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Single photon detectors are indispensable tools in optics, from fundamental measurements to quantum information processing. The ability of superconducting nanowire single photon detectors (SNSPDs) to detect single photons with unprecedented efficiency, short dead time, and high time resolution over a large frequency range enabled major advances in quantum optics. However, combining near-unity system detection efficiency (SDE) with high timing performance remains an outstanding challenge. In this work, we fabricated novel SNSPDs on membranes with 99.5−2.07+0.5% SDE at 1350 nm with 32 ps timing jitter (using a room-temperature amplifier), and other detectors in the same batch showed 94%–98% SDE at 1260–1625 nm with 15–26 ps timing jitter (using cryogenic amplifiers). The SiO2/Au membrane enables broadband absorption in small SNSPDs, offering high detection efficiency in combination with high timing performance. With low-noise cryogenic amplifiers operated in the same cryostat, our efficient detectors reach a timing jitter in the range of 15–26 ps. We discuss the prime challenges in optical design, device fabrication, and accurate and reliable detection efficiency measurements to achieve high performance single photon detection. As a result, the fast developing fields of quantum information science, quantum metrology, infrared imaging, and quantum networks will greatly benefit from this far-reaching quantum detection technology.

Quantum fluctuations in optical amplification are investigated with a nondegenerate optical parametric amplifier whose internal idler mode is coupled to a squeezed vacuum. Reductions of the inherent quantum noise of the amplifier are observed with a minimum noise level 0.7 dB below the usual noise level of the amplifier with its internal idler mode in a vacuum state. With a small coherent field as the signal input, the amplified output exhibits an improvement in signal-to-noise ratio of 0.5 dB for the case of a squeezed vacuum as compared to a vacuum state for the amplifier's internal mode.PACS numbers: 42.50.Lc, 42.50.Dv Quite apart from its significance in technological terms, the question of the fundamental noise performance of an amplifier has a long history in physics because of its intimate relationship to quantum measurement [1][2][3][4][5]. Indeed, if "noiseless" amplification were possible, then the microscopic quantum world could be magnified to a macroscopic scale for our casual inspection. However, the principles of quantum mechanics require an amplifier to add noise to any input that it processes, as has been codified by Caves in a fundamental theorem for phaseinsensitive amplifiers and in an uncertainty relation for phase-sensitive amplifiers [5]. Whatever the particular origin (e.g., spontaneous emission in a laser amplifier), the fundamental excess noise associated with the amplification process can be viewed as arising from the coupling of the signal input to the internal modes of the amplifier and hence depends upon the state of these modes, which in the best case until now has been a vacuum state. For phase-insensitive amplification, the quantum noise added by internal vacuum-state modes is phase insensitive and gives rise to noise at the output which is equivalent to half of a noise photon at the input in the limit of large gain. A coherent field as the signal input will thus suffer a 3 dB degradation in signal-to-noise ratio in the large gain limit; furthermore, nonclassical features of the signal input will be lost for amplification with power gain greater than 3 dB for this kind of amplifier [61.If instead the internal modes of the amplifier are coupled to a squeezed vacuum rather than to the usual vacuum state, then the added quantum noise at the signal output will be phase dependent reflecting the reduced and enhanced fluctuations of a squeezed state relative to the vacuum [7]. Yurke and Denker [8] and others [9][10][11] have in this way suggested that the excess noise for phase-insensitive amplifiers can be effectively eliminated by arranging for signal information to be encoded on the quadrature-phase amplitude of the input corresponding to that with reduced noise at the amplifier's output. Of course in this case the added quantum noise demanded by Caves's amplifier uncertainty principle goes mostly into the (unused) conjugate quadrature; the originally phaseinsensitive amplifier is thus converted to a phase-sensitive amplifier by squeezing its internal modes.In this Letter we presen...

Scatterometry is a well established technique currently utilized in research, as well as in industrial applications, to retrieve the properties of a given scatterer (the target) by looking at how the light coming from a certain source is diffracted in the far field. Currently the light source is often a discharge lamp that, after wavelength filtering, can be thought as a quasi-monochromatic, but spatially incoherent, source. In the present work, benefits of using a focused spot from a spatially coherent light source, as that emitted by a laser, are investigated on a theoretical viewpoint. The focused spot is scanned over the object of interest and, for each scan position, a far-field diffraction pattern is recorded. Our results show that spatially coherent light can sensibly increase the accuracy of the technique with respect to the target's geometrical profile.