arXiv subjects

J. E. Sipe

Publications and source records attributed to J. E. Sipe.

At least 109 records · Page 6Linked to original sources

arXiv2014

Spontaneous parametric downconversion in waveguides: What's loss got to do with it?

We derive frequency correlation and exit probability expressions for photons generated via spontaneous parametric downconversion (SPDC) in nonlinear waveguides that exhibit linear scattering loss. Such loss is included within a general Hamiltonian formalism by connecting waveguide modes to reservoir modes with a phenomenological coupling Hamiltonian, the parameters of which are later related to the usual loss coefficients. In the limit of a low probability of SPDC pair production, the presence of loss requires that we write the usual lossless generated pair state as a reduced density operator, and we find that this density operator is naturally composed of two photon, one photon, and zero photon contributions. The biphoton probability density, or joint spectral intensity (JSI), associated with the two-photon contribution is determined not only by a phase matching term, but also by a loss matching term. The relative size of the loss coefficients within this term lead to three qualitatively different regimes of SPDC JSIs. If either the pump or generated photon loss is much higher than the other, the side lobes of the phase matching squared sinc function are washed out. On the other hand, if pump and generated photon loss are appropriately balanced, the lossy JSI is identical to the lossless JSI. Finally, if the generated photon loss is frequency dependent, the shape of the JSI can be altered more severely, potentially leading to generated photons that are less frequency correlated though also produced less efficiently when compared to photons generated in low-loss waveguides.

quant-ph↗

arXiv2014

Time ordering effects in the generation of entangled photons using nonlinear optical processes

We study the effects of time ordering in photon generation processes such as spontaneous parametric down-conversion (SPDC) and four wave mixing (SFWM). The results presented here are used to construct an intuitive picture that allows us to predict when time ordering effects significantly modify the joint spectral amplitude (JSA) of the photons generated in SPDC and SFWM. These effects become important only when the photons being generated lie with the pump beam that travels through the non-linear material for a significant amount of time. Thus sources of spectrally separable photons are ideal candidates for the observation of modifications of the JSA due to time ordering.

quant-ph↗

arXiv2014

Interference of stimulated electronic Raman scattering and linear absorption in coherent control

We consider quantum interference effects in carrier and photocurrent excitation in graphene using coherent electromagnetic field components at frequencies $ω$ and $2ω$. The response of the material at the fundamental frequency $ω$ is presented, and it is shown that one-photon absorption at $ω$ interferes with stimulated electronic Raman scattering (combined $2ω$ absorption and $ω$ emission) to result in a net contribution to the current injection. This interference occurs with a net energy absorption of $\hbarω$ and exists in addition to the previously studied interference occurring with a net energy absorption of $2\hbarω$ under the same irradiation conditions. Due to the absence of a bandgap and the possibility to block photon absorption by tuning the Fermi level, graphene is the perfect material to study this contribution. We calculate the polarization dependence of this all-optical effect for intrinsic graphene and show that the combined response of the material at both $ω$ and $2ω$ leads to an anisotropic photocurrent injection, whereas the magnitude of the injection current in doped graphene, when transitions at $ω$ are Pauli blocked, is isotropic. By considering the contribution to coherent current control from stimulated electronic Raman scattering, we find that graphene offers tunable, polarization sensitive applications. Coherent control due to the interference of stimulated electronic Raman scattering and linear absorption is relevant not only for graphene but also for narrow-gap semiconductors, topological insulators, and metals.

cond-mat.mes-hall↗

arXiv2014

A micrometer-scale integrated silicon source of time-energy entangled photons

Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip but the sources demonstrated so far require millimeter lengths and pump powers of the order of hundreds of mWs to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been demonstrated. Here we report the first demonstration of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell's inequality by as much as 11 standard deviations. The source is integrated on a silicon chip, operates at sub-mW pump power, emits in the telecom band with a pair generation rate exceeding 10$^7$ Hz per $nm$, and outputs into a photonic waveguide. These are all essential features of an entangled states emitter for a quantum photonic networks.

quant-ph↗

arXiv2014

All-optical injection of charge, spin and valley currents in monolayer transition metal dichalcogenides

Monolayer transition metal dichalcogenides have recently become a playground for spin- and valleytronics research. Their low energy spectrum can be described by Dirac cones on the corners of Brillouin zone, but the physical properties are richer than those of graphene since the spin degeneracy is lifted and the optical selection rules are valley dependent. This has been exploited for the optical injection of spin and valley polarized currents by the application of static electric fields. In this paper we consider an all-optical method for the injection of charge, spin and valley polarized currents. The presence of both a fundamental optical field and its second harmonic can lead to the injection of currents due to a nonlinear effect involving the quantum interference between one- and two-photon absorption processes. We analyze how the injected quantities can be controlled through the parameters of the incident light fields, allowing capabilities of control beyond those achieved with static fields, and discuss the conditions for experimental verification of our results.

cond-mat.mes-hall↗

arXiv2014

Effects of time ordering in quantum nonlinear optics

We study time ordering corrections to the description of spontaneous parametric down-conversion (SPDC), four wave mixing (SFWM) and frequency conversion (FC) using the Magnus expansion. Analytic approximations to the evolution operator that are unitary are obtained. They are Gaussian preserving, and allow us to understand order-by-order the effects of time ordering. We show that the corrections due to time ordering vanish exactly if the phase matching function is sufficiently broad. The calculation of the effects of time ordering on the joint spectral amplitude of the photons generated in spontaneous SPDC and SFWM are reduced to quadrature.

quant-ph↗

arXiv2014

Dynamics of the effective mass and the anomalous velocity in two-dimensional lattices

The semiclassical description of the dynamics of wave packets in periodic potentials and subject to an applied force relies on the concepts of effective mass and anomalous transport. This picture is valid if the force changes slowly in time and space, so that the particle described by the wave packet has time to respond according to the properties of the lattice. We analyze the dynamical corrections to this picture when a uniform force is suddenly applied, identifying separate corrections to the usual group and anomalous velocities. We find approximate semianalytical expressions for generalized "dynamical" group and anomalous velocities, and the associated accelerations. We use a two-dimensional optical lattice with finite Berry curvature to illustrate the semianalytical approximation in a regime where the dynamical corrections are significant, suggesting the possibility of experiments to detect them; we compare the results with a full numerical solution, showing excellent agreement for weak forces.

cond-mat.mes-hall↗

arXiv2014

Photonic band-gap engineering for volume plasmon polaritons in multiscale multilayer hyperbolic metamaterials

We theoretically study the propagation of large-wavevector waves (volume plasmon polaritons) in multilayer hyperbolic metamaterials with two levels of structuring. We show that when the parameters of a subwavelength metal-dielectric multilayer ("substructure") are modulated ("superstructured") on a larger, wavelength scale, the propagation of volume plasmon polaritons in the resulting multiscale hyperbolic metamaterials is subject to photonic band gap phenomena. A great degree of control over such plasmons can be exerted by varying the superstructure geometry. When this geometry is periodic, stop bands due to Bragg reflection form within the volume plasmonic band. When a cavity layer is introduced in an otherwise periodic superstructure, resonance peaks of the Fabry-Perot nature are present within the stop bands. More complicated superstructure geometries are also considered. For example, fractal Cantor-like multiscale metamaterials are found to exhibit characteristic self-similar spectral signatures in the volume plasmonic band. Multiscale hyperbolic metamaterials are shown to be a promising platform for large-wavevector bulk plasmonic waves, whether they are considered for use as a new kind of information carrier or for far-field subwavelength imaging.

physics.optics↗

arXiv2014

From surface to volume plasmons in hyperbolic metamaterials: General existence conditions for bulk high-k waves in metal-dielectric and graphene-dielectric multilayers

We theoretically investigate general existence conditions for broadband bulk large-wavevector (high-k) propagating waves (such as volume plasmon polaritons in hyperbolic metamaterials) in subwavelength periodic multilayer structures. Describing the elementary excitation in the unit cell of the structure by a generalized resonance pole of a reflection coefficient, and using Bloch's theorem, we derive analytical expressions for the band of large-wavevector propagating solutions. We apply our formalism to determine the high-k band existence in two important cases: the well-known metal-dielectric, and recently introduced graphene-dielectric stacks. We confirm that short-range surface plasmons in thin metal layers can give rise to hyperbolic metamaterial properties, and demonstrate that long-range surface plasmons cannot. We also show that graphene-dielectric multilayers tend to support high-k waves and explore the range of parameters for which this is possible, confirming the prospects of using graphene for materials with hyperbolic dispersion. The approach is applicable to a large variety of structures, such as continuous or structured microwave, terahertz (THz) and optical metamaterials.

physics.optics↗

arXiv2014

The Franz-Keldysh effect revisited: Electroabsorption including interband coupling and excitonic effects

We study the linear optical absorption of bulk semiconductors in the presence of a homogeneous constant (dc) electric field with an approach suitable for including excitonic effects while working with many-band models. The absorption coefficient is calculated from the time evolution of the interband polarization excited by an optical pulse. We apply the formalism to a numerical calculation for GaAs using a 14-band $\textbf{k} \cdot \textbf{p}$ model, which allows us to properly include interband coupling, and the exchange self-energy to account for the excitonic effects due to the electron-hole interaction. The Coulomb interaction enhances the features of the absorption coefficient captured by the $\textbf{k} \cdot \textbf{p}$ model. We consider the dependence of the enhancement on the strength of the dc field and the polarization of the optical field.

cond-mat.mes-hall↗

arXiv2014

Coherent control of optical injection of spin and currents in topological insulators

Topological insulators have surface states with a remarkable helical spin structure, with promising prospects for applications in spintronics. Strategies for generating spin polarized currents, such as the use of magnetic contacts and photoinjection, have been the focus of extensive research. While several optical methods for injecting currents have been explored, they have all focused on one-photon absorption. Here we consider the use of both a fundamental optical field and its second harmonic, which allows the injection of spin polarized carriers and current by a nonlinear process involving quantum interference between one- and two-photon absorption. General expressions are derived for the injection rates in a generic two-band system, including those for one- and two-photon absorption processes as well as their interference. Results are given for carrier, spin density and current injection rates on the surface of topological insulators, for both linearly and circularly polarized light. We identify the conditions that would be necessary for experimentally verifying these predictions.

cond-mat.mes-hall↗

arXiv2013

Long Range Surface Plasmons in Multilayer Structures

We present a new strategy, based on a Fresnel coefficient pole analysis, for designing an asymmetric multilayer structure that supports long range surface plasmons (LRSP). We find that the electric field intensity in the metal layer of a multilayer LRSP structure can be even slightly smaller than in the metal layer of the corresponding symmetric LRSP structure, minimizing absorption losses and resulting in LRSP propagation lengths up to 2mm. With a view towards biosensing applications, we also present semi-analytic expressions for a standard surface sensing parameter in arbitrary planar resonant structures, and in particular show that for an asymmetric structure consisting of a gold film deposited on a multilayer of SiO2 and TiO2 a surface sensing parameter G = 1.28(1/nm) can be achieved.

physics.optics↗

arXiv2013

Parasitic nonlinearities in photon pair generation via integrated spontaneous four-wave mixing: critical problem or distraction?

We consider integrated photon pair sources based on spontaneous four-wave mixing and derive expressions for the pump powers at which various nonlinear processes become relevant for a variety of source materials and structures. These expressions serve as rules of thumb in identifying reasonable parameter regimes for the design of such sources. We demonstrate that if pump powers are kept low enough to suppress cross-phase modulation, multi-pair events as well as many other nonlinear effects are often also constrained to negligible levels.

quant-ph↗

arXiv2013

Orbital instability and the loss of quantum coherence

We compare quantum decoherence in generic regular and chaotic systems that interact with a thermal reservoir via a dipole coupling. Using a time-dependent, self-consistent approximation in the spirit of Hartree, we derive in the high temperature limit an expression for the off-diagonal elements of the system density operator that initially corresponds to a coherent superposition of two adjacent wave packets. We relate the decoherence rate to the Lyapunov exponent in the Ehrenfest regime. In this regime, the greater the instability of the system the faster the loss of coherence occurs.

quant-ph↗

arXiv2013

Observing the Onset of Effective Mass

The response of a particle in a periodic potential to an applied force is commonly described by an effective mass which accounts for the detailed interaction between the particle and the surrounding potential. Using a Bose-Einstein condensate of 87-Rb atoms initially in the ground band of an optical lattice, we experimentally show that the initial response of a particle to an applied force is in fact characterized by the bare mass. Subsequently, the particle response undergoes rapid oscillations and only over timescales long compared to that of the interband dynamics is the effective mass observed to be an appropriate description.

quant-ph↗

arXiv2012

Canonical quantization of macroscopic electrodynamics in a linear, inhomogeneous magneto-electric medium

We present a canonical quantization of macroscopic electrodynamics. The results apply to inhomogeneous media with a broad class of linear magneto-electric responses which are consistent with the Kramers-Kronig and Onsager relations. Through its ability to accommodate strong dispersion and loss, our theory provides a rigorous foundation for the study of quantum optical processes in structures incorporating metamaterials, provided these may be modeled as magneto-electric media. Previous canonical treatments of dielectric and magneto-dielectric media have expressed the electromagnetic field operators in either a Green function or mode expansion representation. Here we present our results in the mode expansion picture with a view to applications in guided wave and cavity quantum optics.

quant-ph↗

arXiv2012

Ultra-low power generation of twin photons in a compact silicon ring resonator

We demonstrate efficient generation of correlated photon pairs by spontaneous four wave mixing in a 5 μm radius silicon ring resonator in the telecom band around 1550 nm. By optically pumping our device with a 200 μW continuous wave laser, we obtain a pair generation rate of 0.2 MHz and demonstrate photon time correlations with a coincidence-to-accidental ratio as high as 250. The results are in good agreement with theoretical predictions and show the potential of silicon micro-ring resonators as room temperature sources for integrated quantum optics applications.

physics.optics↗

arXiv2012

Double-heterostructure cavities: from theory to design

We derive a frequency-domain-based approach for radiation (FAR) from double-heterostructure cavity (DHC) modes. We use this to compute the quality factors and radiation patterns of DHC modes. The semi-analytic nature of our method enables us to provide a general relationship between the radiation pattern of the cavity and its geometry. We use this to provide general designs for ultrahigh quality factor DHCs with radiation patterns that are engineered to emit vertically.

physics.optics↗