Patrick Keiffer

Spectroscopic studies of resonant coupling of silver optical antenna arrays to a near-surface quantum well

The coupling of radiation emitted on semiconductor inter-band transitions to resonant optical-antenna arrays allows for enhanced light–matter interaction via the Purcell effect. Semiconductor optical gain also potentially allows for loss reduction in metamaterials. Here we extend our previous work on optically pumped individual near-surface InGaAs quantum wells coupled to silver split-ring-resonator arrays to wire and square-antenna arrays. By comparing the transient pump-probe experimental results with the predictions of a simple model, we find that the effective coupling is strongest for the split rings, even though the split rings have the weakest dipole moment. The effect of the latter must thus be overcompensated by a smaller effective mode volume of the split rings. Furthermore, we also present a systematic variation of the pump-pulse energy, which was fixed in our previous experiments.

Polarization dependent femtosecond laser modification of MBE-grown III-V nanostructures on silicon

We report a novel, polarization dependent, femtosecond laser-induced modification of surface nanostructures of indium, gallium, and arsenic grown on silicon via molecular beam epitaxy, yielding shape control from linear and circular polarization of laser excitation. Linear polarization causes an elongation effect, beyond the dimensions of the unexposed nanostructures, ranging from 88 nm to over 1 µm, and circular polarization causes the nanostructures to flatten out or form loops of material, to diameters of approximately 195 nm. During excitation, it is also observed that the generated second and third harmonic signals from the substrate and surface nanostructures increase with exposure time.

All-optical graphical models for probabilistic inference

Considering that high performance electronic computation has become extremely efficient, for an optical hardware accelerator to be relevant, it must solve a type or a set of problems where its electronic counterpart is still struggling in term of size, energy, or time. We have identified one such challenge as the minimization of large scale Ising Hamiltonians when the number of particles is on the order of a million. Here we discuss an algorithmic approach based on probabilistic inference using graphical model and message passing.

Superconductivity in epitaxially grown self-assembled indium islands: progress towards hybrid superconductor/semiconductor optical sources

Currently, superconducting qubits lead the way in potential candidates for quantum computing. At the same time, transferring quantum information over long distances typically relies on the use of photons as the elementary qubit. Converting between stationary electronic qubits in superconducting systems and traveling photonic qubits is a challenging yet necessary goal for the interface of quantum computing and communication. One promising path to achieving this goal appears to be the integration of superconductivity with optically active semiconductors, with quantum information being transferred between the two by means of the superconducting proximity effect. Obtaining good interfaces between superconductors and semiconductors is the next obvious step for improving these hybrid systems. Here, we report on our observation of superconductivity in a 2.3 μm diameter self-assembled indium structure grown epitaxially on the surface of a semiconductor material.

TEM EDS analysis of epitaxially-grown self-assembled indium islands

Air Force Office of Scientific Research (AFOSR) [FA9550-13-1-0003, 12RY05COR]; National Science Foundation Atomic, Molecular and Optical Physics [NSF-AMOP 1205031]; Engineering Research Center for Integrated Access Networks (NSF ERC-CIAN) [EEC-0812072]; Arizona Technology and Research Initiative Funding (TRIF); Department of Defense through the National Defense Science and Engineering Graduate (NDSEG) Fellowship Program; Department of Energy (DOE) through the Office of Science Graduate Fellowship (SCGF), [DE-AC05-06OR23100]; French technology network RENATECH

Nonlinear optical components for all-optical probabilistic graphical model

The probabilistic graphical models (PGMs) are tools that are used to compute probability distributions over large and complex interacting variables. They have applications in social networks, speech recognition, artificial intelligence, machine learning, and many more areas. Here, we present an all-optical implementation of a PGM through the sum-product message passing algorithm (SPMPA) governed by a wavelength multiplexing architecture. As a proof-of-concept, we demonstrate the use of optics to solve a two node graphical model governed by SPMPA and successfully map the message passing algorithm onto photonics operations. The essential mathematical functions required for this algorithm, including multiplication and division, are implemented using nonlinear optics in thin film materials. The multiplication and division are demonstrated through a logarithm-summation-exponentiation operation and a pump-probe saturation process, respectively. The fundamental bottlenecks for the scalability of the presented scheme are discussed as well.To circumvent the limitations of electronic computers, moving to hybrid optical-electronic or all-optical devices may be useful. Here, Babaeian et al. present an all-optical implementation of the probabilistic graphical model using nonlinear optics in thin films to implement mathematical functions.

Progress of the quantum nano-optics of semiconductors group at Optical Sciences

The history of semiconductor quantum optics group in the College of Optical Sciences will be discussed. The work from planar microcavities including VCSELs, photonic crystal cavities leading to the observation of strong-coupling between an L3 cavity and a quantum dot, and now metallic cavities coupled to quantum wells and quantum dots will be described.

In Situ Growth of Self-assembled Indium Islands in Close Proximity to Semiconductor Quantum Emitters

Self-assembled indium islands on III-V quantum dot (QD) samples with a 7nm cap show a 4x enhancement in the peak intensity of the PL offering a bottom-up platform for studying the resonant coupling between plasmonic structures and semiconductor quantum emitters.

Effect of Metallic Antenna Shape on the Near-Field Coupling to a Semiconductor Quantum Well

Arrays of metallic antennae with wire, square and split-ring shapes are fabricated on a near-surface quantum well. The hybrid system is investigated using photoluminescence, transmission and transient pump-probe experiments.