Quantum Limits of Polarization Switching in Optical Mesoscopic Devices with Distributively Coupled Quantum Modes

The quantum theory of nonlinear dynamics and the switching effect for two distributively coupled modes in optical systems has been developed based on the Hartree approximation. The quantum limits for observation of the switching effect for the polarization characteristics of light has been determined. The creation of a new type of nonclassical mesoscopic states of light like the Schrödinger-cat states and mesoscopic qubit/qutrit states is predicted. The theoretical prediction is confirmed by a numerical estimation of real systems, i.e., tunnel-coupled optical fibers and waveguides, for the experimental realization of the states under consideration.     

Macroscopic pure state of light free of polarization noise

The preparation of completely nonpolarized light is seemingly easy; an everyday example is sunlight. The task is much more difficult if light has to be in a pure quantum state, as required by most quantum-technology applications. The pure quantum states of light obtained so far are either polarized or, in rare cases, manifest hidden polarization; even if their intensities are invariant to polarization transformations, higher-order moments are not. We experimentally demonstrate the preparation of the macroscopic singlet Bell state, which is pure, is completely nonpolarized, and has no polarization noise. Simultaneous fluctuation suppression in three Stokes observables below the shot-noise limit is demonstrated, opening perspectives for noiseless polarization measurements. The state is shown to be invariant to polarization transformations. This robust highly entangled isotropic state promises to fuel important applications in photonic quantum technologies.     

Effect of interdiffusion on nonlinear intraband light absorption in Gaussian-shaped double quantum rings

The effect of interdiffusion on electronic states and nonlinear light absorption in Gaussian-shaped double quantum rings is studied. The confining potential, electron energy spectrum, wave functions and absorption coefficient are obtained for different values of diffusion parameter. The effect of the variation of Gaussian parameters is considered as well. The selection rules for the intraband transitions in the cases of the light polarization parallel and perpendicular to the quantum rings' axis are obtained. It is shown that the interdiffusion can be used as an effective tool for the purposeful manipulation of the electric and optical properties of the considered structure.     

Polarization States of Light and Their Quantum Tomography

The notion and main features of polarization states of light are discussed within the framework of classical and quantum optics. This notion is shown to be correctly defined for arbitrary light beams only within quantum optics by using the P-quasispin formalism developed earlier. Polarization states of quantum light are shown to be fully described by a polarization density operator (PDO) obtained via reducing the total field density operator. Theoretical foundations are given for quantum tomography of polarization states of light fields considered as a way of measuring PDO. Herewith, the main attention is paid to a method where proper polarization tomographic observables (PDO “measurers”) are used. The method is shown to be adequately formulated by means of quasi-spectral tomographic expansions of PDO in special operator bases (given by finite sums of partially orthogonal projectors), which determine probability distributions of tomographic observables as expansion coefficients. Matrix versions of such “tomographic” PDO representations are obtained. In particular, projections of these expansions on quasiclassical operator bases, determining polarization quasiprobability functions, are given. An example of experimental implementation of polarization tomography of unpolarized light (biphoton radiation with hidden polarization) is analyzed.     

Linear optical implementation of optimal unambiguous discrimination among quantum states

In this paper, we present a linear optical scheme for optimal unambiguous discrimination among nonorthogonal quantum states in terms of the multiple-rail and polarization representation of a single photon. In our scheme, discriminated quantum states are expressed by using the spatial degree of freedom of a single photon while the polarization degree of freedom of the single photon is used to act as an auxiliary qubit. The optical components used in our scheme are only passive linear optical elements such as polarizing beam splitters, wave plates, polarizers, single photon detectors, and single photon source.     

Generation and Manipulation of Spin-Orbit Coupling mode via Four-Wave Mixing with Quantum Interference

Recently, the vectorial nonlinear optical processes driven by spin-orbit coupling (SOC) light have come to the fore, leading to striking optical phenomena and important applications both in classical and quantum optics. However, research on the SOC-mediated light-atom interactions is still in its infancy. Here, the generation and manipulation of SOC mode through a vectorial four-wave mixing (FWM) process in ⁸⁵Rb vapor is demonstrated. Under the excitation of two SOC pump beams, multiple FWM paths can be simultaneously established due to the rich atomic Zeeman sublevels coupling with different circularly polarized components of SOC fields. A higher-order cylindrical or more general SOC FWM signal is observed in the vectorial FWM process, which obeys angular momentum conservation and Gouy phase matching. In particular, quantum interference between different FWM paths plays a crucial role in manipulating the SOC mode of the generated FWM signal, revealing that the conversion of SOC mode is intrinsically quantum. This work provides a pathway toward deeper insight into the vectorial nonlinear optical processes and may advance technology for shaping spatially structured light, which is essential in applications such as nonlinear polarization imaging and the optical communication realm.     

Nonlinear Quantum Optical Springs and Their Nonclassical Properties

The original idea of quantum optical spring arises from the requirement of quantization of the frequencyof oscillations in the Hamiltonian of harmonic oscillator. This purpose is achieved by consideringa spring whose constant (and so its frequency) depends on the quantum states of another system.
Recently, it is realized that by the assumption of frequencymodulation ofω toω(1+μa^\dagger a)^1/2the mentioned idea can be established.
In the present paper, we generalize the approach of quantum optical springwith particular attention to thedependence of frequency to the intensity of radiation fieldthatnaturally observes in thenonlinear coherent states}, from which we arrive ata physical system has been called by us as nonlinear quantum optical spring.Then, after the introduction of the generalized Hamiltonian of nonlinear quantum optical spring and it's solution,we will investigate the nonclassical properties of the obtained states. Specially, typical collapse and revivalin the distribution functions and squeezing parameters, as particular quantum features, will berevealed.     

Intra-Cavity Laser Manipulation of High-Dimensional Non-Separable States

Non-separable states of structured light have the analogous mathematical forms with quantum entanglement, which offer an effective way to simulate quantum process. However, the classical multi-partite non-separable states analogue to multi-particle entanglements can only be controlled by bulky free-space modulation of light through coupling multiple degrees of freedom (DoFs) with orbital angular momentum (OAM) to achieve high dimensionality and other DoFs to emulate multi-parties. In this paper, a scheme is proposed to directly emit multi-partite non-separable states from a simple laser cavity to mimic multi-particle quantum entanglement. Through manipulating three DoFs as OAM, polarization, and wavevector inside a laser cavity, the eight-dimensional (8D) tripartite states and all Greenberger-Horne-Zeilinger (GHZ)-like states can be generated and controlled on demand. In addition, an effective method is proposed to perform state tomography employing convolutional neural network (CNN), for measuring the generated GHZ-like states with highest fidelity up to 95.11%. This work reveals a feasibility of intra-cavity manipulation of high-dimensional multipartite non-separable states, opening a compact device for quantum-classical analogy and paving the path for advanced quantum scenarios.     

相干态的叠加态的量子统计性质

本文研究了相干态的叠加态的量子统计性质.结果表明,相干态的叠加态仅存在奇次幂的高阶压缩效应,而不存在偶次幂的高阶压缩效应.给出了高阶压缩和高阶反聚束效应与叠加系数间的函数关系.高阶压缩要求叠加系数的辐角取值满足cosθ>exp(-2|α|²),而高阶反聚束效应则要求0.5π<θ<1.5π.奇偶相干态的有关结果均作为特例应包含在本文的一般结论之中.     

Robust scheme for the preparation of symmetric Dicke states with coherence state via cross-Kerr nonlinearity

A scheme is proposed for generating multiphoton maximally entangled states among four modes. These schemes only use Kerr medium and polarization beam splitters and P homodyne measurements on coherent light fields, which can be efficiently implemented in quantum optical laboratories. It's comparatively easy to realize symmetric Dicke state of light fields in the scheme. The scheme can be generalized to produce N-qubit maximally entangled states.     

Polarization invariance and biphoton coherent states of light

A new classification of polarization states of quantum light fields is given using the concept of the polarization (P) spin due to the polarization gauge SU_p(2) invariance of free light fields [I]. Generalized coherent states (GCS) asNociated with P-scalar biphotons are discussed. We also point out some applications of the results in the optical communication theory.Presented at the International Workshop on Squeezed and Correlated States in Quantum Optics, Moscow, December 3–7, 1990.     

多个量子节点确定性纠缠的建立

量子纠缠是一种重要的量子资源,在多个空间分离的量子存储器间建立确定性的量子纠缠,然后在用户控制的时刻将所存储的量子纠缠转移到量子信道中进行信息的分发和传送,这对于实现量子信息网络是至关重要的.本文介绍了用光学参量放大器制备与铷原子D1吸收线对应的非经典光场,而且在三个空间分离的原子系综中确定性量子纠缠的产生、存储和转移.利用电磁感应透明光和原子相互作用的原理,将制备的多组分光场纠缠态模式映射到三个远距离的原子系综以建立原子自旋波之间的纠缠.然后,存储在原子系综中的纠缠态通过三个量子通道,纠缠态的量子噪声被转移到三束空间分离的正交纠缠光场.三束释放的光场间纠缠的存在验证了该系统具有保持多组分纠缠的能力.这个方案实现了三个量子节点间的纠缠,并且可以直接扩展到具有更多节点的量子网络,为未来实现大型量子网络通信奠定了基础.     

Quantum measurements of the parameters of the Gell-Mann optical field with an SU(3) interferometer

The SU(3) polarization theory in the Hilbert space is developed for quantum Bose systems with Gell-Mann symmetry. The degrees of polarization and isopolarization are determined. An original SU(3) interferometer for measuring the phase-dependent Gell-Mann parameters of an optical field is considered, and the signal-to-noise measurements limiting in quantum noises and based on the use of entangled and squeezed states of light at the entrance of the optical system are analyzed. A new type of quantum (helical) states of optical radiation for which the correlation between the Hermitian quadratures and isospin operators plays a crucial role is revealed for one of these modes in the classical-field approximation.     

Higher-order Poincaré sphere, stokes parameters, and the angular momentum of light

A higher-order Poincaré sphere and Stokes parameter representation of the higher-order states of polarization of vector vortex beams that includes radial and azimuthal polarized cylindrical vector beams is presented. The higher-order Poincaré sphere is constructed by naturally extending the Jones vector basis of plane wave polarization in terms of optical spin angular momentum to the total optical angular momentum that includes higher dimensional orbital angular momentum. The salient properties of this representation are illustrated by its ability to describe the higher-order modes of optical fiber waveguides, more exotic vector beams, and a higher-order Pancharatnam-Berry geometric phase.     

宏观可分辨量子态的产生和检测

本文利用SO(3)旋转群性质得到了非线性双折射介质模型的一个严格解.由此证明相干态进入双折射介质后将产生宏观上可分辨的量子迭加态.为检测它们所产生的干涉条纹,本文采用零拍检测方案,计算了初态为线偏振和圆偏振相干光时零拍检测器输出流的几率分布.     

Simultaneous Preparation of Two Optical Cat States Based on a Nondegenerate Optical Parametric Amplifier

The cat state, known as the superposition of coherent states, has broad applications in quantum computation and quantum metrology. Increasing the number of optical cat states is crucial to implement complex quantum information tasks based on them. Here, two optical cat states are prepared simultaneously based on a nondegenerate optical parametric amplifier. By subtracting one photon from each of two squeezed vacuum states, two odd cat states with orthogonal superposition direction in phase space are prepared simultaneously, which have similar fidelity of 60% and amplitude of 1.2. Compared with the traditional method to generate two odd optical cat states based on two degenerate optical parametric amplifiers, only one nondegenerate optical parametric amplifier is applied in this experiment, which saves half of the quantum resources of nonlinear cavities. The presented results make a step toward preparing the four-component cat state, which has potential applications in fault-tolerant quantum computation.