Efficient bounds on quantum communication rates via their reduced variants

Multiparty quantum secret sharing of secure direct communication

Based on the two-step protocol [Phys. Rev. A68(03)042317], we propose a $(n,n)$-threshold multiparty quantum secret sharing protocol of secure direct communication. In our protocol only all the sharers collaborate can the sender's secure direct communication message be extracted. We show a variant version of this protocol based on the variant two-step protocol. This variant version can considerably reduce the realization difficulty in experiment. In contrast to the use of multi-particle GHZ states in the case that the sharer number is larger than 3, the use and identification of Bell states ar…

Relativistic Doppler effect in quantum communication

When an electromagnetic signal propagates in vacuo, a polarization detector cannot be rigorously perpendicular to the wave vector because of diffraction effects. The vacuum behaves as a noisy channel, even if the detectors are perfect. The ``noise'' can however be reduced and nearly cancelled by a relative motion of the observer toward the source. The standard definition of a reduced density matrix fails for photon polarization, because the transversality condition behaves like a superselection rule. We can however define an effective reduced density matrix which corresponds to a restricted cl…

Quantum Secure Communication with W States

A W state is pair-wisely entangled, belonging to the different class from Greenberger, Horne, and Zeilinger (GHZ) state. We show that the W state enables three variant protocols, that is, quantum key distribution between several parts, quantum secret sharing, and both of them at the same time. It is discussed how one's cheating can be detected in each protocol.

纠缠辅助越多，经典通信轮次越少

More assistance of entanglement, less rounds of classical communication

针对LOCC局域分辨量子态的轮次数问题，本文研究纯两体正交态轮次关系，以d⊗d正交乘积态为例，展示其无纠缠需2d-2轮、1-e比特纠缠辅助降至d且更多纠缠可进一步减少，证明轮次数与纠缠辅助量相关。

突破散粒噪声极限：用于量子优化的缓存回收方差缩减梯度

Breaking the Shot-Noise Barrier: Cached Recycled Variance-Reduced Gradients for Quantum Optimization

针对变分量子算法中梯度估计的精度与成本矛盾，提出缓存回收方差缩减梯度（CRVG），通过中心点缓存和测量回收降低电路复杂度25%，并在理论上给出更优的样本复杂度，实验验证其在特定电路上的优势。

Experimental demonstration of single-shot quantum and classical signal transmission on single wavelength optical pulse

Advances in highly sensitive detection techniques for classical coherent communication systems have reduced the received signal power requirements to a few photons per bit. At this level one can take advantage of the quantum noise to create secure communication, using continuous variable quantum key distribution (CV-QKD). In this work therefore we embed CV-QKD signals within classical signals and transmit classical data and secure keys simultaneously over 25km of optical fibre. This is achieved by using a novel coherent displacement state generator, which has the potential for being used in a …