Super-resolution microscopy seeks to surpass the resolution limit dictated by the diffraction of light. Among the various super-resolution methods, far-field are of the particular interest due to their non-invasive nature. For instance, the substitution of uniform sample illumination with a structured light beam enables resolution enhancement without perturbing the sample. Recent breakthroughs in quantum metrology suggest an alternative path: replacing the conventional intensity measurement in the image plane with spatial mode demultiplexing, also known as Hermite-Gaussian imaging (HGI). In this study, we introduce a novel combined technique that takes advantage from improving both measurement and illumination by implementing HGI within the conventional Image Scanning Microscopy (ISM) approach. Our experimental results demonstrate a 2.5-fold improvement in lateral resolution compared to the generalised Rayleigh limit. The combined approach demonstrates superiority over both ISM and HGI individually, enhancing lateral resolution and minimizing the impact of the artefacts on the final image.
Spatial optical mode sorter is a promising device that can significantly contribute to communication and imaging domains. However, currently available commercial devices fall short in effectively sorting large mode bases with high fidelity, particularly in the visible range.
Traditionally, such sorting has relied on multi-plane light conversion (MPLC) setups, wherein the optical field undergoes iterative bouncing between a mirror and a spatial light modulator programmed with different phase profiles. This configuration can be also thought of as a diffractive optical neural network (DONN), where each phase mask acts like a single layer.
In this work we treat the mode sorter as a DONN and instead of employing iterative algorithms to calculate optimal phase masks with conventional MPLC approaches, we propose training it with machine learning algorithms. We investigate various training methodologies, including backpropagation within simulation environments, hybrid approach that incorporate experimental data, and forward-forward training strategies.
We demonstrate a quantum communication protocol that enables frequency conversion of quantum optical information in an adiabatic way. The protocol is based on electromagnetically induced transparency in sustems with multiple excited levels. The proof-of-principle experiment is performed using the hyperfine levels of the rubidium D1 line.
We report characterization of EIT resonances in the D1 line of Rb 87 under various experimental conditions. The dependence of the EIT linewidth on the power of the control field investigated. Strictly linear behavior between the ground levels as the main source of decoherence. We therefore formulated a new theory assuming pure dephasing to be the main decoherence mechanism. We also performed experiments where we created additional decoherence mechanisms by means of a counter-propagating repumper field. This field caused the ground-state population exchange, thus reproducing conditions in which the original theory is valid.
We present an experimental study of decoherence of the ground energy levels of 87Rb atoms in vapor cells. We measure the decoherence of the ground state using three different methods: measuring the decay constant of the storage of light in atomic vapor, the decay rates of transient coherence oscillations of the ground state, and the width of the electromagnetically induced transparency resonances. The measurements showed decoherence rates on the scale of 104 s-1.
We present experimental homodyne tomography of an optical quantum
bit represented by a single photon split into two optical modes.
The reconstructed four-dimensional density matrix extends over the
entire Hilbert space and thus reveals, for the first time,
complete information about the dual-rail optical qubit as a state
of the electromagnetic field. The experimental data violate the
Bell inequality albeit with a loophole similar to the detection
loophole in photon counting experiments. We also show that a
homodyne measurement on just one of the modes leads to remote
preparation of a single-rail optical qubit in the other mode.
We discuss a classical model allowing one to visualize and
characterize the optical mode of the single photon generated by
means of a conditional measurement on a biphoton produced in
parametric down-conversion. The model is based on Klyshko's
advanced wave interpretation, but extends beyond it, providing a
precise mathematical description of the advanced wave. The optical
mode of the conditional photon is shown to be identical to the
mode of the classical difference-frequency field generated due to
nonlinear interaction of the partially coherent advanced wave with
the pump pulse. With this "nonlinear advanced wave model" most
coherence properties of the conditional photon become manifest,
which permits one to intuitively understand many recent results,
in particular, in quantum imaging.
Second harmonic generation has hitherto been thought of as simultaneous with the excitation pulse which generates it. Recent experiments in Cs vapor demonstrate otherwise. A short two-photon 6D - 6S resonant excitation pulse in Cs vapor generates a superposition state which would radiate immediately were it not for destructive interference arising from the sample being large compared to the radiation wavelength. The radiation pattern of an isolated radiator (atom) starts out with a null in the plane transverse to the polarization (linear) direction but then rotates about the applied transverse magnetic field developing a radiation component along the phase matched direction which we detect. Experimental results are presented in excellent agreement with theory. Previous delay discrepancies have been resolved by using a nonmetallic sample cell. Cascade and yoked superfluorescence take place but not significantly until after the second harmonic emissions. Quantitative measurements of signal intensity are also presented.
Time-delayed second harmonic generation has recently been reported in an atomic vapor of Cs at a temperature near 180 degrees Celsius and situated in a magnetic field of the order of a killogauss. Short 10 ps excitation laser pulses at 885 nm were used to excite a macroscopic electric quadrupole density which was then observed to radiate at 442 nm after a delay of a few hundred picoseconds. The experiment is complicated by the presence of several superfluorescence transitions some of which radiate close to the 442 nm wavelength. These emissions are also delayed and our strategy is to set the experimental conditions so that they only become appreciable after the second harmonic emission is complete. In this paper we show how the second harmonic develops by considering the evolution of the radiation pattern of an isolated atomic radiator (not forbidden to radiate at the second harmonic even in the absence of a magnetic field). We estimate the intensity of the superradiant second harmonic emission and obtain agreement with experiment. Excellent agreement is also obtained between measured and calculated delay.
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