We propose a quantum Wheatstone bridge as a fully quantum analogue to the classical version. The bridge is a few-body boundary-driven spin chain exploiting quantum effects to gain an enhanced sensitivity to an unknown coupling. The sensitivity is explained by a drop in population of an entangled Bell state due to destructive interference as the controllable coupling approaches the unknown coupling. A simple criteria for the destructive interference is found, and an approximate expression for the width of the drop is derived. The sensitivity to the unknown coupling is quantified using the quantum Fisher information, and we show that the state of the bridge can be measured indirectly through the spin current. Our results are robust towards calibration errors and generic in the sense that several of the current state-of-the-art quantum platforms could be used as a means of realization. The quantum Wheatstone bridge may thus find use in fields such as sensing and metrology using near-term quantum devices.
Optimal control theory for measured quantum Schrödinger bridges
Graduate School of Information Sciences, Tohoku University（东北大学情报科学研究院）；Department of Physics, Institute of Science Tokyo（东京科学大学物理学系）；Research and Education Institute for Semiconductors and Informatics, Kumamoto University（熊本大学半导体与信息学研究教育院）；Sigma-i Co., Ltd.（Sigma-i有限公司）；Institute for Quantum Studies, Chapman University（查普曼大学量子研究学院）；The Kennedy Chair in Physics, Chapman University（查普曼大学肯尼迪物理学讲席）；Department of Physics and Astronomy, University of Rochester（罗切斯特大学物理与天文系）
In superconducting quantum devices, air bridges enable increased circuit complexity and density as well as mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from $20~μm$ to $100~μm$, with a yield exceeding $99~\%$ for lengths up to $36~μm$. When used to connect ground planes in coplanar waveguide resonators, the induced loss contributed to the system is negligible, corresponding to a reduction of the quality factor exceeding $1.0\ti…
阐述了M. Pavon，J.Math.Phys.40（1999），5565-5577中，我们在Nelson随机力学中发展了一个简化版本的变分原理，它在位置测量后产生冯诺依曼波包约化。这个随机控制问题与薛定谔桥的问题相似，但运动学不同。这给了一个深刻的意义是什么观察到的薛定谔在1931年关于薛定谔桥：“Merkwuerdige Analogien zur Quantenmechanik，模具mir sehr des Hindenkens wert erscheinen”。
Closed Quantum Boltzmann Bridges: Coherent Revivals, Hidden Microstates, and the Emergence of Classical Two-Time Entropy Conditioning
University of Western Ontario（韦仕敦大学）；National Research Council Canada（加拿大国家研究委员会）；Institut für Physik und Astronomie, Technische Universität Berlin（柏林工业大学物理与天文研究所）
We present a single-exposure fabrication technique for a very large array of microscopic air-bridges using a tri-layer resist process with electron-beam lithography. The technique is capable of forming air-bridges with strong metal-metal or metal-substrate connections. This was demonstrated by its application in an electron tunnelling device consisting of 400 identical surface gates for defining quantum wires, where the air-bridges are used as suspended connections for the surface gates. This technique enables us to create a large array of uniform one-dimensional channels that are open at both…
Coherent Quantum Schrodinger Bridge: Two-Boundary Optimal Control for Quantum Algorithm Design
Graduate School of Information Sciences, Tohoku University（东北大学信息科学研究院）；Department of Physics, Institute of Science（理学院物理系）；Research and Education Institute for Semiconductors and Informatics, Kumamoto University（熊本大学半导体与信息研究教育学院）；Sigma-i Co., Ltd.（Sigma-i有限公司）
Universität des Saarlandes（萨尔兰大学）；Institut de Mathématiques de Toulouse, Université Paul Sabatier（图卢兹数学研究所，保罗·萨巴蒂尔大学）；Ruhr-Universität Bochum（波鸿鲁尔大学）；QMATH, Dept. Math. Sci., U. of Copenhagen（哥本哈根大学数学科学系 QMATH 中心）
We consider graphs with two cut vertices joined by a path with one or two edges, and prove that there can be no quantum perfect state transfer between these vertices, unless the graph has no other vertex. We achieve this result by applying the 1-sum lemma for the characteristic polynomial of graphs, the neutrino identities that relate entries of eigenprojectors and eigenvalues, and variational principles for eigenvalues (Cauchy interlacing, Weyl inequalities and Wielandt minimax principle). We see our result as an intermediate step to broaden the understanding of how connectivity plays a key r…
In this paper, we formally describe the three challenges of mapping surface code on superconducting devices, and present a comprehensive synthesis framework to overcome these challenges. The proposed framework consists of three optimizations. First, we adopt a geometrical method to allocate data qubits which ensures the existence of shallow syndrome extraction circuit. The proposed data qubit layout optimization reduces the overhead of syndrome extraction and serves as a good initial point for following optimizations. Second, we only use bridge qubits enclosed by data qubits and reduce the num…
Out-of-time-order correlators bridge classical transport and quantum dynamics
University of California Berkeley（加州大学伯克利分校）；Stanford University（斯坦福大学）；North Carolina State University（北卡罗来纳州立大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Tulane University（杜兰大学）
We have shown that quantum systems on finite-dimensional Hilbert spaces are equivalent under local transformations. Using these transformations give rise to a gauge group that connects the hamiltonian operators associated with each quantum system. Different quantum systems are connected in such way that studying one of them allows to understand the other. This result can be applied to the field of simulation of quantum systems, in order to mimic more complicated quantum systems from another simulatable quantum system. Given that there is a bridge that allows to simulate a particular quantum sy…
In this essay a quantum-dualistic, perspectival and synchronistic interpretation of quantum mechanics is further developed in which the classical world-from-decoherence which is perceived (decoherence) and the perceived world-in-consciousness which is classical (collapse) are not necessarily identified. Thus, Quantum Reality or "{\it unus mundus}" is seen as both i) a physical non-perspectival causal Reality where the quantum-to-classical transition is operated by decoherence, and as ii) a quantum linear superposition of all classical psycho-physical perspectival Realities which are governed b…
Exact Solutions to the Quantum Schrödinger Bridge Problem
Machine Learning Research, Pfizer Bristol-Myers Squibb, ML Research Cambridge（机器学习研究部，辉瑞百灵益泰，ML研究剑桥）；Pfizer Worldwide Research Development and Medical（辉瑞全球研发与医疗）；Machine Learning Research group, Cambridge, MA, USA（机器学习研究组，剑桥，马萨诸塞州，美国）
We analyze a coupling scheme for qubits in different cavities of circuit-QED architecture. In contrast to the usual scheme where the cavities are coupled by an interface capacitance we employ a bridge qubit connecting cavities to mediate two-qubit coupling. This active coupling scheme makes it possible to switch on/off and adjust the strength of qubit-qubit coupling, which is essential for scalability of quantum circuit. By transforming the Hamiltonian we obtain an exact expression of two-qubit coupling in the rotating-wave approximation. For the general case of $n$ qubits the Hamiltonian can …
