Nguyen Ba An
Fan-even K-quantum nonlinear coherent states are introduced and higher-order amplitude squeezing is investigated in such states. It is shown that for a given K the lowest order in which an amplitude component can be squeezed is 2K and the squeezing appears simultaneously in K directions separated successively in phase by π/K.
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Squeezing and amplitude-squared squeezing for two two-level nonidentical atoms in lossless cavity has been investigated assuming the field to be initially in the coherent state. The time-dependent squeezing parameters has been calculated. The influence of the relative differences of two coupling constants on the squeezing parameters has been analyzed.
The role of non-Markovian dissipation in quantum phase transitions: tricriticality, spin squeezing, and directional symmetry breaking
本文以Lipkin-Meshkov-Glick模型为研究对象，探究非马尔可夫耗散在量子相变中的作用，发现其可融合临界点实现三临界点设计，提出定向自发对称性破缺框架，且自旋压缩可被非马尔可夫效应控制，为量子计量提供可能并指出马尔可夫极限的不足。
We know that the original Schrödinger cat states has no amplitude-squared squeezing. In this paper, we investigate the amplitude-squared squeezing of Schrödinger cat states using postselected von Neumann measurement. The results show that after postselected von Neumann measurement, the amplitude-squared squeezing of Schrödinger cat states change dramatically and this can be considered a result of weak value amplification. The squeezing effect also investigated by studying the Wigner function of Schrödinger cat states after postselected measurement.
We generated -2.2 dB of broadband amplitude squeezing at 1064 nm in a periodically poled KTiOPO_4 (PPKTP) waveguide, by coupling of the fundamental and second harmonic continuous-wave fields. This is the largest amount of squeezing obtained to date in a KTP waveguide, limited by propagation losses. This result paves the way for further improvements by use of lower-loss buried ion-exchanged waveguides.
Quantum squeezing via self-induced transparency in a photonic crystal fiber
本研究采用正$P$表示的完全量子模拟，探究光子晶体光纤自感应透明中的量子压缩，发现脉冲面积在2π-3π间有显著压缩，且自发辐射比升高引发的耦合增强会降低压缩程度。
We present the conditional time evolution of the electromagnetic field produced by a cavity QED system in the strongly coupled regime. We obtain the conditional evolution through a wave-particle correlation function that measures the time evolution of the field after the detection of a photon. A connection exists between this correlation function and the spectrum of squeezing which permits the study of squeezed states in the time domain. We calculate the spectrum of squeezing from the master equation for the reduced density matrix using both the quantum regression theorem and quantum trajector…
We report on the generation of polarization squeezing of intense, short light pulses using an asymmetric fiber Sagnac interferometer. The Kerr nonlinearity of the fiber is exploited to produce independent amplitude squeezed pulses. The polarization squeezing properties of spatially overlapped amplitude squeezed and coherent states are discussed. The experimental results for a single amplitude squeezed beam are compared to the case of two phase-matched, spatially overlapped amplitude squeezed pulses. For the latter, noise variances of -3.4dB below shot noise in the S0 and the S1 and of -2.8dB i…
We analyze the amplitude and phase noise of limit-cycle oscillations in a mechanical resonator coupled parametrically to an optical cavity driven above its resonant frequency. At a given temperature the limit-cycle oscillations have lower amplitude noise than states of the same average amplitude excited by a pure harmonic drive; for sufficiently low thermal noise a sub-Poissonian resonator state can be produced. We also calculate the linewidth narrowing that occurs in the limit-cycle states, and show that while the minimum is set by direct phase diffusion, diffusion due to the optical spring e…
We propose an efficient method to protect spin squeezing under the action of amplitude-damping, depolarizing and phase-damping channels based on measurement reversal from weak measurement, and consider an ensemble of N independent spin-1/2 particles with exchange symmetry. We find that spin squeezing can be enhanced greatly under three different decoherence channels and spin-squeezing sudden death (SSSD) can be avoided undergoing amplitude damping and phase-damping channels.
Nonreciprocal photon bundle emission
研究耦合谐振腔与二能级原子系统中的单向光子束发射，利用定向量子压缩实现非互易双光子束发射，为手性量子发射和抗背向散射光通信提供新方法。
In the present paper, we study spin squeezing under decoherence in the superposition of tripartite maximally entangled GHZ and W states. Here we use amplitude damping, phase damping and depolarisation channel. We have investigated the dynamics of spin squeezing with the interplay of superposition and decoherence parameters with different directions of the mean spin vector. We have found the mixture of GHZ and W states is robust against spin squeezing generation for amplitude damping and phase damping channels for certain directions of the mean spin vector. However, the depolarisation channel p…
We investigate the Nth order amplitude squeezing in the fan-state |ξ;2k,f>_F which is a linear superposition of the 2k-quantum nonlinear coherent states. Unlike in usual states where an ellipse is the symbol of squeezing, a 4k-winged flower results in the fan state. We first derive the analytical expression of squeezing for arbitrary k, N, f and then study in detail the case of a laser-driven trapped ion characterized by a specific form of the nonlinear function f. We show that the lowest order in which squeezing may appear and the number of directions along which the amplitude may be squeezed…
A complete set of solutions |z,u,v>_{sa} of the eigenvalue equation (ua^2+va^{dagger 2})|z,u,v> = z|z,u,v> ([a,a^{dagger}]=1) are constructed and discussed. These and only these states minimize the Schrödinger uncertainty inequality for the squared amplitude (s.a.) quadratures. Some general properties of Schrödinger intelligent states (SIS) |z,u,v> for any two observables X, Y are discussed, the sets of even and odd s.a. SIS |z,u,v;+,-> being studied in greater detail. The set of s.a. SIS contain all even and odd coherent states (CS) of Dodonov, Malkin and Man'ko, the Perelomov SU(1,1) CS and …
Fractional squeezing: spectra and dynamics from generalized squeezing Hamiltonian with fractional orders
本文研究了广义压缩哈密顿量的分数阶压缩问题，确定了临界点的位置并预测了这些点的行为，揭示了频谱从连续到离散转变以及振荡幅度从无限到有限转变的特征。
A Josephson parametric amplifier (JPA) can create squeezed states of microwave light, lowering the noise associated with certain quantum measurements. We experimentally study how the JPA's pump influences the phase-sensitive amplification and deamplification of a coherent tone's amplitude when that amplitude is commensurate with vacuum fluctuations. We predict and demonstrate that by operating the JPA with a pump power greater than the value that maximizes gain, the amplifier distortion is reduced and consequently squeezing is improved. Optimizing the JPA's operation in this fashion, we direct…
We consider a hybrid optomechanical system which is composed of the atomic ensemble and a standard optomechanical cavity driven by the periodically modulated external laser field. We investigate the asymptotic behaviors of Heisenberg operator first moments and clearly show the approaching process between the exact numerical results and analytical solutions. Based on the specific modulation forms of external driving and effective optomechanical coupling, we discuss in detail the atom-mirror entanglement enhancement, respectively. Compared with the constant driving regime, the entanglement can b…
Quantum fluctuations of optical fiber Bragg grating solitons are investigated numerically by the back-propagation method. It is found for the first time that the bandgap effects of the grating act as a nonlinear filter and cause the soliton to be amplitude squeezed. The squeezing ratio saturates after a certain grating length and the fundamental Bragg soliton produces the optimal squeezing ratio.
Recently, in several theoretical investigations, amplitude nth-power squeezing has been studied with $n = 2,~3,~4,~5$. In the present paper, we give a proposal for experimental detection of amplitude $n$th-power squeezing using ordinary homodyning with coherent light for arbitrary power $n$ and discuss in detail its theory. The proposed scheme requires only repeated measurements of the factorial moments of number of photons in the light obtained after homodyning, with various shifts of phase of coherent light, and involves no approximations, whatsoever. This has advantage over the method propo…
In this paper we calculate the position and momentum space information entropies for the quantum states associated with a particular physical system, i.e. the isotonic oscillator Hamiltonian. We present our results for its ground states, as well as for its excited states. We observe that the lower bound of the sum of the position and momentum entropies expressed by the Beckner, Bialynicki-Birula and Mycielski (BBM) inequality is satisfied. Moreover, there exist eigenstates that exhibit squeezing in the position information entropy. In fact, entropy squeezing, which occurs in position, will be …
In this Letter we study the evolution of the higher-order squeezing, namely, $n$th-order single-mode squeezing, sum- and difference-squeezing for the codirectional Kerr nonlinear coupler. We show that the amount of squeezing decreases when $n$, i.e. the squeezing order, increases. For specific values of the interaction parameters squeezing factors exhibit a series of revival-collapse phenomena, which become more pronounced when the value of $n$ increases. Sum-squeezing can provide amounts of squeezing greater than those produced by the $n$th higher-order ($n\geq 2$) squeezing for the same valu…
Broadband amplitude squeezing in electrically driven quantum dot lasers
本文研究电驱动量子点激光器在室温下实现宽带振幅压缩态，实验与随机模拟共同证实其在3–12 GHz频率范围内产生压缩光，为高速连续变量量子信息提供新途径。
Polarization squeezing is shown to occur in non-degenerate parametric amplification of coherent light and the degree of squeezing at interaction time $T$ can be as large as $1-e^{-2T}$. This gives $86.4\%$ polarization squeezing for $T=1$ and $98.2\%$ for $T=2$. One simple case when this occurs is on taking initially plane polarized light having equal amplitudes in the two modes that finally has equal intensities of two circular polarizations. This suggest the experimental settings of parameters to achieve this extent of polarization squeezing in coherent light.
The role of squeezing in quantum key distribution with continuous variables based on homodyne detection and post-selection is investigated for several specific eavesdropping strategies. It is shown that amplitude squeezing creates strong correlations between the signals of the legitimate receiver and a potential eavesdropper. Post-selection of the received pulses can therefore be used to reduce the eavesdropper's knowledge of the raw key, which increases the secret key rate by orders of magnitude over large distances even for modest amounts of squeezing.
We analyze effects of squeezing upon superpositions of coherent states (SCSs) and entangled coherent states (ECSs) for Bell-inequality tests. We find that external squeezing can always increase the degrees of Bell violations, if the squeezing direction is properly chosen, for the case of photon parity measurements. On the other hand, when photon on/off measurements are used, the squeezing operation can enhance the degree of Bell violations only for moderate values of amplitudes and squeezing. We point out that a significant improvement is required over currently available squeezed SCSs in orde…
Squeezing of a thermal bath introduces new features absent in an open quantum system interacting with an uncorrelated (zero squeezing) thermal bath. The resulting dynamics, governed by a Lindblad-type evolution, extends the concept of a generalized amplitude damping channel, which corresponds to a dissipative interaction with a purely thermal bath. Here we present the Kraus representation of this map, which we call the squeezed generalized amplitude damping channel. As an application of this channel to quantum information, we study the classical capacity of this channel.
Loss and decoherence are a major problem in the transmission of non-classical states of light over large distances. It was recently shown that the effects of decoherence can be reduced by applying a probabilistic noiseless attenuator before transmitting a quantum state through a lossy channel, followed by probabilistic noiseless amplification (M. Micuda et al, Phys. Rev. Lett. 109, 180503 (2012)). Here we show that similar results can be obtained for certain kinds of macroscopic quantum states by squeezing the signal before transmission, followed by deterministic amplification and anti-squeezi…
Multimode amplitude squeezing through cascaded nonlinear optical processes
该研究通过级联三波混频与多模非线性腔的 Q 因子工程，实现超过 10 dB 的可调单模振幅压缩及阈值以上多离散频率模式明亮压缩，并揭示合成频率维度中的 Bloch 振荡与长程关联。
A new scheme for generating amplitude squeezed light by means of soliton self-phase modulation is experimentally demonstrated. By injecting 180-fs pulses into an equivalent Mach-Zehnder fiber interferometer, a maximum noise reduction of $4.4 \pm 0.3$ dB is obtained ($6.3 \pm 0.6$ dB when corrected for losses). The dependence of noise reduction on the interferometer splitting ratio and fiber length is studied in detail.
Effects of squeezing on the power broadening and shifts of micromaser lineshapes
本研究探讨压缩效应对微激射器线形的影响，发现压缩相干态下谱线对压缩参数敏感，且等振幅叠加时位移依赖压缩参数及其符号。
Temperature-anisotropy conjugate magnon squeezing in antiferromagnets
本研究针对单轴反铁磁材料中的双模磁振子态，揭示了温度诱导振幅压缩、各向异性导致相位压缩的共轭磁振子压缩效应，明确了两类因素对双模压缩的不同作用及各向异性削弱作用的有界性，给出了提升磁振子压缩因子的条件。
We study the Hillery-type, i.e. $N$-th power, amplitude squeezing in the fan-state $| ξ;2k,f>_{F}$ characterized by $ξ\in \mathcal{C}$, $k=1,2,3,...$ and $f$ a nonlinear operator-valued function. We show that for a given $k$ there exists a critical $ξ_c$ such that for $0<|ξ|\leq|ξ_c|$ squeezing occurs simultaneously in $2k$ directions for the powers $N$ which are a multiple of $2k$. This result does not depend on the concrete form of $f$, i.e. it holds true for both $f\equiv 1$ and $f\neq 1$. However, for $f\neq 1$, which is realized here in the ion trap context, the squeezing directions as we…
Optical nonreciprocity induced by quantum squeezing in temperature sensitive optomechanical systems
本研究探究χ⁽²⁾微环光力学系统中由定向量子压缩诱导的光学非互易性，揭示热声子数对单光子传输隔离比及光子关联统计特性的影响，提出其可用于超低温精密温度测量，丰富量子网络与量子信息处理应用。
In this paper, ordinary and amplitude-squared squeezing as well as Wigner functions of single-photon-added coherent state after postselected von Neumann measurements are investigated. The analytical results show that the von Neumann type measurement which is characterized by post-selection and weak value can significantly change the squeezing feature of single-photon-added coherent state. It is also found that the postselected measurement can increase the nonclassicality of the original state in strong measurement regimes. It is anticipated that this work could may provide an alternate and eff…
A pair of conjugate observables, such as the quadrature amplitudes of harmonic motion, have fundamental fluctuations which are bound by the Heisenberg uncertainty relation. However, in a squeezed quantum state, fluctuations of a quantity can be reduced below the standard quantum limit, at the cost of increased fluctuations of the conjugate variable. Here we prepare a nearly macroscopic moving body, realized as a micromechanical resonator, in a squeezed quantum state. We obtain squeezing of one quadrature amplitude $1.1 \pm 0.4$ dB below the standard quantum limit, thus achieving a long-standin…
We create squeezed light by exploiting the quantum nature of the mechanical interaction between laser light and a membrane mechanical resonator embedded in an optical cavity. The radiation pressure shot noise (fluctuating optical force from quantum laser amplitude noise) induces resonator motion well above that of thermally driven motion. This motion imprints a phase shift on the laser light, hence correlating the amplitude and phase noise, a consequence of which is optical squeezing. We experimentally demonstrate strong and continuous optomechanical squeezing of 1.7 +/- 0.2 dB below the shot …
The use of a Kerr nonlinearity to generate squeezed light is a well-known way to surpass the quantum noise limit along a given field quadrature. Nevertheless, in the most common regime of weak nonlinearity, a single Kerr resonator is unable to provide the proper interrelation between the field amplitude and squeezing required to induce a sizable deviation from Poissonian statistics. We demonstrate experimentally that weakly coupled bosonic modes allow exploration of the interplay between squeezing and displacement, which can give rise to strong deviations from the Poissonian statistics. In par…
Dissipative transfer of quantum correlations from light to atomic arrays
该研究利用原子阵列的光定向集体响应，通过压缩真空场照射实现量子关联的耗散转移以生成自旋压缩稳态，分析了参数影响并探讨其在原子钟中的应用。
Squeezing and measurement of a mechanical quadrature via PID feedback
本文研究了PID反馈在量子系统中对机械四阶振幅和压缩的瞬态与稳态行为的影响，展示了导数反馈对条件和非条件压缩的作用，并演示了如何利用反馈使机械四阶跟踪参考信号，为提高量子态控制和测量精度提供新途径。
Analytical Fock Representation of Two-Mode Squeezing for Quantum Interference
本文提出了一种解析方法，用于在任意挤压强度下分析非线性干涉仪的多光子干涉现象，并提供了新的实验观测可能性。
Generation of entanglement via squeezing on a tripartite-optomechanical system
本文提出通过调节振动模式压缩参数来调控量子比特-腔-谐振器三方混合系统中的量子纠缠，实现了无直接相互作用子系统间的纠缠生成，并分析了损耗影响及推广单配性概念的可能性。
Verification of conditional mechanical squeezing for a mg-scale pendulum near quantum regimes
本研究通过连续线性测量与量子态预测，在毫微克级摆上实验验证了接近量子区域的条件机械压缩，位置和动量标准差分别达零点振幅的36倍和89倍，比先前研究更接近零点运动，为宏观物体量子控制迈出第一步。
Eigenstates of general complex linear combination of SU(1,1) generators (su^c(1,1) algebraic coherent states (ACS)) are constructed and discussed. In case of quadratic boson representation ACS can exhibit strong both linear and quadratic amplitude squeezing. ACS for a given Lie group algebra contain the corresponding Perelomov CS with maximal symmetry.
Encoding classical data into the squeezing of noisy-states for plasmonic communication
本文提出了一种新的等离子体通信方法，通过将经典数据直接编码到表面等离子体极化子（SPPs）的非经典性（如压缩）中，实现了远距离的信息传输，同时利用长寿命相关性在读出阶段通过光束分裂器检索信息，并在THz范围内利用热背景实现高带宽纳米级通信。
We suggest a method to reconstruct the zero-delay-time second-order correlation function $g^{(2)}(0)$ of Gaussian states using a single homodyne detector. To this purpose, we have found an analytic expression of $g^{(2)}(0)$ for single- and two-mode Gaussian states in terms of the elements of their covariance matrix and the displacement amplitude. In the single-mode case we demonstrate our scheme experimentally, and also show that when the input state is nonclassical, there exist a threshold value of the coherent amplitude, and a range of values of the complex squeezing parameter, above which …
Squeezing enhanced homodyne weak force sensing in cavity optomechanics
通过变分零差读出和量子压缩，在腔光力学系统中实现超越标准量子极限的弱力灵敏度提升。
Following the pioneering work of Prof. Hermann A. Haus, a general quantum theory for bi-directional nonlinear optical pulse propagation problems is developed and applied to study the quantum properties of fiber Bragg grating solitons. Fiber Bragg grating solitons are found to be automatically amplitude squeezed after passing through the grating and the squeezing ratio saturates after a certain grating length. The optimal squeezing ratio occurs when the pulse energy is slightly above the fundamental soliton energy. One can also compress the soliton pulsewidth and enhance the squeezing simultane…
We solve the time evolution of a nonlinear optomechanical Hamiltonian with arbitrary time-dependent mechanical displacement, mechanical single-mode squeezing and a time-dependent optomechanical coupling up to the solution of two second-order differential equations. The solution is based on identifying a minimal and finite Lie algebra that generates the time-evolution of the system. This reduces the problem to considering a finite set of coupled ordinary differential equations of real functions. To demonstrate the applicability of our method, we compute the degree of non-Gaussianity of the time…
We analyze the creation of spin squeezed atomic ensembles by simultaneous dispersive interactions with several optical frequencies. A judicious choice of optical parameters enables optimization of an interferometric detection scheme that suppresses inhomogeneous light shifts and keeps the interferometer operating in a balanced mode that minimizes technical noise. We show that when the atoms interact with two-frequency light tuned to cycling transitions the degree of spin squeezing $ξ^2$ scales as $ξ^2\sim 1/d$ where $d$ is the resonant optical depth of the ensemble. In real alkali atoms there …
Magnon-Squeezing-Induced Nonreciprocal Quantum Coherence in a Cavity Magnomechanical System
本文研究腔磁力系统中磁振子压缩驱动的量子相干性，发现压缩幅度与相位可调制有效磁振子频率和阻尼，实现相干性的相位依赖增强与非互易传递，并证明压缩磁振子是控制量子相干性的鲁棒可调资源。
Mitigating sloppiness in joint estimation of successive squeezing parameters
本文针对连续两次同相挤压参数联合估计的不灵敏性问题，提出在两次挤压间引入优化的相移扰乱操作，使量子Fisher信息矩阵非奇异，并证明联合估计优于逐步估计，通用dyne探测可接近最优精度。
Effect of biased noise fluctuations on the degree of squeezing as well as the intensity of a radiation generated by a one-photon coherent beat laser is presented. It turns out that the radiation exhibits squeezing inside and outside the cavity under certain conditions. The degree of squeezing is enhanced by the biased noise input significantly in both regions. Despite the presence of the biased environment modes outside the cavity, the degree of squeezing outside the cavity can be greater than or equal to or even less than the cavity radiation depending on the initial preparation of the atomic…
Entangling gates are an essential component of quantum computers. However, generating high-fidelity gates, in a scalable manner, remains a major challenge in all quantum information processing platforms. Accordingly, improving the fidelity and robustness of these gates has been a research focus in recent years. In trapped ions quantum computers, entangling gates are performed by driving the normal modes of motion of the ion chain, generating a spin-dependent force. Even though there has been significant progress in increasing the robustness and modularity of these gates, they are still sensiti…
A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme, called synodyne detection, which reveals complex squeezing and allows the accounting of …
Quantum squeezing induced quantum entanglement and EPR steering in coupled optomechanical system
该研究提出耦合回音壁模式光力学系统的理论方案，利用χ⁽²⁾非线性谐振腔的量子压缩诱导纠缠与EPR操控，可通过参数调节实现纠缠与操控特性转变，无需强压缩场且操控便捷，为量子技术应用提供新途径。
We study the directional properties of a radiation field emitted by a geometrically small system composed of two identical two-level emitters located at short distances and driven by an optical vortex beam, a Laguerre-Gaussian beam which possesses a structured phase and amplitude. We find that the system may operate as a nanoantenna for controlled and tunable directional emission. Polar diagrams of the radiation intensity are presented showing that a constant phase or amplitude difference at the positions of the emitters plays an essential role in the directivity of the emission. We find that …
Isoenergetic model for optical downconversion and error-specific limits of the parametric approximation
本文提出一种超越标准参数近似的等能量解析模型，考虑了泵浦耗尽与纠缠，确定了参数近似的特定误差极限，并证明其在高斯玻色采样实验中的有效范围。
A general formalism is given in quantum optics within a ring cavity, in which a non-linear material is stored. The method is Feynman graphical one, expressing the transition amplitude or S-matrix in terms of propagators and vertices. The propagator includes the additional damping effect via the non-linear material as well as the reflection and penetration effects by mirrors. Possible application of this formalism is discussed, in estimating the averaged number of produced photons, Husimi function, and the observables to examine beyond the squeezing mechanism of photons.
Nonclassical Cutoff Fluctuations in Squeezed-Light-Driven High-Harmonic Generation
该研究探讨了在压缩光驱动下高次谐波生成（HHG）的截断波动特性，通过量子光学方法揭示了压缩态对HHG观测结果的影响，并展示了压缩如何抑制谐波截断的波动低于标准量子极限。
Does the survival and sudden death of quadripartite steering in curved spacetime truly depend on multi-directionality?
本研究探讨了 Schwarzschild 黑洞背景下 Gaussian 四部量子导引的方向依赖性，发现不同方向的导引在衰减、猝灭及渐近行为上表现出三种截然不同的特性，且不可及导引具有内在不对称性。
We address the performance of an interferometric setup in which a squeezed single photon interferes at a beam splitter with a coherent state. Our analysis in based on both the quantum Fisher information and the sensitivity when a Mach-Zehnder setup is considered and the difference photocurrent is detected at the output. We compare our results with those obtained feeding the interferometer with a squeezed vacuum (with the same squeezing parameter of the squeezed single photon) and a coherent state in order to have the same total number of photons circulating in the interferometer. We find that …
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