13,411 research outputs found
Divergence of an orbital-angular-momentum-carrying beam upon propagation
There is recent interest in the use of light beams carrying orbital angular
momentum (OAM) for creating multiple channels within free-space optical
communication systems. One limiting issue is that, for a given beam size at the
transmitter, the beam divergence angle increases with increasing OAM, thus
requiring a larger aperture at the receiving optical system if the efficiency
of detection is to be maintained. Confusion exists as to whether this
divergence scales linarly with, or with the square root of, the beam's OAM. We
clarify how both these scaling laws are valid, depending upon whether it is the
radius of the Gaussian beam waist or the rms intensity which is kept constant
while varying the OAM.Comment: 4 pages, 2 figure
Experimental Study of Parametric Autoresonance in Faraday Waves
The excitation of large amplitude nonlinear waves is achieved via parametric
autoresonance of Faraday waves. We experimentally demonstrate that phase
locking to low amplitude driving can generate persistent high-amplitude growth
of nonlinear waves in a dissipative system. The experiments presented are in
excellent agreement with theory.Comment: 4 pages, 4 eps figures, to appear in Phys. Rev. Let
Limitations to the determination of a Laguerre-Gauss spectrum via projective, phase-flattening measurement
One of the most widely used techniques for measuring the orbital angular
momentum components of a light beam is to flatten the spiral phase front of a
mode, in order to couple it to a single-mode optical fiber. This method,
however, suffers from an efficiency that depends on the orbital angular
momentum of the initial mode and on the presence of higher order radial modes.
The reason is that once the phase has been flattened, the field retains its
ringed intensity pattern and is therefore a nontrivial superposition of purely
radial modes, of which only the fundamental one couples to a single mode
optical fiber. In this paper, we study the efficiency of this technique both
theoretically and experimentally. We find that even for low values of the OAM,
a large amount of light can fall outside the fundamental mode of the fiber, and
we quantify the losses as functions of the waist of the coupling beam of the
orbital angular momentum and radial indices. Our results can be used as a tool
to remove the efficiency bias where fair-sampling loopholes are not a concern.
However, we hope that our study will encourage the development of better
detection methods of the orbital angular momentum content of a beam of light.Comment: 5 pages, 4 figure
Angular two-photon interference and angular two-qubit states
Using angular-position-orbital-angular-momentum entangled photons, we study angular two-photon interference in a scheme in which entangled photons are made to pass through apertures in the form of double angular slits, and using this scheme, we demonstrate an entangled two-qubit state that is based on the angular-position correlations of entangled photons. The entanglement of the two-qubit state is quantified in terms of concurrence. These results provide an additional means for preparing entangled quantum states for use in quantum information protocols
EPR-based ghost imaging using a single-photon-sensitive camera
Correlated photon imaging, popularly known as ghost imaging, is a technique whereby an image is formed from light that has never interacted with the object. In ghost imaging experiments, two correlated light fields are produced. One of these fields illuminates the object, and the other field is measured by a spatially resolving detector. In the quantum regime, these correlated light fields are produced by entangled photons created by spontaneous parametric down-conversion. To date, all correlated photon ghost imaging experiments have scanned a single-pixel detector through the field of view to obtain spatial information. However, scanning leads to poor sampling efficiency, which scales inversely with the number of pixels, N, in the image. In this work, we overcome this limitation by using a time-gated camera to record the single-photon events across the full scene. We obtain high-contrast images, 90%, in either the image plane or the far field of the photon pair source, taking advantage of the Einstein–Podolsky–Rosen-like correlations in position and momentum of the photon pairs. Our images contain a large number of modes, >500, creating opportunities in low-light-level imaging and in quantum information processing
Amplitude equations and pattern selection in Faraday waves
We present a systematic nonlinear theory of pattern selection for parametric
surface waves (Faraday waves), not restricted to fluids of low viscosity. A
standing wave amplitude equation is derived from the Navier-Stokes equations
that is of gradient form. The associated Lyapunov function is calculated for
different regular patterns to determine the selected pattern near threshold.
For fluids of large viscosity, the selected wave pattern consists of parallel
stripes. At lower viscosity, patterns of square symmetry are obtained in the
capillary regime (large frequencies). At lower frequencies (the mixed
gravity-capillary regime), a sequence of six-fold (hexagonal), eight-fold, ...
patterns are predicted. The regions of stability of the various patterns are in
quantitative agreement with recent experiments conducted in large aspect ratio
systems.Comment: 12 pages, 1 figure, Revte
The Trilinear Hamiltonian: A Zero Dimensional Model of Hawking Radiation from a Quantized Source
We investigate a quantum parametric amplifier with dynamical pump mode,
viewed as a zero-dimensional model of Hawking radiation from an evaporating
black hole. The conditions are derived under which the spectrum of particles
generated from vacuum fluctuations deviates from the thermal spectrum predicted
for the conventional parametric amplifier. We find that significant deviations
arise when the pump mode (black hole) has emitted nearly half of its initial
energy into the signal (Hawking radiation) and idler (in-falling particle)
modes. As a model of black hole dynamics, this finding lends support to the
view that late-time Hawking radiation contains information about the quantum
state of the black hole and is entangled with the black hole's quantum
gravitational degrees of freedom.Comment: 18 pages, 6 figures, Submitted to New Journal of Physics focus issue:
"Classical and Quantum Analogues for Gravitational Phenomena and Related
Effects
Assembly and force measurement with SPM-like probes in holographic optical tweezers
We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ±ℓ and superpositions thereof, with ℓ=1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around ℓ=20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing ℓ, entanglement persists in a large dimensional state space
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