We report a measurement workflow free of systematic errors consisting of a reconfigurable photonnumber-resolving detector, custom electronic circuitry, and faithful data-processing algorithm. We achieve unprecedentedly accurate measurement of various photon-number distributions going beyond the number of detection channels with average fidelity 0.998, where the error is contributed primarily by the sources themselves. Mean numbers of photons cover values up to 20 and faithful autocorrelation measurements range from g (2) = 6 × 10 −3 to 2. We successfully detect chaotic, classical, non-classical, non-Gaussian, and negative-Wigner-function light. Our results open new paths for optical technologies by providing full access to the photon-number information without the necessity of detector tomography.

Spectroscopy of vibrational optical activity has been established as a powerful tool to study molecular structures and interactions. In most cases, only fundamental molecular transitions are analyzed. In the present study, we analyze a broader range of vibrational frequencies (40−4000 cm −1 ), which could be measured on a new Raman optical activity (ROA) instrument. An unexpectedly strong vibrational Raman optical activity of 2-chloropropionitrile has been observed within the low-frequency region (40−150 cm −1 ). On the basis of combined molecular dynamics and density functional theory simulations, it could be assigned to intermolecular vibrations. A detailed analysis also revealed connection between spectral shapes and molecular structure and flexibility, such as bending of the CCN group. At the other edge of the scale, within ∼1500−4000 cm −1 , for the first time, many combination and overtone ROA bands have been observed for 2-chloropropionitrile and α-pinene. These were also partially assigned, using quantumchemical computations. The band assignment was confirmed by a comparison with Raman, absorption, and vibrational circular dichroism spectra. The measurement in the broader vibrational range thus significantly extends the information that can be obtained by optical spectroscopy, including intermolecular interactions of chiral molecules and liquids.

The optical purity of a chiral sample is of particular importance to the analytical chemistry and pharmaceutical industries. In recent years, the vibrational optical activity (VOA) has become established as a sensitive and nondestructive technique for the analysis of chiral molecules in solution. However, the relatively limited accuracy in the range of about 1–2% reported in published papers and the relatively small spread of experimental facilities to date have meant that vibrational spectroscopy has not been considered a common method for determining enantiomeric excess. In this paper, we attempt to describe, in detail, a methodology for the determination of enantiomeric excess using Raman optical activity (ROA). This method achieved an accuracy of 0.05% for neat α-pinene and 0.22% for alanine aqueous solution, after less than 6 h of signal accumulation for each enantiomeric mixture, which we believe is the best result achieved to date using vibrational optical activity techniques. An algorithm for the elimination of systematic errors (polarization artifacts) is proposed, and the importance of normalizing ROA spectra to correct for fluctuations in excitation power is established. Results comparable to those obtained with routinely used chemometric analysis by the partial least squares (PLS) method were obtained. These findings show the great potential of ROA spectroscopy for the quantitative analysis of enantiomeric mixtures.

We report a single-photon Mach-Zehnder interferometer stabilized to a phase precision of 0.05 degrees over 15 hours. To lock the phase, we employ an auxiliary reference light at a different wavelength than the quantum signal. The developed phase locking operates continuously, with negligible crosstalk, and for an arbitrary phase of the quantum signal. Moreover, its performance is independent of intensity fluctuations of the reference. Since the presented method can be used in a vast majority of quantum interferometric networks it can significantly improve phase-sensitive applications in quantum communication and quantum metrology.

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