The true role of entanglement in two-photon virtual-state spectroscopy (Saleh et al 1998 Phys. Rev. Lett. 80 3483), a two-photon absorption spectroscopic technique that can retrieve information about the energy level structure of an atom or a molecule, is controversial. The consideration of closely related techniques, such as multidimensional pump-probe spectroscopy (Roslyak et al 2009 Phys. Rev. A 79, 063409), suggests that spectroscopic information might also be retrieved by using uncorrelated pairs of photons. Here we show that this is not the case. In the two-photon absorption process, the ability to obtain information about the energy level structure of a medium depends on the spectral shape of existing temporal (frequency) correlations between the absorbed photons. In fact, it is a combination of both the presence of frequency correlations (entanglement) and their specific spectral shape that makes the

We demonstrate experimentally a scheme to measure small temporal delays, much smaller than the pulse width, between optical pulses. Specifically, we observe an interference effect, based on the concepts of quantum weak measurements and weak value amplification, through which a sub-pulse-width temporal delay between two femtosecond pulses induces a measurable shift of the central frequency of the pulse. The amount of frequency shift, and the accompanying losses of the measurement, can be tailored by postselecting different states of polarization. Our scheme requires only spectrum measurements and linear optics elements, hence greatly facilitating its implementation. Thus it appears to be a promising technique for measuring small and rapidly varying temporal delays.

We demonstrate a different scheme to perform optical sectioning of a sample based on the concept of induced coherence [Zou et al., Phys. Rev. Lett. 67, 318 (1991)]. This can be viewed as a different type of optical coherence tomography scheme where the varying reflectivity of the sample along the direction of propagation of an optical beam translates into changes of the degree of first-order coherence between two beams. As a practical advantage the scheme allows probing the sample with one wavelength and measuring photons with another wavelength. In a bio-imaging scenario, this would result in a deeper penetration into the sample because of probing with longer wavelengths, while still using the optimum wavelength for detection. The scheme proposed here could achieve submicron axial resolution by making use of nonlinear parametric sources with broad spectral bandwidth emission.

In this article we present the development of a set of opto-mechanical components (a kinematic mount, a translation stage and an integrating sphere) that can be easily built using a 3D printer based on Fused Filament Fabrication (FFF) and parts that can be found in any hardware store. Here we provide a brief description of the 3D models used and some details on the fabrication process. Moreover, with the help of three simple experimental setups, we evaluate the performance of the opto-mechanical components developed by doing a quantitative comparison with its commercial counterparts. Our results indicate that the components fabricated are highly customizable, low-cost, require a short time to be fabricated and surprisingly, offer a performance that compares favorably with respect to low-end commercial alternatives.

We present a proof-of-concept experiment aimed at increasing the sensitivity of Fiber-Bragg-gratings temperature sensors by making use of a weak-value-amplification scheme. The technique requires only linear optics elements for its implementation and appears as a promising method for increasing the sensitivity than state-of the-art sensors can currently provide. The device implemented here is able to generate a shift of the centroid of the spectrum of a pulse of ∼0.035 nm∕°C, a nearly fourfold increase in sensitivity over the same fiber-Bragg-grating system interrogated using standard methods.

We report the experimental observation of spectral interference in a Michelson interferometer, regardless of the relationship between the temporal path difference introduced between the arms of the interferometer and the spectral width of the input pulse. This observation is possible by introducing the polarization degree of freedom into a Michelson interferometer using a typical weak value amplification scenario. c 2018 Optical Society of America OCIS codes: 260.0260, 260.3160,260.5430, 320.5550,120.3180 Interference is a fundamental concept in any theory based on waves, such as classical electromagnetism or quantum theory. The specific experimental arrangement required for the observation of interference depends on the characteristics of the light source, i.e., its spatiotemporal profile and its degree of coherence. For example, for first-order coherent light in a Michelson interferometer, for temporal delays shorter than the pulse width, interference manifests as a delay-dependent change of the intensity at the output port of the interferometer. For longer temporal delays, interference manifest as spectral interference for a given temporal delay. The observation of spectral interference was denoted by Mandel [1, 2] as the Alford-Gold effect [3] and it is well-known in optics [4].Here we report the observation of spectral interference independently of the temporal regime under consideration. The interference is revealed as a reshaping of the input spectrum that is accomplished by introducing the polarization degree of freedom into a Michelson interferometer. This scenario corresponds precisely to the conditions of a typical weak value amplification configuration [5][6][7][8] that although was originally conceived in the framework of a quantum formalism, it is essentially based on the phenomena of interference and can thus be applied to any scenario with waves [9][10][11][12][13].For the sake of clarity, let us start by describing temporal and spectral interference in a typical Michelson interferometer, without considering polarization. Later on, we will describe the effects that the introduction of the polarization degree of freedom has on spectral interference. Consider the situation depicted in Fig. 1(a). A first-order coherent input pulse with amplitude E 0 , central frequency ν 0 , input polarization e in , and temporal duration τ (full width at half maximum) described by follows a different path and after reflection in a mirror the two pulses recombine at the BS. By changing the position of one of the mirrors, a temporal delay (T ) is generated between the two pulses. The intensity measured by a slow detector at the output port of the interferometer as a function of T can be written aswhere I 0 = |E 0 | 2 . Two interesting cases can be distinguished: i) when T ≪ τ , and therefore, the two pulses traveling the different paths overlap in time and ii) when T ≫ τ and the two pulses do not overlap. In the first case, the output intensity as a function of T reduces to1

Weak value amplification (WVA) is a concept that has been extensively used in a myriad of applications with the aim of rendering measurable tiny changes of a variable of interest. In spite of this, there is still an on-going debate about its true nature and whether is really needed for achieving high sensitivity. Here we aim at helping to clarify the puzzle, using a specific example and some basic concepts from quantum estimation theory, highlighting what the use of the WVA concept can offer and what it can not. While WVA cannot be used to go beyond some fundamental sensitivity limits that arise from considering the full nature of the quantum states, WVA can notwithstanding enhance the sensitivity of real and specific detection schemes that are limited by many other things apart from the quantum nature of the states involved, i.e. technical noise. Importantly, it can do that in a straightforward and easily accessible manner.

We report the implementation of a tunable beam displacer, composed of a polarizing beam splitter (PBS) and two mirrors, that divides an initially polarized beam into two parallel beams whose separation can be continuously tuned. The two output beams are linearly polarized with either vertical or horizontal polarization and no optical path difference is introduced between them. The wavelength dependence of the device as well as the maximum separation between the beams achievable is limited mainly by the PBS characteristics.Peer ReviewedPostprint (author’s final draft