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Entanglement Quantification in Low-Temperature Superconducting Flux Qubits

Jianxin Shi

Published Sep 1, 2025• 0 citations
Publisher

Abstract

Abstract This study aims to quantify entanglement in low-temperature superconducting flux qubits using mutual information and concurrence. It presents a theoretical framework, experimental setup for two-qubit systems, and simulations. Results show that the entanglement strength varies periodically with external magnetic flux and saturates with increasing inter-qubit coupling. These results offer guidance for optimizing superconducting quantum circuits in various quantum information processing applications.

DOI
10.21203/rs.3.rs-7336880/v1

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Quantum entanglement is a cornerstone of quantum information science, enabling advancements in quantum computing, cryptography, and metrology. We report a comprehensive experimental study of quantum entanglement in a superconducting circuit comprising two transmon qubits coupled via a tunable bus resonator, operating at ultra-low temperatures (10 mK) in a dilution refrigerator. Using precise microwave control, we generate Bell states with a fidelity of 0.94 ± 0.02 and a concurrence of 0.92 ± 0.03, confirming robust entanglement. Quantum state tomography and coherence measurements yield energy relaxation (T1) times of 92 ± 5 µs and 88 ± 4 µs, and dephasing (T2) times of 85 ± 6 µs and 82 ± 5 µs for qubits Q1 and Q2, respectively, at 10 mK. We systematically investigate the impact of temperature (10 mK, 50 mK, 100 mK) and environmental noise on entanglement persistence. Real-time analysis of recent literature and social media discussions highlights ongoing challenges in scaling superconducting qubit systems due to 1/f noise and material limitations. Our findings demonstrate the viability of superconducting circuits for high-fidelity quantum operations and provide critical insights into optimizing coherence at millikelvin temperatures.
Abstract Superconducting charge qubits represent a cutting-edge technology in the field of quantum computing, offering a promising platform for quantum processing. This study delves into the behaviors of thermal coherence and quantum correlations within a two-superconducting charge qubit system coupled by a fixed capacitance. Specifically, we investigate the effects of thermal noise on entanglement (measured by concurrence), nonclassical correlations (quantified by local quantum uncertainty), and quantum coherence (measured by correlated coherence) within the two-superconducting charge qubit capacitively coupled. Our analysis takes into account the interplay between the equilibrium temperature of the reservoir and various system parameters. Our findings demonstrate that an increase in temperature leads to a decrease in coherence and quantum correlations within the considered system. However, the behavior of these quantum resources is heavily dependent on the system parameters, and a careful selection of these parameters can help mitigate the negative effects of absolute temperature. Additionally, we observe that local quantum uncertainty and correlated coherence are more resilient than thermal entanglement to rising temperatures. These results provide insight into how a two-superconducting charge qubit system can be optimized for achieving quantum advantages.