We experimentally control the spectral structure of photon pairs created via spontaneous four-wave mixing in microstructured fibers. By fabricating fibers with designed dispersion, one can manipulate the photons' wavelengths, joint spectrum, and, thus, entanglement. As an example, we produce photon pairs with no spectral correlations, allowing direct heralding of single photons in pure-state wave packets without filtering. We achieve an experimental purity of (85.9+/-1.6)%, while theoretical analysis and preliminary tests suggest that 94.5% purity is possible with a much longer fiber.

Quantum states and measurements exhibit wave-like -continuous, or particle-like -discrete, character. Hybrid discrete-continuous photonic systems are key to investigating fundamental quantum phenomena [1][2][3], generating superpositions of macroscopic states [4], and form essential resources for quantum-enhanced applications [5], e.g. entanglement distillation [6,7] and quantum computation [8], as well as highly efficient optical telecommunications [9,10]. Realizing the full potential of these hybrid systems requires quantum-optical measurements sensitive to complementary observables such as field quadrature amplitude and photon number [11][12][13]. However, a thorough understanding of the practical performance of an optical detector interpolating between these two regions is absent. Here, we report the implementation of full quantum detector tomography, enabling the characterization of the simultaneous wave and photonnumber sensitivities of quantum-optical detectors. This yields the largest parametrization to-date in quantum tomography experiments, requiring the development of novel theoretical tools. Our results reveal the role of coherence in quantum measurements and demonstrate the tunability of hybrid quantum-optical detectors.Accurate knowledge of a quantum-optical detector is essential for its fruitful utilization, be it in foundational investigations or technological applications. Photodetectors are normally characterized by several parameters, including detectivity, spectral sensitivity and noiseequivalent power [14]. For quantum detectors, additional information is required for a complete specification of the detector. This information is the set of operators that link the input quantum state of the light field to the classical detector output, known as postiveoperator-valued measure (POVM). It may be estimated by means of quantum detector tomogrpahy (QDT) [15][16][17][18], and is needed if the detector is to be used reliably. To date, QDT has been successfully applied to avalanche photodiodes (APDs) [19], time-multiplexed detectors [18,20,21], transition-edge sensors [22], and super-conducting nanowire detectors [23]. The matrix representations of the POVMs for these detectors are diagonal in the photon-number basis. Consequently the reconstruction problem is linear and positive, and therefore amenable to solution by means familiar to classical signal processing [24]. This is not true for a general quantum detector: the POVM elements can have non-zero offdiagonals due to coherent superpositions. Even in conventional optical communications, coherent modulation and detection can increase the data transmission rate by an order of magnitude. Moreover, exploration and utilization of the full Hilbert space of a quantum system requires a detector capable of implementing a tomographically complete set of measurements [25]. Such a capability is also vital to fully harness the potential of hybrid quantum systems operating at the confluence of discrete and continuous variable regimes. To this end, phasesensitiv...

The linear birefringence of uniaxial crystal plates is known since the 17 th century, and it is widely used in numerous optical setups and devices. Here we demonstrate, both theoretically and experimentally, a fine lateral circular birefringence of such crystal plates. This effect is a novel example of the spin-Hall effect of light, i.e., a transverse spin-dependent shift of the paraxial light beam transmitted through the plate. The well-known linear birefringence and the new circular birefringence form an interesting analogy with the Goos-Hänchen and Imbert-Fedorov beam shifts that appear in the light reflection at a dielectric interface. We report the experimental observation of the effect in a remarkably simple system of a tilted half-wave plate and polarizers using polarimetric and quantum-weak-measurement techniques for the beam-shift measurements. In view of great recent interest in spin-orbit interaction phenomena, our results could find applications in modern polarization optics and nano-photonics.

Photonic spin Hall effect in transmission is a transverse beam shift of the out-coming beam depending on polarization of the in-coming beam.The effect can be significantly enhanced by materials with high anisotropy. We report the first experimental demonstration of the photonic spin Hall effect in a multilayer hyperbolic metamaterial at visible wavelengths (wavelengths of 520 nm and 633 nm). The metamaterial is composed of alternating layers of gold and alumina with deeplysubwavelength thicknesses, exhibiting extremely large anisotropy. The angle resolved polarimetric measurements showed the shift of 165 µm for the metamaterial of 176 nm in thickness. Additionally the transverse beam shift is extremely sensitive to the variations of the incident angle changing theoretically by 270 µm with one milli-radian (0.057 • ). These features can lead to minituarized spin Hall switches and filters with high angular resolution.