Fourth-order Interference Research Articles

All-Fiber Fourth-Order OAM Mode Generation Employing a Long Period Fiber Grating Written By Preset Twist

There are great challenges in the generation of higher-order modes for long period fiber grating (LPFG). The cross-coupling coefficient between the fundamental mode and the higher-order azimuthal modes is extremely small due to the difficulty of angular modulation with traditional methods. Therefore, how to generate higher-order orbital angular momentum (OAM) modes with a high efficiency and low insertion loss is an urgent problem to be solved. In this paper, an efficient all-fiber approach to generate fourth-order OAM mode by employing a preset twisted LPFG (PT-LPFG) in a few-mode fiber (FMF) is presented. The difficulty of generating fourth-order mode utilizing traditional single-side exposure carbon dioxide laser manufacturing method and the advantages of the PT-LPFG in enhancing the coupling coefficient are theoretically analyzed in detail. In experiment, the conversion from the fundamental mode to the fourth-order mode is achieved, and the fourth-order interference patterns demonstrated the successful generation of the OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">±4</sub> modes. The conversion efficiency of the OAM modes is over 99% and the purity is measured to be more than 90%. To the best of our knowledge, this is the first time to generate the fourth-order OAM mode in an all-fiber system using single long-period fiber grating.

Unbalanced fourth-order interference beyond coherence time

Interferometry has been used widely in sensing application. However, the technique is limited by the finite coherence time of the light sources when the interference paths are not balanced. Higher-order interference effects involve intensity correlations between multiple detectors and may have the advantage over the traditional second-order interference effect exhibited in only one detector. We discuss various scenarios with unbalanced delays in different paths in fourth-order interference exhibited in coincidence between two detectors. We find, in some cases, interference effect persists even when the delays are much larger than the coherence time of the sources. We also extend the discussion to nonstationary pulsed fields, which need to consider the pulse shape and require a different treatment. These results will be useful in remote sensing applications.

Propagation of temporal mode multiplexed optical fields in fibers: influence of dispersion.

Exploiting two interfering fields which are initially in the same temporal mode but with the spectra altered by propagating through different fibers, we characterize how the spectral profiles of temporal modes change with the fiber induced dispersion by measuring the fourth-order interference when the order number and bandwidth of temporal modes are varied. The experiment is done by launching a pulsed field in different temporal modes into an unbalanced Mach-Zehnder interferometer, in which the fiber lengths in two arms are different. The results show that the mode mismatch of two interfering fields, reflected by the visibility and pattern of interference, is not only dependent upon the amount of unbalanced dispersion but also related to the order number of temporal mode. In particular, the two interfering fields may become orthogonal under a modest amount of unbalanced dispersion when the mode number of the fields is k ≥ 2. Moreover, we discuss how to recover the spectrally distorted temporal mode by measuring and compensating the transmission induced dispersion. Our investigation paves the way for further investigating the distribution of temporally multiplexed quantum states in fiber network.

Maximizing quantum discord from interference in multi-port fiber beamsplitters

Fourth-order interference is an information processing primitive for photonic quantum technologies, as it forms the basis of photonic controlled-logic gates, entangling measurements, and can be used to produce quantum correlations. Here, using classical weak coherent states as inputs, we study fourth-order interference in 4 × 4 multi-port beam splitters built within multi-core optical fibers, and show that quantum correlations, in the form of geometric quantum discord, can be controlled and maximized by adjusting the intensity ratio between the two inputs. Though these states are separable, they maximize the geometric discord in some instances, and can be a resource for protocols such as remote state preparation. This should contribute to the exploitation of quantum correlations in future telecommunication networks, in particular in those that exploit spatially structured fibers.

Nonlocal quantum erasure of phase objects

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 nonlocal quantum erasure technique can have several potential applications such as phase corrections in quantum imaging and microscopy and also user authentication of two foreign distant parties.

Photon bunching and N-photon interference in thermal light

Abstract We investigate the contribution of four-photon bunching term in fourth-order double-slit interference intensity correlation based on two different detection schemes with a pseudo-thermal light source. It is clearly demonstrated that the resolution of intensity correlation is significantly enhanced by using of double-slit in both fourth-order and third-order intensity correlation. Meanwhile, the visibility of fourth-order correlation can be dramatically improved in contrast to the third-order due to the four-photon bunching term by contributing in the visibility of fourth-order correlation. The position and full width at half maximum of interference peaks of fourth-order intensity correlation are same as third-order. We also use two different scanning approaches to change the resolution and visibility of interference intensity correlation. In the first detection scheme, we scan three reference detectors along the same orientation and speed. In second detection scheme we scan two of three reference detectors in the same orientation, and speed of one reference detector is twice that of the other, and simultaneously moving the other two reference detectors with opposite orientation but identical speed. Those investigations can also be promoted to high order intensity correlation of thermal light.

Integrated quantum photonic sensor based on Hong-Ou-Mandel interference.

Photonic-crystal-based integrated optical systems have been used for a broad range of sensing applications with great success. This has been motivated by several advantages such as high sensitivity, miniaturization, remote sensing, selectivity and stability. Many photonic crystal sensors have been proposed with various fabrication designs that result in improved optical properties. In parallel, integrated optical systems are being pursued as a platform for photonic quantum information processing using linear optics and Fock states. Here we propose a novel integrated Fock state optical sensor architecture that can be used for force, refractive index and possibly local temperature detection. In this scheme, two coupled cavities behave as an "effective beam splitter". The sensor works based on fourth order interference (the Hong-Ou-Mandel effect) and requires a sequence of single photon pulses and consequently has low pulse power. Changes in the parameter to be measured induce variations in the effective beam splitter reflectivity and result in changes to the visibility of interference. We demonstrate this generic scheme in coupled L3 photonic crystal cavities as an example and find that this system, which only relies on photon coincidence detection and does not need any spectral resolution, can estimate forces as small as 10(-7) Newtons and can measure one part per million change in refractive index using a very low input power of 10(-10)W. Thus linear optical quantum photonic architectures can achieve comparable sensor performance to semiclassical devices.

Unified view of the second-order and the fourth-order interferences in a single interferometer

Two-photon interferences are very important in quantum optics and other coherence phenomena of quantum mechanics. Here we show that two kinds of interferences, the second- and the fourth-order interferences, can arise in either separate or combined forms in different regions by tuning the time delay in a single interferometer continuously. Particularly, in the combined form we can observe the fourth-order interference in the envelope and the second-order in the fringe. It is also demonstrated that two individual photons behave differently from time–energy entangled photons in this interferometer. This example elucidates clearly that bi-photon phenomena are different from the phenomena with two photons.

Properties of a dielectric plate using entangled two-photon states

We theoretically study the properties of a dielectric plate with a modified Hong—Ou—Mandel interferometer. The fourth-order correlation functions are calculated in two regimes, which are divided depending on the relative size between the thickness of the dielectric plate and the one-photon coherence length. When the thickness of the dielectric plate is less than the one-photon coherence length, a novel modulation behavior of the coincidence rate is observed, which has not been discussed before. If the thickness of the dielectric plate is larger than the one-photon coherence length, coalescence and anti-coalescence are observed. The obtained results highlight the effects of a linear optical element on fourth-order interference.

Characterizing dispersion and absorption parameters of metamaterial using entangled photons

We have theoretically characterized a negative-index metamaterial (NIM) slab with the aid of an entangled photon pair using a modified Hong-Ou-Mandel interferometer. The results we obtained show that the absorption and dispersion properties of the NIM slab can be distinguished in the profile of the fourth-order interference; thus, we can retrieve such parameters easily. A comparison with a coherent light shows the advantages with a quantum field.

Fourth-order interference and the extended phase-space formalism for finite quantum systems

Finite quantum systems where the position $x$ and the momentum $p$ take values in $\mathbb{Z}(d)$ are considered. An extended phase space $x\ensuremath{-}p\ensuremath{-}X\ensuremath{-}P$, where $X$ is position increment and $P$ is momentum increment, is introduced. The extended Wigner function $\mathcal{W}(x,p,X,P)$ and the extended Weyl function $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathcal{W}}({x}^{\ensuremath{'}},{p}^{\ensuremath{'}},{X}^{\ensuremath{'}},{P}^{\ensuremath{'}})$ are defined and their properties are studied. They quantify fourth-order interference. Several examples are discussed.

Resolution-enhanced optical coherence tomography based on classical intensity interferometry

We propose a fourth-order interference scheme for optical coherence tomography operating with broadband incoherent (or quasi-incoherent) light. It is shown that using this proposal, an axial resolution improvement by a factor of sqrt 2 and a better sensitivity for weakly reflecting samples are obtained than with the standard second-order correlation scheme. From a practical perspective, we suggest the use of broadband Q-switched pulses and performing ultrafast intensity correlation with a nonlinear crystal. The global performance of our proposal is illustrated by means of numerical simulations.

High-visibility intensity interference and ghost imaging with pseudo-thermal light

We consider higher-order intensity correlations in thermal light and show that they can be used for observing high-visibility interference of the Hanbury Brown–Twiss-type as well as high-visibility ghost imaging. Experimental results are obtained for third- and fourth-order intensity interference, by processing images made with a digital photographic camera.

Hong-Ou-Mandel interferometer with one and two photon pairs

We study the Hong-Ou-Mandel interferometer in the regime of spontaneous parametric down-conversion with high pump beam power at the crystal. In this regime one and two photons from a pump pulsed laser beam generate one and two pairs of photons, respectively. These photons are then directed to the beam splitter of the interferometer and detected at its exit in coincidence. An interesting phenomenon is observed: The reduction of the visibility of the Hong-Ou-Mandel coincidence peak (or dip) with the increase of pump power. We study the relation between the visibility of the fourth-order interference pattern and the power of the pumping laser beam for type I and type II phase-matching crystals. Our theoretical calculations are in good agreement with the experimental results.

Simulating the fourth-order interference phenomenon of anyons with photon pairs

The generalized Hong-Ou-Mandel interferometer with anyons is studied. Novel interference results different from bosons or fermions are found. An experimental scheme based on linear optics is proposed and realized to simulate the fourth-order interference phenomenon of anyons.

Encoding Two Qubits into a Single Qutrit: An Experiment

We present an optical scheme for the recently proposed protocol for encoding arbitrary non-entangled states of two qubits into a state of one qutrit. Our experimental realization uses spatial-mode encoding. Each qudit is thus represented by a single photon propagating in d different optical fibers. The compression of two qubits into one qutrit is realized by an unbalanced beam splitter and a subsequent measurement. After successful encoding of two qubits the receiver could error-free restore any of the two encoded qubit states but not both of them simultaneously. The principle of experiment is based on the interplay of the second-order and fourth-order interference. Further, we propose a possible way for the simultaneous decoding of both qubits but with fidelities less than one.

Recurrent fourth-order interference dips and peaks with a comblike two-photon entangled state

We demonstrate full selective control over the constructive or destructive character of fourth-order recurrent interferences in a modified version of a Hong-Ou-Mandel interferometer using comblike two-photon states. The comb spectral/temporal structure is obtained by inserting an etalon cavity in the signal path of an entangled photon pair obtained by pulsed spontaneous parametric down-conversion. Both a simple qualitative discussion and a complete theoretical derivation are used to explain and analyze the experimental data.

Entangled Hanbury Brown Twiss effects with edge states

Electronic Hanbury Brown Twiss correlations are discussed for geometries in which transport is along adiabatically guided edge channels. We briefly discuss partition noise experiments and discuss the effect of inelastic scattering and dephasing on current correlations. We then consider a two-source Hanbury Brown Twiss experiment which demonstrates strikingly that even in geometries without an Aharonov–Bohm effect in the conductance matrix (second-order interference), correlation functions can (due to fourth-order interference) be sensitive to a flux. Interestingly, we find that this fourth-order interference effect is closely related to orbital entanglement. The entanglement can be detected via violation of a Bell Inequality in this geometry even so particles emanate from uncorrelated sources.

HOM 간섭계에서 세기가 다른 수직편광된 빔사이의 4차 간섭

매개하향변환과정에서 발생한 광자쌍과 Hong-Ou-Mandel 간섭계를 이용한 4차 간섭실험에서 비고전적인 간섭효과를 관측하였다. 편광방향이 서로 수직인 두 광의 4차 간섭에서 간섭무늬의 선명도가 고전적인 한계인 50%를 넘는 최대 85%의 간섭무늬를 관측하였다. 또한 두 빔의 세기 비율이 증가할수록 간섭무늬의 선명도가 감소하는 고전적인 간섭현상과 달리 두 광의 세기 비율이 1:10인 경우에도 83%의 선명도를 갖는 간섭효과를 측정하였다. We have observed a nonclassical effect in a fourth-order interference experiment with the photon pairs produced by parametric down-conversion and the Hong-Ou-Handel interferometer. For interfering classical fields with orthogonal polarizations, the visibility can be no larger than 50%, and it depends on the ratio of the two beam intensities. It is found that not only is our observed visibility of 85％ well above 50％, but it is also independent of the two beam intensities in coincidence measurements made in a two-photon polarization correlation experiment.

Optical interference with noncoherent states

We examine a typical two-source optical interference apparatus consisting of two cavities, a beam splitter, and two detectors. We show that field-field interference occurs even when the cavities are not initially in coherent states but rather in other nonclassical states. However, we find that the visibility of the second-order interference, that is, the expectation values of the detectors' readings, changes from 100%, when the cavities are prepared in coherent states, to zero visibility when they are initially in single Fock states. We calculate the fourth-order interference, and for the latter case find that it corresponds to a case where the currents oscillate with 100% visibility, but with a random phase for every experiment. Finally, we suggest an experimental realization of the apparatus with nonclassical sources.