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EPJ Web of Conferences

Achieving the ultimate optical resolution

Luis Lorenzo Sánchez-Soto, Z. Hradil, Jaroslav Řeháček, Benjamin Brecht, Christine Silberhorn

Published Jan 1, 2022• 0 citations
Publisher

Abstract

The accurate estimation of the separation between two signals is at the core of many modern technologies. We show new quantum-inspired schemes able to estimate that separation at the quantum limit. The method works in the spatial, temporal, and frequency domains. The question of whether the optical coherence brings any metrological advantage to mode projections is discussed.

DOI
10.1051/epjconf/202226610017

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The accurate estimation of the separation between two signals is at the core of many modern technologies. We show new quantum-inspired schemes able to estimate that separation at the quantum limit. The method works in the spatial, temporal, and frequency domains. The question of whether the optical coherence brings any metrological advantage to mode projections is discussed.
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Measuring small separations between two optical sources, either in space or in time, constitutes an important metrological challenge as standard intensity-only measurements fail for vanishing separations. Contrarily, it has been established that appropriate coherent mode projections can appraise arbitrarily small separations with quantum-limited precision. However, the question of whether the optical coherence brings any metrological advantage to mode projections is still a point of debate. Here, we elucidate this problem by experimentally investigating the effect of varying coherence on estimating the temporal separation between two single-photon pulses. We show that, for an accurate interpretation, special attention must be paid to properly normalize the quantum Fisher information to account for the strength of the signal.
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.
Accurate time-delay measurement is at the core of many modern technologies.We present a temporalmode demultiplexing scheme that achieves the ultimate quantum precision for the simultaneous estimation of the temporal centroid, the time offset, and the relative intensities of an incoherent mixture of ultrashort pulses at the single-photon level.We experimentally resolve temporal separations 10 times smaller than the pulse duration, as well as imbalanced intensities differing by a factor of 10 2 .This represents an improvement of more than an order of magnitude over the best standard methods based on intensity detection.