Spin squeezing in optical lattice clocks via lattice-based QND measurements

Quantum projection noise will soon limit the best achievable precision of optical atomic clocks based on lattice-confined neutral atoms. Squeezing the collective atomic pseudo-spin via measurement of the clock state populations during Ramsey interrogation suppresses the projection noise. We show here that the lattice laser field can be used to perform ideal quantum non-demolition measurements without clock shifts or decoherence and explore the feasibility of such an approach in theory with the lattice field confined in a ring-resonator. Detection of the motional sideband due to the atomic vibration in the lattice wells can yield signal sizes a hundredfold above the projection noise limit.Comment: Substantially expanded versio

Reconstruction of the phase of matter-wave fields using a momentum resolved cross-correlation technique

We investigate the potential of the so-called XFROG cross-correlation technique originally developed for ultrashort laser pulses for the recovery of the amplitude and phase of the condensate wave function of a Bose-Einstein condensate. Key features of the XFROG method are its high resolution, versatility and stability against noise and some sources of systematic errors. After showing how an analogue of XFROG can be realized for Bose-Einstein condensates, we illustrate its effectiveness in determining the amplitude and phase of the wave function of a vortex state. The impact of a reduction of the number of measurements and of typical sources of noise on the field reconstruction are also analyzed.Comment: 7 pages; 9 figures; article with higher resolution figures available from author

Extreme non-linear response of ultra-narrow optical transitions in cavity QED for laser stabilization

We explore the potential of direct spectroscopy of ultra-narrow optical transitions of atoms localized in an optical cavity. In contrast to stabilization against a reference cavity, which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from Brownian thermal noise. Spectroscopy of ultra-narrow optical transitions in a cavity operates in a very highly saturated regime in which non-linear effects such as bistability play an important role. From the universal behavior of the Jaynes-Cummings model with dissipation, we derive the fundamental limits for laser stabilization using direct spectroscopy of ultra-narrow atomic lines. We find that with current lattice clock experiments, laser linewidths of about 1 mHz can be achieved in principle, and the ultimate limitations of this technique are at the 1 $\mu$ Hz level.Comment: 5 pages, 4 figure

Non-destructive cavity QED probe of Bloch oscillations in a gas of ultracold atoms

We describe a scheme for probing a gas of ultracold atoms trapped in an optical lattice and moving in the presence of an external potential. The probe is non-destructive and uses the existing lattice fields as the measurement device. Two counter-propagating cavity fields simultaneously set up a conservative lattice potential and a weak quantum probe of the atomic motion. Balanced heterodyne detection of the probe field at the cavity output along with integration in time and across the atomic cloud yield information about the atomic dynamics in a single run. The scheme is applied to a measurement of the Bloch oscillation frequency for atoms moving in the presence of the local gravitational potential. Signal-to-noise ratios are estimated to be as high as $10^4$.Comment: 8 pages, 6 figures, submitted to Phys. Rev.

Prospects for a mHz-linewidth laser

We propose a new light source based on having alkaline-earth atoms in an optical lattice collectively emit photons on an ultra-narrow clock transition into the mode of a high Q-resonator. The resultant optical radiation has an extremely narrow linewidth in the mHz range, even smaller than that of the clock transition itself due to collective effects. A power level of order $10^{-12}W$ is possible, sufficient for phase-locking a slave optical local oscillator. Realizing this light source has the potential to improve the stability of the best clocks by two orders of magnitude.Comment: minor revisions + shortening; factor 2 algebra mistake correcte

Intensity fluctuations in steady state superradiance

Alkaline-earth like atoms with ultra-narrow optical transitions enable superradiance in steady state. The emitted light promises to have an unprecedented stability with a linewidth as narrow as a few millihertz. In order to evaluate the potential usefulness of this light source as an ultrastable oscillator in clock and precision metrology applications it is crucial to understand the noise properties of this device. In this paper we present a detailed analysis of the intensity fluctuations by means of Monte-Carlo simulations and semi-classical approximations. We find that the light exhibits bunching below threshold, is to a good approximation coherent in the superradiant regime, and is chaotic above the second threshold.Comment: 8 pages, 5 figure

A survey of evidence-based practice, training, supervision and clinician confidence relating to post-traumatic stress disorder (PTSD) therapies in UK child and adolescent mental health professionals

Background: Post-Traumatic Stress Disorder (PTSD) in children and adolescents has received increasing recognition in recent decades. Despite development of treatments and improved dissemination efforts, research has identified a number of barriers to implementing these approaches. Objective: This study sought to understand what interventions mental health professionals working with children and adolescents utilised to treat PTSD, their training and supervision, their confidence in assessing and treating PTSD, and how these factors relate to clinicians characteristics (e.g. age, gender, professional background). Method: The study comprised an internet-delivered survey of clinicians working in child and adolescent mental health services in the UK (N = 716). Results: Many clinicians (>40%) had not received training in working with PTSD, with considerable variation between professional background. Lack of training and supervision was associated with reduced clinician confidence in treating children with PTSD (possible range 0–10; training M = 7.54, SD = 1.65, no training M = 5.49, SD = 2.29; supervision M = 7.53, SD = 1.63, no supervision M = 5.98, SD = 2.35). Evidence-based therapies for PTSD such as Trauma-Focused Cognitive-Behavioural Therapy and Eye Movement Desensitisation and Reprocessing were only endorsed modestly by clinicians (58.4% and 37.5%, respectively). Regression analyses identified that lack of training and supervision were significant barriers to the use of evidence-based interventions. Other predictors of clinician confidence and use of evidence-based interventions included profession and years of experience. Participants almost universally wanted more training in working with PTSD. Conclusions: Evidence-based treatments are not currently universally delivered by mental health professionals in the UK, with certain professions particularly lacking training and confidence with this condition. Training around trauma and PTSD may be an ongoing need to boost and maintain confidence in working with PTSD in youth