Kaur Kuljeet, Sépulcre Théo, Roch Nicolas, Snyman Izak, Florens Serge, Bera Soumya
Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India.
Univ. Grenoble Alpes, CNRS, Institut Néel, F-38000 Grenoble, France.
Phys Rev Lett. 2021 Dec 3;127(23):237702. doi: 10.1103/PhysRevLett.127.237702.
Superconducting circuits are currently developed as a versatile platform for the exploration of many-body physics, by building on nonlinear elements that are often idealized as two-level qubits. A classic example is given by a charge qubit that is capacitively coupled to a transmission line, which leads to the celebrated spin-boson description of quantum dissipation. We show that the intrinsic multilevel structure of superconducting qubits drastically restricts the validity of the spin-boson paradigm due to phase localization, which spreads the wave function over many charge states. Numerical renormalization group simulations also show that the quantum critical point moves out of the physically accessible range in the multilevel regime. Imposing charge discreteness in a simple variational state accounts for these multilevel effects, which are relevant for a large class of devices.
超导电路目前正被开发为一个用于探索多体物理的通用平台，它基于通常被理想化为两能级量子比特的非线性元件。一个典型例子是通过电容耦合到传输线的电荷量子比特给出的，这导致了著名的量子耗散自旋 - 玻色子描述。我们表明，由于相位局域化，超导量子比特的固有多能级结构极大地限制了自旋 - 玻色子范式的有效性，相位局域化会使波函数扩展到许多电荷态上。数值重整化群模拟还表明，在多能级 regime 中量子临界点移出了物理可及范围。在一个简单变分态中引入电荷离散性可以解释这些多能级效应，这些效应与一大类器件相关。
