Measuring a photonic qubit without destroying it

Measuring the polarization of a single photon typically results in its destruction. We propose, demonstrate, and completely characterize a quantum nondemolition (QND) scheme for realizing such a measurement nondestructively. This scheme uses only linear optics and photodetection of ancillary modes to induce a strong nonlinearity at the single-photon level, nondeterministically. We vary this QND measurement continuously into the weak regime and use it to perform a nondestructive test of complementarity in quantum mechanics. Our scheme realizes the most advanced general measurement of a qubit to date: it is nondestructive, can be made in any basis, and with arbitrary strength.

Entanglement and bifurcations in Jahn-Teller models

We compare and contrast the entanglement in the ground state of two Jahn-Teller models. The Exbeta system models the coupling of a two-level electronic system, or qubit, to a single-oscillator mode, while the Exepsilon models the qubit coupled to two independent, degenerate oscillator modes. In the absence of a transverse magnetic field applied to the qubit, both systems exhibit a degenerate ground state. Whereas there always exists a completely separable ground state in the Exbeta system, the ground states of the Exepsilon model always exhibit entanglement. For the Exbeta case we aim to clarify results from previous work, alluding to a link between the ground-state entanglement characteristics and a bifurcation of a fixed point in the classical analog. In the Exepsilon case we make use of an ansatz for the ground state. We compare this ansatz to exact numerical calculations and use it to investigate how the entanglement is shared between the three system degrees of freedom.

Ion trap transducers for quantum electromechanical oscillators

An enduring challenge for contemporary physics is to experimentally observe and control quantum behavior in macroscopic systems. We show that a single trapped atomic ion could be used to probe the quantum nature of a mesoscopic mechanical oscillator precooled to 4 K, and furthermore, to cool the oscillator with high efficiency to its quantum ground state. The proposed experiment could be performed using currently available technology.

Modulating the rate and rhythmicity of perceptual rivalry alternations with the mixed 5-HT2A and 5-HT1A agonist psilocybin

Binocular rivalry occurs when different images are presented simultaneously to corresponding points within the left and right eyes. Under these conditions, the observer's perception will alternate between the two perceptual alternatives. Motivated by the reported link between the rate of perceptual alternations, symptoms of psychosis and an incidental observation that the rhythmicity of perceptual alternations during binocular rivalry was greatly increased 10 h after the consumption of LSD, this study aimed to investigate the pharmacology underlying binocular rivalry and to explore the connection between the timing of perceptual switching and psychosis. Psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine, PY) was chosen for the study because, like LSD, it is known to act as an agonist at serotonin (5-HT)(1A) and 5-HT2A receptors and to produce an altered state sometimes marked by psychosis-like symptoms. A total of 12 healthy human volunteers were tested under placebo, low-dose ( 115 mg/kg) and high-dose ( 250 mg/kg) PY conditions. In line with predictions, under both low- and high-dose conditions, the results show that at 90 min postadministration ( the peak of drug action), rate and rhythmicity of perceptual alternations were significantly reduced from placebo levels. Following the 90 min testing period, the perceptual switch rate successively increased, with some individuals showing increases well beyond pretest levels at the final testing, 360 min postadministration. However, as some subjects had still not returned to pretest levels by this time, the mean phase duration at 360 min was not found to differ significantly from placebo. Reflecting the drug-induced changes in rivalry phase durations, subjects showed clear changes in psychological state as indexed by the 5D-ASC ( altered states of consciousness) rating scales. This study suggests the involvement of serotonergic pathways in binocular rivalry and supports the previously proposed role of a brainstem oscillator in perceptual rivalry alternations and symptoms of psychosis.

Nonclassicality of a photon-subtracted Gaussian field

We investigate the nonclassicality of a photon-subtracted Gaussian field, which was produced in a recent experiment, using negativity of the Wigner function and the nonexistence of well-behaved positive P function. We obtain the condition to see negativity of the Wigner function for the case including the mixed Gaussian incoming field, the threshold photodetection and the inefficient homodyne measurement. We show how similar the photon-subtracted state is to a superposition of coherent states.

Rainfall variability at decadal and longer time scales: signal or noise?

Rainfall variability occurs over a wide range of temporal scales. Knowledge and understanding of such variability can lead to improved risk management practices in agricultural and other industries. Analyses of temporal patterns in 100 yr of observed monthly global sea surface temperature and sea level pressure data show that the single most important cause of explainable, terrestrial rainfall variability resides within the El Nino-Southern Oscillation (ENSO) frequency domain (2.5-8.0 yr), followed by a slightly weaker but highly significant decadal signal (9-13 yr), with some evidence of lesser but significant rainfall variability at interclecadal time scales (15-18 yr). Most of the rainfall variability significantly linked to frequencies tower than ENSO occurs in the Australasian region, with smaller effects in North and South America, central and southern Africa, and western Europe. While low-frequency (LF) signals at a decadal frequency are dominant, the variability evident was ENSO-like in all the frequency domains considered. The extent to which such LF variability is (i) predictable and (ii) either part of the overall ENSO variability or caused by independent processes remains an as yet unanswered question. Further progress can only be made through mechanistic studies using a variety of models.

Bright tripartite entanglement in triply concurrent parametric oscillation

We show that an optical parametric oscillator based on three concurrent chi((2)) nonlinearities can produce, above threshold, bright output beams of macroscopic intensities which exhibit strong tripartite continuous-variable entanglement. We also show that there are two ways that the system can exhibit a three-mode form of the Einstein-Podolsky-Rosen paradox, and calculate the extracavity fluctuation spectra that may be measured to verify our predictions.

A neuro-mechanical model for interpersonal coordination

The present study investigates the coordination between two people oscillating handheld pendulums, with a special emphasis on the influence of the mechanical properties of the effector systems involved. The first part of the study is an experiment in which eight pairs of participants are asked to coordinate the oscillation of their pendulum with the other participant's in an in-phase or antiphase fashion. Two types of pendulums, A and B, having different resonance frequencies (Freq A=0.98 Hz and Freq B=0.64 Hz), were used in different experimental combinations. Results confirm that the preferred frequencies produced by participants while manipulating each pendulum individually were close to the resonance frequencies of the pendulums. In their attempt to synchronize with one another, participants met at common frequencies that were influenced by the mechanical properties of the two pendulums involved. In agreement with previous studies, both the variability of the behavior and the shift in the intended relative phase were found to depend on the task-effector asymmetry, i.e., the difference between the mechanical properties of the effector systems involved. In the second part of the study, we propose a model to account for these results. The model consists of two cross-coupled neuro-mechanical units, each composed of a neural oscillator driving a wrist-pendulum system. Taken individually, each unit reproduced the natural tendency of the participants to freely oscillate a pendulum close to its resonance frequency. When cross-coupled through the vision of the pendulum of the other unit, the two units entrain each other and meet at a common frequency influenced by the mechanical properties of the two pendulums involved. The ability of the proposed model to address the other effects observed as a function of the different conditions of the pendulum and intended mode of coordination is discussed.

Effects of cation substitutions on the physical properties of M2M1T2O6 pyroxenes

In this PhD study, the effects of the cation substitutions on the physical properties of pyroxenes have been discussed. The results of this work extend the knowledge on pyroxenes with different chemical compositions. These properties might be used in the development of ceramic pigments, advanced materials and for the mineralogical phase identification. First of all, the crystallographic differences between Ge and Si pyroxenes have been examined. The structure of C2/c Ca rich Ge clinopyroxenes is very close to the low pressure C2/c structural configuration found in Ca-rich Si-pyroxenes. The shear of the unit cell is very similar, and the difference between a Ge end member and the corresponding Si-rich one is less than 1°. Instead, a remarkable difference exists between Ca-poor Si and Ge clinopyroxenes. First, Ca-poor Ge pyroxenes do not display a P21/c symmetry, but retain the C2/c symmetry; second, the observed C2/c structure shows, at room pressure, the configuration with highly kinked tetrahedral chains characteristic of the high pressure C2/c symmetry of Si Ca-poor pyroxenes. In orthopyroxenes, with Pbca symmetry, Ge-pyroxenes have volume larger than Si-pyroxenes. Samples along the system CaCoGe2O6 - CoCoGe2O6 have been synthesized at three different temperatures: 1050 °C, 1200 °C and 1250 °C. The aim of these solid state syntheses was to obtain a solid solution at ambient pressure, since the analogues Si-system needs high pressure. Unfortunately, very limited solution occurs because the structure forms of the two end member (high temperature for CaCoGe2O6 and high pressure CoCoGe2O6) are incompatible. The phase diagram of this system has been sketched and compared to that of Si. The cobalt end member (CoCoGe2O6) is stable at ambient pressure in two symmetries: at 1050 °C C2/c and 1200 °C Pbca. The impurity phase formed during these experiments is cobalt spinel. Raman spectroscopy has been used to investigate the vibrational properties of Ca-pyroxenes CaCoGe2O6, CaMgGe2O6, CaMgSi2O6 and CaCoSi2O6. A comparison between silicate and germanate pyroxenes shows significant changes in peak positions of the corresponding modes caused mainly by the difference of the Ge-Si atomic weight along with the distortion and compression of the coordination polyhedra. Red shift in Raman spectra of germanates has been calculated by a rough scale factor calculated by a simple harmonic oscillator model, considering the different bond lengths for 4-coordinated Si ~ 1.60- 1.65 Å vs Ge–O distance ~1.70 - 1.80 Å. The Raman spectra of CaMgGe2O6 and CaCoGe2O6 have been classified, in analogy with silicate (Wang et al., 2001) counterparts, in different ranges: - R1 (880-640 cm-1): strong T-O stretching modes of Ge and non-bridging O1 and O2 atoms within the GeO4 tetrahedron; - R2 (640-480 cm-1): stretching/bending modes of Ge-Obr-Ge bonds (chain stretching and chain bending); - R4 (480-360 cm-1): O-Ge-O vibrations; - R3 (360-240 cm-1): motions of the cations in M2 and M1 sites correlated with tetrahedral chain motion and tilting tetrahedra; - R5 (below 240 cm-1): lattice modes. The largest shift with respect to CaMgSi2O6 - CaCoSi2O6 is shown by the T-O stretching and chain modes. High-pressure Raman spectroscopy (up to about 8 GPa) on the same samples of Ca-pyroxenes using an ETH-type diamond anvil cell shows no phase transition within the P-ranges investigated, as all the peak positions vary linearly as a function of pressure. Our data confirm previous experimental findings on Si-diopside (Chopelas and Serghiou, 2000). In the investigated samples, all the Raman peaks shift upon compression, but the major changes in wavenumber with pressure are attributed to the chain bending (Ge-Obr-Ge bonds) and tetrahedra stretching modes (Ge-Onbr). Upon compression, the kinking angle, the bond lengths and T-T distances between tetrahedra decrease and consequently the wavenumber of the bending chain mode and tetrahedra stretching mode increases. Ge-pyroxenes show the higher P-induced peak-position shifts, being more compressible than corresponding silicates. The vibrational properties of CaM2+Ge2O6 (M2+ =Mg, Mn, Fe, Co, Ni, Zn) are reported for the first time. The wavenumber of Ge-Obr-Ge bending modes decreases linearly with increasing ionic radius of the M1 cation. No simple correlation has been found with M1 atomic mass or size or crystallographic parameters for the peak at ~850 cm-1 and in the low wavenumber regions. The magnetic properties of the system CaCoSi2O6 - CoCoSi2O6 have been investigated by magnetometry. The join is always characterized by 1 a.p.f.u. of cobalt in M1 site and this causes a pure collinear antiferromagnetic behaviour of the intra-chain superexchange interaction involving Co ions detected in all the measurements, while the magnetic order developed by the cobalt ions in M2 site (intra-chain) is affected by weak ferromagnetism, due to the non-collinearity of their antiferromagnetic interaction. In magnetically ordered systems, this non-collinearity effect promotes a spin canting of anti-parallel aligned magnetic moments and thus is a source of weak ferromagnetic behaviour in an antiferromagnetic. The weak ferromagnetism can be observed only for the samples with Co content higher than 0.5 a.p.f.u. in M2, when the concentration is sufficiently high to create a long range order along the M2 chain which is magnetically independent of M1 chain. The ferromagnetism was detected both in the M(T) at 10 Oe and M(H).

Independent neuronal oscillators of the rat globus pallidus

In vivo, neurons of the globus pallidus (GP) and subthalamic nucleus (STN) resonate independently around 70 Hz. However, on the loss of dopamine as in Parkinson's disease, there is a switch to a lower frequency of firing with increased bursting and synchronization of activity. In vitro, type A neurons of the GP, identified by the presence of Ih and rebound depolarizations, fire at frequencies (≤80 Hz) in response to glutamate pressure ejection, designed to mimic STN input. The profile of this frequency response was unaltered by bath application of the GABAA antagonist bicuculline (10 μM), indicating the lack of involvement of a local GABA neuronal network, while cross-correlations of neuronal pairs revealed uncorrelated activity or phase-locked activity with a variable phase delay, consistent with each GP neuron acting as an independent oscillator. This autonomy of firing appears to arise due to the presence of intrinsic voltage- and sodium-dependent subthreshold membrane oscillations. GABAA inhibitory postsynaptic potentials are able to disrupt this tonic activity while promoting a rebound depolarization and action potential firing. This rebound is able to reset the phase of the intrinsic oscillation and provides a mechanism for promoting coherent firing activity in ensembles of GP neurons that may ultimately lead to abnormal and pathological disorders of movement.

A preliminary study into emergent behaviours in a lattice of interacting nonlinear resonators and oscillators

Future sensor arrays will be composed of interacting nonlinear components with complex behaviours with no known analytic solutions. This paper provides a preliminary insight into the expected behaviour through numerical and analytical analysis. Specically, the complex behaviour of a periodically driven nonlinear Duffing resonator coupled elastically to a van der Pol oscillator is investigated as a building block in a 2D lattice of such units with local connectivity. An analytic treatment of the 2-device unit is provided through a two-time-scales approach and the stability of the complex dynamic motion is analysed. The pattern formation characteristics of a 2D lattice composed of these units coupled together through nearest neighbour interactions is analysed numerically for parameters appropriate to a physical realisation through MEMS devices. The emergent patterns of global and cluster synchronisation are investigated with respect to system parameters and lattice size.

Techniques for determining bias and stability in satellite altimeters

The case for monitoring large-scale sea level variability is established in the context of the estimation of the extent of anthropogenic climate change. Satellite altimeters are identified as having the potential to monitor this change with high resolution and accuracy. Possible sources of systematic errors and instabilities in these instruments which would be hurdles to the most accurate monitoring of such ocean signals are examined. Techniques for employing tide gauges to combat such inaccuracies are proposed and developed. The tide gauge at Newhaven in Sussex is used in conjunction with the nearby satellite laser ranger and high-resolution ocean models to estimate the absolute bias of the TOPEX, Poseidon, ERS 1 and ERS 2 altimeters. The theory which underlies the augmentation of altimeter measurements with tide gauge data is developed. In order to apply this, the tide gauges of the World Ocean Circulation Experiment are assessed and their suitability for altimeter calibration is determined. A reliable subset of these gauges is derived. A method of intra-altimeter calibration is developed using these tide gauges to remove the effect of variability over long time scales. In this way the long-term instability in the TOPEX range measurement is inferred and the drift arising from the on-board ultra stable oscillator is thus detected. An extension to this work develops a method for inter-altimeter calibration, allowing the systematic differences between unconnected altimeters to be measured. This is applied to the TOPEX and ERS 1 altimeters.

Circannual rhythms of maturation in the female rainbow trout and their entrainment by changes in photoperiod

The importance of endogenous rhythms in the photoperiodic control of the annual reproduction cycle in female rainbow trout was investigated. The effect of photoperiod regimes on the different stages of maturation was assessed by recording the timing of ovulation and from quantifying associated changes in serum oestradiol-17,testosterone and total calcium. Maintained under constant 6L:18D and constant temperature for up to four years, rainbow trout exhibited an endogenous rhythm of maturation with a periodicity of approximately one year. This rhythm of maturation appears to be driven by an autonomous circannual oscillator or clock which can be dissociated from the neuroendocrine mechanisms controlling gonadal maturation. Under conditions of constant 18L:6D or LL the periodicity of the maturation rhythm was 5.5-6 months; it is suggested that this periodicity may be caused by a splitting or uncoupling of at least two circannual clocks involved in the control of maturation. Abrupt changes in the length of the photoperiod act as a zeitgeber to entrain the endogenous rhythm of maturation. Whether the timing of maturation is advanced or delayed depends primarily on the direction of the change in photoperiod and its timing in relation to the phase of the rhythm, with the magnitude of the alteration in photoperiod having only a supplementary effect. The effect of specific changes in photoperiod on the entrainment of the maturation cycle can be described in terms of a phase-response curve. Photic information is transduced, probably by the pineal gland, into a daily rhythm of melatonin; exposure of rainbow trout to skeleton and resonance photoperiod regimes indicated that daylength measurement is effected by endogenous circadian clock(s) rather than by hour-glass mechanisms. A gating mechanism is closely associated with the circannual clock which determines the timing of onset of maturation in virgin female rainbow trout, only allowing fish that have attained a threshold stage of development to undergo gonadal maturation. Collectively the results support the hypothesis that the female rainbow trout exhibits an endogenous circannual rhythm of maturation which can be entrained by changes in photoperiod.

Novel real-time homodyne coherent receiver using a feed-forward based carrier extraction scheme for phase modulated signals

We report a novel real-time homodyne coherent receiver based on a DPSK optical-electrical-optical (OEO) regenerator used to extract a carrier from carrier-less phase modulated signals based on feed-forward based modulation stripping. The performance of this non-DSP based coherent receiver was evaluated for 10.66Gbit/s BPSK signals. Self-homodyne coherent detection and homodyne detection with an injection-locked local oscillator laser was demonstrated. The performance was evaluated by measuring the electrical signal-to-noise (SNR) and recording the eye diagrams. Using injection-locking for the LO improves the performance and enables homodyne detection with optical injection-locking to operate with carrier-less BPSK signals without the need for polarization multiplexed pilot-tones.

Sub-50 fs Yb-doped laser with anomalous-dispersion photonic crystal fiber

We report on the generation of 42 fs pulses at 1 µm in a completely fiber-integrated format, which are, to the best of our knowledge, the shortest from all-fiber-integrated Yb-doped fiber lasers to date. The ring fiber cavity incorporates anomalous-dispersion, solid-core photonic crystal fiber with low birefringence, which acts as a broadband, in-fiber Lyot filter to facilitate mode locking. The oscillator operates in the stretched-pulse regime under slight normal net cavity dispersion. The cavity generates 4.7 ps long pulses with a spectral bandwidth of 58.2 nm, which are dechirped to 42 fs via a grating pair compressor outside of the cavity. Relative intensity noise (RIN) of the laser is characterized, with the integrated RIN found to be 0.026% in the 3 Hz-250 kHz frequency range.