Quantum-type Coherence as a Combination of Symmetry and Semantics

Pure down-conversion photons through sub-coherence length domain engineering

Photonic quantum technology relies on efficient sources of coherent single photons, the ideal carriers of quantum information. Heralded single photons from parametric down-conversion can approximate on-demand single photons to a desired degree, with high spectral purities achieved through group-velocity matching and tailored crystal nonlinearities. Here we propose crystal nonlinearity engineering techniques with sub-coherence-length domains. We first introduce a combination of two existing methods: a deterministic approach with coherence-length domains and probabilistic domain-width annealing.…

Skew information-based coherence generating power of quantum channels

We study the ability of a quantum channel to generate quantum coherence when it applies to incoherent states. We define the measure of coherence generating power (CGP) for a generic quantum channel to be the average coherence generated by the quantum channel acting on a uniform ensemble of incoherent states based on the skew information-based coherence measure. We present explicitly the analytical formulae of the CGP for any arbitrary finite dimensional unitary channels. We derive the mean value of the CGP over the unitary groups and investigate the typicality of the normalized CGP. Furthermor…

On coherence of quantum operations by using Choi-Jamiołkowski isomorphism

In quantum information, most information processing processes involve quantum channels. One manifestation of a quantum channel is quantum operation acting on quantum states. The coherence of quantum operations can be considered as a quantum resource, which can be exploited to perform certain quantum tasks. From the viewpoint of Choi-Jamiołkowski isomorphism, we study the coherence of quantum operations in the framework of resource theory. We define the phase-out superoperation and give the operation which transforms the Choi-Jamiołkowski state of a quantum operation to the Choi-Jamiołkowski st…

相干性对驱动量子系统中非平衡热力学过程贡献的实验研究

Experimental investigation of coherence contributions to a nonequilibrium thermodynamic process in a driven quantum system

该研究在NMR量子处理器中实验探索了驱动量子系统的非平衡热力学过程，揭示了相干性生成对不可逆熵产生的贡献，并验证了不可逆熵产生具有下界的广义克劳修斯不等式。

Effects of photo-neutralization on the emission properties of quantum dots

In this paper we investigate the coherence properties of a quantum dot under two-photon resonant excitation in combination with an additional photo-neutralization laser. The photo-neutralization increases the efficiency of the excitation process and thus, the brightness of the source, by a factor of approximately 1.5 for biexciton-exciton pairs. This enhancement does not degrade the relevant coherences in the system; neither the single photon coherence time, nor the coherence of the excitation process.

Comment on "Quantum Coherence and Sensitivity of Avian Magnetoreception"

In a recent Letter [Phys. Rev. Lett. 109, 110502 (2012), arXiv:1204.6528], Bandyopadhyay, Paterek and Kaszlikowski report their analysis of spin coherence time in the radical pair involved in avian magnetoreception, concluding that is of the order of a microsecond. However, a combination of an erroneous numerical calculation together with an incorrect parameter drawn from an experimental source have resulted in the authors underestimating by two orders of magnitude. Consequently, one must reverse the authors' conclusion that the timescale is consistent with experiments on cryptochrome.

General System theory, Like-Quantum Semantics and Fuzzy Sets

It is outlined the possibility to extend the quantum formalism in relation to the requirements of the general systems theory. It can be done by using a quantum semantics arising from the deep logical structure of quantum theory. It is so possible taking into account the logical openness relationship between observer and system. We are going to show how considering the truth-values of quantum propositions within the context of the fuzzy sets is here more useful for systemics . In conclusion we propose an example of formal quantum coherence.

Fate of symmetry protected coherence in open quantum system

We investigate the fate of coherence in the dynamical evolution of a symmetry protected quantum system. Under the formalism of system-plus-bath for open quantum system, the anti-unitary symmetry exhibits significant difference from the unitary one in protecting initial coherence. Specifically, taking advantage of Lindblad master equation, we find that a pure state in the symmetry protected degenerate subspace will decohere even though both the system Hamiltonian and system-environment interaction respect the same anti-unitary symmetry. In contrast, the coherence will persist when the protectin…

量子相干性的冻结条件

Frozen condition of quantum coherence

本文研究量子相干性在噪声下冻结的条件，给出单比特系统的简洁公式和d维系统的几何条件，并基于此完成相干态的操作理论分类，与LOCC纠缠分类对应。

Quantum Coherence as a Resource

The coherent superposition of states, in combination with the quantization of observables, represents one of the most fundamental features that mark the departure of quantum mechanics from the classical realm. Quantum coherence in many-body systems embodies the essence of entanglement and is an essential ingredient for a plethora of physical phenomena in quantum optics, quantum information, solid state physics, and nanoscale thermodynamics. In recent years, research on the presence and functional role of quantum coherence in biological systems has also attracted a considerable interest. Despit…