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A quantum retrograde canon: complete population inversion in <i>n</i> <sup>2</sup> -state systems
摘要： We present a novel approach for analytically reducing a family of time-dependent multi-state quantum control problems to two-state systems. The presented method translates between related n2-state systems and two-state systems, such that the former undergo complete population inversion (CPI) if and only if the latter reach specific states. For even n, the method translates any two-state CPI scheme to a family of CPI schemes in n2-state systems. In particular, facilitating CPI in a four-state system via real time-dependent nearest-neighbors couplings is reduced to facilitating CPI in a two-level system. Furthermore, we show that the method can be used for operator control, and provide conditions for producing several universal gates for quantum computation as an example. In addition, we indicate a basis for utilizing the method in optimal control problems.
关键词： quantum state transfer,quantum computation,coherent control,quantum information,complete population transfer,quantum control
更新于2025-09-09 09:28:46
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Selective and efficient quantum process tomography in arbitrary finite dimension
摘要： The characterization of quantum processes is a key tool in quantum information processing tasks for several reasons: on one hand, it allows one to acknowledge errors in the implementations of quantum algorithms; on the other, it allows one to characterize unknown processes occurring in nature. Bendersky, Pastawski, and Paz [A. Bendersky, F. Pastawski, and J. P. Paz, Phys. Rev. Lett. 100, 190403 (2008); Phys. Rev. A 80, 032116 (2009)] introduced a method to selectively and ef?ciently measure any given coef?cient from the matrix description of a quantum channel. However, this method heavily relies on the construction of maximal sets of mutually unbiased bases (MUBs), which are known to exist only when the dimension of the Hilbert space is the power of a prime number. In this article, we lift the requirement on the dimension by presenting two variations of the method that work on arbitrary ?nite dimensions: one uses tensor products of maximal sets of MUBs, and the other uses a dimensional cutoff of a higher prime power dimension.
关键词： Hilbert space,quantum channel,quantum information processing,quantum process tomography,mutually unbiased bases
更新于2025-09-09 09:28:46
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Quantum information exchange protocol associated with the quantum cloud
摘要： Quantum cryptography discusses the security of quantum information. Cloud computing has emerged as a computational paradigm and an alternative to the conventional computing. Cloud security is associated with cloud computing. In this paper, we define the new concept about quantum cloud and discuss the security of quantum information exchange in quantum internet. A tripartite simultaneous quantum information exchange protocol associated with the quantum cloud based on entanglement swapping and Bell states is proposed. The proposed secure quantum information exchange protocol can resist intercept-and-resend attack, intercept-and-measure attack, intercept-and-entangle auxiliary attack and denial-of-service attack. It can also be generalised to N-party case that is feasible and efficient.
关键词： intercept-and-resend attack,cloud computing,quantum information exchange,intercept-and-measure attack,intercept-and-entangle auxiliary attack,denial-of-service attack,quantum cloud
更新于2025-09-09 09:28:46
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Testing nonclassicality with exact Wigner currents for an anharmonic quantum system
摘要： Phase-space features of the Wigner flow for an anharmonic quantum system driven by the harmonic oscillator potential modified by the addition of an inverse square (one-dimensional Coulomb-like) contribution are analytically described in terms of Wigner functions and Wigner currents. Reporting about three correlated continuity equations which quantify the flux of quantum information in the phase space, the nonclassicality profile of such an anharmonic system can be consistently obtained in terms of the fluxes of probability, purity, and von Neumann–like entropy. Considering that quantum fluctuations can be identified from distortions over the classical regime, they can be quantified through the above-mentioned information fluxes whenever some classically bounded volume of the phase space is selected. Our results suggest that the Wigner flow approach works as a probe of quantumness and classicality for a large set of anharmonic quantum systems driven by quantum wells.
关键词： anharmonic quantum system,Wigner flow,quantum information,phase space,nonclassicality
更新于2025-09-09 09:28:46
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Effect of the mechanical oscillator on the optical-response properties of an optical trimer system
摘要： We propose theoretically a four-mode coupled optomechanical system to explore the optical-response properties of an optical trimer system consisting of a passive cavity, a no-loss-gain cavity, and an active cavity coupled with a mechanical oscillator. In the study, the passive cavity is driven by an external laser so that the stability of the coupled system depends strongly on the gain-to-loss ratio and the photon tunneling between the adjacent cavities. We ?nd that in the regime near the stable-unstable critical point, the resonance absorption of the optical trimer system changes quickly with the increasing gain of the active cavity. In contrast, when the mechanical oscillator is coupled to the passive cavity, the center absorption peak is split and a phenomenon of optomechanically induced transparency appears. Consequently, two additional resonance peaks in the absorption pro?le are induced by the optomechanical coupling, which hinges on the tunneling between the optical cavities and also on the gain of the active cavity. The dependence of the width of the transparency window on the optomechanical coupling and the driving strength is also discussed in detail. The results obtained here indicate that the optical properties of the trimer system can be manipulated by coupling a mechanical oscillator to the system and therefore have a potential application in quantum optics and quantum information processing.
关键词： optomechanically induced transparency,quantum information processing,mechanical oscillator,quantum optics,optomechanical system,optical trimer system
更新于2025-09-09 09:28:46
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Resource theory of quantum non-Gaussianity and Wigner negativity
摘要： We develop a resource theory for continuous-variable systems grounded on operations routinely available within current quantum technologies. In particular, the set of free operations is convex and includes quadratic transformations and conditional coarse-grained measurements. The present theory lends itself to quantify both quantum non-Gaussianity and Wigner negativity as resources, depending on the choice of the free-state set—i.e., the convex hull of Gaussian states or the states with positive Wigner function, respectively. After showing that the theory admits no maximally resourceful state, we define a computable resource monotone—the Wigner logarithmic negativity. We use the latter to assess the resource content of experimentally relevant states—e.g., photon-added, photon-subtracted, cubic-phase, and cat states—and to find optimal working points of some resource concentration protocols. We envisage applications of this framework to subuniversal and universal quantum information processing over continuous variables.
关键词： Wigner negativity,quantum information processing,quantum non-Gaussianity,continuous-variable systems,resource theory
更新于2025-09-09 09:28:46
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Controllable generation of second-harmonic vortex beams through nonlinear supercell grating
摘要： Lithium niobate (LiNbO3) nonlinear photonic crystals have been widely used in nonlinear wave front modulation for the p-phase difference between the second-harmonic (SH) waves from positive and negative domains. Aided by optimizing algorithms, we can control the diffraction patterns of SH vortex beams by designing nonlinear fork gratings with supercell structures in LiNbO3 crystals. In experiment, we demonstrate that the diffraction energies can be equally distributed in each order or concentrated on certain orders, in agreement with theoretical designs. Potential applications include controllable vortex beam generation, nondestructive parallel vortex detection, and so on.
关键词： quantum information processing,Lithium niobate,optical communication,nonlinear photonic crystals,supercell grating,second-harmonic vortex beams,nonlinear optics
更新于2025-09-09 09:28:46
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Hierarchical and probabilistic quantum information splitting of an arbitrary two-qubit state via two cluster states
摘要： Based on non-maximally entangled four-particle cluster states, we propose a new hierarchical information splitting protocol to probabilistically realize the quantum state sharing of an arbitrary unknown two-qubit state. In this scheme, the sender transmits the two-qubit secret state to three agents who are divided into two grades with two Bell-state measurements, and broadcasts the measurement results via a classical channel. One agent is in the upper grade and two agents are in the lower grade. The agent in the upper grade only needs to cooperate with one of the other two agents to recover the secret state but both of the agents in the lower grade need help from all of the agents. Every agent who wants to recover the secret state needs to introduce two ancillary qubits and performs a positive operator-valued measurement (POVM) instead of the usual projective measurement. Moreover, due to the symmetry of the cluster state, we extend this protocol to multiparty agents.
关键词： hierarchical quantum information splitting,cluster state,positive operator-valued measurement (POVM)
更新于2025-09-09 09:28:46
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Universal Dissipationless Dynamics in Gaussian Continuous-Variable Open Systems
摘要： We investigate the universal dissipationless dynamics of Gaussian continuous-variable systems in the presence of a band-gapped bosonic environment. Our results show that environmental band gaps can induce localized modes, which give rise to the dissipationless dynamics where the system behaves as free oscillators instead of experiencing a full decay in the long-time limit. We present a complete characterization of localized modes and show the existence of the critical system-environment coupling. Beyond the critical values, localized modes can be produced, and the system dynamics become dissipationless. This novel dynamics can be utilized to overcome the environmental noises and protect the quantum resources in the continuous-variable quantum information.
关键词： dissipationless dynamics,Gaussian continuous-variable systems,quantum information,localized modes,band-gapped bosonic environment
更新于2025-09-09 09:28:46
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Mapping Twisted Light into and out of a Photonic Chip
摘要： Twisted light carrying orbital angular momentum (OAM) provides an additional degree of freedom for modern optics and an emerging resource for both classical and quantum information technologies. Its inherently infinite dimensions can potentially be exploited by using mode multiplexing to enhance data capacity for sustaining the unprecedented growth in big data and internet traffic and can be encoded to build large-scale quantum computing machines in high-dimensional Hilbert space. While the emission of twisted light from the surface of integrated devices to free space has been widely investigated, the transmission and processing inside a photonic chip remain to be addressed. Here, we present the first laser-direct-written waveguide being capable of supporting OAM modes and experimentally demonstrate a faithful mapping of twisted light into and out of a photonic chip. The states OAM0, OAM?1, OAMt1, and their superpositions can transmit through the photonic chip with a total efficiency up to 60% with minimal crosstalk. In addition, we present the transmission of quantum twisted light states of single photons and measure the output states with single-photon imaging. Our results may add OAM as a new degree of freedom to be transmitted and manipulated in a photonic chip for high-capacity communication and high-dimensional quantum information processing.
关键词： Photonic chip,Twisted light,Quantum information processing,Orbital angular momentum
更新于2025-09-09 09:28:46