Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
8 results
Search Results
Item Open Access Bell-state measurement exceeding 50% success probability with linear optics(2023) Bayerbach, Matthias J.; D’Aurelio, Simone E.; Loock, Peter van; Barz, StefanieItem Open Access 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.Item Open Access Single-band versus two-band description of magnetism in infinite-layer nickelates(2023) Plienbumrung, Tharathep; Daghofer, Maria; Morée, Jean-Baptiste; Oleś, Andrzej M.We present a weak-coupling analysis of magnetism in infinite-layer nickelates, where we compare a single-band description with a two-band model. Both models predict that (i) hybridization due to hopping is negligible, and (𝑖𝑖) the magnetic properties are characterized by very similar dynamic structure factors, 𝑆(𝑘⃗ ,𝜔), at the points (𝜋,𝜋,0) and (𝜋,𝜋,𝜋). This gives effectively a two-dimensional description of the magnetic properties.Item Open Access Correlations for computation and computation for correlations(2021) Demirel, Bülent; Weng, Weikai; Thalacker, Christopher; Hoban, Matty; Barz, StefanieQuantum correlations are central to the foundations of quantum physics and form the basis of quantum technologies. Here, our goal is to connect quantum correlations and computation: using quantum correlations as a resource for computation - and vice versa, using computation to test quantum correlations. We derive Bell-type inequalities that test the capacity of quantum states for computing Boolean functions within a specific model of computation and experimentally investigate them using 4-photon Greenberger-Horne-Zeilinger (GHZ) states. Furthermore, we show how the resource states can be used to specifically compute Boolean functions - which can be used to test and verify the non-classicality of the underlying quantum states. The connection between quantum correlation and computability shown here has applications in quantum technologies, and is important for networked computing being performed by measurements on distributed multipartite quantum states.Item Open Access Experimental anonymous conference key agreement using linear cluster states(2023) Rückle, Lukas; Budde, Jakob; Jong, Jarn de; Hahn, Frederik; Pappa, Anna; Barz, StefanieItem Open Access Non-adaptive measurement-based quantum computation on IBM Q(2023) Mackeprang, Jelena; Bhatti, Daniel; Barz, StefanieWe test the quantumness of IBM’s quantum computer IBM Quantum System One in Ehningen, Germany. We generate generalised n -qubit GHZ states and measure Bell inequalities to investigate the n -party entanglement of the GHZ states. The implemented Bell inequalities are derived from non-adaptive measurement-based quantum computation (NMQC), a type of quantum computing that links the successful computation of a non-linear function to the violation of a multipartite Bell-inequality. The goal is to compute a multivariate Boolean function that clearly differentiates non-local correlations from local hidden variables (LHVs). Since it has been shown that LHVs can only compute linear functions, whereas quantum correlations are capable of outputting every possible Boolean function it thus serves as an indicator of multipartite entanglement. Here, we compute various non-linear functions with NMQC on IBM’s quantum computer IBM Quantum System One and thereby demonstrate that the presented method can be used to characterize quantum devices. We find a violation for a maximum of seven qubits and compare our results to an existing implementation of NMQC using photons.Item Open Access Proximate ferromagnetic state in the Kitaev model material α-RuCl3(2021) Suzuki, H.; Liu, H.; Bertinshaw, J.; Ueda, K.; Kim, H.; Laha, S.; Weber, D.; Yang, Z.; Wang, L.; Takahashi, H.; Fürsich, K.; Minola, M.; Lotsch, Bettina V.; Kim, B. J.; Yavaş, H.; Daghofer, M.; Chaloupka, J.; Khaliullin, G.; Gretarsson, H.; Keimer, B.α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. We have quantified the spin Hamiltonian of α-RuCl3 by a resonant inelastic x-ray scattering study at the Ru L3 absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism - along with the Kitaev spin liquid - as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of α-RuCl3 in magnetic fields.Item Open Access Hardware-efficient preparation of architecture-specific graph states on near-term quantum computers(2025) Brandhofer, Sebastian; Polian, Ilia; Barz, Stefanie; Bhatti, DanielHighly entangled quantum states are an ingredient in numerous applications in quantum computing. However, preparing these highly entangled quantum states on currently available quantum computers at high fidelity is limited by ubiquitous errors. Besides improving the underlying technology of a quantum computer, the scale and fidelity of these entangled states in near-term quantum computers can be improved by specialized compilation methods. In this work, the compilation of quantum circuits for the preparation of highly entangled architecture-specific graph states is addressed by defining and solving a formal model, i.e., a form of discrete constraint optimization. Our model incorporates information about gate cancellations, gate commutations, and accurate gate timing to determine an optimized graph state preparation circuit. Up to now, these aspects have only been considered independently of each other, typically applied to arbitrary quantum circuits. We quantify the quality of a generated state by performing stabilizer measurements and determining its fidelity. We show that our new method reduces the error when preparing a seven-qubit graph state by 3.5x on average compared to the state-of-the-art Qiskit solution. For a linear eight-qubit graph state, the error is reduced by 6.4x on average. The presented results highlight the ability of our approach to prepare higher fidelity or larger-scale graph states on gate-based quantum computing hardware.