Testing Bell's inequality in constantly coupled Josephson circuits by effective single-qubit operations

Macroscopic Einstein-Podolsky-Rosen pairs in superconducting circuits

We propose an efficient approach to prepare Einstein-Podolsky-Rosen (EPR) pairs in currently existing Josephson nanocircuits with capacitive couplings. In these fixed coupling circuits, two-qubit logic gates could be easily implemented while, strictly speaking, single-qubit gates cannot be easily realized. For a known two-qubit state, conditional single-qubit operation could still be designed to evolve only the selected qubit and keep the other qubit unchanged; the rotation of the selected qubit depends on the state of the other one. These conditional single-qubit operations allow to determini…

可分析的两量子超导哈密顿量下贝尔态相干演变的C_{l_1}范数

Analytic $C_{\ell_1}$ norm of Coherence Evolution for Bell States under a Two-Qubit Superconducting Hamiltonian

本文研究了两量子超导系统中单位元相干动力学，通过推导完整时间演化算符和传播贝尔态初始条件，得到闭合形式的时间依赖纯态密度矩阵和C_{l_1}范数的解析表达式，揭示了两种贝尔态在动态下保持恒定相干，而另外两种则表现出参数依赖的相干振荡。

Decay of nonlocality due to adiabatic and quantum noise in the solid state

We study the decay of quantum nonlocality, identified by the violation of the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality, for two noninteracting Josephson qubits subject to independent baths with broadband spectra typical of solid state nanodevices. The bath noise can be separated in an adiabatic (low-frequency) and in a quantum (high-frequency) part. We point out the qualitative different effects on quantum nonlocal correlations induced by adiabatic and quantum noise. A quantitaive analysis is performed for typical noise figures in Josephson systems. Finally we compare, for this system…

拓扑保护的贝尔-猫态在简单自旋模型中

Topologically protected Bell-cat states in a simple spin model

该研究在简单自旋模型中发现拓扑保护的贝尔-猫态，通过驱动中心自旋实现其渐进创建和移动，并探讨其对噪声的鲁棒性。

Superconducting Qubits Coupled to Nanoelectromechanical Resonators: An Architecture for Solid-State Quantum Information Processing

We describe the design for a scalable, solid-state quantum-information-processing architecture based on the integration of GHz-frequency nanomechanical resonators with Josephson tunnel junctions, which has the potential for demonstrating a variety of single- and multi-qubit operations critical to quantum computation. The computational qubits are eigenstates of large-area, current-biased Josephson junctions, manipulated and measured using strobed external circuitry. Two or more of these phase qubits are capacitively coupled to a high-quality-factor piezoelectric nanoelectromechanical disk reson…

Stationary entanglement and nonlocality of two qubits or qutrits collectively interacting with the thermal environment: The role of Bell singlet state

We investigate the stationary entanglement and stationary nonlocality of two qubits collectively interacting with a common thermal environment. We assume two qubits are initially in Werner state or Werner-like state, and find that thermal environment can make two qubits become stationary nonlocality. The analytical relations among average thermal photon number of the environment, entanglement and nonlocality of two qubits are given in details. It is shown that the fraction of Bell singlet state plays a key role in the phenomenon that the common thermal reservoir can enhance the entanglement of…

利用猫态和时间维度的Bell不等式检验宏观定域实在性

Testing macroscopic local realism using cat-states and Bell inequalities in time

该研究提出基于时间维度Bell不等式的宏观定域实在性检验方法，定义M-标度定域实在性，通过两类非线性相互作用系统的时间演化选择实现Bell违反，可支持宏观尺度的量子非定域性验证。