Observing Coherence Effects in an Overdamped Quantum System

It is usually considered that the spectrum of an optical cavity coupled to an atomic medium does not exhibit a normal-mode splitting unless the system satisfies the strong coupling condition, meaning the Rabi frequency of the coherent coupling exceeds the decay rates of atom and cavity excitations. Here we show that this need not be the case, but depends on the way in which the coupled system is probed. Measurements of the reflection of a probe laser from the input mirror of an overdamped cavity reveal an avoided crossing in the spectrum which is not observed when driving the atoms directly and measuring the Purcell-enhanced cavity emission. We understand these observations by noting a formal correspondence with electromagnetically-induced transparency of a three-level atom in free space, where our cavity acts as the absorbing medium and the coupled atoms play the role of the control field

Reconsidering the quantization of electrodynamics with boundary conditions and some measurable consequences

We show that the commonly known conductor boundary conditions $E_{||}=B_\perp=0$ can be realized in two ways which we call 'thick' and 'thin' conductor. The 'thick' conductor is the commonly known approach and includes a Neumann condition on the normal component $E_\perp$ of the electric field whereas for a 'thin' conductor $E_\perp$ remains without boundary condition. Both types describe different physics already on the classical level where a 'thin' conductor allows for an interaction between the normal components of currents on both sides. On quantum level different forces between a conductor and a single electron or a neutral atom result. For instance, the Casimir-Polder force for a 'thin' conductor is by about 13% smaller than for a 'thick' one.Comment: 22 pages, basic statement weakened, conclusions changed, misprints correcte

T-helper cell polarisation following severe polytrauma

Introduction Severe polytrauma induces an immunosuppressive response and is associated with a very high incidence of nosocomial infections. Previous studies have inferred that this detrimental immune response results from polarisation of the T helper (Th) response towards an anti-inflammatory, TH2 dominated, response at the expense of a bactericidal, Th1 response [1]. Objectives 1) To define alterations in TH cell subsets following severe blunt polytrauma. Methods Patients presenting to the emergency department within 2 hours of severe polytrauma were eligible if intubated either at the scene or in ED. Isolated head injuries and those not expected to survive 24 hours were excluded. EDTA anti-coagulated blood was drawn at 0hr (within 2 hours of injury), at 24 and 72hrs. Samples were immediately lysed, washed, stained and analysed using a standardised human 8-colour TH 1, 2 & 17 panel [2] on an LSR II flow cytometer. A paired white cell count differential was obtained at each sampling point. Patients were followed until discharge or death. Data were analysed using non-parametric statistics, with results presented as median and IQR. Results 15 consecutive severe polytrauma patients requiring Intensive Care Unit (ICU) admission were recruited. Demographic and clinical data are outlined in Figure 1. Twelve (80%) lymphocytosis (3.3x109/L, 2.5 - 4.4x109/L) (Figyre 2A). At 72 hours leukocytes had fallen (P < 0.01, figure 2A) such that 6 (54%) of those surviving were lymphopenic (0.9x109/L, 0.6 - 1.2x109/L). Circulating CD4+ (P = 0.01; Figure 2B) and CD4+CD25+ (P < 0.05) lymphocytes increased over 72 hours. When expressed as a percentage of total circulating lymphocytes no significant change in the proportions of the TH 1, 2 & 17 subpopulations was detected (Figure 2C-E). Conclusions Severe polytrauma patients swiftly become lymphopenic. Although a failure to normalise this during the ICU stay correlates with higher mortality [3] our study of TH cell subtypes demonstrates no evidence of a switch to a detrimental anti-inflammatory TH2 subtype at the expense of the potentially protective bactericidal TH1 subtype

A search for varying fundamental constants using Hz-level frequency measurements of cold CH molecules

Many modern theories predict that the fundamental constants depend on time, position, or the local density of matter. We develop a spectroscopic method for pulsed beams of cold molecules, and use it to measure the frequencies of microwave transitions in CH with accuracy down to 3 Hz. By comparing these frequencies with those measured from sources of CH in the Milky Way, we test the hypothesis that fundamental constants may differ between the high and low density environments of the Earth and the interstellar medium. For the fine structure constant we find \Delta\alpha/\alpha = (0.3 +/- 1.1)*10^{-7}, the strongest limit to date on such a variation of \alpha. For the electron-to-proton mass ratio we find \Delta\mu/\mu = (-0.7 +/- 2.2) * 10^{-7}. We suggest how dedicated astrophysical measurements can improve these constraints further and can also constrain temporal variation of the constants.Comment: 8 pages, 3 figure

Perioperative blood transfusion is associated with a gene transcription profile characteristic of immunosuppression: a prospective cohort study

INTRODUCTION Blood transfusion in the perioperative period has frequently been associated with an excess of nosocomial infections. Whilst transfused whole blood induces specific host immune alteration that may predispose to nosocomial infections, the immunomodulating properties associated with leukodepleted blood remain incompletely understood. In this study, we explore the hypothesis that the transfusion of leukodepleted allogeneic blood during or following major gastrointestinal surgery is associated with an immunosuppressed phenotype, which may in turn predispose to postoperative infectious complications. METHODS Patients aged over 45 years undergoing scheduled inpatient major gastrointestinal surgery were recruited. Gene expression profiles of specific inflammatory genes were assayed from blood collected preoperatively, at 24 and at 48 hours after surgery. Genes were selected based on their ability to represent specific immune pathways. Gene expression was quantified using quantitative real-time polymerase chain reaction (qRT-PCR) to measure messenger RNA (mRNA) levels. Postoperative infections were documented using predefined criteria. RESULTS One hundred and nineteen patients were recruited. Fifteen (13%) patients required blood transfusion within 24 hours of surgery, 44 (37%) patients developed infections and 3 (2%) patients died prior to discharge. Patients receiving a blood transfusion were more likely to develop postoperative infections (P =0.02) and to have lower tumour necrosis factor alpha (TNFα), interleukin (IL)-12, IL-23 and RAR-related orphan receptor gamma T (RORγt) gene expression in the postoperative period (P <0.05). The TNFα/IL-10 mRNA ratio at 24 hours (P =0.0006) and at 48 hours (P =0.01) was lower in patients receiving a blood transfusion over this period. Multivariable analysis confirmed that these observations were independent of the severity of the surgical insult. CONCLUSIONS An association between an immunosuppressive pattern of gene expression and blood transfusion following major elective gastrointestinal surgery is described. This gene expression profile includes a reduction in the activity of innate immunity and T helper cell type 1 (Th1) and T helper cell type 17 (Th17) pathways in those patients receiving a blood transfusion. Blood transfusion was also associated with an excess of infectious complications in this cohort. A mechanistic link is suggested but not proven

Slowing heavy, ground-state molecules using an alternating gradient decelerator

Cold supersonic beams of molecules can be slowed down using a switched sequence of electrostatic field gradients. The energy to be removed is proportional to the mass of the molecules. Here we report deceleration of YbF, which is 7 times heavier than any molecule previously decelerated. We use an alternating gradient structure to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring these molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.Comment: 4 pages, 5 figure

Spontaneous emission of an atom in front of a mirror

Motivated by a recent experiment [J. Eschner {\it et al.}, Nature {\bf 413}, 495 (2001)], we now present a theoretical study on the fluorescence of an atom in front of a mirror. On the assumption that the presence of the distant mirror and a lens imposes boundary conditions on the electric field in a plane close to the atom, we derive the intensities of the emitted light as a function of an effective atom-mirror distance. The results obtained are in good agreement with the experimental findings.Comment: 8 pages, 6 figures, revised version, references adde

Coherent radiation from neutral molecules moving above a grating

We predict and study the quantum-electrodynamical effect of parametric self-induced excitation of a molecule moving above the dielectric or conducting medium with periodic grating. In this case the radiation reaction force modulates the molecular transition frequency which results in a parametric instability of dipole oscillations even from the level of quantum or thermal fluctuations. The present mechanism of instability of electrically neutral molecules is different from that of the well-known Smith-Purcell and transition radiation in which a moving charge and its oscillating image create an oscillating dipole. We show that parametrically excited molecular bunches can produce an easily detectable coherent radiation flux of up to a microwatt.Comment: 4 page

Casimir Force between a Dielectric Sphere and a Wall: A Model for Amplification of Vacuum Fluctuations

The interaction between a polarizable particle and a reflecting wall is examined. A macroscopic approach is adopted in which the averaged force is computed from the Maxwell stress tensor. The particular case of a perfectly reflecting wall and a sphere with a dielectric function given by the Drude model is examined in detail. It is found that the force can be expressed as the sum of a monotonically decaying function of position and of an oscillatory piece. At large separations, the oscillatory piece is the dominant contribution, and is much larger than the Casimir-Polder interaction that arises in the limit that the sphere is a perfect conductor. It is argued that this enhancement of the force can be interpreted in terms of the frequency spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere, there are cancellations between different parts of the spectrum which no longer occur as completely in the case of a sphere with frequency dependent polarizability. Estimates of the magnitude of the oscillatory component of the force suggest that it may be large enough to be observable.Comment: 18pp, LaTex, 7 figures, uses epsf. Several minor errors corrected, additional comments added in the final two sections, and references update

Electric dipole moment of the electron in YbF molecule

Ab initio calculation of the hyperfine, P-odd, and P,T-odd constants for the YbF molecule was performed with the help of the recently developed technique, which allows to take into account correlations and polarization in the outercore region. The ground state electronic wave function of the YbF molecule is found with the help of the Relativistic Effective Core Potential method followed by the restoration of molecular four-component spinors in the core region of ytterbium in the framework of a non-variational procedure. Core polarization effects are included with the help of the atomic Many Body Perturbation Theory for Yb atom. For the isotropic hyperfine constant A, accuracy of our calculation is about 3% as compared to the experimental datum. The dipole constant Ad (which is much smaller in magnitude), though better than in all previous calculations, is still underestimated by almost 23%. Being corrected within a semiempirical approach for a perturbation of 4f-shell in the core of Yb due to the bond making, this error is reduced to 8%. Our value for the effective electric field on the unpaired electron is 4.9 a.u.=2.5E+10 V/cm.Comment: 7 pages, REVTE