We observe and study the phenomenon of Anderson localization in a system of true quantum kicked rotors. Nitrogen molecules in a supersonic molecular jet are cooled down to 27 K and are rotationally excited by a periodic train of 24 high-intensity femtosecond pulses. Exponential distribution of the molecular angular momentum -the most unambiguous signature of Anderson localization -is measured directly by means of coherent Raman scattering. We demonstrate the suppressed growth of the molecular rotational energy with the number of laser kicks and study the dependence of the localization length on the kick strength. Both timing and amplitude noise in the pulse train is shown to destroy the localization and revive the diffusive growth of angular momentum.The periodically kicked rotor is one of the simplest systems whose classical motion is chaotic, as manifested by the unbounded diffusive growth of its energy with the number of kicks. In contrast, the energy growth of a quantum kicked rotor (QKR) is suppressed due to the interference of quantum interaction pathways [1,2]. The effect has been linked to Anderson localization [3] of the electronic wave function in disordered solids [4]. Similarly to the latter, the wave function of the quantum rotor does not grow wider in the angular momentum space with every consecutive kick, but instead localizes near the initial rotational state, with the probability amplitude falling exponentially away from it.The exponential distribution around the localization center is considered a necessary component and a distinct signature of Anderson localization. Although it has been demonstrated [5] in a cold-atom analogue of the QKR [6], exponentially localized states have not yet been observed in a system of true quantum rotors. A natural choice for such a system -a diatomic molecule subject to short kicks from a pulsed external field (microwave, optical or THz), has been discussed in multiple theoretical proposals [7][8][9][10]. In a series of recent works [9,[11][12][13], Averbukh and coworkers suggested a strategy to observe and study a number of QKR effects in an ensemble of molecules exposed to a periodic sequence of ultra-short laser pulses. The effects of a quantum resonance [14,15] and Bloch oscillations [16] have been verified experimentally. An onset of Anderson localization in laser-induced molecular alignment has been reported [17], but the direct evidence of the exponentially localized states and the suppressed growth of the rotational energy has not been shown.The difficulty of demonstrating Anderson localization with molecular rotors stems from a number of experimental challenges. First, the need to assess the shape of the rotational distribution calls for a sensitive detection method capable of resolving individual rotational states. According to the theoretical studies [11], the population of a few tens of rotational states must be measured with high sensitivity over the range of at least two orders of magnitude. Second, for the localized state not to be smeared out due ...

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High-repetition-rate PIV measurements were performed in the trisonic wind tunnel facility at the Bundeswehr University Munich in order to investigate the boundary layer parameters on a generic rocket model and the recirculation area in the wake of the model at Mach numbers up to Mach = 2.6. The data are required for the validation of unsteady flow simulations. Because of the limited run time of the blow-down wind tunnel, a high-repetition-rate PIV system was applied to obtain the flow statistics with high accuracy. The results demonstrate this method's potential to resolve small-scale flow phenomena over a wide field of view in a large Mach number range but also show its limitations for the investigations of wall-bounded flows.

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We experimentally study a system of quantum kicked rotors -an ensemble of diatomic molecules exposed to a periodic sequence of ultrashort laser pulses. In the regime, where the underlying classical dynamics is chaotic, we investigate the quantum phenomenon of dynamical localization by means of state-resolved coherent Raman spectroscopy. We examine the dependence of the exponentially localized angular momentum distribution and of the total rotational energy on the time period between the pulses and their amplitude. The former parameter is shown to provide control over the localization center, whereas the latter one controls the localization length. Similar control of the center and width of a nonlocalized rotational distribution is demonstrated in the limit of classical diffusion, established by adding noise to the periodic pulse sequence.

This collaborative work discusses the results of time-resolved pressure-sensitive paint measurements performed on a model of a generic spacecraft under sub-and transonic test conditions. It is shown that optical pressure measurements using an active layer from platinumporphyrin complexes (PtTFPP) in combination with a polymer-ceramic base layer are able to measure dynamic flow phenomena in the trisonic wind tunnel facility up to sampling rates of 2 kHz. Low amplitude fluctuations in the order of 0.1 kPa were determined by means of this measurement technique. The buffet dynamics, as well as the spatial extent of the recirculation area in the near-wake, compare well with numerical predictions and PIV measurements. Furthermore, characteristic coherent pressure modes on the base were resolved, which were predicted by large-eddy simulations.

We experimentally demonstrate coherent control of a quantum system, whose dynamics is chaotic in the classical limit. Interaction of diatomic molecules with a periodic sequence of ultrashort laser pulses leads to the dynamical localization of the molecular angular momentum, a characteristic feature of the chaotic quantum kicked rotor. By changing the phases of the rotational states in the initially prepared coherent wave packet, we control the rotational distribution of the final localized state and its total energy. We demonstrate the anticipated sensitivity of control to the exact parameters of the kicking field, as well as its disappearance in the classical regime of excitation.PACS numbers: 05.45. Mt, 42.50.Hz Control of molecular dynamics with external fields is a long-standing goal of physics and chemistry research. Great progress has been made by exploiting the coherent nature of light-matter interaction. At the heart of coherent control is the interference of quantum pathways leading to the desired target state from a well-defined initial state [1]. In this context, an exponential sensitivity to the initial conditions, characteristic for classically chaotic systems, poses an important question about the controllability in the quantum limit (for a comprehensive review of this topic, see [2]). As the underlying classical rovibrational dynamics of the majority of large polyatomic molecules is often chaotic, the answer to this question has far reaching implications for the ultimate prospects of using coherence to control chemical reactions.Success in steering the outcome of chemical reactions by means of feedback-based adaptive algorithms [3], using the methods of optimal control theory [4], proved that such control is feasible. Theoretical works on quantum controllability in the presence of chaos, both in general [5] and with regard to specific molecular systems [6,7], pointed at the importance of coherent evolution. To investigate the roles of coherence, chaoticity and quantumness further, Gong and Brumer considered a paradigm system for studying quantum effects on classically chaotic dynamics -the quantum kicked rotor (QKR) [2,6,8]. The latter is known to exhibit dynamical localization (closely related to Anderson localization in disordered solids [9,10]), in which quantum interferences suppress the classically chaotic diffusion after the "quantum break time" [11,12]. Gong and Brumer demonstrated that the energy of the localized state can be controlled by modifying the initial wave packet. They showed that quantum coherences, as opposed to the classical structures in the rotor's phase space [13], are indeed responsible for the achieved control over the chaotic dynamics of the QKR.In this report, we present an experimental proof of the Gong-Brumer control scheme. Following a theoretical proposal of Averbukh and co-workers [14, 15], we investigate the dynamics of true quantum rotors by exposing diatomic molecules to a periodic sequence of ultra-short laser pulses. A number of representative QKR effects h...