Utilizing weak pump depletion to stabilize squeezed vacuum states.

We propose and demonstrate a pump-phase locking technique that makes use of weak pump depletion (WPD) - an unavoidable effect that is usually neglected - in a sub-threshold optical parametric oscillator (OPO). We show that the phase difference between seed and pump beam is imprinted on both light fields by the non-linear interaction in the crystal and can be read out without disturbing the squeezed output. In our experimental setup we observe squeezing levels of 1.96 ± 0.01 dB, with an anti-squeezing level of 3.78 ± 0.02 dB (for a 0.55 mW seed beam at 1064 nm and 67.8 mW of pump light at 532 nm). Our new locking technique allows for the first experimental realization of a pump-phase lock by reading out the pre-existing phase information in the pump field. There is no degradation of the detected squeezed states required to implement this scheme.

Adaptive optical phase estimation using time-symmetric quantum smoothing.

Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. The most commonly used technique for this type of estimation is quantum filtering, using only past observations. We present the first experimental demonstration of quantum smoothing, a time-symmetric technique that uses past and future observations, for quantum parameter estimation. We consider both adaptive and nonadaptive quantum smoothing, and show that both are better than their filtered counterparts. For the problem of estimating a stochastically varying phase shift on a coherent beam, our theory predicts that adaptive quantum smoothing (the best scheme) gives an estimate with a mean-square error up to 2sqrt[2] times smaller than nonadaptive filtering (the standard quantum limit). The experimentally measured improvement is 2.24+/-0.14.

Effects of flossing and rinsing with a fluoridated mouthwash after brushing with a fluoridated toothpaste on salivary fluoride clearance.

The aims of this study were to test the hypothesis that flossing after brushing with a fluoridated toothpaste may lower salivary fluoride (F), and to evaluate the consequence of subsequent F mouthwash use. Twenty adults used 3 oral hygiene regimes in a randomised order: A, brushing with an NaF toothpaste; B, as A but followed by professional flossing; C, as B followed by rinsing with an NaF mouthwash. Saliva samples were collected up to 120 min after each regime and analysed for F. The mean area under the clearance curve value for regime C was statistically significantly greater than the corresponding values for A and B (p < 0.0001), which differed little. The regime that included the mouthwash may provide better anticaries protection.

Homodyne locking of a squeezer.

We report on the successful implementation of an approach to locking the frequencies of an optical parametric oscillator (OPO)-based squeezed-vacuum source and its driving laser. The technique allows the simultaneous measurement of the phase shifts induced by a cavity, which may be used for the purposes of frequency locking, as well as the simultaneous measurement of the sub-quantum-noise-limited (sub-QNL) phase quadrature output of the OPO. The homodyne locking technique is cheap, easy to implement, and has the distinct advantage that subsequent homodyne measurements are automatically phase locked. The homodyne locking technique is also unique in that it is a sub-QNL frequency discriminator.

Discretization in time gives rise to noise-induced improvement of the signal-to-noise ratio in static nonlinearities.

For some nonlinear systems the performance can improve with an increasing noise level. Such noise-induced improvement in static nonlinearities is of great interest for practical applications since many systems can be modeled in that way (e.g., sensors, quantizers, limiters, etc.). We present experimental evidence that noise-induced performance improvement occurs in those systems as a consequence of discretization in time with the achievable signal-to-noise ratio (SNR) gain increasing with decreasing ratio of input noise bandwidth and total measurement bandwidth. By modifying the input noise bandwidth, noise-induced improvement with SNR gain larger than unity is demonstrated in a system where it was not previously thought possible. Our experimental results bring closer two different theoretical models for the same class of nonlinearities and shed light on the behavior of static nonlinear discrete-time systems.

Photostatistics reconstruction via loop detector signatures.

Photon-number resolving detectors are a fundamental building-block of optical quantum information processing protocols. A loop detector, combined with appropriate statistical processing, can be used to convert a binary on/off photon counter into a photon-number-resolving detector. Here we describe the idea of a signature of photon-counts, which may be used to more robustly reconstruct the photon number distribution of a quantum state. The methodology is applied experimentally in a 9-port loop detector operating at a telecommunications wavelength and compared directly to the approach whereby only the number of photon-counts is used to reconstruct the input distribution. The signature approach is shown to be more robust against calibration errors, exhibit reduced statistical uncertainty, and reduced reliance on a-priori assumptions about the input state.

Hybrid electronic/optical synchronized chaos communication system.

A hybrid electronic/optical system for synchronizing a chaotic receiver to a chaotic transmitter has been demonstrated. The chaotic signal is generated electronically and injected, in addition to a constant bias current, to a semiconductor laser to produce an optical carrier for transmission. The optical chaotic carrier is photodetected to regenerate an electronic signal for synchronization in a matched electronic receiver The system has been successfully used for the transmission and recovery of a chaos masked message that is added to the chaotic optical carrier. Past demonstrations of synchronized chaos based, secure communication systems have used either an electronic chaotic carrier or an optical chaotic carrier (such as the chaotic output of various nonlinear laser systems). This is the first electronic/optical hybrid system to be demonstrated. We call this generation of a chaotic optical carrier by electronic injection.

Linearly filtered estimation of the time-domain Green's function from measurements of ambient noise.

It is possible to estimate the time-domain Green's function of a channel based on measurements of ambient noise by sensors at either end of the channel. This paper presents theoretical results for the impact of filtering on this problem. These results lead to the development of two experimental rules-of-thumb. It is shown that there exists a relationship between system bandwidth and sensor separation, which determines the resolvability of the measurements. The relationship between high-pass filtering and differentiation is discussed, contributing to the debate about whether or not differentiation is required to estimate the time-domain Green's function.

Digital transmission for improved synchronization of analog chaos generators in communications systems.

We present a method for synchronization of chaos generators based on transmission of an analog chaotic waveform in a digital form. Experimental comparisons between digital and analog transmission of chaos from a delayed differential feedback system are performed. Synchronization is demonstrated to be between 18 and 39 dB (or equivalently 63 to 7943 times) better for digital transmission than analog. Coherent chaotic modulation and demodulation is demonstrated in a situation where there is no effective synchronization using analog transmission.

Observation of a comb of optical squeezing over many gigahertz of bandwidth.

We experimentally demonstrate the generation of optical squeezing at multiple longitudinal modes and transverse Hermite-Gauss modes of an optical parametric amplifier. We present measurements of approximately 3 dB squeezing at baseband, 1.7 GHz, 3.4 GHz and 5.1 GHz which correspond to the first, second and third resonances of the amplifier. We show that both the magnitude and the bandwidth of the squeezing at the higher longitudinal modes is greater than can be observed at baseband. The squeezing observed is the highest frequency squeezing reported to date.

Coherent analysis of quantum optical sideband modes.

We demonstrate a device that allows for the coherent analysis of a pair of optical frequency sidebands in an arbitrary basis. We show that our device is quantum noise limited, and hence applications for this scheme may be found in discrete and continuous variable optical quantum information experiments.

Statistical issues for combining multiple caries diagnostics for demonstrating caries efficacy.

Caries efficacy in clinical trials has been based primarily on visual examinations supplemented by Fiber Optic Transillumination (FOTI) and radiography, with the assessments combined at the surface level to classify each surface as to its caries status. Newer caries diagnostics techniques measure the caries process in a quantitative manner and so thus yield continuous rather than ordinal results. The objective of this study was to examine various methods for the analysis of multiple outcomes in clinical trials and to compare their usefulness for the analysis of caries trials. Four global tests (rank sum, ordinary least squares, general least squares, and generalized estimating equations) and two caries indices (based on average and maximum values of the methods) were evaluated with the use of one-year follow-up data from 1063 children in a recent caries trial. A new hybrid method was also developed and evaluated. All of the methods performed well when the diagnostic measures showed product differences in caries in the same direction. Ease of use, interpretability, and distributional assumptions must be considered before a consensus method for analysis of multiple diagnostic measures in caries trials can be determined.

Development of a method in situ to study toothpaste abrasion of dentine. Comparison of 2 products.

BACKGROUND/AIMS: The abrasivity of toothpastes is usually determined using in vitro methods; as such, the clinical significance of the findings is uncertain. The aim of the present study was to develop and evaluate a method in situ to study abrasion of dentine by two toothpastes of different Relative Dentine Abrasivity (RDA). METHOD: The study was a single blind, randomised, 2 way cross over design involving 10 healthy dentate volunteers. Subjects wore an maxillary removable acrylic appliance containing two flat human dentine specimens, taped to expose a window of tissue, from 9 am to 4 pm during the two 10 working day study periods. No food or drink was consumed when the appliance was in place. On five occasions each day, the appliances were removed and the dentine windows brushed ex vivo with the allocated paste for 60 s each. Dentine abrasion at days 5 and 10 was measured using a profilometer. RESULTS: Both toothpastes produced measurable abrasion in all subjects and the depth increased in most subjects between 5 and 10 days. There was significant subject and specimen variation both within and between toothpastes. There was significantly increased abrasion by the toothpaste with the higher RDA value and in mean terms the ratio of abrasion between the two pastes was similar to the ratio of the RDA values. CONCLUSION: The method in situ, already used to study dental hard tissue erosion, appears ideally suitable to study dental abrasion alone and the interaction between aetiological factors involved in tooth wear.

A method to compare four mouthrinses: time to gingivitis level as the primary outcome variable.

BACKGROUND AND AIM: The experimental gingivitis model is a well-established method in comparing the chemical antiplaque activity of agents and products. The aim of the present study was to use time in order to achieve an exit level of bleeding on probing (BOP) as the primary outcome variable. METHODS: The study was a single blind, randomised four treatment parallel group design employing 76 healthy volunteers. The cohort was accepted into the study proper if they achieved a level of /= 50% BOP. Using the baseline and exit BOP, MGI and plaque, a deterioration rate for each parameter was derived and used as the unit of analysis. RESULTS: There were highly significant treatment differences for all three parameters. Paired analyses revealed chlorhexidine was highly significantly more effective than the other rinses for all three parameters. CPC and triclosan were not different from the control for BOP, but CPC was significantly different from the control for MGI and plaque, and triclosan was different from the control for plaque. There were no differences between the CPC and triclosan rinses. CONCLUSIONS: The method achieved the expected result of differentiating between the chlorhexidine and the other rinses. Some modification of the method, primarily to group sizes, should improve specificity. The method has the considerable volunteer appeal of early exit, particularly when allocated to control or low activity treatments for plaque.

A randomised controlled trial of the efficacy of supervised toothbrushing in high-caries-risk children.

Scottish children have one of the highest levels of caries experience in Europe. Only 33% of 5-year-old children in Dundee who developed caries in their first permanent molars by 7 brushed their teeth twice a day. High-caries-risk children should benefit if they brush more often with fluoridated toothpaste. The aim of this clinical trial was to determine the reduction in 2-year caries increment that can be achieved by daily supervised toothbrushing on school-days with a toothpaste containing 1,000 ppm fluoride (as sodium monofluorophosphate) and 0.13% calcium glycerophosphate, combined with recommended daily home use, compared to a control group involving no intervention other than 6-monthly clinical examinations. Five hundred and thirty-four children, mean age 5.3, in schools in deprived areas of Tayside were recruited. Each school had two parallel classes, one randomly selected to be the brushing class and the other, the control. Local mothers were trained as toothbrushing supervisors. Children brushed on school-days and received home supplies. A single examiner undertook 6-monthly examinations recording plaque, caries (D(1) level), and used FOTI to supplement the visual caries examination. For children in the brushing classes, the 2-year mean caries increment on first permanent molars was 0.81 at D(1) and 0.21 at D(3) compared to 1.19 and 0.48 for children in the control classes (significant reductions of 32% at D(1) and 56% at D(3)). In conclusion, high-caries-risk children have been shown to have significantly less caries after participating in a supervised toothbrushing programme with a fluoridated toothpaste.

An abbreviated caries clinical trial design validated over 24 months.

Conventional caries trials last from 24 to 36 months. This study evaluated whether the previously established difference in efficacy between 1000- and 2500-ppm-fluoride dentifrices could be detected after 12 months. Caries was assessed by clinical visual assessment (CVA-simplified version of Dundee Selectable Threshold Method - DSTM), bitewing radiography, and Fiber Optic Transillumination (FOTI). Changes in status for individual surfaces were classified by means of pre-prepared matrices as 0 (unchanged), +1 (initiation or progression), or -1 (regression) and summed for each subject to yield an event score. Mean group event scores were calculated for each product. DSTM at the D(1) [enamel and dentin] threshold showed significant inter-group differences in mean event scores (p < 0.003) and D(1)MFS increment (< 0.007) at 12 months; these were confirmed at 24 months by traditional increment analysis (CVA & FOTI at the D(3) (dentin only) threshold + radiography, p < 0.03). This study confirms the validity of an abbreviated trial protocol.

Comparison of a conventional and modified tooth stain index.

OBJECTIVES: To evaluate a modified tooth stain index and determine the effect of dietary factors on stain formation. METHODS: At baseline, 182 adult volunteers were given a full oral prophylaxis followed by stain assessment using a modification of the Lobene index. This involved assigning separate scores to the mesial (M) and distal (D) sites of each tooth, in addition to the standard gingival area (G) and tooth body (B). For each site, stain intensity and areas were scored. The sum of (intensity X area) scores was calculated for all sites (GBMD-value) and for the gingival and body sites only (GB-value). The subjects used a standard abrasive dentifrice and a soft toothbrush for 6 weeks. RESULTS: Stain was reassessed and the average increase in GBMD-value was 20.9 (sd=9.9) (buccal aspect) and 29.9 (sd=18.0) (lingual aspect). The corresponding GB-values were 4.4 (sd=4.8) and 12.5 (sd=10.2). The coefficients of variation of the GBMD index values were consistently lower than those of the GB values. Smoking and tea-drinking were found to be the only significant (p<0.001) factors investigated for stain formation. CONCLUSIONS: It is concluded that the modified index may well be advantageous to its conventional counterpart because sites with most visible stain are assessed separately and because it may also offer higher discriminatory power due to a lower coefficient of variation.

An intervention programme to establish regular toothbrushing: understanding parents' beliefs and motivating children.

AIMS/OBJECTIVES: To determine the benefit of twice daily toothbrushing on newly erupted first permanent molars. To investigate, through the Health Belief Model, how parents' beliefs influence the likelihood of their children brushing twice a day. To identify aspects of a toothbrushing intervention programme that can be used in general dental practice. DESIGN: Randomised controlled trial. SETTING: Schools in deprived communities in Scotland. PARTICIPANTS: 461, 5-year-old children. INTERVENTIONS/METHODS: Supervised toothbrushing on school-days with a 1,000 ppm chalk-based fluoride toothpaste for two years. A school and home-based incentive scheme including toothbrushing charts, 6-monthly dental examinations and parental questionnaires. MAIN OUTCOME MEASURES: Caries increment and twice daily toothbrushing. RESULTS: In the control group, children who brushed once a day or less had 64% more caries than those who brushed at least twice a day (P = 0.001). In the intervention group this difference in caries was reduced to 16% (P > 0.05). The most significant parental belief explaining variation in twice-daily brushing was whether parents feel strongly that there is time to check their child's toothbrushing (P = 0.0001). The odds of these parents reporting that their child brushes twice daily are nearly three times greater. 95% of parents felt that toothbrushing charts would be a good way for dentists in practice to encourage children to brush regularly. CONCLUSIONS: The benefit of twice daily toothbrushing on caries development in newly erupted first permanent molar teeth is around 50% compared to brushing once a day or less. Parents' beliefs do influence the likelihood of their children brushing twice a day. Key parts of the intervention programme can be used when children attend general dental practice and would be welcomed by parents.

Prevalence of dental caries in Latvian 11- to 15-year-Old children and the enhanced diagnostic yield of temporary tooth separation, FOTI and electronic caries measurement.

The aim of this study was to test the feasibility of employing clinical visual examination at the D(1) (enamel and dentine caries) diagnostic threshold, fibre-optic transillumination (FOTI), elective temporary tooth separation (ETTS) and electronic caries measurement (ECM) in the environment of an epidemiological study or clinical trial. It also aimed to compare the diagnostic yield of these diagnostic aides and methods. The sample consisted of 182 Latvian children, mean age 13.3 years (range = 10.6-15.7). For 12-year-old subjects the mean D(3)MFS was 10.58 (SD 6.05) and the mean D(1)MFS was 19.97 (SD 10.47). The additional diagnostic yield from FOTI examination of approximal sites was 40.0% at the D(1) threshold. The additional apparent yield for ETTS was 52.8% at the D(1) threshold. ETTS detected 38.3% more carious surfaces than FOTI at the D(1) threshold. Conversely 57 surfaces thought to be carious on FOTI examination were judged sound following ETTS. Although the ECM appeared practical to use, it broke early in the trial and the results obtained prior to breakdown appeared inaccurate. In conclusion, all diagnostic methods were feasible under the conditions of an epidemiological study or clinical trial.