Multimode theory of measurement-induced non-Gaussian operation on wideband squeezed light

We present a multimode theory of non-Gaussian operation induced by an imperfect on/off-type photon detector on a splitted beam from a wideband squeezed light. The events are defined for finite time duration $T$ in the time domain. The non-Gaussian output state is measured by the homodyne detector with finite bandwidh $B$. Under this time- and band-limitation to the quantm states, we develop a formalism to evaluate the frequency mode matching between the on/off trigger channel and the conditional signal beam in the homodyne channel. Our formalism is applied to the CW and pulsed schemes. We explicitly calculate the Wigner function of the conditional non-Gaussian output state in a realistic situation. Good mode matching is achieved for BT\alt1, where the discreteness of modes becomes prominant, and only a few modes become dominant both in the on/off and the homodyne channels. If the trigger beam is projected nearly onto the single photon state in the most dominant mode in this regime, the most striking non-classical effect will be observed in the homodyne statistics. The increase of $BT$ and the dark counts degrades the non-classical effect.Comment: 20 pages, 14 figures, submitted to Phys. Rev.

Symmetry restoring bifurcation in collective decision-making.

How social groups and organisms decide between alternative feeding sites or shelters has been extensively studied both experimentally and theoretically. One key result is the existence of a symmetry-breaking bifurcation at a critical system size, where there is a switch from evenly distributed exploitation of all options to a focussed exploitation of just one. Here we present a decision-making model in which symmetry-breaking is followed by a symmetry restoring bifurcation, whereby very large systems return to an even distribution of exploitation amongst options. The model assumes local positive feedback, coupled with a negative feedback regulating the flow toward the feeding sites. We show that the model is consistent with three different strains of the slime mold Physarum polycephalum, choosing between two feeding sites. We argue that this combination of feedbacks could allow collective foraging organisms to react flexibly in a dynamic environment

Quantum criticality in ferroelectrics

Materials tuned to the neighbourhood of a zero temperature phase transition often show the emergence of novel quantum phenomena. Much of the effort to study these new effects, like the breakdown of the conventional Fermi-liquid theory of metals has been focused in narrow band electronic systems. Ferroelectric crystals provide a very different type of quantum criticality that arises purely from the crystalline lattice. In many cases the ferroelectric phase can be tuned to absolute zero using hydrostatic pressure or chemical or isotopic substitution. Close to such a zero temperature phase transition, the dielectric constant and other quantities change into radically unconventional forms due to the quantum fluctuations of the electrical polarization. The simplest ferroelectrics may form a text-book paradigm of quantum criticality in the solid-state as the difficulties found in metals due to a high density of gapless excitations on the Fermi surface are avoided. We present low temperature high precision data demonstrating these effects in pure single crystals of SrTiO3 and KTaO3. We outline a model for describing the physics of ferroelectrics close to quantum criticality and highlight the expected 1/T2 dependence of the dielectric constant measured over a wide temperature range at low temperatures. In the neighbourhood of the quantum critical point we report the emergence of a small frequency independent peak in the dielectric constant at approximately 2K in SrTiO3 and 3K in KTaO3 believed to arise from coupling to acoustic phonons. Looking ahead, we suggest that in ferroelectric materials supporting mobile charge carriers, quantum paraelectric fluctuations may mediate new effective electron-electron interactions giving rise to a number of possible states such as superconductivity.Comment: 10 pages, 4 figure

Direction of polarization

The structure of isotope-substituted SrTi18O3 (STO18) below Tc=24 K has not been made fully understood yet. We have shown that it is orthorhombic C2v with polarization ${\vec{P}}$ parallel to [110]c, but other groups reported other structures such as ${\vec{P}}\Vert [111]_c$ and ${\vec{P}}\Vert [100]_c$. In this paper, it is shown that the dipole interaction between the rhombohedral polar clusters which has been revealed by NMR (Blinc R. et al., Phys. Rev. Lett., 94 (2005) 147601) is the very probable reason for the formation of ${\vec{P}}\Vert [110]_{c}$. The dipole interaction model is consistent with various peculiarities observed in the Raman spectra (Shigenari T. et al., Phys. Rev. B, 74 (2006) 174121) such as the inhomogeneity, the imperfect softening and the appearance of the relaxational mode near Tc

Nonlinear response of photothermal and optical absorption for erythrosine B dye in epoxy resin

Photothermal measurement using thermistor is applied to study the heat generation by nonradiative processes in erythrosine B dye in epoxy resin. It shows that the incident light intensity dependence of heat generation using an Ar ion laser is nonlinear and corresponds to that for the transmission of erythrosine B in epoxy resin. The increase of the signal intensity of the heat generation is different from that of total rate of optical energy absorption