arXiv subjects

Yanhua Shih

Publications and source records attributed to Yanhua Shih.

At least 19 recordsLinked to original sources

arXiv2025

Entangled laser beams and quantum ghost frequency comb

This letter reports on the study of entangled laser beams, or entangled coherent states, from their generation to their nonlocal coherent behavior. Although in continuous wave operation, the entangled laser beams are able to produce comb-like correlation with 100\% contrast in distant joint photodetection. We name this comb-function quantum ghost frequency comb (QGFC). What is the cause of these periodic sharp correlations? Can we trust zero-coincidences, or anti-correlation, in the joint measurement of CW laser beams? Besides its fundamental interests, bright QGFCs make important contributions to the fields of nonlocal precision spectroscopy, positioning, and time transfer. Superior to entangled photon pairs, measurements of entangled laser beams do not rely on photon counting and can be performed over greater distance in shorter time with higher resolution and accuracy.

quant-ph↗

arXiv2024

Experimental Demonstration of Turbulence-resistant Lidar via Quantum Entanglement

We report a proof-of-principle experimental demonstration of a turbulence-resistant quantum Lidar system. As a key technology for sensing and ranging, Lidar has drawn considerable attention for a study from quantum perspective, in search of proven advantages complementary to the capabilities of conventional Lidar technologies. Environmental factors such as strong atmospheric turbulence can have detrimental effects on the performance of these systems. We demonstrate the possibility of turbulence-resistant operation of a quantum Lidar system via two-photon interference of entangled photon pairs. Additionally, the reported quantum Lidar also demonstrates the expected noise resistance. This study suggests a potential high precision timing-positioning technology operable under turbulence and noise.

quant-ph↗

arXiv2021

Non-invasive imaging of object behind strongly scattering media via cross-spectrum

We develop a method based on the cross-spectrum of an intensity-modulated CW laser, which can extract a signal from an extremely noisy environment and image objects hidden in turbid media. We theoretically analyzed our scheme and performed the experiment by scanning the object placed in between two ground glass diffusers. The image of the object is retrieved by collecting the amplitudes at the modulation frequency of all the cross-spectra. Our method is non-invasive, easy-to-implement, and can work for both static and dynamic media.

physics.optics↗

arXiv2021

Entangled-photon interferometry for plasmas

Sub-picosecond coincidence timing from nonlocal intensity interference of entangled photons allows quantum interferometry for plasmas. Using a warm plasma dispersion relation, we correlate phase measurement sensitivity with different plasma properties or physics mechanisms over 6 orders of magnitude. Due to $N^α$ ($α\leq -1/2$) scaling with the photon number $N$, quantum interferometry using entangled light can probe small signals in plasmas not previously accessible. As an example, it is predicted that plasmas will induce shifts to a Gaussian dip, a well-known quantum optics phenomenon that is yet to be demonstrated for plasmas.

quant-ph↗

arXiv2021

High order Coherence Functions and Spectral Distributions as given by the Quantum Theory of Laser Radiation

We propose and demonstrate a method for measuring the time evolution of the off-diagonal elements $ρ_{n,n+k}(t)$ of the reduced density matrix obtained from the quantum theory of the laser. The decay rates of the off-diagonal matrix element $ρ_{n,n+k}(t)$ (k=2,3) are measured for the first time and compared with that of $ρ_{n,n+1}(t)$, which corresponds to the linewidth of the laser. The experimental results agree with the quantum theory of the laser.

physics.optics↗

arXiv2020

Strong scattering and parallel guiding of ultracold neutrons

For ultracold neutrons with a kinetic energy below 10 neV, strong scattering, characterized by $2πl_{c} / λ\leq 1$, can be obtained in metamaterials of C and $^7$Li. Here $l_{c}$ and $λ$ are the coherent scattering mean free path and the neutron wavelength, respectively. UCN interferometry and high-resolution spectroscopy (nano-electronvolt to pico-electronvolt resolution) in parallel waveguide arrays of neutronic metamaterials are given as examples of new experimental possibilities.

physics.ins-det↗

arXiv2020

Two-photon X-ray Ghost Microscope

X-ray imaging allows for a non-invasive image of the internal structure of an object. The most common form of X-ray imaging, projectional radiography, is simply a projection or "shadow" of the object rather than a point-to-point image possible with a lens. This technique fails to take advantage of the resolving capabilities of short-wavelength X rays. Various X-ray microscopes, typically operating with soft X rays (< 10 keV), use focusing X-ray optics to obtain higher resolution images of the internal structure of an object. Due to the short focal length of focusing X-ray optics, it becomes difficult to focus on the internal structure of larger objects in such a way to provide significant magnification to be resolvable. Here we present an imaging mechanism that utilizes two-photon X-ray ghost imaging to produce a true point-to-point image of the internal structure of an object, with the potential to introduce focusing X-ray optics or a scintillator-lens pairing to produce a magnified secondary ghost image. The focusing X-ray optics would image the primary ghost image (which has no physical structure to it) allowing the imaging of internal structures deeper than a standard X-ray microscope would allow. In principle, once some experimental barriers are overcome, this X-ray "ghost microscope" may achieve nanometer spatial resolution and open up new capabilities that would be of interest to the fields of physics, material science, and medical imaging.

physics.optics↗

arXiv2018

Thermal x-ray diffraction and near-field phase contrast imaging

Using higher-order coherence of thermal light sources, the resolution power of standard x-ray imaging techniques can be enhanced. In this work, we applied the higher-order measurement to far-field x-ray diffraction and near-field phase contrast imaging (PCI), in order to achieve superresolution in x-ray diffraction and obtain enhanced intensity contrast in PCI. The cost of implementing such schemes is minimal compared to the methods that achieve similar effects by using entangled x-ray photon pairs.

physics.optics↗

arXiv2017

Radiation-damage-free ghost diffraction with atomic resolution

The X-ray free electron lasers (XFEL) can enable diffractive structural determination of protein crystals or single molecules that are too radiation-sensitive for conventional X-ray analysis. However the electronic form factor could have been modified during the ultrashort X-ray pulse due to photoionization and electron cascade caused by the intense X-ray pulse. For general X-ray imaging techniques, to minimize radiation damage effect is of major concern to ensure faithful reconstruction of the structure. Here we show that a radiation-damage-free diffraction can be achieved with an atomic spatial resolution, by using X-ray parametric down-conversion (XPDC), and two-color two-photon ghost diffraction. We illustrate that the formation of the diffraction patterns satisfies a condition analogous to the Bragg equation, with a resolution that could be as fine as the lattice length scale of several Angstrom. Because the samples are illuminated by the optical photons of low energy, they can be free of radiation damage.

quant-ph↗

arXiv2017

Spatial interference between pairs of disjoint optical paths with a single chaotic source

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.

quant-ph↗

arXiv2016

Super-resolution imaging using the spatial-frequency filtered intensity fluctuation correlation

We report an experimental demonstration of a nonclassical imaging mechanism with super-resolving power beyond the Rayleigh limit. When the classical image is completely blurred out due to the use of a small imaging lens, by taking advantage of the intensity fluctuation correlation of thermal light, the demonstrated camera recovered the image of the resolution testing gauge. This method could be adapted to long distance imaging, such as satellite imaging, which requires large diameter camera lenses to achieve high image resolution.

physics.optics↗

arXiv2015

New factorization algorithm based on a continuous representation of truncated Gauss sums

In this paper, we will describe a new factorization algorithm based on the continuous representation of Gauss sums, generalizable to orders j>2. Such an algorithm allows one, for the first time, to find all the factors of a number N in a single run without precalculating the ratio N/l, where l are all the possible trial factors. Continuous truncated exponential sums turn out to be a powerful tool for distinguishing factors from non-factors (we also suggest, with regard to this topic, to read an interesting paper by S. Woelk et al. also published in this issue [Woelk, Feiler, Schleich, J. Mod. Opt. in press]) and factorizing different numbers at the same time. We will also describe two possible M-path optical interferometers, which can be used to experimentally realize this algorithm: a liquid crystal grating and a generalized symmetric Michelson interferometer.

quant-ph↗

arXiv2015

Factoring numbers with a single interferogram

We construct an analog computer based on light interference to encode the hyperbolic function f(ζ) = 1/ζ into a sequence of skewed curlicue functions. The resulting interferogram when scaled appropriately allows us to find the prime number decompositions of integers. We implement this idea exploiting polychromatic optical interference in a multipath interferometer and factor seven-digit numbers. We give an estimate for the largest number that can be factored by this scheme.

quant-ph↗

arXiv2009

Observation of Anti-correlation of Classical Chaotic Light

We wish to report an experimental observation of anti-correlation from first-order incoherent classical chaotic light. We explain why the classical statistical theory does not apply and provide a quantum interpretation. In quantum theory, either correlation or anti-correlation is a two-photon interference phenomenon, which involves the superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of producing a joint-photodetection event.

quant-ph↗

arXiv2009

The Physics of Ghost Imaging

One of the most surprising consequences of quantum mechanics is the nonlocal multi-particle interference observable in joint-detection of distant particle-detectors. Ghost imaging is one of such phenomena. Two types of ghost imaging have been experimentally demonstrated since 1995. Type-one ghost imaging uses entangled photon pairs as the light source. The nonlocal point-to-point image-forming correlation is the result of a constructive-destructive superposition among a large number of biphoton amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of producing a joint-detction event between distant photodetectors. Type-two ghost imaging uses chaotic-thermal light. The type-two image-forming correlation is the result of interferences between paired two-photon amplitudes, corresponding to two different yet indistinguishable alternative ways of triggering a join-detection event by two independent photons. A great deal of confusion about ghost imaging comes from "ghost shadow". Similar to x-ray photography, a ghost shadow can be made in coincidences by "blocking-partial blocking-unblocking" of either co-rotating laser beams or classically correlated "speckles". "Ghost shadow" is indeed a classical phenomenon. The physics of ghost imaging, however, is fundamentally different. This article is aimed at exploring the nonlocal two-photon interference nature of ghost imaging.

quant-ph↗

arXiv2009

3rd Order Temporal Correlation Function of Pseudo-Thermal Light

This experiment reports a nontrivial third-order temporal correlation of chaotic-thermal light in which the randomly radiated thermal light is observed to have a 6-times greater chance of being captured by three individual photodetectors simultaneously than that of being captured by three photodetectors at different times (separated by the coherent time of pseudo-thermal light), indicating a "three-photon bunching" effect. The nontrivial correlation of thermal light is the result of multi-photon interference.

quant-ph↗

arXiv2008

Spatial Resolution Enhancement in Quantum Imaging beyond the Diffraction Limit Using Entangled Photon-Number State

In this paper we study the resolution of images illuminated by sources composed of $N+1$ photons in which one non-degenerate photon is entangled with $N$ degenerate photons. The $N$ degenerate photons illuminate an object and are collected by an $N$ photon detector. The signal from the $N$ photon detector is measured in coincidence with the non-degenerate photon giving rise to a ghost image. We discuss the case of three photons in various configurations and generalize to $N+1$. Using the Rayleigh criterion, we find that the system may give an improvement in resolution by a factor of $N$ compared to using a classical source. For the case that the $N$-photon number detector is a point detector, a coherent image is obtained. If the $N$-photon detector is a bucket detector, the image is incoherent. The visibility of the image in both cases is 1. In the opposite case in which the non-degenerate photon is scattered by the object, then, using an $N$-photon point detector may reduce the Airy disk by a factor of $N$.

quant-ph↗

arXiv2007

Quantum Imaging

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distant particles. Although questions regarding fundamental issues of quantum theory still exist, quantum entanglement has started to play important roles in practical engineering applications. Quantum imaging is one of these exciting areas. Quantum imaging has demonstrated two peculiar features: (1) reproducing "ghost" images in a "nonlocal" manner, and (2) enhancing the spatial resolution of imaging beyond the diffraction limit. In this article, we start with the review of classical imaging to establish the basic concepts and formalisms of imaging. We then analyze two-photon imaging with particular emphasis on the physics of spatial resolution enhancement and the "ghost" imaging phenomenon.

quant-ph↗