Abstract-Wavelength conversion through plasmon-coupled surface states

 

Deniz Turan, Ping Keng Lu, Nezih T. Yardimci, Zhaoyu Liu, Liang Luo, Joong-Mok Park, Uttam Nandi, Jigang Wang, Sascha Preu, Mona Jarrahi

Wavelength conversion through plasmon-coupled surface states.

Built-in electric field profile and its impact on the wavelength conversion efficiency.

https://www.nature.com/articles/s41467-021-24957-1

Surface states generally degrade semiconductor device performance by raising the charge injection barrier height, introducing localized trap states, inducing surface leakage current, and altering the electric potential. We show that the giant built-in electric field created by the surface states can be harnessed to enable passive wavelength conversion without utilizing any nonlinear optical phenomena. Photo-excited surface plasmons are coupled to the surface states to generate an electron gas, which is routed to a nanoantenna array through the giant electric field created by the surface states. The induced current on the nanoantennas, which contains mixing product of different optical frequency components, generates radiation at the beat frequencies of the incident photons. We utilize the functionalities of plasmon-coupled surface states to demonstrate passive wavelength conversion of nanojoule optical pulses at a 1550 nm center wavelength to terahertz regime with efficiencies that exceed nonlinear optical methods by 4-orders of magnitude.

Physicists use light waves to accelerate supercurrents, enable ultrafast quantum computing

Jigang Wang and his collaborators have demonstrated light-induced acceleration of supercurrents, which could enable practical applications of quantum mechanics such as computing, sensing and communicating. Larger image. Image courtesy of Jigang Wang.

https://www.news.iastate.edu/news/2019/07/01/supercurrents

AMES, Iowa – Jigang Wang patiently explained his latest discovery in quantum control that could lead to superfast computing based on quantum mechanics: He mentioned light-induced superconductivity without energy gap. He brought up forbidden supercurrent quantum beats. And he mentioned terahertz-speed symmetry breaking.

Then he backed up and clarified all that. After all, the quantum world of matter and energy at terahertz and nanometer scales – trillions of cycles per second and billionths of meters – is still a mystery to most of us.

“I like to study quantum control of superconductivity exceeding the gigahertz, or billions of cycles per second, bottleneck in current state-of-the-art quantum computation applications,” said Wang, a professor of physics and astronomy at Iowa State University whose research has been supported by the Army Research Office. “We’re using terahertz light as a control knob to accelerate supercurrents.”

Superconductivity is the movement of electricity through certain materials without resistance. It typically occurs at very, very cold temperatures. Think -400 Fahrenheit for “high-temperature” superconductors.

Terahertz light is light at very, very high frequencies. Think trillions of cycles per second. It’s essentially extremely strong and powerful microwave bursts firing at very short time frames.

Wang and a team of researchers demonstrated such light can be used to control some of the essential quantum properties of superconducting states, including macroscopic supercurrent flowing, broken symmetry and accessing certain very high frequency quantum oscillations thought to be forbidden by symmetry.

It all sounds esoteric and strange. But it could have very practical applications.

“Light-induced supercurrents chart a path forward for electromagnetic design of emergent materials properties and collective coherent oscillations for quantum engineering applications,” Wang and several co-authors wrote in a research paper just published online by the journal Nature Photonics.

In other words, the discovery could help physicists “create crazy-fast quantum computers by nudging supercurrents,” Wang wrote in a summary of the research team’s findings.

Finding ways to control, access and manipulate the special characteristics of the quantum world and connect them to real-world problems is a major scientific push these days. The National Science Foundation has included the “Quantum Leap” in its “10 big ideas” for future research and development.

“By exploiting interactions of these quantum systems, next-generation technologies for sensing, computing, modeling and communicating will be more accurate and efficient,” says a summary of the science foundation’s support of quantum studies. “To reach these capabilities, researchers need understanding of quantum mechanics to observe, manipulate and control the behavior of particles and energy at dimensions at least a million times smaller than the width of a human hair.”

Wang and his collaborators – Xu Yang, Chirag Vaswani and Liang Luo from Iowa State, responsible for terahertz instrumentation and experiments; Chris Sundahl, Jong-Hoon Kang and Chang-Beom Eom from the University of Wisconsin-Madison, responsible for high-quality superconducting materials and their characterizations; Martin Mootz and Ilias E. Perakis from the University of Alabama at Birmingham, responsible for model building and theoretical simulations – are advancing the quantum frontier by finding new macroscopic supercurrent flowing states and developing quantum controls for switching and modulating them.

A summary of the research team’s study says experimental data obtained from a terahertz spectroscopy instrument indicates terahertz light-wave tuning of supercurrents is a universal tool “and is key for pushing quantum functionalities to reach their ultimate limits in many cross-cutting disciplines” such as those mentioned by the science foundation.

And so, the researchers wrote, “We believe that it is fair to say that the present study opens a new arena of light-wave superconducting electronics via terahertz quantum control for many years to come.”

Abstract-Ultrafast Terahertz Probes of Interacting Dark Excitons in Chirality-specific Single-walled Carbon Nanotubes

Liang Luo, Ioannis Chatzakis, Aaron Patz, and Jigang Wang
https://www.osapublishing.org/abstract.cfm?uri=CLEO_QELS-2015-FM1B.1

Ultrafast terahertz intra-excitonic transition ~6 meV reveals stable quasi-1D many-exciton states that evolve uniquely from a predominant dark exciton population to complex phase-space filling of both dark and bright pair states in (6,5) SWNTs

© 2015 OSA

PDF Article

Abstract-Ultrafast Terahertz Probes of Interacting Dark Excitons in Chirality-Specific Semiconducting Single-Walled Carbon Nanotubes

Liang Luo, Ioannis Chatzakis, Aaron Patz, and Jigang Wang

Phys. Rev. Lett. 114, 107402 – Published 13 March 2015

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.107402

Ultrafast terahertz spectroscopy accesses the dark excitonic ground state in resonantly excited (6,5) single-walled carbon nanotubes via internal, direct dipole-allowed transitions between the lowest-lying dark-bright pair state of ∼6  meV. An analytical model reproduces the response that enables the quantitative analysis of transient densities of dark excitons and e−h plasma, oscillator strength, transition energy renormalization, and dynamics. Nonequilibrium, yet stable, quasi-one-dimensional quantum states with dark excitonic correlations rapidly emerge even with increasing off-resonance photoexcitation and experience a unique crossover to complex phase-space filling of both dark and bright pair states, different from dense two- and three-dimensional excitons influenced by the thermalization, cooling, and ionization to free carriers.

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Abstract-One- and two-dimensional photo-imprinted diffraction gratings for manipulating terahertz waves

Ioannis Chatzakis^1,a), Philippe Tassin^1,b), Liang Luo¹, Nian-Hai Shen¹, Lei Zhang¹, Jigang Wang^1,c), Thomas Koschny¹ and C. M. Soukoulis^1,2,d)
http://scitation.aip.org/content/aip/journal/apl/103/4/10.1063/1.4813620
a) Present address: Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
b) Author to whom correspondence should be addressed: Electronic mail: tassin@ameslab.gov
c) Electronic mail: jgwang@iastate.edu, jwang@ameslab.gov
d) Electronic mail: soukoulis@ameslab.gov
Appl. Phys. Lett. 103, 043101 (2013); http://dx.doi.org/10.1063/1.4813620

Emerging technology based on artificial materials containing metallic structures has raised the prospect for unprecedented control of terahertz waves. The functionality of these devices is static by the very nature of their metallic composition, although some degree of tunability can be achieved by incorporating electrically biased semiconductors. Here, we demonstrate a photonic structure by projecting the optical image of a metal mask onto a thin GaAs substrate using a femtosecond pulsed laser source. We show that the resulting high-contrast pattern of photo-excited carriers can create diffractive elements operating in transmission, potentially providing a route to terahertz components with reconfigurable functionality.

Abstract-Broadband terahertz generation from metamaterials

• Liang Luo,
• Ioannis Chatzakis,
• Jigang Wang,
• Fabian B. P. Niesler,
• Martin Wegener,
• Thomas Koschny
• & Costas M. Soukoulis

http://www.nature.com/ncomms/2014/140108/ncomms4055/full/ncomms4055.html

The terahertz spectral regime, ranging from about 0.1–15 THz, is one of the least explored yet most technologically transformative spectral regions. One current challenge is to develop efficient and compact terahertz emitters/detectors with a broadband and gapless spectrum that can be tailored for various pump photon energies. Here we demonstrate efficient single-cycle broadband THz generation, ranging from about 0.1–4 THz, from a thin layer of split-ring resonators with few tens of nanometers thickness by pumping at the telecommunications wavelength of 1.5 μm (200 THz). The terahertz emission arises from exciting the magnetic-dipole resonance of the split-ring resonators and quickly decreases under off-resonance pumping. This, together with pump polarization dependence and power scaling of the terahertz emission, identifies the role of optically induced nonlinear currents in split-ring resonators. We also reveal a giant sheet nonlinear susceptibility ~10⁻¹⁶ m² V⁻¹ that far exceeds thin films and bulk non-centrosymmetric materials.