Bright squeezed vacuum in a nonlinear interferometer: frequency/temporal Schmidt-mode description

Control over the spectral properties of the bright squeezed vacuum (BSV), a highly multimode non-classical macroscopic state of light that can be generated through high-gain parametric down conversion, is crucial for many applications. In particular, in several recent experiments BSV is generated in a strongly pumped SU(1,1) interferometer to achieve phase supersensitivity, perform broadband homodyne detection, or tailor the frequency spectrum of squeezed light. In this work, we present an analytical approach to the theoretical description of BSV in the frequency domain based on the Bloch-Messiah reduction and the Schmidt-mode formalism. As a special case we consider a strongly pumped SU(1,1) interferometer. We show that different moments of the radiation at its output depend on the phase, dispersion and the parametric gain in a nontrivial way, thereby providing additional insights on the capabilities of nonlinear interferometers. In particular, a dramatic change in the spectrum occurs as the parametric gain increases

Properties of bright squeezed vacuum at increasing brightness

A bright squeezed vacuum (BSV) is a nonclassical macroscopic state of light, which is generated through high-gain parametric down-conversion or four-wave mixing. Although the BSV is an important tool in quantum optics and has a lot of applications, its theoretical description is still not complete. In particular, the existing description in terms of Schmidt modes with gain-independent shapes fails to explain the spectral broadening observed in the experiment as the mean number of photons increases. Meanwhile, the semiclassical description accounting for the broadening does not allow us to decouple the intermodal photon-number correlations. In this work, we present a new generalized theoretical approach to describe the spatial properties of a multimode BSV. In the multimode case, one has to take into account the complicated interplay between all involved modes: each plane-wave mode interacts with all other modes, which complicates the problem significantly. The developed approach is based on exchanging the (k, t ) and (ω, z) representations and solving a system of integrodifferential equations. Our approach predicts correctly the dynamics of the Schmidt modes and the broadening of the angular distribution with the increase in the BSV mean photon number due to a stronger pumping. Moreover, the model correctly describes various properties of a widely used experimental configuration with two crystals and an air gap between them, namely, an SU(1,1) interferometer. In particular, it predicts the narrowing of the intensity distribution, the reduction and shift of the side lobes, and the decline in the interference visibility as the mean photon number increases due to stronger pumping. The presented experimental results confirm the validity of the new approach. The model can be easily extended to the case of the frequency spectrum, frequency Schmidt modes, and other experimental configurations

From Avalanches to Fluid Flow: A Continuous Picture of Grain Dynamics Down a Heap

Surface flows are excited by steadily adding spherical glass beads to the top of a heap. To simultaneously characterize the fast single-grain dynamics and the much slower collective intermittency of the flow, we extend photon-correlation spectroscopy via fourth-order temporal correlations in the scattered light intensity. We find that microscopic grain dynamics during an avalanche are similar to those in the continuous flow just above the transition. We also find that there is a minimum jamming time, even arbitrarily close to the transition

Functional MRI with active, fully implanted, deep brain stimulation systems: Safety and experimental confounds

We investigated safety issues and potential experimental confounds when performing functional magnetic resonance imaging (fMRI) investigations in human subjects with fully implanted, active, deep brain stimulation (DBS) systems. Measurements of temperature and induced voltage were performed in an in vitro arrangement simulating bilateral DBS during magnetic resonance imaging (MRI) using head transmit coils in both 1.5 and 3.0 T MRI systems. For MRI sequences typical of an fMRI study with coil-averaged specific absorption rates (SARs) less than 0.4 W/kg, no MRI-induced temperature change greater than the measurement sensitivity (0.1 °C) was detected at 1.5 T, and at 3 T temperature elevations were less than 0.5 °C, i.e. within safe limits. For the purposes of demonstration, MRI pulse sequences with SARs of 1.45 W/kg and 2.34 W/kg (at 1.5 T and 3 T, respectively) were prescribed and elicited temperature increases (> 1 °C) greater than those considered safe for human subjects. Temperature increases were independent of the presence or absence of active stimulator pulsing. At both field strengths during echo planar MRI, the perturbations of DBS equipment performance were sufficiently slight, and temperature increases sufficiently low to suggest that thermal or electromagnetically mediated experimental confounds to fMRI with DBS are unlikely. We conclude that fMRI studies performed in subjects with subcutaneously implanted DBS units can be both safe and free from DBS-specific experimental confounds. Furthermore, fMRI in subjects with fully implanted rather than externalised DBS stimulator units may offer a significant safety advantage. Further studies are required to determine the safety of MRI with DBS for other MRI systems, transmit coil configurations and DBS arrangements

Diffusion at constant speed in a model phase space

We reconsider the problem of diffusion of particles at constant speed and present a generalization of the Telegrapher process to higher dimensional stochastic media ($d>1$), where the particle can move along $2^d$ directions. We derive the equations for the probability density function using the ``formulae of differentiation'' of Shapiro and Loginov. The model is an advancement over similiar models of photon migration in multiply scattering media in that it results in a true diffusion at constant speed in the limit of large dimensions.Comment: Final corrected version RevTeX, 6 pages, 1 figur

Educational partnerships

A key objective of the professional forestry program in the School of Forestry at Northern Arizona University (NAU) has been to prepare students to become practicing land managers. But in a state where the vast majority of the commercial forestland ownership rests with the federal government or in tribal holdings, providing NAU students with exposure to private forestland management practices is difficult

A Redescription of the First Instar of Rhantus calidus (Fabricius) (Coleoptera: Dytiscidae) with Notes on its Biology

First instars of Rhantus calidus (Fabricius) representing a Georgia population are described and illustrated. Dimensions are provided along with an analysis of the primary chaetotaxy of legs, head, and last abdominal segment. The presence of first instars at the study site demonstrated that R. calidus either requires or is at least tolerant of warmer temperatures for completion of its life cycle. Habitats with temperatures comparable to this site were likely present in a warm Atlantic coastal enclave during the last glacial maximum (LGM), making it probable that the LGM dytiscid fauna of Georgia included R. calidus