Generating the curvature perturbation at the end of inflation in string theory

In brane inflationary scenarios, the cosmological perturbations are supposed to originate from the vacuum fluctuations of the inflaton field corresponding to the position of the brane. We show that a significant, and possibly dominant, contribution to the curvature perturbation is generated at the end of inflation through the vacuum fluctuations of fields, other than the inflaton, which are light during the inflationary trajectory and become heavy at the brane-antibrane annihilation. These fields appear generically in string compactifications where the background geometry has exact or approximate isometries and parametrize the internal angular directions of the brane.     

Does Operator Ordering Need Wormhole Dominance in the Wavefunction of the Universe?

In dealing with the wavefunction of the universe there is a debate on the various proposals about the boundary condition of the wavefunction of the universe. At present we have three proposals, namely, the Hartle-Hawking proposal, the tunneling proposal and the Linde proposal. Recently it has been argued that the operator ambiguity factor has a decisive role in deciding the consequences of the various wavefunction at the zero scale factor region. In the present paper we discuss the role of operator ordering in the light of wormhole dominance proposal proposed by one of the authors and compare the results with that of others obtained earlier. We present an interpretation of operator ordering as a contribution of some sort of matter fields and discuss the role of complex path WKB analysis in avoiding the initial singularity and allowing us to incorporate the contribution of wormhole in the wavefunction of the universe.     

Seesaw mechanism for scalar fields as possible basis for dark energy

We propose a novel mechanism for dark energy, based on an extended seesaw for scalar fields, which does not require any new physics at energies below the TeV scale. A very light quintessence mass is usually considered to be technically unnatural, unless it is protected by some symmetry broken at the new very light scale. We propose that one can use an extended seesaw mechanism to construct technically natural models for very light fields, protected by supersymmetry softly broken above a TeV.     

Sharper focus for a radially polarized light beam

We experimentally demonstrate for the first time that a radially polarized field can be focused to a spot size significantly smaller [0.16(1)lambda(2)] than for linear polarization (0.26lambda(2)). The effect of the vector properties of light is shown by a comparison of the focal intensity distribution for radially and azimuthally polarized input fields. For strong focusing, a radially polarized field leads to a longitudinal electric field component at the focus which is sharp and centered at the optical axis. The relative contribution of this component is enhanced by using an annular aperture.     

Entanglement and nonclassicality evolution of the atom in a squeezed vacuum

As an important parameter, von Neumann entropy has been used to characterize the entanglement between atom and light field. We discussed the entanglement and nonclassicality evolution of an atom in a squeezed vacuum—a typical nonclassical field, and compare it with that of the coherent state. It shows that the atom-field entanglement in squeezed vacuum is much stronger and stabler than that in coherent state, whereas the nonclassicality of the light field depends on its initial status. This investigation is trying to find a new insight into the relation between entanglement of atom-field system and nonclassicality of light fields. The result shows that the entanglement between the atom and the field can be maintained well in the squeezed vacuum and this implies better control of atom and photon mutually.     

Minimization of the temperature coefficient of resonance frequency shift in the coherent population trapping clock

We studied the relationship between the frequency shift of coherent population trapping resonance and the cell temperature of (85)Rb. Results show that the temperature coefficient of the frequency shift can be reduced by buffer gas pressure adjustment and light shift optimization. When the contribution of buffer gas collision to temperature coefficient of frequency shift is less than 0.3 Hz/K, the contribution of light shift to the temperature coefficient of frequency shift becomes obvious. Under this cancelling effect, we can reduce the rate of total frequency shift to near zero.     

Beyond-limit light focusing in the intermediate zone

We experimentally verify that a new nanolens of a designed plasmonic aperture can focus visible light to a single line with its width smaller than the limit of half the wavelength in the intermediate zone. The experimental measurement indicates that while the near field plays a role to increase the spot size in the near zone, it is negligible at the beyond-limit focused region; i.e., the focused light is dominated by the radiative fields. The image taken by the optical microscope shows that the fields focused have propagated to the far zone. Besides being of academic interest, the nanolens capable in achieving a lower diffraction limit in the intermediate zone is important for application possibilities.     

Can extra dimensions accessible to the SM explain the recent measurement of anomalous magnetic moment of the muon?

We investigate whether models with flat extra dimensions in which SM fields propagate can give a significant contribution to the anomalous magnetic moment of the muon (MMM). In models with only SM gauge and Higgs fields in the bulk, the contribution to the MMM from Kaluza–Klein (KK) excitations of gauge bosons is very small. This is due to the constraint on the size of the extra dimensions from tree-level effects of KK excitations of gauge bosons on precision electroweak observables such as Fermi constant. If the quarks and leptons are also allowed to propagate in the (same) bulk (“universal” extra dimensions), then there are no contributions to precision electroweak observables at tree-level. However, in this case, the constraint from one-loop contribution of KK excitations of (mainly) the top quark to T parameter again implies that the contribution to the MMM is small. We show that in models with leptons, electroweak gauge and Higgs fields propagating in the (same) bulk, but with quarks and gluon propagating in a sub-space of this bulk, both the above constraints can be relaxed. However, with only one Higgs doublet, the constraint from the process b→sγ requires the contribution to the MMM to be smaller than the SM electroweak correction. This constraint can be relaxed in models with more than one Higgs doublet.     

Supercurrent and Its Quantum Statistical Properkies in Mesoscopic Josephson Junction in the Presence of Nonclassical Light Fields

In this paper, we study the supercurrent in a mesoscopic Josephson junction (MJJ) and its quantum statistical properties in the presence of nonclassical light fields. We investigate in detail the influence of external nonclassical light fields on current-voltage step structures of the MJJ. We also study in detail quantum statistical properties of the supercurrent when the external quantum electromagnetic fields are even and odd coherent-sta!e light fields. It is shown that the supercurrent in the MJJ exhibits both squeezing effect and quantum coherence. It is demonstrated that the MJJ can feel the difference not only between classical light fields and nonclassical light fields but also between different nonclassical light fields.     

Scalar Tachyons in the de Sitter Universe

We provide a construction of a class of local and de Sitter covariant tachyonic quantum fields which exist for discrete negative values of the squared mass parameter and which have no Minkowskian counterpart. These quantum fields satisfy an anomalous non-homogeneous Klein–Gordon equation. The anomaly is a covariant field which can be used to select the physical subspace (of finite co-dimension) where the homogeneous tachyonic field equation holds in the usual form. We show that the model is local and de Sitter invariant on the physical space. Our construction also sheds new light on the massless minimally coupled field, which is a special instance of it.     

Detection of domain-wall position and magnetization reversal in nanostructures using the magnon contribution to the resistivity

We show that magnetization reversal detection can be achieved at room temperature using the contribution of magnons to resistivity, in 50 nm wide nanowires with either perpendicular anisotropy (FePt) or in-plane magnetization (NiFe). Even though these nanowires are made from single layers, simple magnetoresistance measurements can be used to measure switching fields, or to detect the position of a domain wall along a nanowire. Surprisingly, in NiFe nanowires, and for applied fields nearly parallel to the wire, the magnon contribution is found to dominate the classical anisotropic magnetoresistance.     

Evidence of anisotropic Landau level splitting in topological semimetal ZrSiS under high magnetic fields

Magneto-transport study has been performed in topological semimetal ZrSiS single crystals under high pulsed magnetic fields. Obvious dependence of Landau level splitting on temperature and angular was investigated. The strong three-dimensional anisotropic nature of Landau level splitting under high pulsed magnetic fields was revealed by the angular dependent measurements, in which the orbital contribution is more dominant than Zeeman splitting. Our studies provide more insights into the physical properties of topological semimetals ZrSiS and shed light on future spintronic applications of ZrSiS.     

Optically biased photoreflectance spectroscopy of a GaAs epitaxial layer and an AlGaAs/GaAs quantum well

We propose optically biased photoreflectance (OBPR) spectroscopy, which is performed by continuous illumination of a secondary monochromatic light on a sample with conventional photoreflectance (PR), as a useful tool to investigate the internal electric fields dependence of the PR signals associated with band to band and quantum level transitions. Line shape of the PR signal has a strong dependence on the internal electric field. In OBPR, if a secondary incident light is absorbed, the internal electric field is suppressed by the photo-generated electron–hole pairs. On the other hand, if the secondary light is not absorbed, the internal electric field is not affected. Through the OBPR investigation of a GaAs epitaxial layer and an AlGaAs/GaAs quantum well, we are able to obtain an absorption like spectrum by performing a wavelength scan of a secondary monochromatic light. The results of OBPR measurements at each PR peak position show the contribution of the electric fields modification by the photo-generated carriers in each layers to the PR signals that are related to band gap and quantum level transitions.     

Quark mixing in the discrete dark matter model

We consider a model in which dark matter is stable as it is charged under a Z₂ symmetry that is residual after an A₄ flavour symmetry is broken. We consider the possibility to generate the quark masses by charging the quarks appropriately under A₄. We find that it is possible to generate the CKM mixing matrix by an interplay of renormalisable and dimension-six operators. In this set-up, we predict the third neutrino mixing angle to be large and the dark matter relic density to be in the correct range. Low energy observables - in particular meson-antimeson oscillations - are hard to facilitate. We find that only in a situation where there is a strong cancellation between the Standard Model contribution and the contribution of the new Higgs fields, B meson oscillations are under control.     

Polarization squeezing by optical faraday rotation

We show that it is possible to generate continuous-wave fields and pulses of polarization squeezed light by sending classical, linearly polarized laser light twice through an atomic sample which causes an optical Faraday rotation of the field polarization. We characterize the performance of the process and we show that an appreciable degree of squeezing can be obtained under realistic physical assumptions.     

High-field magnetoresistance of noble metals containing rare-earth impurities

We report on magnetoresistance measurements in longitudinal and transverse magnetic fields up to 320 kG for silver and gold containing rare-earth impurities. We focus mainly on the strong anisotropy of the magnetoresistance related to the scattering of conduction electrons by the 4f quadrupoles (non-S ions) and we derive the magnitude of the electron-quadrupole interaction from the analysis of the results. We also consider the isotropic contribution to the magnetoresistance due to exchange scattering. In a number of alloys this contribution is negative in low fields, as this is usually observed in magnetic alloys, but becomes positive in high fields. This change of spin can be ascribed to crystal-field effects.     

Quantum and classical coincidence imaging

Coincidence, or ghost, imaging is a technique that uses two correlated optical fields to form an image of an object. In this work we identify aspects of coincidence imaging which can be performed with classically correlated light sources and aspects which require quantum entanglement. We find that entangled photons allow high-contrast, high-resolution imaging to be performed at any distance from the light source. We demonstrate this fact by forming ghost images in the near and far fields of an entangled photon source, noting that the product of the resolutions of these images is a factor of 3 better than that which is allowed by classical diffraction theory.     

Four-wave mixing signals from extended exciton states above the mobility edge in GaAs/(Ga,Al)As multiple quantum wells

We investigate the dependence of four-wave mixing response on the photon energy close to the fundamental exciton (X) resonance in GaAs quantum wells. We find that cross-polarised incident fields give rise to a non-linear signal which decays faster at energies below the X line centre than above. We show that this behaviour cannot be assigned to biexciton transitions alone but rather suggests that the delocalised X states above the mobility edge are excited off-resonantly by the laser light having slightly lower energies.     

Phase control of squeezed state in double electromagnetically induced transparency system with a loop-transition structure

We theoretically study the squeezed probe light passing through a double electromagnetically induced transparency (DEIT) system, in which a microwave field and two coupling lights drive a loop transition. It is shown that the output squeezing can be maintained in both two transparency windows of DEIT, and it can also be manipulated by the relative phase of the three driving fields. The influence of the intensity of applied fields and the optical depth of atoms on the squeezing is also investigated. This study offers possibilities to manipulate the squeezing propagation in atomic media by the phase of electromagnetic fields.     

Gravity and the quantum vacuum inertia hypothesis

In previous work it has been shown that the electromagnetic quantum vacuum, or electromagnetic zero‐point field, makes a contribution to the inertial reaction force on an accelerated object. We show that the result for inertial mass can be extended to passive gravitational mass. As a consequence the weak equivalence principle, which equates inertial to passive gravitational mass, appears to be explainable. This in turn leads to a straightforward derivation of the classical Newtonian gravitational force. We call the inertia and gravitation connection with the vacuum fields the quantum vacuum inertia hypothesis . To date only the electromagnetic field has been considered. It remains to extend the hypothesis to the effects of the vacuum fields of the other interactions. We propose an idealized experiment involving a cavity resonator which, in principle, would test the hypothesis for the simple case in which only electromagnetic interactions are involved. This test also suggests a basis for the free parameter η(ν) which we have previously defined to parametrize the interaction between charge and the electromagnetic zero‐point field contributing to the inertial mass of a particle or object.