Research Project: Kuantum Metrolojide Sınır Etkileri
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Contributors
Funders
ID
TB.00780
Authors
Müstecaplıoğlu, Özgür Esat
Faculty Member
Publications
Optimal strategies for transient and equilibrium quantum thermometry using Gaussian and non-Gaussian probes
(American Physical Society, 2025) Ullah, Asghar; Müstecaplıoğlu, Özgür Esat; Ullah, Asghar; Naseem, M. Tahir; Department of Physics; Yes; College of Sciences
We study temperature estimation using quantum probes, including single-mode initial states and two-mode states generated via stimulated parametric down-conversion in a nonlinear crystal at finite temperature. We explore both transient and equilibrium regimes and compare the performance of Gaussian and non-Gaussian probe states for temperature estimation. In the nonequilibrium regime, we show that single-mode non-Gaussian probe states-such as Fock, odd cat, and Gottesman-Kitaev-Preskill states-can significantly enhance the speed of estimation, particularly at short interaction times. In the two-mode setting, entangled states such as the two-mode squeezed vacuum, NOON state, and entangled cat state can enable access to temperature information at earlier times. In the equilibrium regime, we analyze temperature estimation using two-mode squeezed thermal states, which outperform single-mode strategies. We evaluate practical measurement strategies and find that energy-based observables yield optimal precision, population difference observables provide near-optimal precision, while quadrature-based measurements are suboptimal. The precision gain arises from squeezing, which suppresses fluctuations in the population difference.
Spin squeezing enhanced quantum magnetometry with nitrogen-vacancy center qutrits
(Iop Publishing Ltd, 2025) Gassab, Lea; Müstecaplıoğlu, Özgür Esat; Gassab, Lea; Department of Physics; Yes; College of Sciences
We explore the utility of quantum spin squeezing in quantum magnetometry, focusing on three-level (qutrit) Nitrogen-Vacancy (NV) centers within diamond, utilizing a standard Ramsey interferometry pulse protocol. Our investigation incorporates the effects of dephasing and relaxation on NV centers' dynamics during Ramsey measurements, modeled via the Lindblad quantum master equation. We conduct a comparative analysis between the metrological capabilities of a single NV center and a pair of NV centers, considering quantum Fisher information both with and without spin squeezing. The quantum correlations between NV centers are assessed through the evaluation of the Kitagawa-Ueda spin squeezing parameter within a two-level manifold. Additionally, parallel calculations are conducted using a two-level model (qubit) for NV centers. Our findings reveal that leveraging qutrits and spin squeezing yields enhanced magnetometric precision, albeit constrained by dephasing effects. Nevertheless, even in the absence of dynamical decoupling methods to mitigate environmental dissipation, strategic timing of squeezing and free evolution can sustain the advantages of qutrit-based magnetometry.
Quantum thermometry for ultra-low temperatures using probe and ancilla qubit chains
(MDPI, 2025) Ullah, Asghar; Müstecaplıoğlu, Özgür Esat; Ullah, Asghar; Upadhyay, Vipul; Department of Physics; Yes; College of Sciences
We propose a scheme to enhance the range and precision of ultra-low temperature measurements by employing a probe qubit coupled to a chain of ancilla qubits. Specifically, we analyze a qubit chain governed by Heisenberg XX and Dzyaloshinskii-Moriya (DM) interactions. The precision limits of temperature measurements are characterized by evaluating quantum Fisher information (QFI). Our findings demonstrate that the achievable precision bounds, as well as the number of peaks in the QFI as a function of temperature, can be controlled by adjusting the number of ancilla qubits and the system's model parameters. These results are interpreted in terms of the influence of energy transitions on the range and the number of QFI peaks as a function of temperature. This study highlights the potential of the probe qubit-ancilla chain system as a powerful and precise tool for quantum thermometry in the ultra-low temperature regime.
Steady-state entanglement generation via casimir-polder interactions
(Nature Research, 2025) Izadyari, Mohsen; Müstecaplıoğlu, Özgür Esat; Izadyari, Mohsen; Pusuluk, Onur; Sinha, Kanu; Department of Physics; Yes; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Sciences
We investigate the generation of steady-state entanglement between two atoms resulting from the fluctuation-mediated Casimir-Polder (CP) interactions near a surface. Starting with an initially separable state of the atoms, we analyze the atom-atom entanglement dynamics for atoms placed at distances in the range of nm away from a planar medium, examining the effect of medium properties and geometrical configuration of the atomic dipoles. We show that perfectly conducting and superconducting surfaces yield an optimal steady-state concurrence value of approximately 0.5. Furthermore, although the generated entanglement decreases with medium losses for a metal surface, we identify an optimal distance from the metal surface that assists in entanglement generation by the surface. While fluctuation-mediated interactions are typically considered detrimental to the coherence of quantum systems at nanoscales, our results demonstrate a mechanism for leveraging such interactions for entanglement generation. © 2025 Elsevier B.V., All rights reserved.
Configuration-dependent precision in magnetometry and thermometry using multiqubit quantum sensors
(American Physical Society, 2026) Ullah, Asghar; Müstecaplıoğlu, Özgür Esat; Ullah, Asghar; Paris, Matteo G. A.; Department of Physics; Yes; College of Sciences
We study the performance of quantum sensors composed of four qubits arranged in different geometries for magnetometry and thermometry. The qubits interact via the transverse-field Ising model with both ferromagnetic and antiferromagnetic couplings, maintained in thermal equilibrium with a heat bath under an external magnetic field. Using quantum Fisher information, we evaluate the metrological precision of these sensors. For ferromagnetic couplings, weakly connected graphs (e.g., the chain graph P4) perform optimally in estimating weak magnetic fields, whereas highly connected graphs (e.g., the complete graph K4) excel at strong fields. Conversely, K4 achieves the highest sensitivity for temperature estimation in the weak-field regime. In the antiferromagnetic case, we uncover a fundamental trade-off dictated by spectral degeneracy: Configurations with nondegenerate energy spectra, such as the panlike graph (three qubits in a triangle with the fourth attached), exhibit strong-magnetic-field sensitivity due to their pronounced response to perturbations. In contrast, symmetric structures like the square graph, featuring degenerate energy levels (particularly ground-state degeneracy), are better suited for precise thermometry. Notably, our four-qubit sensors achieve peak precision in the low-temperature weak-field regime. Finally, we introduce a spectral sensitivity measure that quantifies energy spectrum deformations under small perturbations, providing a simple heuristic indicator of metrological sensitivity.
