Polarization Of Emitted Photons Research Articles

Controllable spin-resolved photon emission enhanced by a slow-light mode in photonic crystal waveguides on a chip.

We report the slow-light enhanced spin-resolved in-plane emission from a single quantum dot (QD) in a photonic crystal waveguide (PCW). The slow light dispersions in PCWs are designed to match the emission wavelengths of single QDs. The resonance between two spin states emitted from a single QD and a slow light mode of a waveguide is investigated under a magnetic field with Faraday configuration. Two spin states of a single QD experience different degrees of enhancement as their emission wavelengths are shifted by combining diamagnetic and Zeeman effects with an optical excitation power control. A circular polarization degree up to 0.81 is achieved by changing the off-resonant excitation power. Strongly polarized photon emission enhanced by a slow light mode shows great potential to attain controllable spin-resolved photon sources for integrated optical quantum networks on chip.

Nanoscale chiral valley-photon interface

Nanophotonics Occupation of different valleys within the band structure of some materials can be used to encode information. That information is typically encoded in terms of the chirality or polarization of emitted photons. Gong et al. combined a plasmonic silver nanowire with a flake of the transition metal dichalcogenide WS2 to form a nanophotonic platform for the transfer of solid-state spin into optical information over mesoscopic distances. The direction of light emission from the nanowire was strongly dependent on the spin-orbit coupling of light and the WS2 layer. Such a highly efficient interface should prove useful for developing valleytronics into a practical on-chip technology. Science , this issue p. [443][1] [1]: /lookup/doi/10.1126/science.aan8010

Nanoscale chiral valley-photon interface through optical spin-orbit coupling.

The emergence of two-dimensional transition metal dichalcogenide materials has sparked intense activity in valleytronics, as their valley information can be encoded and detected with the spin angular momentum of light. We demonstrate the valley-dependent directional coupling of light using a plasmonic nanowire-tungsten disulfide (WS2) layers system. We show that the valley pseudospin in WS2 couples to transverse optical spin of the same handedness with a directional coupling efficiency of 90 ± 1%. Our results provide a platform for controlling, detecting, and processing valley and spin information with precise optical control at the nanoscale.

Single photon detection and circular polarized emission manipulated with individual quantum dot

Studies on quantum dots (QDs) provide great opportunities in single photon detection as well as single circular polarized photon emission, which are the key technology for future quantum information processing. For single photon detection, the quantum-dot-resonant-tunneling-diode (QD-RTD) is evaluated as one of the most promising scheme but still suffering from the ultralow working temperature (～5 K) and lack the capability to discriminate photon numbers. Here we demonstrate a photon-number-resolving detector based on quantum dot coupled resonant tunneling diodes (QD-cRTD). Individual QDs coupled closely with adjacent quantum well (QW) of resonant tunneling diode operate as photon-gated switches which turn on (off) the RTD tunneling current when they trap photon-generated holes (recombine with injected electrons). With proper decision regions defined, 1-photon and 2-photon states are resolved in 4.2 K with excellent propabilities of accuracy of 90% and 98% respectively. Further, by identifying step-like photon responses, the photon-number-resolving capability is sustained to 77 K, making the detector a promising candidate for advanced quantum information applications where photon-number-states should be accurately distinguished. On the other hand, we firstly performed the magneto-optical studies on single InGaAs/GaAs self-assembled QDs. We observed the exciton Zeeman splitting and diamagnetic shift of a single QD under magnetic field, and the exciton g factor and diamagnetic coefficient was extracted by fitting the magnetic field dependent PL energies. By comparing with theories, we discussed on the effect of QD size, shape and composition on these two parameters. Based on these work, we investigated the single QD exciton-cavity mode coupling effect under external magnetic field. By first time we observed the interaction of Zeeman splitted exciton spin states with the cavity mode and realized the selective enhancement of the SE rate of the exciton state with specific spin configuration by means of magnetic manipulation of Purcell effect. In this sense, single QD emission with higher circular polarization degree under non-polarized excitation was realized. Our results have high potential to open up a way to novel quantum light sources and quantum information processing applications based on cavity quantum electrodynamics effects.

Direct generation of linearly polarized photon emission with designated orientations from site-controlled InGaN quantum dots

Semiconductor quantum dots (QDs) have been demonstrated viable for efficient light emission applications, in particular for the emission of single photons on demand. However, the preparation of QDs emitting photons with predefined and deterministic polarization vectors has proven arduous. Access to linearly polarized photons is essential for various applications. In this report, a novel concept to directly generate linearly-polarized photons is presented. This concept is based on InGaN QDs grown on top of elongated GaN hexagonal pyramids, by which the predefined elongation determines the polarization vectors of the emitted photons from the QDs. This growth scheme should allow fabrication of ultracompact arrays of photon emitters, with a controlled polarization direction for each individual emitter. Researchers in Sweden have unveiled a scheme for fabricating quantum dots that emit linearly polarized light. Anders Lundskog and co-workers from Linköping University controlled the emission from InGaN quantum dots by growing them on top of miniature hexagonal GaN pyramids with elongated bases. They found that the polarization of the emitted light was aligned with the axis of elongation. In principle, the wavelength of the light emitted by the quantum dots can be tuned from ultraviolet to the infrared by adjusting the amount of indium in the InGaN. Benefits of the approach include its compatibility with high-temperature operation and large-area wafer-processing techniques. In the future, this technique could allow the realization of quantum dot-based single-photon emitters with controllable polarization on a single chip.

Photon emission and electron-positron photoproduction processes in the planar field of a bent single crystal

The process of photon emission by a high-energy electron or positron moving in a bent single crystal with a constant curvature is considered. The relations for differential energy losses of particles and polarization of emitted photons are obtained. Corrections due to multiphoton production are found. The comparison of calculations with existing experimental data is carried out. The process of photoproduction of electron-positron pairs in a bent single crystal is also studied. The differential probabilities of the process taking into account the photon polarization are presented. Equations are obtained which determine the variation of the Stokes parameters of $\ensuremath{\gamma}$ quanta, and their solutions are given.

Beaming circularly polarized photons from quantum dots coupled with plasmonic spiral antenna

Coupling nanoscale emitters via optical antennas enables comprehensive control of photon emission in terms of intensity, directivity and polarization. In this work we report highly directional emission of circularly polarized photons from quantum dots coupled to a spiral optical antenna. The structural chirality of the spiral antenna imprints spin state to the emitted photons. Experimental results reveal that a circular polarization extinction ratio of 10 is obtainable. Furthermore, increasing the number of turns of the spiral gives rise to higher antenna gain and directivity, leading to higher field intensity and narrower angular width of emission pattern in the far field. For a five-turn Archimedes' spiral antenna, field intensity increase up to 70-fold simultaneously with antenna directivity of 11.7 dB has been measured in the experiment. The highly directional circularly polarized photon emission from such optically coupled spiral antenna may find important applications in single molecule sensing, quantum optics information processing and integrated photonic circuits as a nanoscale spin photon source.

Statistics property of polarized photon emission driven bya pair of pulses in single quantum dot

We study the properties of the x- and the y-polarized photons of the single quantum dot system driven by a pair of pulses using the generating function approach. Our results show that the quantum interference effects on the line shapes and the Mandels parameter Q of the x- and y-polarized photons and the linear and the nonlinear cross correlations are important.

Polarized photon emission and virtual photon process, in single quantum dot

We theoretically investigate the polarized photon emission statistics and the virtual photon process in single Quantum Dot driven by continuous wave (cw) field and pulse field based on the generating function approach developed recently. The line shapes, Mandel's Q parameters are demonstrated. The results show that the general decay constants strongly affect the line shapes and Mandel's Q parameters. Moreover, we also study the linear and nonlinear cross correlations of x- and y-polarized photon.

Photon emission of single quantum dot driven by continuous external field studied by using the generating function

We studied the properties of the X- and Y- polarized photon emission from the single quantum dot system driven by external cw laser using the generating function approach developed recently. The results demonstrate that the X- and Y- polarized photon show sine or cosine behavior with the field direction in the weak field region. They show, however, stronger nonlinear behavior in the strong field region.

Radiation from polarized electrons in oriented crystals at high energy

Radiation from high-energy electrons in an oriented crystal can be considered in a frame of the quasiclassical operator method which appears to be a most satisfactory approach to the problem. Under some quite generic assumptions the general expression is derived for the probability of circularly polarized photon emission from the longitudinally polarized electron in oriented crystal. The particular mechanism of radiation depends on interrelation between the angle of incidence ϑ0 (angle between the momentum of initial electron and axis (plane) of crystal) and angle ϑv≡V0/m (V0 is the scale of a potential of axis or a plane relative to which the angle ϑ0 is defined). When ϑ0≪ϑv one has magnetic bremsstrahlung type of radiation (with corrections ∝ϑ02 which are due to inhomogeneous character of field in crystal). When ϑ0≫ϑv one obtains the theory of coherent bremsstrahlung, while for ϑ0⩾ϑv one arrives to the modified theory of coherent bremsstrahlung. At high-energy radiation in oriented crystals is strongly enhanced comparing with standard bremsstrahlung.

Hard polarized photon emission in single crystals by high energy electrons for planar crystal orientations

The radiation emission spectra of polarized photons emitted from charged particle in single crystals are obtained in the semiclassical theory in Baier–Katkov–Strakhovenko approximation for planar crystal orientation. Optimal crystal orientations for producing unpolarized and polarized photon beams are also found.

Circularly polarized photon emission spectroscopy of keV ions scattering off (un-)magnetized surfaces

To study the interaction of 2–15 keV He + ions with (un-)magnetized surfaces we use the degree of circular polarization of photons emitted by the neutralized ions. The general features of the relation between circular polarization and the magnetic substate distributions of the neutralized particles are indicated. They provide the basis for discussing the results obtained for a magnetized Fe(110) single crystal. Different models are discussed and used to understand at least qualitatively the general trends in the measured data.

Forward circularly polarized photon emission in longitudinally polarized e +e − collisions

We discuss the emission of circularly polarized forward photons in high energy e +e − collisions with longitudinally polarized beams. We find substantial asymmetry under inversion of longitudinal electron polarization, thus supporting the proposal that measurement of circular polarization of forward emitted photons may allow for monitoring of longitudinal beam polarization.

Odd-Coherence in Beam-Foil Excitation of He+Ion

This paper presents measurement of polarized photon emission from the foil-excited 4 He + ion in an external static electric field parallel to the ion beam. Strong asymmetry was observed when the direction of the external field is reversed. The result is interpreted in terms of coherent superposition of excited states of opposite parity.

Polarized photon emission following He +He charge capture collisions

The polarization of 3889 Å photons from the 2 3S3 3P transition of fast helium atoms produced by charge capture in a He +He collision has been measured as a function of the reduced angle τ= Eθ. An impact parameter selection method was employed with ions having energies between 2 and 3 keV, and at scattering angles of a few degrees. Circular polarizations, and in some cases linear polarization, of the light was measured. Large circular polarization, corresponding to collisional orientation, were observed. The results are discussed with reference to other measurements, and to the electron promotion model.

Iso-Tensor Component in the S=0 Weak Process and I =1/2 Rule

The existence of large discrepancy be­ tween theoretical value and observed one -of !he circular polarization of emitted photon in n + p~d + r process is one of the most important problems.!) Recently, Mckellar has suggested2> 'that this discrepancy orig­ inates in not to take into account the large contribution of iso-tensor component in the .JS=O process. Further lie has emphasized that iso-tensot dominance is not contradic­ tory to other experiments; the a decay of 2- (8.88 MeV) state of 160 8> and the 110 ke V r-transition in 19 F. 4) However, iso-tensor dominance conflicts with the conventional model of ILl II = 1/2 rule; 8 enhancement and/or 27 suppression. Then, his conclu­ sion can be made_ use 'Df for a ch'ai.ce of model of I.Jll =1/2 rule. This note is con­ cerned with this proolem. In this note, we examine, as _a prototype, a few types of model of I.Jll =1/2 rule.*> In the model a) Bose statistics of quarks, 5> all ·27 components vanish automatically. Th.en, this model cannot allow the existence of iso·tensor component. Similar conclu­ sion also holds for the models based on b) *> Let us remember that in the usual Cabibbo theory, the non-leptonic interaction Hamiltonian has general' schematic form,