1,475 research outputs found
Adaptive Quantum Optics with Spatially Entangled Photon Pairs
Light shaping facilitates the preparation and detection of optical states and
underlies many applications in communications, computing, and imaging. In this
Letter, we generalize light shaping to the quantum domain. We show that
patterns of phase modulation for classical laser light can also shape higher
orders of spatial coherence, allowing deterministic tailoring of
high-dimensional quantum entanglement. By modulating spatially entangled photon
pairs, we create periodic, topological, and random patterns of quantum
illumination, without effect on intensity. We then structure the quantum
illumination to simultaneously compensate for entanglement that has been
randomized by a scattering medium and to characterize the medium's properties
via a quantum measurement of the optical memory effect. The results demonstrate
fundamental aspects of spatial coherence and open the field of adaptive quantum
optics
General model of photon-pair detection with an image sensor
We develop an analytic model that relates intensity correlation measurements
performed by an image sensor to the properties of photon pairs illuminating it.
Experiments using both an effective single-photon counting (SPC) camera and a
linear electron-multiplying charge-coupled device (EMCCD) camera confirm the
model
Nonlinear Optical Response of Simple Molecules and Two-Photon Semiconductor Lasers
This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, white-light continuum generation, all-optical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the third-order response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or two-photon absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the bound-electrons. Thus both the bound-electronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a two-photon gain medium. A two-photon laser has been a goal of nonlinear optics since shortly after the original laser*s development. In this case, two-photons are emitted from a single electronic transition rather than only one. This processes is known as two-photon gain (2PG). Semiconductors have large two-photon absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ћωa≈10ћωb. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pump-probe experiments. This constitutes, to my knowledge, the first report of nondegenerate two-photon gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate three-photon absorption (ND-3PA), in both cases are theoretically analyzed. Experimental measurements of ND-3PA agree with this analysis and show that it is enhanced much more than ND-2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the two-photon gain, preventing the possibility of a two-photon semiconductor laser
Quantum Phase Imaging using Spatial Entanglement
Entangled photons have the remarkable ability to be more sensitive to signal
and less sensitive to noise than classical light. Joint photons can sample an
object collectively, resulting in faster phase accumulation and higher spatial
resolution, while common components of noise can be subtracted. Even more, they
can accomplish this while physically separate, due to the nonlocal properties
of quantum mechanics. Indeed, nearly all quantum optics experiments rely on
this separation, using individual point detectors that are scanned to measure
coincidence counts and correlations. Scanning, however, is tedious, time
consuming, and ill-suited for imaging. Moreover, the separation of beam paths
adds complexity to the system while reducing the number of photons available
for sampling, and the multiplicity of detectors does not scale well for greater
numbers of photons and higher orders of entanglement. We bypass all of these
problems here by directly imaging collinear photon pairs with an
electron-multiplying CCD camera. We show explicitly the benefits of quantum
nonlocality by engineering the spatial entanglement of the illuminating photons
and introduce a new method of correlation measurement by converting time-domain
coincidence counting into spatial-domain detection of selected pixels. We show
that classical transport-of-intensity methods are applicable in the quantum
domain and experimentally demonstrate nearly optimal (Heisenberg-limited) phase
measurement for the given quantum illumination. The methods show the power of
direct imaging and hold much potential for more general types of quantum
information processing and control
Future prospects for exploring present day anomalies in flavour physics measurements with Belle II and LHCb
A range of flavour physics observables show tensions with their corresponding
Standard Model expectations: measurements of leptonic flavour-changing neutral
current processes and ratios of semi-leptonic branching fractions involving
different generations of leptons show deviations of the order of four standard
deviations. If confirmed, either would be an intriguing sign of new physics. In
this manuscript, we analyse the current experimental situation of such
processes and for the first time estimate the combined impact of the future
datasets of the Belle II and LHCb experiments on the present tensions with the
Standard Model expectations by performing scans of the new physics contribution
to the Wilson coefficients. In addition, the present day and future sensitivity
of tree-level CKM parameters, which offer orthogonal tests of the Standard
Model, are explored. Three benchmark points in time are chosen for a direct
comparison of the estimated sensitivity between the experiments. A high
complementarity between the future sensitivity achieved by the Belle II and
LHCb experiments is observed due to their relative strengths and weaknesses. We
estimate that all of the anomalies considered here will be either confirmed or
ruled out by both experiments independently with very high significance by the
end of data-taking at Belle II and the LHCb upgrade
Understanding reverse osmosis polyamide active layer macrostructure and performance through indirect microscopic observation of film growth
Given the random nature of reverse osmosis polyamide macrostructure, it is difficult to understand the relationship between its structure and its separation characteristics. Many have addressed this subject and a few have reached significant conclusions to date. Acknowledging that membrane chemistry is the most important lever in controlling performance and not structure, to truly understand which features of the polyamide film can be manipulated to affect performance, there may be value in understanding its formation mechanism. Building upon a basic grasp of this mechanism, it may be possible to fine tune membrane performance through structure manipulation.
While direct observation of polyamide film growth is not yet possible on a microscopic scale, new methods have been developed for indirect observation of the process. These methods, pseudo-stop-motion imaging and reactive post-polymerization potting, have provided valuable insight on the formation mechanism. The pseudo-stop-motion imaging technique was developed to view the polyamide structure on a microscopic scale at discrete points in time during the interfacial polymerization, from the first appearance of polyamide material on the support surface to the end of the polymerization. Essentially watching the process occur diminished the need for complex modeling to produce a basic growth hypothesis. Furthermore, the method can be used for any type of polyamide, and is limited only by the resolution of electron microscopy.
Reactive post-polymerization potting is a technique developed to understand the structure of polyamide in its as-formed state. Historical microscopy has been performed on dried membranes, but not on films immediately following polymerization. The resulting structures are strikingly different from those observed in the literature via SEM and TEM, and when taken in context with the growth mechanism proposed from pseudo-stop-motion imaging, it further supports a mechanism of polyp inflation rather than continuous film formation. Well-controlled pilot-scale polyamide casting has been performed to corroborate the proposed mechanistic theory, and the theory will be framed within the broader context of polyamide membrane development
Optimizing the signal-to-noise ratio of biphoton distribution measurements
Single-photon-sensitive cameras can now be used as massively parallel
coincidence counters for entangled photon pairs. This enables measurement of
biphoton joint probability distributions with orders-of-magnitude greater
dimensionality and faster acquisition speeds than traditional raster scanning
of point detectors; to date, however, there has been no general formula
available to optimize data collection. Here we analyze the dependence of such
measurements on count rate, detector noise properties, and threshold levels. We
derive expressions for the biphoton joint probability distribution and its
signal-to-noise ratio (SNR), valid beyond the low-count regime up to detector
saturation. The analysis gives operating parameters for global optimum SNR that
may be specified prior to measurement. We find excellent agreement with
experimental measurements within the range of validity, and discuss
discrepancies with the theoretical model for high thresholds. This work enables
optimized measurement of the biphoton joint probability distribution in
high-dimensional joint Hilbert spaces.Comment: 9 pages, 5 figures, 1 tabl
Biphoton transmission through non-unitary objects
Losses should be accounted for in a complete description of quantum imaging
systems, and yet they are often treated as undesirable and largely neglected.
In conventional quantum imaging, images are built up by coincidence detection
of spatially entangled photon pairs (biphotons) transmitted through an object.
However, as real objects are non-unitary (absorptive), part of the transmitted
state contains only a single photon, which is overlooked in traditional
coincidence measurements. The single photon part has a drastically different
spatial distribution than the two-photon part. It contains information both
about the object, and, remarkably, the spatial entanglement properties of the
incident biphotons. We image the one- and two-photon parts of the transmitted
state using an electron multiplying CCD array both as a traditional camera and
as a massively parallel coincidence counting apparatus, and demonstrate
agreement with theoretical predictions. This work may prove useful for photon
number imaging and lead to techniques for entanglement characterization that do
not require coincidence measurements.Comment: 7 pages, 5 figure
Quantum image distillation
Imaging with quantum states of light promises advantages over classical approaches in terms of resolution, signal-to-noise ratio, and sensitivity. However, quantum detectors are particularly sensitive sources of classical noise that can reduce or cancel any quantum advantage in the final result. Without operating in the single-photon counting regime, we experimentally demonstrate distillation of a quantum image from measured data composed of a superposition of both quantum and classical light. We measure the image of an object formed under quantum illumination (correlated photons) that is mixed with another image produced by classical light (uncorrelated photons) with the same spectrum and polarization, and we demonstrate near-perfect separation of the two superimposed images by intensity correlation measurements. This work provides a method to mix and distinguish information carried by quantum and classical light, which may be useful for quantum imaging, communications, and security
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