Lars M. Johansen
A conditional kinetic energy is defined in terms of the Wigner distribution. It is shown that this kinetic energy may become negative for negative Wigner distributions. A free particle wave packet with negative kinetic energy will spread in a nonclassical manner.
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Starting with the quasi-Bell states of the qubit-oscillator system, we obtain time evolution of the density matrix under the adiabatic approximation. The composite density matrix leads to, via partial tracing of the qubit degree of freedom, the reduced density matrix of the oscillator that is utilized to obtain the quasi-probability distributions such as Glauber-Sudarshan P function, Wigner W function and Husimi Q function. The negativity of the Wigner function acts as a measure of the nonclassicality of the state. The negativity becomes particularly relevant in understanding a comparison betw…
We show that with an efficiency exceeding 99% one can use a monolithic total-internal-reflection resonator in order to ascertain the presence of an object without transferring a quantum of energy to it. We also propose an experiment on the probabilistic meaning of the electric field that contains only a very few photons.
Motivated by the proposal to simulate para-Bose oscillators in a trapped-ion setup [C. Huerta Alderete and B. M. Rodríguez-Lara, Phys. Rev. A 95, 013820 (2017)], we introduce an overcomplete, nonorthogonal basis for para-Bose Hilbert spaces. The states spanning these bases can be experimentally realized in the trapped-ion simulation via time evolution. The para-Bose states show both nonclassical and semiclassical statistics on their Fock state distribution, asymmetric field quadrature variances, and do not minimize the uncertainty relation for the field quadratures. These properties are analyt…
There are quantum states of light that can be expressed as finite superpositions of Fock states (FSFS). We demonstrate the nonclassicality of an arbitrary FSFS by means of its phase space distributions such as the Wigner function and the $Q$-function. The decoherence of the FSFS is studied by considering the time evolution of its Wigner function in amplitude decay and phase damping channels. As examples, we determine the nonclassicality and decoherence of generalized and reciprocal binomial states.
A two-mode optical parity-time (PT) symmetric system, with gain and damping, described by a quantum quadratic Hamiltonian with additional small Kerr-like nonlinear terms, is analyzed from the point of view of nonclassical-light generation. Two kinds of stationary states with different types of (in)stability are revealed. Properties of one of these are related to the presence of semiclassical exceptional points, i.e., exotic degeneracies of the non-Hermitian Hamiltonian describing the studied system without quantum jumps. The evolution of the logarithmic negativity, principal squeezing variance…
The marginal distribution of squeezed and rotated quadrature for two types of nonclassical states of trapped ion -- for squeezed and correlated states and for squeezed even and odd coherent states (squeezed Schrödinger cat states) is studied. The obtained marginal distribution for the two types of states is shown to satisfy classical dynamical equation equivalent to standard quantum evolution equation for density matrix (wave function) derived in symplectic tomography scheme.
Gravity gradient is known as a serious systematic effect in atomic tests of the universality of free fall, where the initial central position and velocity of atoms need to be exactly controlled. In this paper, we study quantum free fall with high-order gravity gradients. It is shown that the cubic terms in the Newtonian potential shall generate a new phase shift in atom interferometers, which depends on the position and velocity uncertainties of the incident atoms. We further investigate the nonclassicality of free fall and show that, due to the cubic potential, the gravitational Wigner equati…
The transient evolution of nonclassical radiation fields interacting with an atom in a cavity is correlated to the atomic dynamics. Connection between the atomic phases of collapse and revival, and the Wigner function pattern is explored. Initial classical coherent field can evolve into nonclassical field. Schrodinger cat state field is generate during the atomic collapse phase. For initial Schrodinger cat field state, the state dissolves with time but revives during the atomic phase that corresponds with the initial phase. More intricate but orderly characteristics are found between the colla…
Quantum speed limit and nonclassicality in open quantum system models using the Wigner function
该研究利用Wigner函数，通过相位协变模型及双量子比特与压缩热库的位置依赖耦合模型，探究开放量子系统的量子速度极限与非经典性，发现非马尔可夫行为、量子性和量子速度极限间的相互作用及量子关联对演化的加速作用。
Low-Energy Free-Electron Nonclassical Lasing
本文提出低能自由电子非经典激光理论，利用光子晶体腔中非相干电子的集体动力学实现室温高保真度福克态非经典激光发射，具备可调谐、可集成、高能效、可扩展的优势。
A simple model allows us to study the nonclassical behavior of slowly moving atoms interacting with a quantized field. Atom and field become entangled and their joint state can be identified as a mesoscopic "Schroedinger-cat". By introducing appropriate observables for atom and field and by analyzing correlations between them based on a Bell-type inequality we can show the corresponding nonclassical behavior.
Quantum resource theory is perhaps the most revolutionary framework that quantum physics has ever experienced. It plays vigorous roles in unifying the quantification methods of a requisite quantum effect as wells as in identifying protocols that optimize its usefulness in a given application in areas ranging from quantum information to computation. Moreover, the resource theories have transmuted radical quantum phenomena like coherence, nonclassicality and entanglement from being just intriguing to being helpful in executing realistic thoughts. A general quantum resource theoretical framework …
Probing the nonclassical dynamics of a quantum particle in a gravitational field
研究量子粒子在引力场中的非经典动力学，通过干涉仪测量不对称质量配置的影响，验证薛定谔方程的准确性。
Quanutm-State Texture as a Resource: Measures and Nonclassical Interdependencies
本文研究量子态纹理资源理论，提出两种新度量及凸顶构造形式，确定自由操作下态变换的最大概率，并揭示其与相干性、虚数性和可预测性的联系。
Adaptively partitioned analog quantum simulation on near-term quantum computers: The nonclassical free-induction decay of NV centers in diamond
针对近期量子计算机噪声大、连接受限导致难以开展大规模模拟量子模拟的问题，提出自适应分区环境的方法，在IBM量子平台上实现了金刚石NV中心自由感应衰减模拟并验证了非经典特性，为噪声近期量子机模拟大尺度材料提供灵活方案。
In this thesis concrete quantum systems are investigated in the framework of the environment induced decoherence. The focus is on the dynamics of highly nonclassical quantum states, the Wigner function of which are negative over some regions of their domains. One of the chosen physical systems is a diatomic molecule, where the potential energy of the nuclei is an anharmonic function of their distance. A system of two-level atoms, which can be important from the viewpoint of quantum information technology, is also investigated. A method is described that is valid in both systems and can determi…
Quasiprobability distributions (QDs) in open quantum systems are investigated for $SU(2)$, spin like systems, having relevance to quantum optics and information. In this work, effect of both quantum non-demolition (QND) and dissipative open quantum systems, on the evolution of a number of spin QDs are investigated. Specifically, compact analytic expressions for the $W$, $P$, $Q$, and $F$ functions are obtained for some interesting single, two and three qubit states, undergoing general open system evolutions. Further, corresponding QDs are reported for an N qubit Dicke model and a spin-1 system…
In this paper we discuss the quantum properties for superposition of squeezed displaced number states against multiphoton Jaynes-Cummings model (JCM). In particular, we investigate atomic inversion, photon-number distribution, purity, quadrature squeezing, Mandel $Q$ parameter and Wigner function. We show that the quadrature squeezing for three-photon absorption case can exhibit revivals and collapses typical to those occurring in the atomic inversion for one-photon absorption case. Also we prove that for odd number absorption parameter there is a connection between the evolution of the atomic…
Resource theories play an important role in quantum information theory, as they identify resourceful states and channels that are potentially useful for the accomplishment of tasks that would be otherwise unreachable. The elementary structure of such theories, which is based on the definition of free states and free operations, successfully accommodates different nonclassical aspects, such as quantum coherence and entanglement, but it is still not clear whether and how far such formal framework can be extended. In this work, by taking information as the most primitive quantum resource and defi…
Nonclassical energy-change distribution as a witness of non-Markovian quantum dynamics
通过测量系统能量变化分布的Kirkwood-Dirac准概率的非正值来检测非马尔可夫量子动力学，并证明其与CP不可分性的关联。
A continuous-mode quantum-optical representation of finite strong-field laser pulses in free space
该研究构建了自由空间有限强场激光脉冲的连续模式量子光学表示，实现了相干与非经典脉冲的统一处理，为量子光学计算提供了能量一致的脉冲接口。
Towards Schrödinger Cat States in the Second Harmonic Generation
研究强泵耗尽条件下第二谐波生成中泵场的量子演化，发现泵场形成类似薛定谔猫态的非经典相空间结构，揭示了真空波动诱导的相不稳定性是其成因，表明非线性频率转换可生成宏观叠加态。
Wave-particle correlations in multiphoton resonances of coherent light-matter interaction
本文通过波粒相关器研究JC模型多光子共振中的非经典演化，揭示量子拍频与正交振幅压缩，并展示波动回归的不对称性。
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