As an alternative to traditional adaptive optics systems, wavefront shaping techniques show promise in controlling light propagation through turbulent channels. This study explores the feasibility of measuring the transmission matrix and using it to enhance communication in turbulent conditions.
The problem of resolving pointlike light sources not only serves as a benchmark for optical resolution but also holds various practical applications ranging from microscopy to astronomy. In this study, we aim to resolve two thermal sources sharing arbitrary mutual coherence using the spatial mode demultiplexing technique. Our analytical moment-based approach covers scenarios where the coherence and the emission rate of the sources depend on the separation between them, and is not limited to the Poissonian approximation. Studying the examples of the interactive dipoles imaging and imaging of the reflective particles under external illumination, we demonstrate that separation-dependent coherence, which arises in this scenario, can significantly enhance optical resolution.
We show that this effect is robust in the presence of the emitters dephasing and detection noise.
The resolution of optical systems, formulated as the smallest possible distance between two point sources for which they still can be dissolved, was for a long time believed to be limited by diffraction, formulated by the Rayleigh criterion. Recent advancements in quantum metrology have shown, by evaluation of the Quantum Cramér Rao bound (QCRB), that the Rayleigh criterion is not a fundamental limit. In our experiment, spatial mode demultiplexing (SPADE) is used to estimate the separation of the sources orders of magnitude below the Rayleigh limit. The experiment is extended to incorporate the measurement of additional parameters, such as power imbalance and centroid position of the two sources, bringing it closer to real-world applicability.
We experimentally implement the separation estimation between to incoherent optical sources. Our method, relying on spatial-mode demultiplexing and intensity measurements, saturates the Cramèr-Rao bound, with a five orders of magnitude gain compared to the Rayleigh limit.
Resolving light sources below the diffraction limit is a fundamental task both for astronomy and microscopy. Several recent works, analysed this problem through the lens of quantum parameter estimation theory and proved that the separation between two point sources can be estimated at the quantum limit using intensity measurements after spatial-mode demultiplexing. However, most previous works have either consider low-intensity, or thermal sources.
To broaden the applicability of this approach, it is important to extend these results to more general light sources.
To this goal, we will present an analytical expression for the Quantum Fisher Information, determining the ultimate resolution limit, for the separation between two sources in an arbitrary Gaussian state.
Applying this result to different quantum states, we can shine some light on some relevant questions. We can for example explore the role of partial coherence considering displaced and correlated thermal states, or investigate the importance of quantum correlations by considering squeezed light.
In addition to the ultimate quantum limit, we will discuss a simple estimation technique, requiring access only to the mean value of a linear combination of demultiplexed intensity measurements, which is often sufficient to saturate these limits, and can easily be adapted to incorporate the most common noise sources.
Finally, we will present our experimental setup that allows for the generation of the images of two sources with different photon statistics, as well as for spatial mode demultiplexing and we will discuss the first practical implementations if the above mentioned estimation techniques.
Recent works showed that the separation between two point sources can be estimated at the quantum limit using intensity measurements after spatial-mode demultiplexing. However, so far these results have been either limited to low-intensity, or thermal sources. In this talk, we will present an analytical expression for the Quantum Fisher Information for the separation between two sources in an arbitrary Gaussian states. This expression allows us to determine the ultimate resolution limit for a series of practically relevant states, e.g. correlated or displaced thermal states (corresponding to partially coherent sources) and squeezed states (exhibiting quantum correlations). Moreover, we will show how a simple estimation technique, requiring access only to the mean value of a linear combination of demultiplexed intensity measurements can be used to saturate these limits. Finally, we will discuss the applicability of the proposed methods in present experimental setups.
Recently, it has been demonstrated that demultiplexing Hermite-Gauss (HG) modes represents the quantum-optimal measurement to estimate the distance between two incoherent sources. However, it remains unclear how to practically combine the information contained into several demultiplexing measurements to reach the ultimate resolution limits. In this contribution, we show how estimators saturating the Cramér-Rao bound for the distance between two thermal point sources can be constructed from an optimised linear combination of intensity measurements in a given number of HG modes, in presence of practical imperfection such as misalignment, crosstalk and detector noise. Moreover, we demonstrate that our strategy saturates the quantum Cramér-Rao bound, in the noiseless case, if sufficiently many modes are measured.
Superresolution techniques based on intensity measurements after a spatial mode decomposition can overcome the precision of diffraction-limited direct imaging. We present both the experimental implementation of simultaneous spatial multimode demultiplexing as a distance measurement tool and the theoretical analysis of the actual sensitivity limits given the main experimental imperfection: cross-talks between channels. We demonstrate the distance estimation between two incoherent beams in both directions of the transverse plane, and find a perfect accordance with theoretical predictions, given a proper calibration of the demultiplexer. We show that, even though sensitivity is limited by the cross-talk between channels, we can perform measurements in two dimensions much beyond the Rayleigh limit over a large dynamic range. Combining statistical and analytical tools, we obtain the scaling of the precision limits for weak, generic crosstalk from a device-independent model as a function of the crosstalk probability and N.
Recent works revealed that transmission of light beams carrying orbital-angular-momentum (OAM) through turbulence causes the optical vortex defining these beams to split into multiple vortices with unit topological charge. Here, we consider the numerical propagation of orbital-angular-momentum (OAM) modes through a horizontal atmospheric channel. By analysing the beam's phase front after transmission through turbulence, we confirm the occurence of vortex splitting, but we also witness the emergence of vortex-antivortex pairs. Moreover, by performing performing a decomposition of the transmitted wave into OAM modes, we show that while adaptive optics cannot cancel vortex splitting, it still is pretty efficient in diminishing the turbulence-induced crosstalk between different OAM modes.
We carry out a numerical analysis of the spatial structure of the eigenmodes of light in atmospheric turbulence and assess the distribution of the singular values under variable turbulence conditions characterized by the Fried parameter and Rytov variance. Under weak scintillation, the highly transmitting eigenmodes found here possess a modal structure that is reminiscent of Laguerre-Gaussian (LG) modes and their simple superpositions. When scintillation becomes significant, we establish that the optimal eigenmodes for communication differ substantially from LG modes and tend to have highly localized transverse intensity distributions.
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