08 Fakultät Mathematik und Physik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9

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Institute: search.filters.UBSInstitut.3. Physikalisches InstitutStart date: 2020

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Now showing 1 - 10 of 29
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    Nanoscale magnetic resonance spectroscopy with nitrogen-vacancy centers in diamond
    (2021) Paone, Domenico; Wrachtrup, Jörg (Prof. Dr.)
    Stickstoff-Fehlstellen (NV-Zentren) in Diamant bilden interessante Quantensysteme, welche für Quanten-Sensing Protokolle genutzt werden können. In der vorliegenden Arbeit, werden NV-Zentren genutzt, um einzelne Molekülsysteme auszulesen und supraleitende Proben lokal zu charakterisieren. Zusätzlich werden Methoden entwickelt, um die Spineigenschaften der NV-Zentren zu optimieren, welche dann Einfluss auf das Sensorikverhalten des Systems haben.
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    Heterodyne sensing of microwaves with a quantum sensor
    (2021) Meinel, Jonas; Vorobyov, Vadim; Yavkin, Boris; Dasari, Durga; Sumiya, Hitoshi; Onoda, Shinobu; Isoya, Junichi; Wrachtrup, Jörg
    Diamond quantum sensors are sensitive to weak microwave magnetic fields resonant to the spin transitions. However, the spectral resolution in such protocols is ultimately limited by the sensor lifetime. Here, we demonstrate a heterodyne detection method for microwaves (MW) leading to a lifetime independent spectral resolution in the GHz range. We reference the MW signal to a local oscillator by generating the initial superposition state from a coherent source. Experimentally, we achieve a spectral resolution below 1 Hz for a 4 GHz signal far below the sensor lifetime limit of kilohertz. Furthermore, we show control over the interaction of the MW-field with the two-level system by applying dressing fields, pulsed Mollow absorption and Floquet dynamics under strong longitudinal radio frequency drive. While pulsed Mollow absorption leads to improved sensitivity, the Floquet dynamics allow robust control, independent from the system’s resonance frequency. Our work is important for future studies in sensing weak microwave signals in a wide frequency range with high spectral resolution.
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    Readout and control of an endofullerene electronic spin
    (2020) Pinto, Dinesh; Paone, Domenico; Kern, Bastian; Dierker, Tim; Wieczorek, René; Singha, Aparajita; Dasari, Durga; Finkler, Amit; Harneit, Wolfgang; Wrachtrup, Jörg; Kern, Klaus
    Atomic spins for quantum technologies need to be individually addressed and positioned with nanoscale precision. C60 fullerene cages offer a robust packaging for atomic spins, while allowing in-situ physical positioning at the nanoscale. However, achieving single-spin level readout and control of endofullerenes has so far remained elusive. In this work, we demonstrate electron paramagnetic resonance on an encapsulated nitrogen spin (14N@C60) within a C60 matrix using a single near-surface nitrogen vacancy (NV) center in diamond at 4.7 K. Exploiting the strong magnetic dipolar interaction between the NV and endofullerene electronic spins, we demonstrate radio-frequency pulse controlled Rabi oscillations and measure spin-echos on an encapsulated spin. Modeling the results using second-order perturbation theory reveals an enhanced hyperfine interaction and zero-field splitting, possibly caused by surface adsorption on diamond. These results demonstrate the first step towards controlling single endofullerenes, and possibly building large-scale endofullerene quantum machines, which can be scaled using standard positioning or self-assembly methods.
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    Quantum Fourier transform for nanoscale quantum sensing
    (2021) Vorobyov, Vadim; Zaiser, Sebastian; Abt, Nikolas; Meinel, Jonas; Dasari, Durga; Neumann, Philipp; Wrachtrup, Jörg
    The quantum Fourier transformation (QFT) is a key building block for a whole wealth of quantum algorithms. Despite its proven efficiency, only a few proof-of-principle demonstrations have been reported. Here we utilize QFT to enhance the performance of a quantum sensor. We implement the QFT algorithm in a hybrid quantum register consisting of a nitrogen-vacancy (NV) center electron spin and three nuclear spins. The QFT runs on the nuclear spins and serves to process the sensor - i.e., the NV electron spin signal. Specifically, we show the application of QFT for correlation spectroscopy, where the long correlation time benefits the use of the QFT in gaining maximum precision and dynamic range at the same time. We further point out the ability for demultiplexing the nuclear magnetic resonance (NMR) signals using QFT and demonstrate precision scaling with the number of used qubits. Our results mark the application of a complex quantum algorithm in sensing which is of particular interest for high dynamic range quantum sensing and nanoscale NMR spectroscopy experiments.
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    Fabrication and characterization of single-crystal diamond membranes for quantum photonics with tunable microcavities
    (2020) Heupel, Julia; Pallmann, Maximilian; Körber, Jonathan; Merz, Rolf; Kopnarski, Michael; Stöhr, Rainer; Reithmaier, Johann Peter; Hunger, David; Popov, Cyril
    The development of quantum technologies is one of the big challenges in modern research. A crucial component for many applications is an efficient, coherent spin-photon interface, and coupling single-color centers in thin diamond membranes to a microcavity is a promising approach. To structure such micrometer thin single-crystal diamond (SCD) membranes with a good quality, it is important to minimize defects originating from polishing or etching procedures. Here, we report on the fabrication of SCD membranes, with various diameters, exhibiting a low surface roughness down to 0.4 nm on a small area scale, by etching through a diamond bulk mask with angled holes. A significant reduction in pits induced by micromasking and polishing damages was accomplished by the application of alternating Ar/Cl2 + O2 dry etching steps. By a variation of etching parameters regarding the Ar/Cl2 step, an enhanced planarization of the surface was obtained, in particular, for surfaces with a higher initial surface roughness of several nanometers. Furthermore, we present the successful bonding of an SCD membrane via van der Waals forces on a cavity mirror and perform finesse measurements which yielded values between 500 and 5000, depending on the position and hence on the membrane thickness. Our results are promising for, e.g., an efficient spin–photon interface.
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    Algorithms and resources for quantum technology, sensing and random number generation
    (2020) Greiner, Johannes N.; Wrachtrup, Jörg (Prof. Dr.)
    This dissertation presents theoretical results as well as proposed and conducted experiments in the areas of Quantum Sensing, Quantum State Engineering, Bound Entanglement, Quantum Contextuality and Quantum Random Number Generation. A novel detection scheme to improve Quantum Sensing by indirect sensing with the help of an ancillary quantum system is introduced. Sensing information is shown to be obtainable both by direct and indirect sensors, even though their quantum states are not cloned or explicitly transferred. The steps of sensing an external signal and the transfer of information to an ancillary Qubit are combined in one asymmetric pulse sequence. Squeezed spin states, which are a well-known resource for Quantum Sensing due to their robustness to Decoherence, are also discussed. Particularly, their creation in systems of Nitrogen-Vacancy Centers (NVs) in diamond and surrounding nuclear spins, as well as ensembles of such NVs is implemented with specifically tailored sequences. In terms of Quantum State Engineering, a method to purify unpolarized Qubits surrounding and coupled to a central spin is introduced. Repeated projective measurements are used to instil a Zeno-like effect, extendable to a general unpolarized spin bath. Given a suitable trajectory of measurement outcomes, whose crucial role is explored, said projections are shown to enable driving the quantum states of the surrounding nuclear spins towards pure entangled states. Sufficient generality of the approach is shown by applying it to both NVs and superconducting qubits as physical systems. A wide range of target states of the environmental spins can be reached, including pairwise correlated Singlet states, while maximal entanglement is reachable. Advantages for Quantum Sensing granted by specific states obtained by the introduced Purficiation method are described. Concerning Qudits or quantum systems with arbitrarily high dimensionality as a resource, the possibility for generation and measurement of Bound Entanglement with NVs is investigated and an experimental implementation is proposed. Additionally, an experimental violation of a KCBS Inequality, in order to demonstrate Quantum Contextuality with NVs is proposed and details of an implementation are discussed. It is moreover shown how Contextuality can be used as a resource towards Certified Quantum Random Number generation with NVs. Other approaches to Quantum Random Number Generation are also introduced, including a standard single-photon Ansatz using NVs as well as a scheme utilizing the period-doubling state of an Optical Parametric Oscillator.
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    Spectroscopy and engineering of single rare-earth solid-state qubits
    (2020) Kornher, Thomas; Wrachtrup, Jörg (Prof. Dr.)
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    Coupling single electron spins to external degrees of freedom
    (2020) Oeckinghaus, Thomas; Wrachtrup, Jörg (Prof. Dr.)
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    Thermodynamics of quantum spin-bath depolarization
    (2023) Dasari, Durga Bhaktavatsala Rao
    We analyze here through exact calculations the thermodynamical effects in depolarizing a quantum spin-bath initially at zero temperature through a quantum probe coupled to an infinite temperature bath by evaluating the heat and entropy changes. We show that the correlations induced in the bath during the depolarizing process does not allow for the entropy of the bath to increase towards its maximal limit. On the contrary, the energy deposited in the bath can be completely extracted in a finite time. We explore these findings through an exactly solvable central spin model, wherein a central spin-1/2 system is homogeneously coupled to a bath of identical spins. Further, we show that, upon destroying these unwanted correlations, we boost the rate of both energy extraction and entropy towards their limiting values. We envisage that these studies are relevant for quantum battery research wherein both charging and discharging processes are key to characterizing the battery performance.