S. Rebic, D. Vitali, C. Ottaviani, P. Tombesi
A novel effect of population transfer in a five-level system is analyzed. This population transfer effect is found to be a version of a Raman process, which is facilitated and assisted by coherence effects, acting to close other available decay channels.
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It has been shown in recent years that incoherent pumping through multiple atomic levels provides a mechanism for the production of highly anti-bunched light, and that as the number of incoherent steps is increased the light becomes increasingly regular. We show that in a resonance fluorescence situation, a multi-level atom may be multiply coherently driven so that the fluorescent light is highly anti-bunched. We show that as the number of coherently driven levels is increased, the spontaneous emissions may be made increasingly more regular. We present a systematic method for designing the lev…
We investigate the dispersion and the absorption properties of a weak probe field in a three-level Lambda-type atomic system. We use just an incoherent field for controlling the group velocity of light. It is shown that the slope of dispersion changes from positive to negative just with changing the intensity of the indirect incoherent pumping field. Gain-assisted superluminal light propagation appears in this system. No laser field is used in the pumping processes.
Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photo-systems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate a situation that in the absence of dephasing noises the coherent evolution of the system has no role in the energy transport in the network. Therefore, incoherent evolution via application…
Incoherent GRAPE (inGRAPE) for optimization of quantum systems with environmentally assisted control
本文回顾了非相干 GRAPE (inGRAPE) 方法在环境辅助下优化开放量子系统的应用，通过求解三次方程获得密度矩阵演化解析式，并揭示了不同量子门控制景观的特性。
Stochastic perturbation of two-level atoms strongly driven by a coherent light field is analyzed by the quantum trajectory method. A new method is developed for calculating the resonance fluorescence spectra from numerical simulations. It is shown that in the case of dominant incoherent perturbation, the stochastic noise can unexpectedly create phase correlation between the neighboring atomic dressed states. This phase correlation is responsible for quantum interference between the related transitions resulting in anomalous modifications of the resonance fluorescence spectra.
In the task of assisted coherence distillation via the set of operations X, where X is either local incoherent operations and classical communication (LICC), local quantum-incoherent operations and classical communication (LQICC), separable incoherent operations (SI), or separable quantum incoherent operations (SQI), two parties, namely Alice and Bob, share many copies of a bipartite joint state. The aim of the process is to generate the maximal possible coherence on the subsystem of Bob. In this paper, we investigate the assisted coherence distillation of some special mixed states, the states…
Environment-assisted squeezing in a coherently driven non-Hermitian degenerate parametric oscillator
研究相干驱动非厄米简并参量振荡器，利用输入 - 输出理论获得相关闭式表达式，发现非厄米贡献能增强压缩，打开工作窗口，所得参数图确定了实验可测试窗口，展示了库工程与相干驱动结合增强压缩的环境辅助方法。
The remarkable phenomenon of catalyst tells us that adding a catalyst could help state transformation. In this paper, we consider the problem of catalyst-assisted probabilistic coherence distillation for mixed states under strictly incoherent operations. To this end, we first present the necessary and sufficient conditions for distilling a target pure coherent state from an initial mixed state via stochastic strictly incoherent operations and the maximal probability of obtaining the target pure state from the initial state. With the help of these results, we present the necessary and sufficien…
We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally-detuned laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20 % with respect to strictly resonant excitation can be achieved at T = 9 K. Laser frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the photoluminescence is introduced which predicts a broadband incoherent…
Strongly driven transmon as an incoherent noise source
强驱动下的transmon因混沌效应产生非相干噪声并传播至相邻自由度，研究通过量子模型与半经典分析揭示其对旁观者二能级系统的作用可建模为随机扩散过程。
Control landscape of measurement-assisted transition probability for a three-level quantum system with dynamical symmetry
本文针对具有动力学对称性的三能级量子系统，完整刻画测量辅助跃迁概率随欧拉角变化的控制景观及其临界点类型，并比较不同能级跃迁与测量方案。
Memory-assisted squeezed light velocimetry under realistic loss and incoherent noise
提出一种基于双存储M-Z干涉仪的压缩光速度传感器，通过经典Fisher信息分析速度灵敏度、量子增益阈值和最优存储时间，在近期参数下非相干噪声不消除优势，但优化后改进受限于损耗。
Coherently excited Hong-Ou-Mandel effects using frequency-path correlation
提出相干版 Hong-Ou-Mandel 效应，利用衰减激光和同步调制器在独立 Mach-Zehnder 干涉仪中制备频率相关相干光子对，揭示反关联与纠缠的基础物理机制。
We address two-level systems arranged in ring configurations affected by static disorder. In particular we investigate the role of dephasing in the transport of an excitation along the ring. We compare the efficiency of the transfer process on isotropic rings and on biomimetic rings modelled according to the structure of light-harvesting complexes. Our analysis provides a simple but clear and interesting example of how an interplay between the coherent dynamics of the system and the incoherent action of the environment can enhance the transfer capabilities of disordered lattices.
We give the first systematic study on the second order asymptotics of the operational task of coherence distillation with and without assistance. In the unassisted setting, we introduce a variant of randomness extraction framework where free incoherent operations are allowed before the incoherent measurement and the randomness extractors. We then show that the maximum number of random bits extractable from a given quantum state is precisely equal to the maximum number of coherent bits that can be distilled from the same state. This relation enables us to derive tight second order expansions of…
Environment assisted superballistic scaling of conductance
本研究发现周围环境的弱非相干效应可使最近邻紧束缚链的零温电导在带边处随系统长度呈超弹道幂律增长，标度区间可通过降低环境耦合扩展，其源于非相干效应与转移矩阵例外点的复杂相互作用。
We study two ions confined in a Penning trap. We show that electronically highly excited states exist in which an electron is delocalized among the two ions forming a giant molecule of several micrometer size. At energies close to the top of the Coulomb barrier these molecular states can be regarded as superpositions of Rydberg states of individual ions. We illuminate the possibility to observe coherent charge transfer between the ions. Beyond a critical principal quantum number the electron can coherently tunnel through the Coulomb barrier to an adjacent doubly charged ion. The tunneling occu…
Transport phenomena at the nanoscale are of interest due to the presence of both quantum and classical behavior. In this work, we demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the system Hamiltonian with pure dephasing induced by a fluctuating environment. This is in contrast to fully coherent hopping that leads to localization in disordered systems, and to highly incoherent transfer that is eventually suppressed by the quantum Zeno effect. We study these phenomena in the Fenna-Matthews-Olson protein complex as a prototype for larger photosynthetic e…
Collective magnetic excitation modes, magnons, can be coherently coupled to microwave photons in the single excitation limit. This allows for access to quantum properties of magnons and opens up a range of applications in quantum information processing, with the intrinsic magnon linewidth representing the coherence time of a quantum resonator. Our measurement system consists of a yttrium iron garnet (YIG) sphere and a three-dimensional (3D) microwave cavity at temperatures and excitation powers typical for superconducting quantum circuit experiments. We perform spectroscopic measurements to de…
We introduce and study the task of assisted coherence distillation. This task arises naturally in bipartite systems where both parties work together to generate the maximal possible coherence on one of the subsystems. Only incoherent operations are allowed on the target system while general local quantum operations are permitted on the other, an operational paradigm that we call local quantum-incoherent operations and classical communication (LQICC). We show that the asymptotic rate of assisted coherence distillation for pure states is equal to the coherence of assistance, an analog of the ent…
We investigate manipulations of pure quantum states under incoherent or strictly incoherent operations assisted by a coherence battery, that is, a storage device whose degree of coherence is allowed to fluctuate in the process. This leads to the derivation of fluctuation relations for quantum coherence, analogous to Jarzynski's and Crooks' relations for work in thermodynamics. Coherence is thus revealed as another instance of a physical resource, in addition to athermality and entanglement, for which a connection is established between the majorisation framework (regulating pure state transfor…
A general rate theory for resonance energy transfer is formulated to incorporate any degrees of freedom (e.g., rotation, vibration, exciton, and polariton) as well as coherently-coupled composite states. The compact rate expression allows us to establish useful relationships: (i) detailed balance condition when the donor and acceptor are at the same temperature; (ii) proportionality to the overlap between donor's emission and acceptor's absorption spectra; (iii) scaling with the effective coherent size, i.e., the number of coherently coupled molecules; (iv) spatial and orientational dependence…
In the spectrum of systems showing chaos-assisted tunneling, three-state crossings are formed when a chaotic singlet intersects a tunnel doublet. We study the dissipative quantum dynamics in the vicinity of such crossings. A harmonically driven double well coupled to a bath serves as a model. Markov and rotating-wave approximations are introduced with respect to the Floquet spectrum of the time-dependent central system. The resulting master equation is integrated numerically. We find various types of transient tunneling, determined by the relation of the level width to the inherent energy scal…
On-chip photon entanglement-assisted topology loading and transfer
本文提出在片上将光子拓扑编码到单光子自旋纹理量子态中，并通过纠缠分发实现拓扑的非局域转移，在噪声和扰动下保持拓扑保护与量子关联，为分布式量子互连和量子信息技术提供新途径。
Experimental challenges and prospects for quantum-enhanced energy conversion: Stationary Fano coherence in V-type qutrits interacting with polarized incoherent radiation
研究探讨了V型三能级系统在极化非相干辐射下实现稳态Fano相干性的可能性及其在能量转换中的应用。
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