Stephen P. Walborn, Marcelo O. Terra Cunha, Sebastião Pádua, Carlos H. Monken
Recent experiments in quantum optics have shed light on the foundations of quantum physics. Quantum erasers - modified quantum interference experiments - show that quantum entanglement is responsible for the complementarity principle.
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The two-photon ghost interference experiment, generalized to the case of massive particles, is theoretically analyzed. It is argued that the experiment is intimately connected to a double-slit interference experiment where, the which-path information exists. The reason for not observing first order interference behind the double-slit, is clarified.It is shown that the underlying mechanism for the appearance of ghost interference is, the more familiar, quantum erasure.
Interference comes from coherent mixing. It can be suppressed by entanglement, and the latter can be erased so as to revive interference. If the entanglement is a mimal-term one (with minimal-term mixing), as is the case in most thought and real experiments reported, there appears the possibility of counter erasure and counter interference. This peculiar phenomenon of minimal-term mixing and minimal-term entanglement is investigated in detail. In particular, all two-term mixings of an (arbitrary) given minimal-term mixed state are explicitly exhibited. And so are their possible laboratory real…
It is known that quantum interference can disappear with the mere possibility of distinguishability without actually performing the act. We create such distinguishability in an unbalanced SU(1,1) interferometer and indeed observe no interference in the direct photodetection of the outputs. On the other hand, such distinguishability can be erased with a projective measurement. Here, we report a method of homodyne detection that can also recover interference effect. We find that it is the indistinguishability in amplitude measurement that leads to the recovery of interference, and the quantum na…
The notion of wave-particle duality may be quantified by the inequality V^2+K^2 <=1, relating interference fringe visibility V and path knowledge K. With a single-photon interferometer in which polarization is used to label the paths, we have investigated the relation for various situations, including pure, mixed, and partially-mixed input states. A quantum eraser scheme has been realized that recovers interference fringes even when no which-way information is available to erase.
In an interferometer, path information and interference visibility are incompatible quantities. Complete determination of the path will exclude any possibility of interference, rendering the visibility zero. However, if the composite object and probe state is pure, it is, under certain conditions, possible to trade the path information for improved (conditioned) visibility. Such a procedure is called quantum erasure. We have performed such experiments with polarization entangled photon pairs. Using a partial polarizer we could vary the degree of entanglement between object and probe. We could …
We combine the eyebrow-raising quantum phenomena of erasure and counterfactuality for the first time, proposing a simple yet unusual quantum eraser: A distant Bob can decide to erase which-path information from Alice's photon, dramatically restoring interference, without previously-shared entanglement, and without Alice's photon ever leaving her lab.
In the optical Stern-Gerlach effect the two branches in which the incoming atomic packet splits up can display interference pattern outside the cavity when a field measurement is made which erases the which-way information on the quantum paths the system can follow. On the contrary, the mere possibility to acquire this information causes a decoherence effect which cancels out the interference pattern. A phase space analysis is also carried out to investigate on the negativity of the Wigner function and on the connection between its covariance matrix and the distinguishability of the quantum pa…
We present a didactical approach to the which-way experiment and the counterintuitive effect of the quantum erasure for one-particle quantum interferences. The fundamental concept of entanglement plays a central role and highlights the complementarity between quantum interference and knowledge of which path is followed by the particle.
The Franson interference is a fourth order interference effect, which unlike the better known Hong-Ou-Mandel interference, does not require the entangled photon pairs to be present at the same space-time location for interference to occur - it is nonlocal. Here, we use a modified Franson interferometer to experimentally demonstrate the nonlocal erasure and correction of an image of a phase-object taken through coincidence imaging. This non-local quantum erasure technique can have several potential applications such as phase corrections in quantum imaging and microscopy and also user authentica…
Quantum computers use the quantum interference of different computational paths to enhance correct outcomes and suppress erroneous outcomes of computations. A common pattern underpinning quantum algorithms can be identified when quantum computation is viewed as multi-particle interference. We use this approach to review (and improve) some of the existing quantum algorithms and to show how they are related to different instances of quantum phase estimation. We provide an explicit algorithm for generating any prescribed interference pattern with an arbitrary precision.
Often cited dictums in Quantum Mechanics include "observation disturbance causes loss of interference" and "ignorance is interference". In this paper we propose and describe a series of experiments with modified Mach-Zehnder interferometers showing that one has to be careful when applying such dictums. We are able to show that without interacting in any way with the light quantum (or quanta) expected to behave "wave-like", interference fringes can be lost by simply gaining (or having the potential to gain) the which-path knowledge. Erasing this information may revive the interference fringes. …
Many-body entangled states are key elements in quantum information science and quantum metrology. One important problem in establishing a high degree of many-body entanglement using optical techniques is the leakage of the system information via the light that creates such entanglement. We propose an all-optical interference-based approach to erase this information. Unwanted atom-light entanglement can be removed by destructive interference of three or more successive atom-light interactions, with only the desired effective atom-atom interaction left. This quantum erasure protocol allows imple…
Coupling undetected sensing modes by quantum erasure
本文提出并实现了一种利用偏振态量子擦除方法在IC-IUP和NI-IUP操作模式间连续切换的新装置，为优化未被探测光子成像的干涉提供新途径。
Using the deterministic, on-demand generation of two entangled phonons, we demonstrate a quantum eraser protocol in a phononic interferometer where the which-path information can be heralded during the interference process. Omitting the heralding step yields a clear interference pattern in the interfering half-quanta pathways; including the heralding step suppresses this pattern. If we erase the heralded information after the interference has been measured, the interference pattern is recovered, thereby implementing a delayed-choice quantum erasure. The test is implemented using a closed surfa…
Marcella in 2002 published a "quantum-mechanical" treatment of the famous single- and double-slit interference experiment in classical wave optics by a simple assumption that quantum mechanical wave function is a constant anywhere within a slit. Rothman and Boughn in 2011 commented that Marcella introduced no quantum physics into the problem other than\ a symbol substitution $p=\hbar k$, and the used essentially the classical wave optics. In present comment, we point out that though Marcella made a fundamental mistake, the problem is nevertheless remediable to give the satisfactory quantum mec…
By engineering and manipulating quantum entanglement between incoming photons and experimental apparatus, we construct single-photon detectors which cannot distinguish between photons of very different wavelengths. These color erasure detectors enable a new kind of intensity interferometry, with potential applications in microscopy and astronomy. We demonstrate chromatic interferometry experimentally, observing robust interference using both coherent and incoherent photon sources.
Marcella [arXiv:quant-ph/0703126] has presented a straightforward technique employing the Dirac formalism to calculate single- and double-slit interference patterns. He claims that no reference is made to classical optics or scattering theory and that his method therefore provides a purely quantum mechanical description of these experiments. He also presents his calculation as if no approximations are employed. We show that he implicitly makes the same approximations found in classical treatments of interference and that no new physics has been introduced. At the same time, some of the quantum…
Entangled K0 anti-K0 pairs are shown to be suitable to discuss extensions and tests of Bohr's complementarity principle through the quantum marking and quantum erasure techniques suggested by M. O. Scully and K. Druehl [Phys. Rev. A 25, 2208 (1982)]. Strangeness oscillations play the role of the traditional interference pattern linked to wave-like behaviour, whereas the distinct propagation in free space of the K_S and K_L components mimics the two possible interferometric paths taken by particle-like objects.
Partial measurement turns the initial superposition not into a definite outcome but into a greater probability for it. The probability can approach 100%, yet the measurement can undergo complete quantum erasure. In the EPR setting, we prove that i) every partial measurement nonlocally creates the same partial change in the distant particle; and ii) every erasure inflicts the same erasure on the distant particle's state. This enables an EPR experiment where the nonlocal effect does not vanish after a single measurement but keeps "traveling" back and forth between particles. We study an experime…
The counterintuitive features of quantum physics challenge many common-sense assumptions. In an interferometric quantum eraser experiment, one can actively choose whether or not to erase which-path information, a particle feature, of one quantum system and thus observe its wave feature via interference or not by performing a suitable measurement on a distant quantum system entangled with it. In all experiments performed to date, this choice took place either in the past or, in some delayed-choice arrangements, in the future of the interference. Thus in principle, physical communications betwee…
Delayed Choice Quantum Eraser Experiment Revisited: Causality and Informational Coherence
本文通过延迟选择量子擦除实验，利用单光子干涉检测区分因果性和信息一致性假说，无需后选择。
Quantum erasure based on phase structure
本研究聚焦光子相位结构，提出基于相位结构的量子擦除理论框架，通过集成螺旋相位板的马赫-曾德尔干涉仪实验验证了轨道角动量相关路径信息的擦除效应，拓展了量子擦除的研究维度并挑战经典因果观。
Quantum Erasure Imaging: Complementary Modalities from Delayed-Choice Erasure
提出量子擦除成像协议，通过延迟选择擦除和远程辅助比特的回顾性分类，从单次时间标记符合测量中同时重建吸收和相位敏感余弦正交两种模态，并推导了平衡双端口估计器和Fisher信息，证明了与标记随机化时间划分的等价性。
Wave-particle duality is a bizarre feature at the heart of quantum mechanics which refers to the mutually exclusive dual attributes of quantum objects as the wave and the particle. Quantum eraser presents a counterintuitive aspect of the wave-particle duality. In this work, we show that quantum eraser can be quantitatively understood in terms of the recently developed duality--entanglement relation. In other words, we show that wave-particle-entanglement triality captures all the physics of the quantum erasure. We find that a controllable partial erasure of the which-path information is attain…
We report a quantum eraser experiment which actually uses a Young double-slit to create interference. The experiment can be considered an optical analogy of an experiment proposed by Scully, Englert and Walther. One photon of an entangled pair is incident on a Young double-slit of appropriate dimensions to create an interference pattern in a distant detection region. Quarter-wave plates, oriented so that their fast axes are orthogonal, are placed in front of each slit to serve as which-path markers. The quarter-wave plates mark the polarization of the interfering photon and thus destroy the in…
Quantum MIMO Channel Modeling in Turbulent Free-Space Optical Links
本文提出基于波光学传播的量子MIMO信道原理模型，考虑了模间串扰、有限探测孔径和空间模式投影引起的系统-环境分离，区分可区分和不可区分光子 regime，展示不可区分性导致的多体干涉效应，通过擦除扩展编码将湍流引起的泄漏和光子损失映射为擦除态，得到相关n-qubit擦除信道。
A new quantum eraser setup exploiting for the first time the time-energy complementarity relation in the x-ray regime is investigated theoretically. Starting point is the interference process between x-ray quanta driving two nuclear hyperfine transitions in a nuclear forward scattering setup. We show that which-way information can be obtained by marking the scattering paths with orthogonal polarization states, thus leading to the disappearance of the interference pattern. In turn, erasure of the which-way information leads to the reappearance of the interference fringes. We put forward two sch…
The aim of this contribution is to illustrate two basic aspects of quantum mechanics applied to the neutral kaon system. We first describe a recent quantitative formulation of Bohr's complementarity principle for free--space evolution of single kaons and entangled kaon pairs. We then show that the neutral kaon system is also suitable for an optimal demonstration of the ``quantum eraser'', including its operation in the ``delayed choice'' mode. In our discussions, strangeness oscillations play the role of the traditional interference pattern linked to wave--like behaviour. The role of the two i…
In a delayed-choice quantum eraser, interference fringes are obtained by erasing which-way information after the interfering particle has already been irreversibly detected. Following an introductory review of delayed-choice experiments and quantum erasure, we describe the experimental realization of an optical delayed-choice quantum eraser, suitable for advanced undergraduates, based on polarization-entangled pairs of single photons. In our experiment, the delay of the erasure is implemented using two different setups. The first setup employs an arrangement of mirrors to increase the optical …
The famous gedanken experiments of quantum mechanics have played crucial roles in developing the Copenhagen interpretation. They are studied here from the perspective of standard quantum mechanics, with no ontological interpretation involved. Bohr's investigation of these gedanken experiments, based on the uncertainty relation with his interpretation, was the origin of the Copenhagen interpretation and is still widely adopted, but is shown to be not consistent with the quantum mechanical view. We point out that in most of these gedanken experiments, entanglement plays a crucial role, while its…
The hypothesis of quantum self-interference is not directly observable, but has at least three necessary implications. First, a quantum entity must have no less than two open paths. Second, the size of the interval between any two consecutive quanta must be irrelevant. Third, which-path information must not be available to any observer. All of these predictions have been tested and found to be false. A similar demonstration is provided for the hypothesis of quantum erasure. In contrast, if quanta are treated as real particles, acting as sources of real waves, then all types of interference can…
The double slit experiment is iconic and widely used in classrooms to demonstrate the fundamental mystery of quantum physics. The puzzling feature is that the probability of an electron arriving at the detector when both slits are open is not the sum of the probabilities when the slits are open separately. The superposition principle of quantum mechanics tells us to add amplitudes rather than probabilities and this results in interference. This experiment defies our classical intuition that the probabilities of exclusive events add. In understanding the emergence of the classical world from th…
Piecemeal method revisited
针对单望远镜艾里斑分辨率限制，扩展分段法减少观测基线数量，其原始与扩展版本对基线误差鲁棒，且在实际条件下精度高于其他弱光干涉方法，助力遥远目标角度和轨道检测。
Rabi oscillations of a two-level atom appear as a quantum interference effect between the amplitudes associated to atomic superpositions, in analogy with the classic double-slit experiment which manifests a sinusoidal interference pattern. By extension, through direct detection of time-resolved resonance fluorescence from a quantum-dot neutral exciton driven in the Rabi regime, we experimentally demonstrate triple-slit-type quantum interference via quantum erasure in a V-type three-level artificial atom. This result is of fundamental interest in the experimental studies of the properties of V-…
Here we analyze the relationship between quantum contextuality and decoherence in interference experiments with matter particles by means of a simple reduced quantum-trajectory model, which attempts to simulate the behavior of the projections of multi-dimensional, system-plus-environment Bohmian trajectories onto the subspace of the reduced system. This model allows us to understand the crossing of the subsystem trajectories as a combined effect of interference quenching and erasure of ``which-way'' information, which can be of utility to interpret decoherence effects in many-dimensional syste…
Carpet-type structures constitute an ideal laboratory to study and analyze the robustness of the interference process that underlies this phenomenon against the harmful effects of decoherence. Here, without losing any generality, for simplicity, the case of a particle with a mass m is considered and described by a localized state corresponding to the ground state of a square box of width w, which is released inside a wider cavity (with a width L > w). The effects of decoherence are then numerically investigated by means of a simple dynamical model that captures the essential features of the ph…
Explicitly Quantum-parallel Computation by Displacements
本文提出利用不同光学模式的相对位移或光子数编码信息，通过位移协议生成高保真度的压缩态叠加态，优于传统猫态制备，并讨论了基于差分光子数编码的光学量子退火机实现关键问题。
Dynamics, locality and weak measurements: trajectories and which-way information in the case of a simplified double-slit setup
本文研究包含弱耦合指针的简化双缝装置，通过“弱轨迹”推断局域动力学，并与模动量方法和 de Broglie-Bohm 图像等非局域动力学描述进行对比。
Theory of Deterministic Photon-Loss Subspaces for Quantum Interferences
该研究提出确定性光子损耗子空间（DPLS）理论，揭示有损耗光学系统中量子相干性、退相干与光子数减少的相互作用，可用于精确控制量子干涉及相关量子信息处理。
Photon-mediated interactions between atomic systems can arise via coupling to a common electromagnetic mode or by quantum interference. Here, we probe the role of coherence in cooperative emission arising from two distant but indistinguishable solid-state emitters because of path erasure. The primary signature of cooperative emission, the emergence of "bunching" at zero delay in an intensity correlation experiment, is used to characterise the indistinguishability of the emitters, their dephasing, and the degree of correlation in the joint system that can be coherently controlled. In a stark de…
Double-slit experiment revisited
针对双缝实验中位置-时间联合分布的理论共识缺失问题，本文基于玻姆力学模拟了高斯波包穿过双缝及飞行中关单缝的分布，指出需初始波包足够纵向展宽才能探测时间分布的量子性，并以经典氦原子双缝实验作例证。
Light reflection on a mirror can be thought as a simple physical effect. However if this happens when the mirror moves a rich scenario opens up. Here we aim at analyzing it from a quantum communication perspective. In particular, we study the kind of quantum channel that arises from (Gaussian) light reflection upon an accelerating mirror. Two competing mechanisms emerge in such a context, namely photons production by the mirror's motion and {\blu interference between modes}. As consequence we find out a quantum amplifier channel and quantum lossy channel respectively below and above a threshol…
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