Atoms and Molecules in Cavities: From Weak to Strong Coupling in QED Chemistry

In this work, we provide an overview of how well-established concepts in the fields of quantum chemistry and material sciences have to be adapted when the quantum nature of light becomes important in correlated matter-photon problems. Therefore, we analyze model systems in optical cavities, where the matter-photon interaction is considered from the weak- to the strong coupling limit and for individual photon modes as well as for the multi-mode case. We identify fundamental changes in Born-Oppenheimer surfaces, spectroscopic quantities, conical intersections and efficiency for quantum control. We conclude by applying our novel recently developed quantum-electrodynamical density-functional theory to single-photon emission and show how a straightforward approximation accurately describes the correlated electron-photon dynamics. This paves the road to describe matter-photon interactions from first-principles and addresses the emergence of new states of matter in chemistry and material science

Kohn-Sham Approach to Quantum Electrodynamical Density Functional Theory: Exact Time-Dependent Effective Potentials in Real Space

The density-functional approach to quantum electrodynamics is extending traditional density-functional theory and opens the possibility to describe electron-photon interactions in terms of effective Kohn-Sham potentials. In this work, we numerically construct the exact electron-photon Kohn-Sham potentials for a prototype system which consists of a trapped electron coupled to a quantized electromagnetic mode in an optical high-Q cavity. While the effective current that acts on the photons is known explicitly, the exact effective potential that describes the forces exerted by the photons on the electrons is obtained from a fixed-point inversion scheme. This procedure allows us to uncover important beyond-mean-field features of the effective potential which mark the breakdown of classical light-matter interactions. We observe peak and step structures in the effective potentials, which can be attributed solely to the quantum nature of light, i.e., they are real-space signatures of the photons. Our findings show how the ubiquitous dipole interaction with a classical electromagnetic field has to be modified in real-space in order to take the quantum nature of the electromagnetic field fully into account

Cavity Born-Oppenheimer Approximation for Correlated Electron-Nuclear-Photon Systems

In this work, we illustrate the recently introduced concept of the cavity Born-Oppenheimer approximation for correlated electron-nuclear-photon problems in detail. We demonstrate how an expansion in terms of conditional electronic and photon-nuclear wave functions accurately describes eigenstates of strongly correlated light-matter systems. For a GaAs quantum ring model in resonance with a photon mode we highlight how the ground-state electronic potential-energy surface changes the usual harmonic potential of the free photon mode to a dressed mode with a double-well structure. This change is accompanied by a splitting of the electronic ground-state density. For a model where the photon mode is in resonance with a vibrational transition, we observe in the excited-state electronic potential-energy surface a splitting from a single minimum to a double minimum. Furthermore, for a time-dependent setup, we show how the dynamics in correlated light-matter systems can be understood in terms of population transfer between potential energy surfaces. This work at the interface of quantum chemistry and quantum optics paves the way for the full ab-initio description of matter-photon systems

Joint Antenna Array Attitude Tracking and Spoofing Detection Based on Phase Difference Measurements

Spoofing attacks are a serious problem for civil GNSS applications with safety content, such as airplane landing or maritime navigation in harbors. Also many strategically important infrastructures, such as electric power grids or mobile communications networks, are becoming increasingly dependent on GNSS services. Military GNSS users solve that problem by signal encryption at chip level. This reduces the threat to only allow for meaconing, i.e. retransmitting the GNSS signals from a certain location, since the exact waveform is unpredictable. Civil users cannot rely on encryption at the moment and most likely in the near future. They must be protected by additional techniques, which are able to detect and mitigate spoofing attacks. A number of receiver-autonomous solutions for the spoofing problem have been proposed in the last decade. For single antenna receivers the detection of spoofing attacks can rely on the observation of the time evolution of different signal parameters such as power and Doppler frequency shift, the PRN code delay and its rates, the correlation function shape as well as the cross-correlation of the signal components at different carrier frequencies. However, the most advanced protection against the sophisticated spoofing attacks can be provided by utilizing the spatial domain for signal processing available by using antenna arrays ([1], [2], [3], [4], [5]). A GNSS receiver with an antenna array is able to estimate the directions of arrival of the impinging waveforms and so to discriminate between the authentic and counterfeit signals. Moreover the malicious signals can be mitigated by generating a spatial zero into the array antenna reception pattern in the direction of the spoofing source(s). The use of the array-aided joint estimation of the array attitude and spoofing detection was investigated by the authors in [1], [3], [5]. A post-correlation estimation of the signal direction of arrival (DOA) was utilized as the first step of the corresponding signal processing chain. This approach however still suffers from the effects of short-term distortions in the receiver tracking loops and the resulting unavailability of the DOA estimations during the spoofing attack. Two approaches have been identified to overcome this effect. On the one hand, a more accurate direction of arrival detection and antenna calibration can be used. On the other hand, the attitude estimation can be made more robust by skipping the DOA estimation step and using instead directly the post-correlation array outputs in the underlining measurement model, similar to method 2 in [6]. The latter possibility will be exploited throughout the current paper. One of the main challenges here is to design robust and computationally effective attitude estimation when the post-correlation array outputs consist of the superposition of the authentic and counterfeit signals. This problem, for example, is not adequately handled in [6] and [7]. In the aforementioned approaches, the estimation of the actual direction of arrival in terms of (antenna local) azimuth and elevation was done explicitly before the attitude was estimated. The approach presented in the paper will avoid this (computationally expensive) step, by introducing an adequate measurement model. This model connects the measured relative phases between the antennas elements (spatial signature) to the ones expected from the almanac. This interconnection involves the receiver attitude, which is the state to be estimated. In a second step, the model fit (i.e. residuals of least square fit) is used to detect anomalies. Further processing is done by comparing the spatial signature for different satellites. Contrary to using the cyclic nature of PRN codes to detect the direction in the pre-correlation domain as described in [2], the spatial signature in the post-correlation domain is used. If one dominant direction is present, the likelihood of spoofing or meaconing is considered high. If detected, a second processing stage is triggered, capable of spatially filtering out the spoofers signature (post-correlation nulling). Finally a second run of the aforementioned procedure is done to estimate the antennas attitude using a spatially filtered signal. Theoretical results as well as hardware simulations ([8]) show, that if a GPS/CA or Galileo receiver already tracks a certain PRN, the likelihood of success is very low for an unsynchronized spoofer. In this context (un)synchronized is related to the PRNs current frequency shift (caused by the Doppler Effect), as well as code delay. The code delay error should not be larger than one chip in general. The tolerable frequency mismatch however, highly depends on the receivers implementation (i.e. FLL and PLL parameters and stages), but should not be bigger than a few multiples of 50 Hz. A synchronized spoofer or meaconing signal which is turned on when the receiver already tracks the corresponding PRN will be considered in the context of the paper. The described methods will be evaluated using software simulations. Scenarios without spoofing or meaconing are used to demonstrate the attitude estimation. Scenarios with repeaters will be used to demonstrate the two-stage approach with spatial filtering. [1] M. Meurer, A. Konovaltsev, M. Cuntz, and C. Hättich, “Robust Joint Multi-Antenna Spoofing Detection and Attitude Estimation using Direction Assisted Multiple Hypotheses RAIM,” in Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), September 2012, Nashville, TN, USA., 2012. [2] S. Daneshmand, A. Jafarnia-Jahromi, A. Broumandon, and G. Lachapelle, “A low-complexity GPS anti-spoofing method using a multi-antenna array,” in Proc. ION GNSS 2012, 2012, pp. 1233–1243. [3] A. Konovaltsev, M. Cuntz, C. Haettich, and M. Meurer, “Autonomous Spoofing Detection and Mitigation in a GNSS Receiver with an Adaptive Antenna Array,” in Proc. ION GNSS+ 2013, 2013, p. 12. [4] M. Appel, A. Konovaltsev, and M. Meurer, “Robust Spoofing Detection and Mitigation based on Direction of Arrival Estimation,” in Proc. ION GNSS+ 2015, 2015, pp. 3335–3344. [5] M. Meurer, A. Konovaltsev, M. Appel, M. Cuntz, E. M. Meurer, A. Konovaltsev, M. Appel, and M. C. De, “Direction-of-Arrival Assisted Sequential Spoofing Detection and Mitigation,” in ION ITM 2016, 2016. [6] M. Markel, E. Sutton, and H. Zmuda, “An antenna array-based approach to attitude determination in a jammed environment,” in Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), 2001, pp. 2914–2926. [7] S. Daneshmand, N. Sokhandan, and G. Lachapelle, “Precise GNSS Attitude Determination Based on Antenna Array Processing,” in Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation, ION GNSS+ 2014, Tampa, Florida, September 8-12, 2014, 2014. [8] M. Appel, A. Hornbostel, and C. Haettich, “Impact of meaconing and spoofing on galileo receiver performance,” 7th ESA Workshop on Satellite Navigation Technologies NAVITEC, 2014

Towards a Consistent Service Lifecycle Model in Service Governance

Introducing an SOA in a company brings new challenges for the existing management. Small loosely coupled services allow the Enterprise Architecture to flexibly adapt to existing business processes that themselves depend on changing market environments. SOA, however, introduces a new implicit system complexity. Service Governance approaches address this issue by introducing management processes and techniques, and best practices to cope with the new heterogeneity. Service lifecycle management is one aspect. Existing definitions of service lifecycles vary greatly.. In this paper, we compare existing service lifecycle approaches concerning defined phases and process. In particular, we challenge the purpose of the distinctions made between design time, runtime, and change time. Concluding, we propose a consolidated service lifecycle model for usage in Service Governance