We experimentally demonstrate quantum imaging where the images are stored in both space and time. Quantum images of remote objects are produced with either one or two beams of chaotic laser light and two sensors measuring the reference field and bucket field at different space-time points. Chaotic laser light is produced by laser light passing through rotating ground glass. Experiments were performed in both turbulent and nonturbulent conditions. Interestingly, quantum images are produced using the two sensors of quantum imaging when both single and double beams are implemented in the experimental setup. Also, we observed that the quantum images move depending on the time delay between the sensor measurements. The experiments provide a new testbed for exploring the time and space scale fundamental physics of quantum imaging and suggest new pathways for quantum information storage and processing. The research is applicable to making ghost imaging movies of moving objects and implementation of space-time imaging for enhanced imaging.
We experimentally demonstrate turbulence-free space-time quantum imaging. Quantum images of remote objects are produced with two sensors measuring at different space-time points under turbulent conditions. The quantum images generated move depending on the time delay between the two sensor measurements and the speed of a rotating ground glass that is part of a chaotic laser light source. For small delay times turbulence has virtually no adverse affect on the moving quantum images. The experimental setup and findings contribute to understanding the fundamentals of multi-photon quantum interference in complex media. Furthermore, the space-time memory demonstrated in our research provides important new pathways for investigating quantum imaging, quantum information storage and quantum computing. The turbulence-free space-time quantum imaging procedure greatly increases the information content of each photon measured. The moved quantum images are in fact new images that are stored in a space-time virtual memory process. The images are stored within the same quantum imaging data sets and thus quantum imaging can produce more information per photon measured than was previously realized.
We report on an experimental demonstration of quantum imaging where the images are stored in both space and time. Quantum images of remote objects are produced with rotating ground glass induced chaotic laser light and two sensors measuring at different space-time points. Quantum images are observed to move depending on the time delay between the sensor measurements. The experiments provide a new testbed for exploring the time and space scale fundamental physics of quantum imaging and suggest new pathways for quantum information storage and processing. The moved quantum images are in fact new images that are stored in a space-time virtual memory process. The images are stored within the same quantum imaging data sets and thus quantum imaging can produce more information per photon measured than was previously realized.
Enabling secure communication, unparalleled computing capabilities, and fundamental nonlocality physics exploration,
the development of quantum repeaters is the key quantum information processing technology advance
needed for implementing real world quantum networks beyond the laboratory environment. Currently, components
exist for intra-laboratory quantum networks but no system exists for connecting distant ( 1 km ) quantum
memories in the real world. We present a physics analysis of quantum repeater network designs for intracity
optical fiber connections between nodes based on atomic memories and linear optics. Long distances will necessitate
the use of (1) two-photon Hong-Ou-Mandel style interference between atomic ensembles for entanglement
swapping, and (2) photonic qubit wavelength conversion between atomic emissions and photons at telecommunication
wavelengths in fiber. We report on our experimental progress towards implementing A Quantum Network
with Atoms and Photons (QNET-AP), a quantum repeater network test-bed, between the US Army Research
Laboratory (ARL) and the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology
(NIST) and the University of Maryland (UMD).
Experiments were performed at the Army Research Laboratory (ARL) that observed turbulence-free positive and negative thermal light ghost images from independently recorded event histories of a “bucket” photo-detector and a charged coupled device (CCD) array. The positive (negative) ghost images were computed from the “bucket” detector counts which were above (below) their means, and the ghost images were not degraded by the turbulence. This paper provides a quantum interference model which effectively explains how the “bucket” photon counts yield positive or negative ghost images with a distant CCD array.
We present results from experiments performed at the Army Research Laboratory (ARL) demonstrating a single sensor virtual ghost imaging (VGI) configuration using Bessel beams. These experiments were performed in conditions of partially obscuring media or turbulent media to generate images of remote objects. Randomly translated Bessel beams provided improved illumination capabilities for resolving small distant targets in difficult imaging environments. When the object was illuminated through obscuring or turbulent media or a small offset aperture VGI recovered the image of the object when using a relatively coarse Bessel beam. Our experimental results show that VGI using Bessel beams can have advantages over Gaussian beams for imaging remote objects in adverse conditions.
Turbulence is a serious problem for long distance imaging such as from satellites or ground based telescopes.
In this paper we discuss our turbulence-free ghost imaging1 approach that is virtually free from the degrading
effects of turbulence. We discuss motivation for the experiments, theory, experimental setup, procedures, and
results. The results suggest that thermal two-photon interference may not only be used to improve imaging
through turbulence but may also lead to a resource for quantum information processing.
Atmospheric turbulence creates index of refraction variations that affect the paths of light propagation and
provide a media for the quantum interference phenomena of quantum ghost imaging. The usual techniques for
characterization of conventional optical turbulence are not generally sufficient for characterization of the effects
of turbulence on quantum ghost imaging. In this paper we explore improved measurement and characterization
of turbulence for improved analysis of quantum ghost imaging experiments including Turbulence-Free Ghost
Imaging experiments.1-3
Worldwide free-space quantum communications (QC) experiments over the past decade are reviewed and discussed
with attention to technological QC trends. Experiments reported in the open literature have included
those conducted along horizontal propagation paths of varying distances, as well as communication paths from
ground-to-aircraft, ground-to-space, and demonstrations in the laboratory. Available data characterize propagation
distances, transmission speeds, quantum key distribution (QKD) protocols, and quantum bit error rates
(QBER). While fiber optic implementations of quantum communications technologies are currently being tested
for communications infrastructure it is important to also consider that free-space quantum communications
will play an important role in securing such applications as earth-to-satellite, end of line connects, and defense
implementations.
In a previous experiment (Tunick, 2008: Optics Express 16, 14645-14654), values for the refractive index structure
constant and the Fried parameter were calculated from measurements of signal intensity and angle-of-arrival statistics
based on idealized models. Calculated turbulence parameters were evaluated in comparison to scintillometer-based
measurements for several cases. It was found that the idealized models alone were insufficient to accurately describe
complex, non-uniform microclimate and turbulence conditions. In addition, the signal intensity and focal spot
displacement measurements were quite sensitive to platform and light source jitter. In order to compensate for adverse
effects such as platform vibrations, an alternative differential image motion method is explored for optical turbulence
parameter characterization. Hence, further experimental research is conducted along a 2.33 km free-space laser path to
capture differential image centroid data from which Fried parameter and refractive index structure constant information
can be obtained. This research is intended to provide useful information for US Army laser communications, long-range
imaging and energy-on-target.
Optical turbulence research contributes to improved laser communications and adaptive optics systems. This paper presents experimental measurements of scintillation and focal spot displacement to obtain optical turbulence information along a near-horizontal 2.33 km free-space laser propagation path. Calculated values for optical turbulence intensity (C2n) and Fried parameter (r0) are compared to scintillometer-based measurements for several cases in winter and spring. Scintillation index estimates from recorded signal intensities were corrected to account for aperture averaging. Optical measurements provided better estimates for C2n and r0 when a more incoherent laser source was used during the second part of the experiment (λ= 808 nm) in comparison to a more coherent laser source (λ= 1064 nm) used for the first part. Apparently, an calculation criterion for this kind of laser signal analysis is that the propagating light beacon be partially incoherent and uniformly illuminated across the transmitting aperture. Similarly, estimates of C2n and r0 based on focal spot displacement analysis were improved using the more incoherent laser source, particularly in strong turbulence conditions.
The probability distribution of aperture averaged signal intensity from free-space laser optical systems depends on the
optical turbulence along the optical path. For most current free-space laser systems, random fluctuations of signal
intensity are assumed to be statistically homogeneous and isotropic. Moreover, it is assumed that probability
distributions are generally log-normal and that Kolmogorov -5/3 wave number turbulence power law represents the
signal intensity data. In this paper, the Kolmogorov model is investigated for an optical path that traverses a complex
non-uniform topography. Experimental research is conducted to determine the characteristic behavior of high frequency
(2000 Hz) signal intensity data collected over a 2.33 km optical path at the Army Research Laboratory (ARL)
Atmospheric Laser Optics Testbed (A_LOT) Facility. Results focus mainly on calculated power spectra and frequency
distributions. In addition, a model is developed to calculate optical turbulence intensity (C2/n) as a function of receiving
(and transmitting) aperture diameter, log-amplitude variance, and path length. Here, initial comparisons of calculated to
measured C2/n data are favorable. It is anticipated that this kind of signal data analysis will benefit laser communication
systems development and testing at the ARL.
Optical turbulence is important because it can significantly degrade the performance of electro-optical and infrared sensors, such as free-space laser communications and infrared imaging systems. Changes in the refractive index of air along the transmission path of an optical system in free space can influence traveling light waves temporally and spatially causing blurring, scintillation, and bean wander. If left uncompensated, these effects could cause fades and surges in transmitted signals and result in high bit errors in communicated data. An earlier paper discussed the growing need for increasingly accurate and reliable numerical models to predict optical turbulence conditions, especially in complex (non-uniform) signal propagation environments. Hence, we present a finite-difference computer model to predict the microphysical (microclimate) influences on optical turbulence (Cn2) around the ARL A_LOT Facility and its surroundings, e.g., forests and multiple buildings. Our multi-dimensional prototypical model begins to address optical turbulence conditions along more complex optical lines-of-site and account for inhomogeneities in Cn2 brought about by horizontal changes in landscape, wind flow, temperature, and humidity. We anticipate that this kind of computational research will be an important vehicle for investigating Cn2 and related laser-optic propagation effects in complex areas.
Optical turbulence information is important because it describes an atmospheric effect that can significantly degrade the performance of electromagnetic systems and sensors, e.g., free-space optical communications and infrared imaging. However, analysis of selected past research indicates that there are some areas (i.e., data and models) in which optical turbulence information is lacking. For example, optical turbulence data coupled with atmospheric characterization models in hilly terrain, coastal areas, and within cities are few in number or non-existent. In addition, the bulk of existing atmospheric computer models being used to provide estimates of optical turbulence (Cn2) intensity are basically one-dimensional in nature and assume uniform turbulence conditions over large areas. As a result, current program codes may be deficient or in error for non-uniform areas, such as environments with changing topography and energy budgets. By exploring alternate (non-similarity) numerical models for momentum, Reynolds stress, and heat flux we suggest that some very practical computational research can be performed to provide better characterization of optical turbulence (Cn2) and related effects beyond current limitations.
It is well known that the presence of aerosols in the atmospheric boundary layer can have a significant impact on electromagnetic propagation, and the underlying physical processes involving extinction, multiple scattering, and thermal emission are reasonably well understood. In this paper we examine a related, but less well understood, aspect which we term aerosol-induced `radiative damping' that can alter the local atmospheric stability and the vertical profiles of temperature and humidity which, in turn, can alter the vertical profiles of optical turbulence and hence image propagation.
Data collected over barren and vegetated ground surfaces were used to obtain estimates of Cn2 for the damp unstable boundary layer. These data consisted of latent and sensible heat fluxes. Results from this study show that moisture effects on Cn2 can be larger than generally reported in the literature. Results presented emphasize the relative contributions of temperature and moisture to Cn2 for visible, infrared, radio, and millimeter wavelengths.
The optical turbulence structure parameter Cn2 typically appears in formulations used to estimate the effects of temperature and moisture (gradients) on imagery and electro- magnetic propagation. Temperature and moisture gradients can be approximated from sensible and latent heat flux estimates, and these fluxes can be obtained from radiation/energy balance equations. Numerous energy balance models exist requiring different kinds and numbers of inputs. The semiempirical model developed and presented in this paper was constrained to require a minimum number of conventional measurements at a reference level (2 m). These measurements include temperature, pressure, relative humidity, and windspeed. The model also requires a judgment of soil type and moisture (dry, moist, or saturated), cloud characteristics (tenths of cloud cover and density and an estimation of cloud height), day of the year, time of day, and longitude and latitude of the site of interest. Model estimates of net radiation, sensible and latent heat fluxes, and Cn2 are compared with measured values.
Several sets of experimental micrometeorological data were used to obtain estimates of vertical profiles of C2n for damp unstable conditions. These data consisted of two types: (1) latent and sensible heat fluxes and (2) vertical profiles of wind, temperature, and specific humidity. Estimates of the scaling lengths of virtual potential temperature and specific humidity obtained from these data were used to calculate their vertical gradients and, in turn, to estimate C2n in accordance with Tatarski. Results from these data sets are presented to emphasize the relative contributions of temperature and moisture to C2n.
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