New hole-punched crystal clears a path for quantum light

February 15, 2018

Optical highways for light are at the heart of modern communications. But when it comes to guiding individual blips of light called photons, reliable transit is far less common. Now, a collaboration of researchers from the University of Maryland's Joint Quantum Institute (JQI), led by Associate Professor Mohammad Hafezi and Professor Edo Waks, has created a photonic chip that both generates single photons, and steers them around. Hafezi and Waks are both JQI Fellows with affiliations in the Departments of Electrical and Computer Engineering and Physics and Institute for Research in Electronics and Applied Physics.

The device, described in the journal Science, features a way for the quantum light to seamlessly move, unaffected by certain obstacles.

"This design incorporates well-known ideas that protect the flow of current in certain electrical devices," says Hafezi. "Here, we create an analogous environment for photons, one that protects the integrity of quantum light, even in the presence of certain defects."

The chip starts with a photonic crystal, which is an established, versatile technology used to create roadways for light. They are made by punching holes through a sheet of semiconductor. For photons, the repeated hole pattern looks very much like a real crystal made from a grid of atoms. Researchers use different hole patterns to change the way that light bends and bounces through the crystal. For instance, they can modify the hole sizes and separations to make restricted lanes of travel that allow certain light colors to pass, while prohibiting others.

Sometimes, even in these carefully fabricated devices, there are flaws that alter the light's intended route, causing it to detour into an unexpected direction. But rather than ridding their chips of every flaw, the JQI team mitigates this issue by rethinking the crystal's hole shapes and crystal pattern. In the new chip, they etch out thousands of triangular holes in an array that resembles a bee's honeycomb. Along the center of the device they shift the spacing of the holes, which opens a different kind of travel lane for the light. Previously, these researchers predicted that photons moving along that line of shifted holes should be impervious to certain defects because of the overall crystal structure, or topology. Whether the lane is a switchback road or a straight shot, the light's path from origin to destination should be assured, regardless of the details of the road.

The light comes from small flecks of semiconductor--dubbed quantum emitters--embedded into the photonic crystal. Researchers can use lasers to prod this material into releasing single photons. Each emitter can gain energy by absorbing laser photons and lose energy by later spitting out those photons, one at time. Photons coming from the two most energetic states of a single emitter are different colors and rotate in opposite directions. For this experiment, the team uses photons from an emitter found near the chip's center.

The team tested the capabilities of the chip by first changing a quantum emitter from its lowest energy state to one of its two higher energy states. Upon relaxing back down, the emitter pops out a photon into the nearby travel lane. They continued this process many times, using photons from the two higher energy states. They saw that photons emitted from the two states preferred to travel in opposite directions, which was evidence of the underlying crystal topology.

To confirm that the design could indeed offer protected lanes of traffic for single photons, the team created a 60 degree turn in the hole pattern. In typical photonic crystals, without built-in protective features, such a kink would likely cause some of the light to reflect backwards or scatter elsewhere. In this new chip, topology protected the photons and allowed them to continue on their way unhindered.

"On the internet, information moves around in packets of light containing many photons, and losing a few doesn't hurt you too much," says co-author Sabyasachi Barik, a graduate student at JQI. "In quantum information processing, we need to protect each individual photon and make sure it doesn't get lost along the way. Our work can alleviate some forms of loss, even when the device is not completely perfect."

The design is flexible, and could allow researchers to systematically assemble pathways for single photons, says Waks. "Such a modular approach may lead to new types of optical devices and enable tailored interactions between quantum light emitters or other kinds of matter."
-end-
The A. James Clark School of Engineering at the University of Maryland serves as the catalyst for high-quality research, innovation, and learning, delivering on a promise that all graduates will leave ready to impact the Grand Challenges (energy, environment, security, and human health) of the 21st century. The Clark School is dedicated to leading and transforming the engineering discipline and profession, to accelerating entrepreneurship, and to transforming research and learning activities into new innovations that benefit millions. Visit us online at http://www.eng.umd.edu and follow us on Twitter @ClarkSchool.

University of Maryland

Related Photons Articles from Brightsurf:

An electrical trigger fires single, identical photons
Researchers at Berkeley Lab have found a way to generate single, identical photons on demand.

Single photons from a silicon chip
Quantum technology holds great promise: Quantum computers are expected to revolutionize database searches, AI systems, and computational simulations.

Physicists "trick" photons into behaving like electrons using a "synthetic" magnetic field
Scientists have discovered an elegant way of manipulating light using a ''synthetic'' Lorentz force -- which in nature is responsible for many fascinating phenomena including the Aurora Borealis.

Scientists use photons as threads to weave novel forms of matter
New research from the University of Southampton has successful discovered a way to bind two negatively charged electron-like particles which could create opportunities to form novel materials for use in new technological developments.

The nature of nuclear forces imprinted in photons
IFJ PAN scientists together with colleagues from the University of Milano (Italy) and other countries confirmed the need to include the three-nucleon interactions in the description of electromagnetic transitions in the 20O atomic nucleus.

Pushing photons
UC Santa Barbara researchers continue to push the boundaries of LED design a little further with a new method that could pave the way toward more efficient and versatile LED display and lighting technology.

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.

An advance in molecular moviemaking shows how molecules respond to two photons of light
Some of the molecules' responses were surprising and others had been seen before with other techniques, but never in such detail or so directly, without relying on advance knowledge of what they should look like.

The imitation game: Scientists describe and emulate new quantum state of entangled photons
A research team from ITMO University, MIPT and Politecnico di Torino, has predicted a novel type of topological quantum state of two photons.

What if we could teach photons to behave like electrons?
The researchers tricked photons - which are intrinsically non-magnetic - into behaving like charged electrons.

Read More: Photons News and Photons Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.