigated how single- or multimode-transparency windows can be designed by eliminating the absorption to a set of odd or even vibrational levels of a molecule covered by the spectral bandwidth of the pulses. Suppression of absorption can be achieved by controlling the quantum interference of two vibrational wave packets excited by these two pulses, leading to destructive interference of transition amplitudes for one set of vibrational levels even or odd. Simuntaneously the interference becomes constructive for the other set of odd or even vibrational levels, leading to absorption to these levels. Thus, a set of transparency windows is designed in between two absorption peaks at two consecutive odd (even) vibrational levels by eliminating absorption at even (odd) vibrational levels between two absorption peaks. If the spectral bandwidth of the pulse [full width at half maximum (FWHM)] is less than the energy difference between two consecutive absorption peaks, the pulse will be transmitted without absorption through the transparency window. However, for pulses with a larger spectral bandwidth (FWHM), a set of broad transparency windows will be generated and different bands of pulse frequencies will be transmitted through these windows. We have shown that coherent control of the design of transparency windows can be achieved by controlling pulse duration, carrier frequency, delay, and the phase difference of two ultrashort pulses.
We have shown that electromagnetically induced transparency can be achieved by control-probe interferometry using two delayed phase-locked ultrashort pulses. Two vibrational wavepackets on the excited state, excited by two delayed phase-locked ultrashort pulses, interfere constructively or destructively leading to enhancement or suppression of absorption to a selective set of vibrational levels. Depending on the phase difference and the delay between the pulses with same carrier frequency, one can design different transparency windows between absorption peaks at consecutive even(odd) vibrational levels by eliminating absorption at odd(even) vibrational levels. We have shown that by switching the phase difference of two delayed femtosecond pulses, one can switch to complete elimination of absorption from enhanced absorption to a particular set of vibrational levels in the excited state. Thus, switching of transparency through window between odd vibrational levels to that between even vibrational levels is possible. By properly choosing the temporal width and the carrier frequency of the pulses, lossless transmission of complete or bands of frequencies of the pulses can be achieved through these transparency windows. Hence, designing of single- or multi-mode transparency windows in NaH molecule is feasible by control-probe quantum interferometry.
Experimental and theoretical work is presented on the control of wave packet dynamics in atomic and molecular systems. Using sequences of phase-locked optical pulses, the link between optical phase and quantum mechanical phase is explored in the Na atom and Naj dimer, representing a step towards the logical engineering of quantum states in more complicated systems. A novel apparatus, constructed to study and control the vibrational dynamics of vibrational wave packets on the Na ionic potential surface, is described in chapter 3. Theoretical simulations for proposed experiment are presented in chapter 4. Control is achieved by exploiting the phase-evolution of the constituent vibrational quantum states within the wave packet superposition. The phase relationship and the accumulated phase difference between the various components of the wave packet is determined, and a sequence of phase-locked optical pulses is employed to selectively enhance or depopulate specific vibrational states, or sets of vibrational states. The quantum state composition of the resulting wave packet, and the efficiency of the control scheme, is determined by calculating the multi-pulse response of the time-dependent vibrational state populations. In chapter 5, the quantum interference between Rydberg electron wave packets in the Na atom is investigated using pairs of phase-locked wave packets, allowing manipulation of the total orbital angular momentum of Na Rydberg atoms. Initially the wave packet is composed of a superposition of s and d Rydberg series. Exploitation of the difference between the quantum defects of the two series allows specific angular momentum compositions within the resultant wave packet to be engineered. Experimentally, this final quantum state distribution is analysed in the frequency domain using state selective field ionisation, and in the time domain using the optical Ramsey method. The theoretical calculations show how the phase difference between pairs of optical pulses is linked to the corresponding Rydberg frequency spectrum, therefore enabling the control of the quantum state composition of the wave packets.
Coherent manipulation of single-photon wave packets is essentially important for optical quantum communication and quantum information processing. In this paper, we realize controllable splitting and modulation of single-photon-level pulses by using a tripod-type atomic medium. The adoption of two control beams enable us to store one signal pulse into superposition of two distinct atomic collective excitations. By controlling the time delay between the two control pulses, we observe splitting of a stored wave packet into two temporally distinct modes. By controlling the frequency detuning of the control beams, we observe both temporal and frequency-domain interference of the retrieval signal pulses, which provides a method for pulse modulation and multisplitting of the signal photons.
Induced transparency and absorption effects can be observed in the throughput of an optical microresonator that has two coresonant modes with very different quality factors. There are several different methods for achieving these effects, which enable slow light and fast light, i.e., the delay or advancement of an incident resonant pulse. For example, mode coupling can be employed. This coupling can take place between modes of the same polarization or modes of orthogonal polarization. Another method is based on superposition, when two orthogonally polarized modes are driven simultaneously by linearly polarized input light and throughput of the same polarization as the input is detected. In general, induced transparency is accompanied by pulse delay, whereas induced absorption can be accompanied by pulse advancement or delay. A number of different methods for producing induced transparency or absorption are compared here. Several properties are considered for comparison. One involves the widths of the induced transparency or absorption window and of the corresponding spectral region of steep dispersion. Achievable pulse delays or advancements, along with pulse distortion and delay-bandwidth (or advancement-bandwidth) products, are also compared. Different methods allow for different amounts of control over various system parameters, and these are compared as well. The differences among the several methods are evaluated in consideration of suitability for employment in various applications.
Coherent control is a technique to manipulate the amplitudes and phases of wave functions by exploiting the coherent property of light. It is of great importance for the development of quantum technologies including quantum information processing and chemical reaction control as well as for addressing fundamental problems in quantum mechanics such as the quantum–classical boundary. In this chapter, we describe the development and applications of coherent control based on wave-packet interferometry with attosecond precision, which has been made possible by tuning the delay between two laser pulses on the attosecond time scale. This technique has been applied to several different hierarchies from simple to complex quantum systems: (i) isolated iodine molecules in the gas phase, (ii) molecular crystals of para-hydrogen, and (iii) single crystals of bismuth. In system (i), we have controlled and visualized the interference of vibrational wave packets in the isolated iodine molecules, and that wave-packet interference has been utilized to develop a molecular computer, which executes ultrafast Fourier transform. In system (ii), we have manipulated vibrational wave-functions delocalized in a para-hydrogen crystal. The long coherence lifetime of para-hydrogen crystals is a promising resource to preserve quantum information in bulk solids. In system (iii), we have controlled the excitation ratio of two orthogonal coherent phonon modes, whose coherent superposition has allowed for active control of ultrafast two-dimensional atomic motions in a single crystal of bismuth. Those atomic motions have been visualized by density functional theory calculations. Finally, the coherent control of an ensemble of ultracold Rydberg atoms is briefly discussed as future perspectives for exploring the quantum–classical boundary.
We investigate the power control behavior of odd-order multiwave mixing in an electromagnetically induced transparency window. We successfully obtain the evolution from pure enhancement (bright state), half-enhancement, and half-suppression, to pure suppression (dark state) in a four-wave mixing (FWM) channel. The correlations of two bright and two dark states of FWM are studied under four different kinds of power configurations. Moreover, the power-controlled quantum interference among multiple dark states is also studied in FWM and six-wave mixing channels. Such selective switching among multiple frequency channels could have potential applications in optical switching, optical communication, and quantum information processing.