arXiv subjects

J. E. Sipe

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

At least 127 records · Page 7Linked to original sources

arXiv2012

From Classical Four-Wave Mixing to Parametric Fluorescence in Silicon micro-ring resonators

Four-wave mixing can be stimulated or occur spontaneously. The first process is intrinsically much stronger, and well understood through classical nonlinear optics. The latter, also known as parametric fluorescence, can be explained only in the framework of a quantum theory of light. We experimentally demonstrate that, in a micro-ring resonator, there exists a simple relation between the efficiencies of these two processes, which is independent of the nonlinearity and size of the ring. In particular we show that the average power generated by parametric fluorescence can be immediately estimated from a classical FWM experiment. These results suggest that classical nonlinear characterization of a photonic integrated structure can provide accurate information on its nonlinear quantum properties.

quant-ph↗

arXiv2012

First-principles method for high-$Q$ photonic crystal cavity mode calculations

We present a first-principles method to compute radiation properties of ultra-high quality factor photonic crystal cavities. Our Frequency-domain Approach for Radiation (FAR) can compute the far-field radiation pattern and quality factor of cavity modes $\sim 100$ times more rapidly than conventional finite-difference time domain calculations. It also provides a simple rule for engineering the cavity's far-field radiation pattern.

physics.optics↗

arXiv2012

Positive Quantum Brownian Evolution

Using the independent oscillator model with an arbitrary system potential, we derive a quantum Brownian equation assuming a correlated total initial state. Although not of Lindblad form, the equation preserves positivity of the density operator on a restricted set of initial states.

quant-ph↗

arXiv2012

Response of a particle in a one-dimensional lattice to an applied force: Dynamics of the effective mass

We study the behaviour of the expectation value of the acceleration of a particle in a one-dimensional periodic potential when an external homogeneous force is suddenly applied. The theory is formulated in terms of modified Bloch states that include the interband mixing induced by the force. This approach allows us to understand the behaviour of the wavepacket, which responds with a mass that is initially the bare mass, and subsequently oscillates around the value predicted by the effective mass. If Zener tunneling can be neglected, the expression obtained for the acceleration of the particle is valid over timescales of the order of a Bloch oscillation, which are of interest for experiments with cold atoms in optical lattices. We discuss how these oscillations can be tuned in an optical lattice for experimental detection.

quant-ph↗

arXiv2011

Two-photon Indirect Optical Injection and Two-color Coherent Control in Bulk Silicon

Using an empirical pseudopotential description of electron states and an adiabatic bond charge model for phonon states in bulk silicon, we theoretically investigate two-photon indirect optical injection of carriers and spins and two-color coherent control of the motion of the injected carriers and spins. For two-photon indirect carrier and spin injection, we identify the selection rules of band edge transitions, the injection in each conduction band valley, and the injection from each phonon branch at 4 K and 300 K. At 4 K, the TA phonon-assisted transitions dominate the injection at low photon energies, and the TO phonon-assisted at high photon energies. At 300 K, the former dominates at all photon energies of interest. The carrier injection shows anisotropy and linear-circular dichroism with respect to light propagation direction. For light propagating along the $<001>$ direction, the carrier injection exhibits valley anisotropy, and the injection into the $Z$ conduction band valley is larger than that into the $X/Y$ valleys. For $σ^-$ light propagating along the $<001>$ ($<111>$) direction, the degree of spin polarization gives a maximum value about 20% (6%) at 4 K and -10% (20%) at 300 K, and at both temperature shows abundant structure near the injection edges due to contributions from different phonon branches. Forthe two-color coherent current injection with an incident optical field composed of a fundamental frequency and its second harmonic, the response tensors of the electron (hole) charge and spin currents are calculated at 4 K and 300 K. We show the current control for three different polarization scenarios. The spectral dependence of the maximum swarm velocity shows that the direction of charge current reverses under increase in photon energy.

cond-mat.mtrl-sci↗

arXiv2011

Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial Graphene from Polarization Dependent Coherently Controlled Photocurrent Generation

Most experimental studies to date of multilayer epitaxial graphene on C-face SiC have indicated that the electronic states of different layers are decoupled as a consequence of rotational stacking. We have measured the third order nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer electronic coupling, by studying THz emission from coherently controlled photocurrents as a function of the optical pump and THz beam polarizations. We find that the polarization dependence of the coherently controlled THz emission expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not observed. We hypothesize that the observed angular dependence arises from weak coupling between the layers; a model calculation of the angular dependence treating the multilayer structure as a stack of independent bilayers with variable interlayer coupling qualitatively reproduces the polarization dependence, providing evidence for coupling.

cond-mat.mes-hall↗

arXiv2011

Optical injection and terahertz detection of the macroscopic Berry curvature

We propose an experimental scheme to probe the Berry curvature of solids. Our method is sensitive to arbitrary regions of the Brillouin zone, and employs only basic optical and terahertz techniques to yield a background free signal. Using semiconductor quantum wells as a prototypical system, we discuss how to inject Berry curvature macroscopically, and probe it in a way that provides information about the underlying microscopic Berry curvature.

cond-mat.mes-hall↗

arXiv2011

Electric field-induced quantum interference control in a semiconductor: A new manifestation of the Franz-Keldysh effect

In (100)-oriented GaAs illuminated at normal incidence by a laser and its second harmonic, interference between one- and two-photon absorption results in ballistic current injection, but not modulation of the overall carrier injection rate. Results from a pump-probe experiment on a transversely biased sample show that a constant electric field enables coherent control of the carrier injection rate. We ascribe this to the nonlinear optical Franz-Keldysh effect and calculate it for a two-band parabolic model. The mechanism is relevant to centrosymmetric semiconductors as well.

cond-mat.other↗

arXiv2011

Current injection by coherent one- and two-photon excitation in graphene and its bilayer

Coherent control of optically-injected carrier distributions in single and bilayer graphene allows the injection of electrical currents. Using a tight-binding model and Fermi's golden rule, we derive the carrier and photocurrent densities achieved via interference of the quantum amplitudes for two-photon absorption at a fundamental frequency, $ω$, and one-photon absorption at the second harmonic, $2ω$. Strong currents are injected under co-circular and linear polarizations. In contrast, opposite-circular polarization yields no net current. For single-layer graphene, the magnitude of the current is unaffected by the rotation of linear-polarization axes, in contrast with the bilayer and with conventional semiconductors. The dependence of the photocurrent on the linear-polarization axes is a clear and measurable signature of interlayer coupling in AB-stacked multilayer graphene. We also find that single and bilayer graphene exhibit a strong, distinct linear-circular dichroism in two-photon absorption.

cond-mat.mtrl-sci↗

arXiv2011

Full Band Structure Calculation of Two-photon Indirect Absorption in Bulk Silicon

Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. We perform a full band structure calculation to investigate two-photon indirect absorption in bulk silicon, using a pseudopotential description of the energy bands and an adiabatic bond charge model to describe phonon dispersion and polarization. Our results agree well with some recent experimental results. The transverse acoustic/optical phonon-assisted processes dominate.

cond-mat.mtrl-sci↗

arXiv2011

Theory of optical spin orientation in silicon

We theoretically investigate the indirect optical injection of carriers and spins in bulk silicon, using an empirical pseudopotential description of electron states and an adiabatic bond charge model for phonon states. We identify the selection rules, the contribution to the carrier and spin injection in each conduction band valley from each phonon branch and each valence band, and the temperature dependence of these processes. The transition from the heavy hole band to the lowest conduction band dominates the injection due to the large joint density of states. For incident light propagating along the $[00\bar{1}]$ direction, the injection rates and the degree of spin polarization of injected electrons show strong valley anisotropy. The maximum degree of spin polarization is at the injection edge with values 25% at low temperature and 15% at high temperature.

cond-mat.mtrl-sci↗

arXiv2010

Polarization dependence of the two-photon Franz-Keldysh effect

The effect of a constant electric field on two-photon absorption in a direct band gap semiconductor is calculated using an independent-particle theory. Two band structure models for GaAs are used: a two-band parabolic model and an eight-band "k dot p" model. Both predict a strong dependence of the two-photon electroabsorption spectrum on the polarization of the light with respect to the constant field. We attribute the polarization dependence to the strong effect of a constant field on intraband dynamics.

cond-mat.mes-hall↗

arXiv2009

Mode coupling and evolution in broken-symmetry plasmas

The control of nonlinear processes and possible transitions to chaos in systems of interacting particles is a fundamental physical problem. We propose a new nonuniform solid-state plasma system, produced by the optical injection of current in two-dimensional semiconductor structures, where this control can be achieved. Due to an injected current, the system symmetry is initially broken. The subsequent nonequilibrium dynamics is governed by the spatially varying long-range Coulomb forces and electron-hole collisions. As a result, inhomogeneities in the charge and velocity distributions should develop rapidly, and lead to previously unexpected experimental consequences. We suggest that the system eventually evolves into a behavior similar to chaos.

cond-mat.mes-hall↗

arXiv2007

Hydrodynamic model for relaxation of optically injected currents in quantum wells

We use a hydrodynamic model to describe the relaxation of optically injected currents in quantum wells on a picosecond time scale, numerically solving the continuity and velocity evolution equations with the Hermite-Gaussian functions employed as a basis. The interplay of the long-range Coulomb forces and nonlinearity in the equations of motion leads to rather complex patterns of the calculated charge and current densities. We find that the time dependence of even the first moment of the electron density is sensitive to this complex evolution.

cond-mat.other↗

arXiv2007

THz emission from ultrafast optical orientation

We show both theoretically and experimentally that the magnetization density accompanying ultrafast excitation of a semiconductor with circular polarized light varies rapidly enough to produce a detectable THz field.

cond-mat.mtrl-sci↗

arXiv2006

Coherent spin dynamics in quantum wells in quantizing magnetic field

We investigate theoretically the coherent longitudinal and transversal spin relaxation of photoexcited electrons in quantum wells in quantized magnetic fields. We find the relaxation time for typical quantum well parameters between 100 and 1000 ps. For a realistic random potential the relaxation process depends on the electron energy and g-factor, demonstrating oscillations in the spin polarization accompanying the spin relaxation. The dependence of spin relaxation on applied field, and thus on the corresponding "magnetic" length, can be used to characterize the spatial scale of disorder in quantum wells.

cond-mat.dis-nn↗

arXiv2006

Photon wave functions and quantum interference experiments

We present a general theory to describe two-photon interference, including a formal description of few photon intereference in terms of single-photon amplitudes. With this formalism, it is possible to describe both frequency entangled and separable two-photon interference in terms of single-photon wave functions. Using this description, we address issues related to the physical interpretation of two-photon interference experiments. We include a discussion on how few-photon interference can be interpreted as a bosonic exchange effect, and how this relates to traditional exchange effects with fermions.

quant-ph↗

arXiv2006

Ultrafast extrinsic spin-Hall currents

We consider the possibility of ultrafast extrinsic spin-Hall currents, generated by skew scattering following the optical injection of charge or pure spin currents. We propose a phenomenological model for this effect in quantum well structures. An injected charge current leads to a spin-Hall-induced pure spin current, and an injected pure spin current leads to a spin-Hall-induced charge current. The resulting spin or charge accumulation can be measured optically.

cond-mat.other↗