Universität Stuttgart

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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Zentrum für integrierte Quantenwissenschaft und -technologie (IQST)Institute: search.filters.UBSInstitut.Max-Planck-Institut für Festkörperforschung

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Now showing 1 - 6 of 6
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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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    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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    Character of doped holes in Nd1-xSrxNiO2
    (2021) Plienbumrung, Tharathep; Schmid, Michael Thobias; Daghofer, Maria; Oleś, Andrzej M.
    We investigate charge distribution in the recently discovered high-𝑇𝑐 superconductors, layered nickelates. With increasing value of charge-transfer energy, we observe the expected crossover from the cuprate to the local triplet regime upon hole doping. We find that the 𝑑-𝑝 Coulomb interaction 𝑈𝑑𝑝 makes Zhang-Rice singlets less favorable, while the amplitude of local triplets at Ni ions is enhanced. By investigating the effective two-band model with orbitals of 𝑥2-𝑦2 and s symmetries we show that antiferromagnetic interactions dominate for electron doping. The screened interactions for the s band suggest the importance of rare-earth atoms in superconducting nickelates.
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    Quantum nonlinear spectroscopy of single nuclear spins
    (2022) Meinel, Jonas; Vorobyov, Vadim; Wang, Ping; Yavkin, Boris; Pfender, Mathias; Sumiya, Hitoshi; Onoda, Shinobu; Isoya, Junichi; Liu, Ren-Bao; Wrachtrup, Jörg
    Conventional nonlinear spectroscopy, which use classical probes, can only access a limited set of correlations in a quantum system. Here we demonstrate that quantum nonlinear spectroscopy, in which a quantum sensor and a quantum object are first entangled and the sensor is measured along a chosen basis, can extract arbitrary types and orders of correlations in a quantum system. We measured fourth-order correlations of single nuclear spins that cannot be measured in conventional nonlinear spectroscopy, using sequential weak measurement via a nitrogen-vacancy center in diamond. The quantum nonlinear spectroscopy provides fingerprint features to identify different types of objects, such as Gaussian noises, random-phased AC fields, and quantum spins, which would be indistinguishable in second-order correlations. This work constitutes an initial step toward the application of higher-order correlations to quantum sensing, to examining the quantum foundation (by, e.g., higher-order Leggett-Garg inequality), and to studying quantum many-body physics.
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    Nanoscale mapping of magnetic auto-oscillations with a single spin sensor
    (2025) Hache, Toni; Anshu, Anshu; Shalomayeva, Tetyana; Richter, Gunther; Stöhr, Rainer; Kern, Klaus; Wrachtrup, Jörg; Singha, Aparajita
    Spin Hall nano-oscillators convert DC to magnetic auto-oscillations in the microwave regime. Current research on these devices is dedicated to creating next-generation energy-efficient hardware for communication technologies. Despite intensive research on magnetic auto-oscillations within the past decade, the nanoscale mapping of those dynamics remained a challenge. We image the distribution of free-running magnetic auto-oscillations by driving the electron spin resonance transition of a single spin quantum sensor, enabling fast acquisition (100 ms/pixel). With quantitative magnetometry, we experimentally demonstrate for the first time that the auto-oscillation spots are localized at magnetic field minima acting as local potential wells for confining spin-waves. By comparing the magnitudes of the magnetic stray field at these spots, we decipher the different frequencies of the auto-oscillation modes. The insights gained regarding the interaction between auto-oscillation modes and spin-wave potential wells enable advanced engineering of real devices.
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    Cyclic cooling of quantum systems at the saturation limit
    (2021) Zaiser, Sebastian; Cheung, Chun Tung; Yang, Sen; Dasari, Durga; Raeisi, Sadegh; Wrachtrup, Jörg
    The achievable bounds of cooling quantum systems, and the possibility to violate them is not well-explored experimentally. For example, among the common methods to enhance spin polarization (cooling), one utilizes the low temperature and high-magnetic field condition or employs a resonant exchange with highly polarized spins. The achievable polarization, in such cases, is bounded either by Boltzmann distribution or by energy conservation. Heat-bath algorithmic cooling schemes (HBAC), on the other hand, have shown the possibility to surpass the physical limit set by the energy conservation and achieve a higher saturation limit in spin cooling. Despite, the huge theoretical progress, and few principle demonstrations, neither the existence of the limit nor its application in cooling quantum systems towards the maximum achievable limit have been experimentally verified. Here, we show the experimental saturation of the HBAC limit for single nuclear spins, beyond any available polarization in solid-state spin system, the Nitrogen-Vacancy centers in diamond. We benchmark the performance of our experiment over a range of variable reset polarizations (bath temperatures), and discuss the role of quantum coherence in HBAC.