Quantum enhanced non-interferometric quantitative phase imaging

Quantum entanglement and squeezing have significantly improved phase estimation and imaging in interferometric settings beyond the classical limits.However,for a wide class of non-interferometric phase imaging/retrieval methods vastly used in the classical domain,e.g.,ptychography and diffractive imaging,a demonstration of quantum advantage is still missing.Here,we fill this gap by exploiting entanglement to enhance imaging of a pure phase object in a non-interferometric setting,only measuring the phase effect on the free-propagating field.This method,based on the so-called"transport of intensity equation",is quantitative since it provides the absolute value of the phase without prior knowledge of the object and operates in wide-field mode,so it does not need time-consuming raster scanning.Moreover,it does not require spatial and temporal coherence of the incident light.Besides a general improvement of the image quality at a fixed number of photons irradiated through the object,resulting in better discrimination of small details,we demonstrate a clear reduction of the uncertainty in the quantitative phase estimation.Although we provide an experimental demonstration of a specific scheme in the visible spectrum,this research also paves the way for applications at different wavelengths,e.g.,X-ray imaging,where reducing the photon dose is of utmost importance.

Efficient mid-infrared single-photon detection using superconducting NbTiN nanowires with high time resolution in a Gifford-McMahon cryocooler

Shortly after their inception, superconducting nanowire single-photon detectors(SNSPDs) became the leading quantum light detection technology. With the capability of detecting single-photons with near-unity efficiency,high time resolution, low dark count rate, and fast recovery time, SNSPDs outperform conventional single-photon detection techniques. However, detecting lower energy single photons(<0.8 eV) with high efficiency and low timing jitter has remained a challenge. To achieve unity internal efficiency at mid-infrared wavelengths, previous works used amorphous superconducting materials with low energy gaps at the expense of reduced time resolution(close to a nanosecond), and by operating them in complex milli Kelvin(mK) dilution refrigerators. In this work,we provide an alternative approach with SNSPDs fabricated from 5 to 9.5 nm thick NbTiN superconducting films and devices operated in conventional Gifford-McMahon cryocoolers. By optimizing the superconducting film deposition process, film thickness, and nanowire design, our fiber-coupled devices achieved >70% system detection efficiency(SDE) at 2 μm and sub-15 ps timing jitter. Furthermore, detectors from the same batch demonstrated unity internal detection efficiency at 3 μm and 80% internal efficiency at 4 μm, paving the road for an efficient mid-infrared single-photon detection technology with unparalleled time resolution and without mK cooling requirements. We also systematically studied the dark count rates(DCRs) of our detectors coupled to different types of mid-infrared optical fibers and blackbody radiation filters. This offers insight into the trade-off between bandwidth and DCRs for mid-infrared SNSPDs. To conclude, this paper significantly extends the working wavelength range for SNSPDs made from polycrystalline NbTiN to 1.5–4 μm, and we expect quantum optics experiments and applications in the mid-infrared range to benefit from this far-reaching technology.