Stefano Mancini, Rodolfo Bonifacio
We study the effects of time uncertainty in the interaction of atoms with a standing light wave. We discuss its physical origin and the possibility to observe intrinsic decoherence effects by measuring the atomic momentum distribution.
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Some unexplored decoherence aspects within the Caldeira-Leggett master equation are analyzed and discussed. The decoherence process is controlled by the two environment parameters, the relaxation rate or friction and the temperature, leading to a gradual transition from the quantum to classical regime. Arrival time distributions, nonminimum-uncertainty-product or stretching Gaussian wave packets, identical particles and diffraction in time display interesting features during the decoherence process undergone by the time dependent interference patterns. We show that the presence of a constant f…
We study the diffraction of quantum degenerate fermionic atoms off of quantized light fields in an optical cavity. We compare the case of a linear cavity with standing wave modes to that of a ring cavity with two counter-propagating traveling wave modes. It is found that the dynamics of the atoms strongly depends on the quantization procedure for the cavity field. For standing waves, no correlations develop between the cavity field and the atoms. Consequently, standing wave Fock states yield the same results as a classical standing wave field while coherent states give rise to a collapse and r…
The loss of contrast in double-slit electron-diffraction due to dephasing and decoherence processes is studied. It is shown that the spatial correlation function of diffraction patterns can be used to distinguish between dephasing and decoherence. This establishes a measure of time-reversibility that does not require the determination of coherence terms of the density matrix, while von Neumann entropy, another measure of time-reversibility, does require coherence terms. This technique is exciting in view of the need to understand and control the detrimental experimental effects of contrast los…
We study theoretically the decoherence of a gas of bosonic atoms induced by the interaction with a largely detuned laser beam. It is shown that for a standing laser beam decoherence coincides with the single-particle result. For a running laser beam many-particle effects lead to significant modifications.
Matter-wave interferometry has been largely studied in the last few years. Usually, the main problem in the analysis of the diffraction experiments is to establish the causes for the loss of coherence observed in the interference pattern. In this work, we use different type of environmental couplings to model a two slit diffraction experiment with massive particles. For each model, we study the effects of decoherence on the interference pattern and define a visibility function that measures the loss of contrast of the interference fringes on a distant screen. Finally, we apply our results to t…
Decoherence can be provided by a dissipative environment as described by the Caldeira-Leggett equation. This equation is foundational to the theory of quantum dissipation. However, no experimental test has been performed that measures for one physical system both the dissipation and the decoherence. Anglin and Zurek predicted that a resistive surface could provide such a dissipative environment for a free electron wave passing close to it. We propose that the electron wave's coherence and energy loss can be measured simultaneously by using Kapitza-Dirac scattering for varying light intensity.
We demonstrate the theoretical feasibility of spin-dependent diffraction and spin-polarization of an electron in two counter-propagating, circularly polarized laser beams. The spin-dynamics appears in a two-photon process of the Kapitza-Dirac effect in the Bragg regime. We show the spin-dependence of the diffraction process by comparison of the time-evolution of a spin-up and spin-down electron in a relativistic quantum simulation. We further discuss the spin properties of the scattering by studying an analytically approximated solution of the time-evolution matrix. A classification scheme in …
The characteristic of the angular distributions of accelerated Bose-Einstein condensate (BEC) atoms incidence on the surface is designed using the mathematical modeling method. Here, we proposed the idea to study the retroreflection and diffraction of a BEC from an evanescent standing wave potential (ESWP). The ESWP is formed by multiple reflections of the laser beam from the surface of the prism under the influence of gravity. After BEC's reflection and diffraction, the so-called BEC's density rainbow patterns develop due to the interference which depends on the surface structure which we mod…
We generalize the notion of the Franhoufer diffraction from a single slit and a circular aperture to the case of partially temporal coherent and quasimonochromatic light. The problem is studied analytically and the effect of coherence length on the diffraction pattern is investigated. In this case the far-field distribution of the irradiance depends on the newly introduced parameter(decoherence parameter) which governs the deviation of the diffraction pattern from the usual one. The corrections due to temporal decoherency on the irradiance distribution in the far field is obtained. Numerical s…
Diffraction of walking drops by a standing Faraday wave
本文报告了导波流体力学中行走液滴被驻立 Faraday 波偏转并产生类 Kapitza-Dirac 效应衍射图样的现象，揭示了由失谐引发的非共振效应及 ponderomotive 效应。
We study the effects of strong inter-particle interaction on diffraction of a Bose-Einstein condensate of $^6Li_2$ molecules from a periodic potential created by pulses of a far detuned optical standing wave. For short pulses we observe the standard Kapitza-Dirac diffraction, with the contrast of the diffraction pattern strongly reduced for very large interactions due to interaction dependent loss processes. For longer pulses diffraction shows the characteristic for matter waves impinging on an array of tubes and coherent channeling transport. We observe a slowing down of the time evolution go…
A study of the effects of Gaussian distribution of coherence length of source on the diffraction of partial temporal coherence beam from multi slits: Theory and simulation
本文将单缝时间相干光衍射推广至任意n缝，研究退相干参数对衍射图样的影响，并进一步引入高斯分布的光源相干长度进行数值模拟，以更贴近实际地分析远场衍射效应。
In this paper, we apply the full new method of quantum theory to study the double-slit diffraction of ${C_{60}}$ molecules. We calculate the double-slit wave functions of ${C_{60}}$ molecules by Schrödinger equation, and calculate the diffraction wave function behind the slits with the Feynman path integral quantum theory, and then give the relation between the diffraction intensity of double-slit and diffraction pattern position. We compare the calculation results with two different double-slit diffraction experiments. When the decoherence effects are considered, the calculation results are i…
Double-slit interference with charged particles. Density matrices and decoherence from time-dependent quantum Monte Carlo
本文利用含时量子蒙特卡洛方法研究带电粒子双缝干涉中的退相干，并展示可直接由单粒子波函数构建含时密度矩阵，无需迹掉环境粒子，从而为理解多体量子动力学提供新途径。
We review recent theoretical models and experiments dealing with the diffraction of neutral atoms from a reflection grating, formed by a standing evanescent wave. We analyze diffraction mechanisms proposed for normal and grazing incidence, point out their scopes and confront the theory with experiment.
Perturbative solution approach for computing the two-photon Kapitza-Dirac effect in a Gaussian beam standing light wave
本文提出一种相对论框架下的微扰解法，通过动量空间傅里叶变换计算高斯光束驻波光场中的双光子Kapitza-Dirac电子衍射，避免了时间步进并具有二次方标度和易并行化特点。
The effects of incoherence and decoherence in the double--slit experiment are studied using both optical and quantum--phenomenological models. The results are compared with experimental data obtained with cold neutrons.
We demonstrate that structures made of light can be used to coherently control the motion of complex molecules. In particular, we show diffraction of the fullerenes C60 and C70 at a thin grating based on a standing light wave. We prove experimentally that the principles of this effect, well known from atom optics, can be successfully extended to massive and large molecules which are internally in a thermodynamic mixed state and which do not exhibit narrow optical resonances. Our results will be important for the observation of quantum interference with even larger and more complex objects.
We propose a super-resolution quantum lithography scheme based on coherent population trapping in lambda-type atoms coupled to temporally-cascaded standing-wave driving fields. By realizing effective multiplication of optical intensity profiles on an atomic state density distribution, the scheme enables an arbitrarily high degree of resolution enhancement without modifying the atomic level structure of the photographic medium or the light source configuration. It is also shown that the visibility of the super-resolution patterns is preserved under a significant atomic state decoherence rate.
We have built and operated an atom interferometer of the Mach-Zehnder type. The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors and beam-splitters for the atomic wave are based on elastic Bragg diffraction on laser standing waves at 671 nm. We give here a detailed description of our experimental setup and of the procedures used to align its components. We then present experimental signals, exhibiting atomic interference effects with a very high visibility, up to 84.5 %. We describe a series of experiments testing the sensitivity of the fringe visibility to the main …
Precision measurement of small separations between two atoms or molecules has been of interest since the early days of science. Here, we discuss a scheme which yields spatial information on a system of two identical atoms placed in a standing wave laser field. The information is extracted from the collective resonance fluorescence spectrum, relying entirely on far-field imaging techniques. Both the interatomic separation and the positions of the two particles can be measured with fractional-wavelength precision over a wide range of distances from bout lambda/550 to lambda/2.
Parameter space investigation for spin-dependent electron diffraction in the Kapitza-Dirac effect
本文通过引入广义量化规范并利用Newton梯度迭代求解优化问题，证明在Kapitza-Dirac效应双光子Bragg散射中可在宽范围横向电子动量下实现自旋相关电子衍射，且低动量条件可放宽实验参数约束。
We present a semiclassical perturbation method for the description of atomic diffraction by a weakly modulated potential. It proceeds in a way similar to the treatment of light diffraction by a thin phase grating, and consists in calculating the atomic wavefunction by means of action integrals along the classical trajectories of the atoms in the absence of the modulated part of the potential. The capabilities and the validity condition of the method are illustrated on the well-known case of atomic diffraction by a Gaussian standing wave. We prove that in this situation the perturbation method …
A model of the asymmetric coherent scattering process (caused by initial atomic wave-packet splitting in the momentum space) taking place at the large detuning and adiabatic course of interaction for an effective two-state system interacting with a standing wave of laser radiation is discussed. We show that the same form of initial wave-packet splitting may lead to different, in general, diffraction patterns for opposite, adiabatic and resonant, regimes of the standing-wave scattering. We show that the scattering of the Gaussian wave packet in the adiabatic case presents refraction (a limiting…
Electron-Enabled Nanoparticle Diffraction
提出利用电子在纳米粒子亚纳米晶格处的Bragg衍射生成高质量量子叠加态，实现比传统双光子反冲大约1000倍的相干动量分裂，显著缩短干涉时间并减轻退相干，为透射电子显微镜中宏观量子效应测试开辟新途径。
We present a combined theoretical and experimental study of solid-state spin decoherence in an electronic spin bath, focusing specifically on ensembles of nitrogen vacancy (NV) color centers in diamond and the associated substitutional nitrogen spin bath. We perform measurements of NV spin free induction decay times $T_2^*$ and spin-echo coherence times $T_2$ in 25 diamond samples with nitrogen concentrations [N] ranging from 0.01 to 300\,ppm. We introduce a microscopic model and perform numerical simulations to quantitatively explain the degradation of both $T_2^*$ and $T_2$ over four orders …
We propose a novel scheme for asymmetric light diffraction of a weak probe field into a one-dimensional (1D) and two-dimensional (2D) lattice occupied with cold atoms. The atoms are driven into the double lambda-type configuration by a standing wave, two coupling laser fields and a probe. Our study suggests the proposed scheme is capable of forming an asymmetric diffraction as a result of inducing optical parity-time symmetry in both 1D and 2D lattices. Moreover it is demonstrated that the asymmetric pattern of diffraction can be dynamically manipulated by means of adjusting the relative phase…
We have constructed an atom interferometer of the Mach-Zehnder type, operating with a supersonic beam of lithium. Atom diffraction uses Bragg diffraction on laser standing waves. With first order diffraction, our apparatus has given a large signal and a very good fringe contrast (74%), which we believe to be the highest ever observed with atom interferometers. This apparatus will be applied to high sensitivity measurements
The Kapitza - Dirac effect is the diffraction of a well - collimated particle beam by a standing wave of light. Why is this interesting? Comparing this situation to the introductory physics textbook example of diffraction of a laser beam by a grating, the particle beam plays the role of the incoming wave and the standing light wave the role of the material grating, highlighting particle - wave duality. Apart from representing such a beautiful example of particle - wave duality, the diffracted particle beams are coherent. This allows the construction of matter interferometers and explains why t…
We study localization of atomic position when a three-level atom interacts with a quantized standing-wave field in the Ramsey interferometer setup. Both the field quadrature amplitude and the atomic internal state are measured to obtain the atomic position information. It is found that this dual measurement scheme produces an interference pattern superimposed on a diffraction-like pattern in the atomic position distribution, where the former pattern originates from the state-selective measurement and the latter from the field measurement. The present scheme results in a better resolution in th…
Path-Degenerate Quantum Interferometry for Decoherence Mitigation in Gravitational-Wave Detectors
提出路径简并量子干涉方案，通过消除额外光学子系统并集成变分输出来抑制退相干，实验证明可增强信号并提升引力波探测器的量子噪声抑制能力。
Spatial Characterization of Fraunhofer Diffraction in a Four-Level Light-Matter Coupling System
本文研究四能级N型原子系统中夫琅禾费衍射的空间特性，通过将探测极化率展开到驻波场二阶并利用轨道角动量操控，实现了对不同衍射阶次空间分布的精确控制。
Quadrature squeezing enhances Wigner negativity in a mechanical Duffing oscillator
提出利用运动压缩态有效增强量子非谐谐振子的非谐性，加速 Wigner 分布负性产生并抑制能量阻尼，为宏观机械系统制备真正量子态提供了理论与实验平台分析。
Precise knowledge of optical lattice depths is important for a number of areas of atomic physics, most notably in quantum simulation, atom interferometry and for the accurate determination of transition matrix elements. In such experiments, lattice depths are often measured by exposing an ultracold atomic gas to a series of off-resonant laser-standing-wave pulses, and fitting theoretical predictions for the fraction of atoms found in each of the allowed momentum states by time of flight measurement, after some number of pulses. We present a full analytic model for the time evolution of the ato…
We present the possibility of spin-dependent Kapitza-Dirac scattering based on a two-photon interaction only. The interaction scheme is inspired from a Compton scattering process, for which we explicitly show the mathematical correspondence to the spin-dynamics of an electron diffraction process in a standing light wave. The spin effect has the advantage that it already appears in a Bragg scattering setup with arbitrary low field amplitudes, for which we have estimated the diffraction count rate in a realistic experimental setup at available X-ray free-electron laser facilities.
Atom interferometry is the most successful technique for precision metrology. However, current interferometers using ultracold atoms allows one to probe the interference pattern only momentarily and has finite duty cycle, resulting in an aliasing effect and a low-bandwidth measurement -- also known as Dick effect. Interferometry with a continuous-wave atom laser shows promise in overcoming these limitations due a continuous monitoring of the interference pattern. In this work, we demonstrate a key step towards such an interferometry by demonstrating a diffraction of an `atom laser' in the Rama…
Two-dimensional simulation of the spin-flip in the Kapitza-Dirac effect
本文在相对论框架下用FFT分裂算符法二维求解Dirac方程，模拟高斯驻光波中的Kapitza–Dirac散射，证明无近似条件下自旋翻转可发生，并分析平面波近似、纵向偏振和高阶衍射峰。
Decoherence is the main process behind the quantum to classical transition. It is a purely quantum mechanical effect by which the system looses its ability to exhibit coherent behavior. The recent experimental observation of diffraction and interference patterns for large molecules raises some interesting questions. In this context, we identify possible agents of decoherence to take into account when modeling these experiments and study theirs visible (or not) effects on the interference pattern. Thereby, we present an analysis of matter wave interferometry in the presence of a dynamic quantum…
We present experimental observations of diffusion resonances for the quantum kicked rotor with weak decoherence. Cold caesium atoms are subject to a pulsed standing wave of near-resonant light, with spontaneous emission providing environmental coupling. The mean energy as a function of the pulse period is determined during the late-time diffusion regime for a constant probability of spontaneous emission per unit time. Structure in the late-time energy is seen to increase with physical kicking strength. The observed structure is related to Shepelyansky's predictions of the initial quantum diffu…
We study Bragg scattering at 1D atomic lattices. Cold atoms are confined by optical dipole forces at the antinodes of a standing wave generated inside a laser-driven cavity. The atoms arrange themselves into an array of lens-shaped layers located at the antinodes of the standing wave. Light incident on this array at a well-defined angle is partially Bragg-reflected. We measure reflectivities as high as 30%. In contrast to a previous experiment devoted to the thin grating limit [S. Slama, et al., Phys. Rev. Lett. 94, 193901 (2005)] we now investigate the thick grating limit characterized by mul…
We demonstrate nanometer-scale spatial control of inter-atomic interactions in a Bose-Einstein condensate of ytterbium(Yb). A pulsed optical standing wave, tuned near an optical Feshbach resonance varies the s-wave scattering length continuously across the standing wave pattern. The modulated mean-field energy with a spatial period of every 278 nm is monitored by a diffraction pattern in a time-of-flight image. We observe a wide scattering length control of up to 160 nm. The demonstrated spatial modulation of the scattering length proves that the high resolution control of atomic interactions …
Decoherence in matter-wave Talbot interference: A hydrodynamic probability-flow analysis
研究环境诱导退相干对物质波塔尔博干涉的抑制，通过流体动力学概率流分析揭示退相干对干涉图案和动量分布的影响，展示退相干不必然同时导致干涉消失和动态路径分离丧失。
We present a theory for the diffraction of large molecules or nanoparticles at a standing light wave. Such particles can act as a genuine photon absorbers due to their numerous internal degrees of freedom effecting fast internal energy conversion. Our theory incorporates the interplay of three light-induced properties: the coherent phase modulation due to the dipole interaction, a non-unitary absorption-induced amplitude modulation described as a generalized measurement, and a coherent recoil splitting that resembles a quantum random walk in steps of the photon momentum. We discuss how these e…
In the Kapitza-Dirac effect, atoms, molecules, or swift electrons are diffracted off a standing wave grating of the light intensity created by two counter-propagating laser fields. In ultrafast electron optics, such a coherent beam splitter offers interesting perspectives for ultrafast beam shaping. Here, we study, both analytically and numerically, the effect of the inclination angle between two laser fields on the diffraction of pulsed, low-energy electron beams. For sufficiently high light intensities, we observe a rich variety of complex diffraction patterns. These do not only reflect inte…
We report on the observation of the coherent enhancement of the return probability ("enhanced return to the origin" , ERO) in a periodically kicked cold-atom gas. By submitting an atomic wave packet to a pulsed, periodically shifted laser standing wave, we induce an oscillation of ERO in time and explain it in terms of a periodic, reversible dephasing in the weak-localization interference sequences responsible for ERO. Monitoring the temporal decay of ERO, we exploit its quantum coherent nature to quantify the decoherence rate of the atomic system.
Probing molecular photophysics in a matter-wave interferometer
本文提出利用驻激光波上的物质波衍射精确测量分子光物理参数，通过Wigner表示解析计算分析干涉图样特征，并评估有限粒子数下参数估计的精度。
Two-Body Kapitza-Dirac Scattering of One-Dimensional Ultracold Atoms
研究一维谐振子中两原子在光格子中的双体Kapitza-Dirac散射，分析相互作用强度、晶格深度等参数对衍射图案的影响，提供精确的少体基准。
We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without an optical access to a single site) and pair …
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