Entanglement robustness in trace decreasing quantum dynamics caused by depolarization and polarization dependent losses

Capacity of trace decreasing quantum operations and superadditivity of coherent information for a generalized erasure channel

Losses in quantum communication lines severely affect the rates of reliable information transmission and are usually considered to be state-independent. However, the loss probability does depend on the system state in general, with the polarization dependent losses being a prominent example. Here we analyze biased trace decreasing quantum operations that assign different loss probabilities to states and introduce the concept of a generalized erasure channel. We find lower and upper bounds for the classical and quantum capacities of the generalized erasure channel as well as characterize its de…

Trace decreasing quantum dynamical maps: Divisibility and entanglement dynamics

Trace decreasing quantum operations naturally emerge in experiments involving postselection. However, the experiments usually focus on dynamics of the conditional output states as if the dynamics were trace preserving. Here we show that this approach leads to incorrect conclusions about the dynamics divisibility, namely, one can observe an increase in the trace distance or the system-ancilla entanglement although the trace decreasing dynamics is completely positive divisible. We propose solutions to that problem and introduce proper indicators of the information backflow and the indivisibility…

Semi-Loss-Tolerant Strong Coin Flipping Protocol Using EPR Pairs

In this paper, we present a quantum strong coin flipping protocol. In this protocol, an EPR pair and a quantum memory storage are made use of, and losses in the quantum communication channel and quantum memory storage are all analyzed. We obtain the bias in the fair scenario as a function of $p$, where $p$ is the probability that the particle in Bob's quantum memory storage is lost, which means our bias varies as the degree of losses in the quantum memory storage changes. Therefore we call our protocol semi-loss-tolerant. We also show that the bias decreases with decreasing $p$. When $p$ appro…

减轻与缺陷模式强耦合的超导量子比特的损耗

Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes

该研究通过92个可调频量子比特的交换光谱量化强耦合缺陷模式，并结合热循环、约瑟夫森结尺寸缩小与表面清洗实验，证明减小结尺寸可降低此类损耗。

利用偏振纠缠光子对进行量子照明以增强目标检测

Quantum illumination using polarization-entangled photon pairs for enhanced object detection

本文实验证明偏振纠缠光子对量子照明可检测反射率低至0.05、信噪比0.003的目标，CHSH类关联度量对损耗噪声鲁棒，并能估计反射率。

Robust cryogenic matched low-pass coaxial filters for quantum computing applications

Electromagnetic noise is one of the key external factors decreasing superconducting qubits coherence. Matched coaxial filters can prevent microwave and IR photons negative influence on superconducting quantum circuits. Here, we report on design and fabrication route of matched low-pass coaxial filters for noise-sensitive measurements at milliKelvin temperatures. A robust transmission coefficient with designed linear absorption (-1dB/GHz) and ultralow reflection losses less than -20 dB up to 20 GHz is achieved. We present a mathematical model for evaluating and predicting filters transmission p…