876 research outputs found
Amplification of Angular Rotations Using Weak Measurements
We present a weak measurement protocol that permits a sensitive estimation of
angular rotations based on the concept of weak-value amplification. The shift
in the state of a pointer, in both angular position and the conjugate orbital
angular momentum bases, is used to estimate angular rotations. This is done by
an amplification of both the real and imaginary parts of the weak-value of a
polarization operator that has been coupled to the pointer, which is a spatial
mode, via a spin-orbit coupling. Our experiment demonstrates the first
realization of weak-value amplification in the azimuthal degree of freedom. We
have achieved effective amplification factors as large as 100, providing a
sensitivity that is on par with more complicated methods that employ quantum
states of light or extremely large values of orbital angular momentum.Comment: 5 pages, 3 figures, contains supplementary informatio
Experimental generation of an optical field with arbitrary spatial coherence properties
We describe an experimental technique to generate a quasi-monochromatic field
with any arbitrary spatial coherence properties that can be described by the
cross-spectral density function, . This is done by using a
dynamic binary amplitude grating generated by a digital micromirror device
(DMD) to rapidly alternate between a set of coherent fields, creating an
incoherent mix of modes that represent the coherent mode decomposition of the
desired . This method was then demonstrated experimentally
by interfering two plane waves and then spatially varying the coherent between
these two modes such that the interference fringe visibility was shown to vary
spatially between the two beams in an arbitrary and prescribed way.Comment: 6 pages, 5 figur
Quantum-secured imaging
We have built an imaging system that uses a photon's position or
time-of-flight information to image an object, while using the photon's
polarization for security. This ability allows us to obtain an image which is
secure against an attack in which the object being imaged intercepts and
resends the imaging photons with modified information. Popularly known as
"jamming," this type of attack is commonly directed at active imaging systems
such as radar. In order to jam our imaging system, the object must disturb the
delicate quantum state of the imaging photons, thus introducing statistical
errors that reveal its activity.Comment: 10 pages (double spaced), 5 figure
State transfer based on classical nonseparability
We present a state transfer protocol that is mathematically equivalent to
quantum teleportation, but uses classical nonseparability instead of quantum
entanglement. In our implementation we take advantage of nonseparability among
three parties: orbital angular momentum (OAM), polarization, and the radial
degrees of freedom of a beam of light. We demonstrate the transfer of arbitrary
OAM states, in the subspace spanned by any two OAM states, to the polarization
of the same beam
Multiplexing Free-Space Channels using Twisted Light
We experimentally demonstrate an interferometric protocol for multiplexing
optical states of light, with potential to become a standard element in
free-space communication schemes that utilize light endowed with orbital
angular momentum (OAM). We demonstrate multiplexing for odd and even OAM
superpositions generated using different sources. In addition, our technique
permits one to prepare either coherent superpositions or statistical mixtures
of OAM states. We employ state tomography to study the performance of this
protocol, and we demonstrate fidelities greater than 0.98.Comment: 4 pages, 3 figure
Compressive Object Tracking using Entangled Photons
We present a compressive sensing protocol that tracks a moving object by
removing static components from a scene. The implementation is carried out on a
ghost imaging scheme to minimize both the number of photons and the number of
measurements required to form a quantum image of the tracked object. This
procedure tracks an object at low light levels with fewer than 3% of the
measurements required for a raster scan, permitting us to more effectively use
the information content in each photon.Comment: 10 pages, 4 figure
The eyes donāt have it: Eye movements are unlikely to reflect refreshing in working memory
There is a growing interest in specifying the mechanisms underlying refreshing, i.e., the use of attention to keep working memory (WM) contents accessible. Here, we examined whether participantsā visual fixations during the retention interval of a WM task indicate the current focus of internal attention, thereby serving as an online measure of refreshing. Eye movements were recorded while participants studied and maintained an array of colored dots followed by probed recall of one (Experiments 1A and 1B) or all (Experiment 2) of the memoranda via a continuous color wheel. Experiments 1A and 2 entailed an unfilled retention interval in which refreshing is assumed to occur spontaneously, and Experiment 1B entailed a retention interval embedded with cues prompting the sequential refreshment of a subset of the memoranda. During the retention interval, fixations revisited the locations occupied by the memoranda, consistent with a looking-at-nothing phenomenon in WM, but the pattern was only evident when placeholders were onscreen in Experiment 2, indicating that most of these fixations may largely reflect random gaze. Furthermore, spontaneous fixations did not predict recall precision (Experiments 1A and 2), even when ensuring that they did not reflect random gaze (Experiment 2). In Experiment 1B, refreshing cues increased fixations to the eventually tested target and predicted better recall precision, which interacted with an overall benefit of target fixations, such that the benefit of fixations decreased as the number of refreshing cues increased. Thus, fixations under spontaneous conditions had no credible effect on recall precision, whereas the beneficial effect of fixations under instructed refreshing conditions may indicate situations in which cues were disregarded. Consequently, we conclude that eye movements do not seem suitable as an online measure of refreshing
Rapid Generation of Light Beams Carrying Orbital Angular Momentum
We report a technique for encoding both amplitude and phase variations onto a
laser beam using a single digital micro-mirror device (DMD). Using this
technique, we generate Laguerre-Gaussian and vortex orbital-angular-momentum
(OAM) modes, along with modes in a set that is mutually unbiased with respect
to the OAM basis. Additionally, we have demonstrated rapid switching among the
generated modes at a speed of 4 kHz, which is much faster than the speed
regularly achieved by spatial light modulators (SLMs). The dynamic control of
both phase and amplitude of a laser beam is an enabling technology for
classical communication and quantum key distribution (QKD) systems that employ
spatial mode encoding
Measurement of the Photon-Plasmon Coupling Phase
Scattering processes have played a crucial role in the development of quantum
theory. In the field of optics, scattering phase shifts have been utilized to
unveil interesting forms of light-matter interactions. Here, we investigate the
mode-coupling phase of single photons to surface plasmon polaritons in a
quantum plasmonic tritter. We observe that the coupling process induces a phase
jump that occurs when photons scatter into surface plasmons and vice versa.
This interesting coupling phase dynamics is of particular relevance for quantum
plasmonic experiments. Furthermore, it is demonstrated that this photon-plasmon
interaction can be modeled through a quantum-mechanical tritter. We show that
the visibility of a double-slit and a triple-slit interference patterns are
convenient observables to characterize the interaction at a slit and determine
the coupling phase. Our accurate and simple model of the interaction, validated
by simulations and experiments, has important implications not only for quantum
plasmonic interference effects, but is also advantageous to classical
applications
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