Jean Claude Garreau
The relations between quantum coherence and quantum interference are discussed. A general method for generation of quantum coherence through interference-induced state selection is introduced and then applied to `simple' atomic systems under two-photon transitions, with applications in quantum optics and laser cooling.
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We propose the concept of pair-wise coherence to study the relation between the l1 norm of coherence and the quantum interference in Young's multi-photon multi-path experiments, where the input photons may be entangled each other. We find that only the local coherence of each single photon can make quantum interference and the collective coherence between photons has no contribution to quantum interference. The visibility of interference fringe is commonly less than the l1norm of coherence of the corresponding input state, suggesting that the l1 norm of coherence is only the necessary but not …
We develop a rigorous connection between statistical properties of an interference pattern and the coherence properties of the underlying quantum state. With explicit examples, we demonstrate that even for inaccurate reconstructions of interference patterns properly defined statistical moments permit a reliable characterization of quantum coherence.
A quantitative measure of quantum coherence was recently introduced, in the context of quantum information theory. This measure has also been propounded as a good quantifier of the wave nature of quantum objects. However, actually measuring coherence in an experiment is still considered a challenge. A procedure for measuring coherence in a multi-slit interference is proposed here. It can be used for experimentally testing duality relations for interference experiments involving more than two slits.
The interference observed for a quanton, traversing more than one path, is believed to characterize its wave nature. Conventionally, the sharpness of interference has been quantified by its visibility or contrast, as defined in optics. Based on this visibility, wave-particle duality relations have been formulated for two-path interference. However, as one generalizes the situation to multi-path interference, it is found that conventional interference visibility is not a good quantifier. A recently introduced measure of quantum coherence has been shown to be a good quantifier of the wave nature…
One-dimensional discrete-time quantum walk has played an important role in development of quantum algorithms and protocols for different quantum simulations. The speedup observed in quantum walk algorithms is attributed to quantum interference and coherence of the wave packet in position space. Similarly, localization in quantum walk due to disorder is also attributed to quantum interference effect. Therefore, it is intriguing to have a closer look and understand the way quantum interference manifests in different forms of quantum walk dynamics. Quantum coherence in the system is responsible f…
A well known result for the interference of two single-mode fields is that the degree of coherence and the degree of indistinguishablity are same when we consider the detection of a single photon. In this article we present the relation between degree of coherence, path indistinguishability and the fringe visibility considering interference of multiple number of single-mode fields while being interested in the detection of a single photon only . We will also mention how Born's rule of interference for multiple sources is reflected in these results.
We report observation of a counter-intuitive phenomenon in multi-path correlation interferometry with thermal light. The intensity correlation between the outputs of two unbalanced Mach-Zehnder interferometers (UMZI) with two classically correlated beams of thermal light at the input exhibits genuine second-order interference with the visibility of $1/3$. Surprisingly, the second-order interference does not degrade at all no matter how much the path length difference in each UMZI is increased beyond the coherence length of the thermal light. Moreover, the second-order interference is dependent…
Coherence squeezing in optical interference
本文提出双缝干涉中的相干压缩概念，通过构建相干算符揭示相干不确定性关系，并展示其在干涉条纹不确定性的应用，为量子增强干涉测量提供新思路。
We describe a detector that measures the mutual coherence of two optical fields directly using quantum interference, free from photon noise of the individual irradiances. Our approach utilizes Raman transition in an atomic system where the state evolution is driven by the mutual coherence of the fields interacting with the atoms. Feedback control is used to balance the interaction of the fields being characterized, providing a measure of the mutual coherence. We show that the sensitivity of the coherence measurement can be enhanced significantly above that of conventional interferometric metho…
We present experimental observations of interference between an atomic spin coherence and an optical field in a Λ-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple Λ transitions driving a single spin coherence. In principle, the interference in each scheme can yield a near unity visibility.
The classic example of the destruction of interference fringes in a ``which-way'' experiment, caused by an environmental interaction, may be viewed as the destruction of first-order coherence as defined by Glauber many years ago (Glauber). However, the influence of an environment can also destroy the $n$th-order quantum coherence in a quantum system, where this high order coherence is captured. We refer to this phenomenon as the $n$% th-order decoherence. In this paper we show that, just as the first-order coherence can be understood as the interference of the amplitudes for two distinct paths…
A novel thermal light interferometer was recently introduced in V. Tamma and J. Seiler, New J. Phys. 18, 032002 (2016). Here, two classically correlated beams, obtained by beam splitting a thermal light beam, propagate through two unbalanced Mach-Zehnder interferometers. Remarkably, second-order interference between the long and the short paths in the two interferometers was predicted independently of how far, in principle, the length difference between the long and short paths is beyond the coherence length of the source. This phenomenon seems to contradict our common understanding of second …
Observation of the First-Order Interference Fringes Beyond Coherence Length Employing Commercial Continuous-wave Multi-mode Laser Diode: A Sight of Two-photon Interference
本文利用商用连续波多模激光二极管在远超相干长度的条件下观测到一阶干涉条纹，提出该现象可由时间分辨双光子干涉机制解释，为量子信息科学提供了新方法。
Impact of temporal correlations, coherence, and postselection on two-photon interference
该研究探讨了级联光子对固有的时间相关性对双光子干涉的负面影响，揭示了其与退相干及时间后选择的相互作用机制，并找出了通过时间后选择提升干涉可见度的条件与关键参数。
We propose a method called `coherence swapping' which enables us to create superposition of a particle in two distinct paths, which is fed with initially incoherent, independent radiations. This phenomenon is also present for the charged particles, and can be used to swap the effect of flux line due to Aharonov-Bohm effect. We propose an optical version of the experimental set-up to test the coherence swapping. The phenomenon, which is simpler than entanglement swapping or teleportation, raises some fundamental questions about true nature of wave-particle duality, and also opens up the possibi…
In an asymmetric multislit interference experiment, a quanton is more likely to pass through certain slits than some others. In such a situation one may be able to predict which slit a quanton is more likely to go through, even without using any path-detecting device. This allows one to talk of path predictability. It has been shown earlier that for a two-slit interference, the predictability and fringe visibility are constrained by the inequality $P^2+V^2\le 1$. Generalizing this relation to the case of more than two slits is still an unsolved problem. A new definition for predictability for …
We derive a generalized wave-particle duality relation for arbitrary multipath quantum interference phenomena. Beyond the conventional notion of the wave nature of a quantum system, i.e., the interference fringe visibility, we introduce a quantifier as the normalized quantum coherence, recently defined in the framework of quantum information theory. To witness the particle nature, we quantify the path distinguishability or the which-path information based on unambiguous quantum state discrimination. Then, the Bohr complementarity principle for multipath quantum interference can be stated as a …
The visibilities of second-order (single-photon) and fourth-order (two-photon) interference have been observed in a Young's double-slit experiment using light generated by spontaneous parametric down-conversion and a photon-counting intensified CCD camera. Coherence and entanglement underlie one-and two-photon interference, respectively. As the effective source size is increased, coherence is diminished while entanglement is enhanced, so that the visibility of single-photon interference decreases while that of two-photon interference increases. This is the first experimental demonstration of t…
The working substance fueling a quantum heat engine may contain coherence in its energy basis, depending on the dynamics of the engine cycle. In some models of quantum Otto heat engines, energy coherence has been associated with entropy production and quantum friction. We considered a quantum Otto heat engine operating at finite time. Coherence is generated and the working substance does not reach thermal equilibrium after interacting with the hot heat reservoir, leaving the working substance in a state with residual energy coherence. We observe an interference-like effect between the residual…
By utilizing single particle interferometry, the fidelity or coherence of a pair of quantum states is identified with their capacity for interference. We consider processes acting on the internal degree of freedom (e.g., spin or polarization) of the interfering particle, preparing it in states ρ_{A} or ρ_{B} in the respective path of the interferometer. The maximal visibility depends on the choice of interferometer, as well as the locality or non-locality of the preparations, but otherwise depends only on the states ρ_{A} and ρ_{B} and not the individual preparation processes themselves. This …
Measurement-Feedback Quantum Information Engine: Coherence-Transition Interference and Correlated Work Statistics
该研究针对量子信息引擎，建立机制分辨的功统计与时间关联理论，揭示相干性转变干涉的映射规律，发现反馈记忆可降低记录重置成本，关联相干功统计与信息热力学。
The coherence time constitutes one of the most critical parameters that determines whether or not interference is observed in an experiment. For photons, it is traditionally determined by the effective spectral bandwidth of the photon. Here we report on multi-photon interference experiments in which the multi-photon coherence time, defined by the width of the interference signal, depends on the number of interfering photons and on the measurement scheme chosen to detect the particles. A theoretical analysis reveals that all multi-photon interference with more than two particles features this d…
Quantum nonlocal double slit interference with partially coherent qubits
研究部分相干量子纠缠光束的相干性变化对非局域双缝量子干涉的影响，发现通过控制泵浦参数可实现高质量且接近1的干涉可见度，增强抗介质畸变鲁棒性。
We report the results of two experiments performed with two-photon light, produced via collinear degenerate optical spontaneous parametric downconversion (SPDC), in which both second-order (one-photon) and fourth-order (two-photon) interferograms are recorded in a Mach-Zehnder interferometer (MZI). In the first experiment, high-visibility fringes are obtained for both the second- and fourth-order interferograms. In the second experiment, the MZI is modified by the removal of a mirror from one of its arms; this leaves the fourth-order interferogram unchanged, but extinguishes the second-order i…
The exactly analytical solutions for the dynamics of the dissipative three-level V-type and $Λ$-type atomic systems in the vacuum Lorentzian environments are presented. Quantum interference phenomenon between the two transitions in V-type atomic system is studied and the intuitive interference conditions are derived. For the dissipative $Λ$-type atomic system, we demonstrate that the similar quantum interference phenomenon does not exist. Finally, we study the dynamical evolution of quantum Fisher information, quantum entanglement and quantum coherence for the V-type atomic system. We find tha…
We analyze signal coherence in the setup of Wang, Zou and Mandel, where two optical downconverters have indistinct idler modes. Quantum interference, caused by indistinguishability of paths, has a visibility proportional to the transmission amplitude between idlers. Classical interference, caused by induced emission, may be complete for any finite transmission.
We show that temporal two-photon interference effects involving the signal and idler photons created by parametric down-conversion can be fully characterized in terms of the variations of two length parameters--called the biphoton path-length difference and the biphoton path-asymmetry- length difference--which we construct using the six different length parameters that a general two-photon interference experiment involves. We perform an experiment in which the effects of the variations of these two parameters can be independently controlled and studied. In our experimental setup, which does no…
It is well known that in classical optics, the visibility of interference, in a two-beam light interference, is related to the optical coherence of the two beams. A wave-particle duality relation can be derived using this mutual coherence. The issue of wave-particle duality in classical optics is analyzed here, in the more general context of multipath interference. New definitions of interference visibility and path distinguishability have been introduced, which lead to a duality relation for multipath interference. The visibility is shown to be related to a new multi-point optical coherence f…
Photon interference among distant quantum emitters is a promising method to generate large scale quantum networks. Interference is best achieved when photons show long coherence times. For the nitrogen-vacancy defect center in diamond we measure the coherence times of photons via optically induced Rabi oscillations. Experiments reveal a close to Fourier transform (i.e. lifetime) limited width of photons emitted even when averaged over minutes. The projected contrast of two-photon interference (0.8) is high enough to envisage the applications in quantum information processing. We report 12 and …
In this work, the effects of quantum interference and spontaneously generated coherence (SGC) are theoretically analyzed in a four level system of a $^{87}\mathrm{Rb}$ atom. For the effects of SGC, we find that a new kind of EIT channel can be induced due to destructive interference, and the nonlinear Kerr absorption can be coherently narrowed or eliminated under different strengths of the coupling and switching fields.
Optical coherence tomography has become an important imaging technology in cardiology and ophthalmology, with other applications under investigations. Major advances in optical coherence tomography (OCT) imaging are likely to occur through a quantum field approach to the technology. In this paper, which is the first part in a series on the topic, the quantum basis of OCT first order correlations is expressed in terms of full field quantization. Specifically first order correlations are treated as the linear sum of single photon interferences along indistinguishable paths. Photons and the elect…
We analyze the notion of quantum coherence in an interference experiment. We let the phase shifts fluctuate according to a given statistical distribution and introduce a decoherence parameter, defined in terms of a generalized visibility of the interference pattern. One might naively expect that a particle ensemble suffers a greater loss of quantum coherence by interacting with an increasingly randomized distribution of shifts. As we shall see, this is not always true.
Heralded Induced-Coherence Interferometry in a Noisy Environment
本文研究了热背景噪声对ZWM诱导相干干涉测量的影响，发现热光子会引入非相干偏移降低干涉对比度，并提出通过最优衰减、三SPDC配置或预示检测来恢复高对比度干涉条纹。
The interference pattern in electron double-slit diffraction is a hallmark of quantum mechanics. A long standing question for stochastic electrodynamics (SED) is whether or not it is capable of reproducing such effects, as interference is a manifestation of quantum coherence. In this study, we use excited harmonic oscillators to directly test this quantum feature in SED. We use two counter-propagating dichromatic laser pulses to promote a ground-state harmonic oscillator to a squeezed Schrödinger cat state. Upon recombination of the two well-separated wavepackets, an interference pattern emerg…
The subtle and fundamental issue of indistinguishability and interference between independent pathways to the same target state is examined in the context of coherent control of atomic and molecular processes, with emphasis placed on possible "which-way" information due to quantum entanglement established in the quantum dynamics. Because quantum interference between independent pathways to the same target state occurs only when the independent pathways are indistinguishable, it is first shown that creating useful coherence (as defined in the paper) between nondegenerate states of a molecule fo…
We consider the possibility of a control field opening up multiple pathways and thereby leading to new interference and coherence effects. We illustrate the idea by considering the $J=1/2\leftrightarrow J=1/2$ transition. As a result of the additional pathways, we show the possibilities of nonzero refractive index without absorption and gain without inversion. We explain these results in terms of the coherence produced by the opening of an extra pathway.
We analyze a double-slit experiment when the interfering particle is "mesoscopic" and one endeavors to obtain Welcher Weg information by shining light on it. We derive a compact expression for the visibility of the interference pattern: coherence depends on both the spatial and temporal features of the wave function during its travel to the screen. We set a bound on the temperature of the mesoscopic particle in order that its quantum mechanical coherence be maintained.
Pure-state photon-pair source with a long coherence time for large-scale quantum information processing
本文提出在PPKTP晶体中通过选择合适泵浦激光和滤波器生成具有长相干时间的纯态光子对源方案，实验演示了780nm光子对源并实现超过经典极限的HOM干涉，为大规模量子网络应用提供潜力。
We describe spontaneous parametric down-conversion experiments in which induced coherence across two coupled interferometers results in high-visibility single-photon interference. Opening additional photon channels allows "which-path" information and reduces the visibility of the singlephoton interference, but results in nearly perfect visibility when photons are counted in coincidence. A simplified theoretical model accounts for these complementary observations and attributes them directly to the relations among the vacuum fields at the different crystals.
Interference effects in quantum transitions, giving rise to amplification without inversion, optical transparency and to enhancements in nonlinear optical frequency conversions are considered. Review of the relevant early theoretical and experimental results is given. The role of relaxation processes, spontaneous cascade of polarizations, local field effects, Doppler-broadening, as well as specific features of the interference in the spectral continuum are discussed.
Single photon first order interferences of spatially separated regions from the cone structure of spontaneous parametric down conversion allow for analyzing the role of the mode function in quantum optics. In earlier experiments the role of the vacuum fields could be demonstrated in induced coherence experiments as the source of complementarity \cite{Heu14}. Here the spatial coherence properties of these vacuum fields are measured and as the physical reason for complementarity in single photon quantum optics demonstrated.
Interferometry is an indispensable tool across all the natural sciences. Recently, a new type of interferometer based on phase-sensitive Fano resonances has been proposed and implemented. In these Fano interferometers, the two arms are formed by a spectrally broad continuum channel, and a spectrally narrow resonant bound state scattering channel, respectively. We show that the textbook relation between interference visibility and coherence known from double-slit- or Mach-Zehnder-interferometers does not apply to Fano interferometers, because the physical origin of the interference extrema is d…
Coherent superpositions are one of the hallmarks of quantum mechanics and are vital for any quantum mechanical device to outperform the classically achievable. Generically, superpositions are verified in interference experiments, but despite their longstanding central role we know very little about how to extract the number of coherently superposed amplitudes from a general interference pattern. A fundamental issue is that performing a phase-sensitive measurement is as challenging as creating a coherent superposition, so that assuming a perfectly implemented measurement for verification of qua…
Temporal-order-driven asymmetric quantum interference and temporal coherence enhancement in spontaneous six-wave mixing
针对自发六波混频三光子W态缺乏严格理论的问题，本文建立五能级冷原子EIT系统的解析框架，揭示时间顺序导致的非对称三重符合量子干涉。
It is well known that fringe contrast is not a good quantifier of the wave nature of a quanton in multipath interference. A new interference visibility, based on the Hilbert-Schmidt coherence is introduced. It is demonstrated that this visibility is a good quantifier of wave nature, and can be experimentally measured. A generalized path predictability is introduced, which reduces to the predictability of Greenberger and Yasin, for the case of two paths. In a multipath, which-way interference experiment, the new visibility, the predictability and the I-concurrence (quantifying the entanglement …
We show that the quantum interference between downconverted photon pairs and photons from coherent laser light can produce a maximally path entangled N-photon output component with a fidelity greater than 90% for arbitrarily high photon numbers. A simple beam splitter operation can thus transform the 2-photon coherence of down-converted light into an almost optimal N-photon coherence.
We demonstrate a novel second-order spatial interference effect between two indistinguishable pairs of disjoint optical paths from a single chaotic source. Beside providing a deeper understanding of the physics of multi-photon interference and coherence, the effect enables retrieving information on both the spatial structure and the relative position of two distant double-pinhole masks, in the absence of first order coherence. We also demonstrate the exploitation of the phenomenon for simulating quantum logic gates, including a controlled-NOT gate operation.
We experimentally demonstrate a bright pulsed source of correlated photon pairs at 1550 nm telecom band by pumping 300 m dispersion shifted fiber with a 4 ps pulse train. We investigate the coherence property of the source by measuring the second order intensity correlation function $g^{(2)}$ of individual signal (idler) photons. A preliminary Hong-Ou-Mandel type two-photon interference experiment with two such sources confirms the high temporal and spatial coherence of the source. The source is suitable for multi-photon quantum interference of independent sources, required in quantum informat…
Chirped-pulse interferometry (CPI) captures the metrological advantages of quantum Hong-Ou-Mandel (HOM) interferometry in a completely classical system. Modified HOM interferometers are the basis for a number of seminal quantum-interference effects. Here, the corresponding modifications to CPI allow for the first observation of classical analogues to the HOM peak and quantum beating. They also allow a new classical technique for generating phase super-resolution exhibiting a coherence length dramatically longer than that of the laser light, analogous to increased two-photon coherence lengths i…
We show that radiative coupling between two multilevel atoms having near-degenerate states can produce new interference effects in spontaneous emission. We explicitly demonstrate this possibility by considering two identical V systems each having a pair of transition dipole matrix elements which are orthogonal to each other. We discuss in detail the origin of the new interference terms and their consequences. Such terms lead to the evolution of certain coherences and excitations which would not occur otherwise. The special choice of the orientation of the transition dipole matrix elements enab…
Wave-particle duality in multi-path interference is fraught with issues despite substantial progress in recent years. It was experimentally shown that in certain specific conditions, getting path information in a multi-path experiment can actually increase the visibility of interference. As a result, it was argued that in multi-path interference experiments, visibility of interference and 'which-path' information are not always complementary observables. In the present work, a new wave-particle duality relation is presented, based on a sum of visibilities of interference from individual pairs …
Dicke superradiance, i.e., the enhanced spontaneous emission of coherent radiation, is often attributed to radiation emitted by synchronized dipoles coherently oscillating in phase. At the same time, Dicke derived superradiance assuming atoms in entangled Dicke states which do not display any dipole moment. To shed light on this apparent paradox, we study the intensity distribution arising from two identical two-level atoms prepared either in an entangled Dicke state or in a separable atomic state with non-vanishing dipole moment. We find that the two configurations produce similar far field i…
Quantum information technologies harness the intrinsic nature of quantum theory to beat the limitations of the classical methods for information processing and communication. Recently, the application of quantum features to metrology has attracted much attention. Quantum optical coherence tomography (QOCT), which utilizes two-photon interference between entangled photon pairs, is a promising approach to overcome the problem with optical coherence tomography (OCT): As the resolution of OCT becomes higher, degradation of the resolution due to dispersion within the medium becomes more critical. H…
Three-slit interference with a which-path memory ancilla: A bright-dark state formulation
该研究在亮-暗态框架下分析带路径记忆辅助比特的三缝干涉，明确二维暗子空间结构，证明亮-暗相干性的基矢不变性，揭示多路径下的额外相干贡献，并区分可恢复与不可约的相干损耗。
We study C70 fullerene matter waves in a Talbot-Lau interferometer as a function of their temperature. While the ideal fringe visibility is observed at moderate molecular temperatures, we find a gradual degradation of the interference contrast if the molecules are heated before entering the interferometer. A method is developed to assess the distribution of the micro-canonical temperatures of the molecules in free flight. This way the heating-dependent reduction of interference contrast can be compared with the predictions of quantum theory. We find that the observed loss of coherence agrees q…
Quantum coherence is one of the clearest departures from classical physics, exhibited when a system is in a superposition of different basis states. Here the coherent superposition of three motional Fock states of a single trapped ion is experimentally certified, with a procedure provably robust against imperfect operation. As the motional state cannot be directly interrogated, our scheme uses an interference pattern generated by projective measurement of the coupled qubit state. The minimum number of coherently superposed states is inferred from a series of threshold values based on analysis …
We investigate the dynamical behavior of the atom-photon entanglement in a V-type three-level quantum system using the atomic reduced entropy. It is shown that an atom and photons are entangled at the steady-state; however disentanglement can also be achieved in an especial condition. It is demonstrated that in the presence of quantum interference induced by spontaneous emission, the reduced entropy and the atom-photon entanglement are phase-dependent. Non-stationary solution is also obtained when the quantum interference due to the spontaneous emission is completely included.
Quantum coherence and interference of a single moiré exciton in nano-fabricated twisted semiconductor heterobilayers
本研究通过纳米制备在扭转半导体异质双层中实现单个莫尔激子的量子相干与干涉光学观测，相干时间超10皮秒，并揭示不同势阱间激子耦合，助力莫尔量子技术应用。
Quantum Optical Coherence Tomography (Q-OCT) presents many advantages over its classical counterpart, Optical Coherence Tomography (OCT): it provides an increased axial resolution and is immune to even orders of dispersion. The core of Q-OCT is quantum interference of negatively correlated entangled photon pairs obtained in a Hong-Ou-Mandel configuration. This two-photon interference can be observed in the time domain in the form of dips or in the Fourier domain by means of a joint spectrum. The latter approach proved to be practical in the sense that it alleviated the requirement posed on lig…
An interference experiment with entangled particles is theoretically analyzed, where one of the entangled pair (particle 1) goes through a multi-slit before being detected at a fixed detector. In addition, one introduces a mechanism for finding out which of the n slits did particle 1 go through. The other particle of the entangled pair (particle 2) goes in a different direction, and is detected at a variable, spatially separated location. In coincident counting, particle 2 shows n-slit interference. It is shown that the normalized quantum coherence of particle 2, $\mathcal{C}_2$, and the path-…
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