111 research outputs found
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
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
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
Pattern formation in a ring cavity with temporally incoherent feedback
We present a theoretical and experimental study of modulation instability and pattern formation in a passive nonlinear optical cavity that is longer than the coherence length of the light circulating in it. Pattern formation in this cavity exhibits various features of a second-order phase transition, closely resembling laser action
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
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