Preparation of pure and mixed polarization qubits and the direct measurement of figures of merit

Photodetector figures of merit in terms of POVMs

A photodetector may be characterized by various figures of merit such as response time, bandwidth, dark count rate, efficiency, wavelength resolution, and photon-number resolution. On the other hand, quantum theory says that any measurement device is fully described by its POVM, which stands for Positive-Operator-Valued Measure, and which generalizes the textbook notion of the eigenstates of the appropriate hermitian operator (the "observable") as measurement outcomes. Here we show how to define a multitude of photodetector figures of merit in terms of a given POVM. We distinguish classical an…

权衡品质因子下量子谐振子 Otto 发动机与制冷机的性能分析

Performance analysis of quantum harmonic Otto engine and refrigerator under a trade-off figure of merit

本文以效率与功输出（或性能系数与制冷负荷）乘积为权衡目标，解析分析绝热与突然切换频率调制下量子谐振 Otto 热机和制冷机的最优性能，发现权衡优化仅在绝热驱动下有利。

Figures of merit for quantum transducers

Recent technical advances have sparked renewed interest in physical systems that couple simultaneously to different parts of the electromagnetic spectrum, thus enabling transduction of signals between vastly different frequencies at the level of single photons. Such hybrid systems have demonstrated frequency conversion of classical signals and have the potential of enabling quantum state transfer, e.g., between superconducting circuits and traveling optical signals. This article describes a simple approach for the theoretical characterization of the performance of quantum transducers. Given th…

存在外磁场时自旋半量子热机在最大$\dotΩ$品质因数下的效率

Efficiency at maximum $\dotΩ$ figure of merit of a spin half quantum heat engine in the presence of external magnetic field

本文研究外磁场下以自旋半粒子为工质的有限时间量子热机，发现其在最大$\dotΩ$品质因数下的效率可超过已知界限并接近卡诺效率，表明粒子布居数的集体量子效应能显著提升热机性能。

基于群体编码的海森堡标度

Heisenberg scaling based on population coding

针对Fisher信息无法反映全局结构的问题，提出以互信息作为群体编码视角下的替代品质因数，并证明若干酉模型可实现海森堡标度。

Generalized figure of merit for qubit readout

Many promising approaches to fault-tolerant quantum computation require repeated quantum nondemolition (QND) readout of binary observables such as quantum bits (qubits). A commonly used figure of merit for readout performance is the error rate for binary assignment in a single repetition. However, it is known that this figure of merit is insufficient. Indeed, real-world readout outcomes are typically analog instead of binary. Binary assignment therefore discards important information on the level of confidence in the analog outcomes. Here, a generalized figure of merit that fully captures the …

Grover优值：用于NISQ时代量子后端表征的通用优值

GroverFigureOfMerit: An Agnostic Figure of Merit for Quantum Backend Characterization in the NISQ Era

针对NISQ时代量子后端选择难题，提出基于Grover算法的优值，结合成功概率与惩罚因素全面评估性能，经实验验证对多因素敏感，能统一区分后端性能，为量子计算后端表征提供新方法。

增强型Hong-Ou-Mandel流形及相同微环谐振器线性链的品质因数

Enhanced Hong-Ou-Mandel Manifolds and figures of merit for linear chains of identical micro-ring resonators

本文推导了相同微环谐振器线性链Hong-Ou-Mandel曲线的精确解析表达式，证明其高鲁棒性，并提出最小τ值、曲率和5%容差三个品质因数，用于指导线性链的设计与制造。

Thermoelectric coefficients and the figure of merit for large open quantum dots

We consider the thermoelectric response of chaotic or disordered quantum dots in the limit of phase-coherent transport, statistically described by random matrix theory. We calculate the full distribution of the thermoelectric coefficients (Seebeck $S$ and Peltier $Π$), and the thermoelectric figure of merit $ZT$, for large open dots at arbitrary temperature and external magnetic field, when the number of modes in the left and right leads ($N_{\rm L}$ and $N_{\rm R}$) are large. Our results show that the thermoelectric coefficients and $ZT$ are maximal when the temperature is half the Thouless …