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- Trapped-ions form a promising platform to realize a future large scale quantum computing device.
**Qubits**are typically stored in internal electronic states, which are coupled using their joint motion in the trap potential. In this thesis this control paradigm is reversed. The harmonic motion of a trapped calcium ion forms the main subject of studies, which is controlled via the internal electronic states. A number of new techniques are introduced and examined, primarily based on the implementation of modular variable measurements. These are realized combining an internal state dependent optical dipole force with readout of the internal states. Modular measurements are used to investigate large "Schrödinger cat'' states of the ion's motion, to violate Leggett-Garg tests of macroscopic realism, and finally to realize a logical**qubit**encoded in an error-correcting code based on the trapped-ion**oscillator**. The latter offers an alternative to the standard**qubit**based quantum information processing approach, which when embedded in systems of coupled**oscillators**could lead to a large-scale quantum computer. Measurements of a particle's modular position and momentum have been the focus of various discussions of foundational quantum mechanics. Such modular measurements of the trapped-ion's motion are studied in depth in this thesis, in particular their ability to commute, which forms a key element for the latter work on error-correcting codes. Here we make use of the ability to investigate sequences of measurements on a single harmonic**oscillator**, and study correlations between their results, as well as quantum measurement disturbances between the measurements. In order to achieve the major results of the thesis, it was necessary to characterize and control multiple wave packets in phase space. On the characterization side, the need to cope with states with high energy occupations led to the development of multiple new methods for quantum state tomography, including the use of a squeezed eigenstate basis, and the direct extraction of the characteristic function of the**oscillator**using state-dependent forces. These were used to analyze some of the largest**oscillator**"Schrödinger cat'' states which have been produced to date. The main result of this thesis is encoding and full control of a logical**qubit**in the motional**oscillator**space using a code proposed 18 years ago by Gottesman, Kitaev and Preskill. Logical code states are realized and manipulated using sequences of up to five modular measurements applied to an ion initially prepared in a squeezed motional state. Such sequences realize superpositions of multiple squeezed wave packets, which form the code words. The usage of the**oscillator**enables to encode and in principle correct a logical**qubit**within a single trapped ion, which when compared to typical**qubit**-array based approaches simplifies control and hardware. While the discussion above focuses on the new physics in this thesis, in addition the work required technical upgrades to the system, improving control of both**qubit**and**oscillator**. These form important components which have impact on all experiments in our setup, beyond the bounds of the current thesis.,ISBN:5800134927809,Data Types:- Document

- Semiconductor
**qubits**rely on the control of charge and spin degrees of freedom of electrons or holes confined in quantum dots. They constitute a promising approach to quantum information processing, complementary to superconducting**qubits**. Here, we demonstrate coherent coupling between a superconducting transmon**qubit**and a semiconductor double quantum dot (DQD) charge**qubit**mediated by virtual microwave photon excitations in a tunable high-impedance SQUID array resonator acting as a quantum bus. The transmon-charge**qubit**coherent coupling rate (~21 MHz) exceeds the linewidth of both the transmon (~0.8 MHz) and the DQD charge**qubit**(~2.7 MHz). By tuning the**qubits**into resonance for a controlled amount of time, we observe coherent**oscillations**between the constituents of this hybrid quantum system. These results enable a new class of experiments exploring the use of two-**qubit**interactions mediated by microwave photons to create entangled states between semiconductor and superconducting**qubits**.,Nature Communications, 10 (1),ISSN:2041-1723,Data Types:- Document

- Spin
**qubits**and superconducting**qubits**are among the promising candidates for realizing a solid state quantum computer. For the implementation of a hybrid architecture which can profit from the advantages of either approach, a coherent link is necessary that integrates and controllably couples both**qubit**types on the same chip over a distance that is several orders of magnitude longer than the physical size of the spin**qubit**. We realize such a link with a**frequency**-tunable high impedance SQUID array resonator. The spin**qubit**is a resonant exchange**qubit**hosted in a GaAs triple quantum dot. It can be operated at zero magnetic field, allowing it to coexist with superconducting**qubits**on the same chip. We spectroscopically observe coherent interaction between the resonant exchange**qubit**and a transmon**qubit**in both resonant and dispersive regimes, where the interaction is mediated either by real or virtual resonator photons.,Nature Communications, 10 (1),ISSN:2041-1723,Data Types:- Document

- Circadian clocks have long been known to be essential for the maintenance of physiological and behavioral processes in a variety of organisms ranging from plants to humans. Dysfunctions that subvert gene expression of oscillatory circadian-clock components may result in severe pathologies, including tumors and metabolic disorders. While the underlying molecular mechanisms and dynamics of complex gene behavior are not fully understood, synthetic approaches have provided substantial insight into the operation of complex control circuits, including that of oscillatory networks. Using iterative cycles of mathematical model-guided design and experimental analyses, we have developed a novel low-
**frequency**mammalian**oscillator**. It incorporates intronically encoded siRNA-based silencing of the tetracycline-dependent transactivator to enable the autonomous and robust expression of a fluorescent transgene with periods of 26 h, a circadian clock-like oscillatory behavior. Using fluorescence-based time-lapse microscopy of engineered CHO-K1 cells, we profiled expression dynamics of a destabilized yellow fluorescent protein variant in single cells and real time. The novel**oscillator**design may enable further insights into the system dynamics of natural periodic processes as well as into siRNA-mediated transcription silencing. It may foster advances in design, analysis and application of complex synthetic systems in future gene therapy initiatives.,Nucleic Acids Research, 38 (8),ISSN:1362-4962,ISSN:0301-5610,Data Types:- Document

- Mesoscopic oscillatory reaction systems, for example in cell biology, can exhibit stochastic
**oscillations**in the form of cyclic random walks even if the corresponding macroscopic system does not**oscillate**. We study how the intrinsic noise from molecular discreteness influences the**frequency**spectrum of mesoscopic**oscillators**using as a model system a cascade of coupled Brusselators away from the Hopf bifurcation. The results show that the spectrum of an**oscillator**depends on the level of noise. In particular, the peak**frequency**of the**oscillator**is reduced by increasing noise, and the bandwidth increased. Along a cascade of coupled**oscillators**, the peak**frequency**is further reduced with every stage and also the bandwidth is reduced. These effects can help understand the role of noise in chemical**oscillators**and provide fingerprints for more reliable parameter identification and volume measurement from experimental spectra.,Scientific Reports, 1,ISSN:2045-2322,Data Types:- Document

- Circuit quantum electrodynamics (QED) is a powerful approach to study excitations of and engineer and control interactions between superconducting
**qubits**using microwave quantum fields. Recently, the potential of circuit QED has also been explored in the context of semiconductor quantum systems motivated by the possibility to study their excitations in new**frequency**regimes and the progress towards quantum information architectures based on semiconductor nanostructures. Two hybrid circuit QED architectures are explored in this thesis. They consist of gate-defined semiconductor double quantum dots acting as two-level quantum systems dipole coupled to single photonic modes of microwave cavities. In the first type of device, the double quantum dot charge**qubit**couples to a superconducting coplanar waveguide resonator at a rate lower than its decoherence rate. This weakly coupled system already provides an interesting platform to study the physics of the quantum dots at microwave**frequencies**. This thesis discusses experiments exploring microwave emission from a voltage-biased double quantum dot. We detect radiation emitted in inelastic electron tunneling processes between the dots and the leads and in interdot transitions resonant with the cavity. The dependence of the emission signal on the quantum dot level configuration provides a novel way to probe the hybridization and broadening of the electronic double dot states. In the second device architecture, the double quantum dot is coupled to a**frequency**-tunable high impedance resonator consisting of an array of superconducting quantum interference devices. Due to the high characteristic impedance of these resonators, the coupling strength is increased beyond the decay rates of**qubit**and resonator – the condition defining the strong coupling regime. Strong coupling is demonstrated in measurements of the vacuum Rabi mode splitting showing a coupling strength of 155 MHz, which is the highest coupling strength reported in comparable systems.The**qubit**linewidth of 40 MHz is independently extracted in spectroscopy measurements. Achieving strong coupling to microwave cavities poses a crucial step towards semiconductor-based quantum information architectures as it enables e.g. time-resolved measurements, quantum non-demolition readout or the coupling of distant**qubits**or different types of**qubits**via the resonator.Data Types:- Document

- Background The mammalian brain expresses a wide range of state-dependent network
**oscillations**which vary in**frequency**and spatial extension. Such rhythms can entrain multiple neurons into coherent patterns of activity, consistent with a role in behaviour, cognition and memory formation. Recent evidence suggests that locally generated fast network**oscillations**can be systematically aligned to long-range slow**oscillations**. It is likely that such cross-**frequency**coupling supports specific tasks including behavioural choice and working memory. Principal Findings We analyzed temporal coupling between high-**frequency****oscillations**and EEG theta activity (4–12 Hz) in recordings from mouse parietal neocortex. Theta was exclusively present during active wakefulness and REM-sleep. Fast**oscillations**occurred in two separate**frequency**bands: gamma (40–100 Hz) and fast gamma (120–160 Hz). Theta, gamma and fast gamma were more prominent during active wakefulness as compared to REM-sleep. Coupling between theta and the two types of fast**oscillations**, however, was more pronounced during REM-sleep. This state-dependent cross-**frequency**coupling was particularly strong for theta-fast gamma interaction which increased 9-fold during REM as compared to active wakefulness. Theta-gamma coupling increased only by 1.5-fold. Significance State-dependent cross-**frequency**-coupling provides a new functional characteristic of REM-sleep and establishes a unique property of neocortical fast gamma**oscillations**. Interactions between defined patterns of slow and fast network**oscillations**may serve selective functions in sleep-dependent information processing.,PLoS ONE, 6 (12),ISSN:1932-6203,Data Types:- Document

- Photon-based strongly correlated lattice models like the Jaynes–Cummings and Rabi lattices differ from their more conventional relatives like the Bose–Hubbard model by the presence of an additional tunable parameter: the
**frequency**detuning between the pseudo-spin degree of freedom and the harmonic mode**frequency**on each site. Whenever this detuning is large compared to relevant coupling strengths, the system is said to be in the dispersive regime. The physics of this regime is well-understood at the level of a single Jaynes–Cummings or Rabi site. Here, we extend the theoretical description of the dispersive regime to lattices with many sites, for both strong and ultra-strong coupling. We discuss the nature and spatial range of the resulting**qubit**–**qubit**and photon–photon coupling, demonstrate the emergence of photon-pairing and squeezing and illustrate our results by exact diagonalization of the Rabi dimer.,New Journal of Physics, 15,ISSN:1367-2630,Data Types:- Document

- superconducting
**qubits**...**qubits**Data Types:- Document

- ELECTRONIC TUBE OSCILLATORSC + THERMIONIC VALVE
**OSCILLATORS**(ELECTRICAL**OSCILLATION**TECHNOLOGY)Data Types:- Document