The Quantum Bridge

Dong Xie, Chunling Xu, Xiwei Yao +1 more

The quantum version of a special classical Wheatstone bridge built with a boundary-driven spin system has recently been proposed. We propose a quantum Wheatstone bridge consisting of Bose systems, which can simulate the general classical Wheatstone bridge. Unknown coupling can be obtained when the quantum Wheatstone bridge is balanced, which can be determined simply by homodyne detection. When the expectation value of the homodyne detection is 0, the quantum Wheatstone bridge is unbalanced. When the expectation value of the homodyne detection is proportional to the square root of the initial number of bosons by regulating a known coupling strength, the quantum Wheatstone bridge is balanced. By calculating the quantum Fisher information, we show that the measurement precision is optimal when the quantum Wheatstone bridge is balanced. And the homodyne detection is close to the optimal measurement in the case of low-temperature baths.

Alexa Keating

Aleksey N. Bolgar, Daria A. Kalacheva, Viktor B. Lubsanov +4 more

Air-bridges play a crucial role in the performance of microwave circuits integrated with superconducting quantum bits, and their mechanical stability is important for reliable operation. This study is devoted to the technological issues that lead to air-bridge instability. We propose an optimized bridge geometry designed to improve the mechanical properties. Through systematic testing, we established that bridges incorporating this novel geometry achieved complete stability for lengths up to 170μm in our technological processes. The findings provide insight into the problem and a practical solution for technologists facing the challenges of the air-bridge stability. The implementation of our technology has the potential to improve significantly the mechanical robustness of air-bridges in multi-qubit circuits for quantum computations.

Kenneth J. Epstein

Yoshihito Kawanishi

13-Apr-2026(V1.0): Gamma-DG and the Quantum–Spacetime Bridge: Toward a Unified Structural Theory This paper develops an original structural framework, Gamma-DG, for the quantum–spacetime bridge. The central problem is not merely how to connect a quantum-primitive foundational layer and a relativistically readable spacetime layer, but how to describe a controlled, admissible, and structurally coherent passage between these distinct regimes. The paper formulates a unified perspective in which bridge formation, bridge validation, and bridge culmination are treated as successive aspects of a single theoretical program. Core I and Core II provide the foundational basis of the framework, while the present paper focuses on the minimal structural ideas needed for the current synthesis.

Travis S. Taylor