photonics

On the cover of the Pink Floyd album Dark Side of the Moon, a prism splits a ray of light into all the colors of the rainbow. This multicolored medley, which owes its emergence to the fact that light travels as a wave, is almost always hiding in plain sight; a prism simply reveals that it was there.

JQI Fellow Alicia Kollár has received a prestigious Faculty Early Career Development (CAREER) award from the National Science Foundation (NSF) for a proposal aimed at developing a new window into the physics of particles interacting inside of materials and performing educational outreach. The award will provide $675,000 of funding over five years for her proposal titled “Engineering Interacting Photons in Superconducting-Circuit Lattices.” Kollár will use the funds to investigate new physics that might be revealed by making particles of light (called photons) behave more like particles of matter (like electrons). Her plan is to tailor environments for photons by combining superconducting components into specialized circuits. 

Identical twins might seem “indistinguishable,” but in the quantum world the word takes on a new level of meaning. While identical twins share many traits, the universe treats two indistinguishable quantum particles as intrinsically interchangeable. This opens the door for indistinguishable particles to interact in unique ways—such as in quantum interference—that are needed for quantum computers. While generating a crowd of photons—particles of light—is as easy as flipping a light switch, it’s trickier to make a pair of indistinguishable photons. And it takes yet more work to endow that pair with a quantum mechanical link known as entanglement. JQI researchers and their colleagues describe a new way to make entangled twin particles of light and to tune their properties using a method conveniently housed on a chip, a potential boon for quantum technologies that require a reliable source of well-tailored photon pairs.

Photons—the quantum particles of light—normally don’t have any sense of personal space. A laser crams tons of photons into a tight beam, and they couldn’t care less that they are packed on top of each other. Two beams can even pass through each other without noticing. This is all well and good when making an extravagant laser light show or using a laser level to hang a picture frame straight, but for researchers looking to develop quantum technologies that require precise control over just one or two photons, this lack of interaction often makes life difficult. Now, a group of UMD researchers has come together to create tailored interactions between photons in an experiment where, at least for photons, two’s company but three’s a crowd. The technique builds on many previous experiments that use atoms as intermediaries to form connections between photons that are akin to the bonds between protons, electrons and other kinds of matter. These interactions, along with the ability to control them, promises new opportunities for researchers to study the physics of exotic interactions and develop light-based quantum technologies.

One of the chief obstacles facing quantum computer designers—correcting the errors that creep into a processor’s calculations—could be overcome with a new approach by physicists from and the California Institute of Technology, who may have found a way to design quantum memory switches that would self-correct. The team’s theory paper, which was published Dec. 8, 2020 in the journal Physical Review Letters, suggests an easier path to creating stable quantum bits, or qubits, which ordinarily are subject to environmental disturbances and errors. Finding methods of correcting these errors is a major issue in quantum computer development, but the research team’s approach to qubit design could sidestep the problem. 

The digital age has seen electronics, including computer chips, shrink in size at an amazing rate, with ever tinier chips powering devices like smartphones, laptops and even autonomous drones. In the wake of this progress, another miniature technology has been gaining steam: integrated photonics. Photons, which are the quantum particles of light, have some advantages over electrons, the namesakes of electronics. For some applications, photons offer faster and more accurate information transfer and use less power than electrons. And because on-chip photonics are largely built using the same technology created for the electronics industry, they carry the promise of integrating electronics and photonics on the same chip.

Flashlight beams don’t clash together like lightsabers because individual units of light—photons—generally don’t interact with each other. Two beams don’t even flicker when they cross paths. But by using matter as an intermediary, scientists have unlocked a rich world of photon interactions. In these early days of exploring the resulting possibilities, researchers are tackling topics like producing indistinguishable single photons and investigating how even just three photons form into basic molecules of light. The ability to harness these exotic behaviors of light is expected to lead to advances in areas such as quantum computing and precision measurement. In a paper recently published in Physical Review Research, JQI Fellow Alexey Gorshkov, JQI postdoctoral researcher Przemyslaw Bienias, and their colleagues describe an experiment that investigates how to extract a train of single photons from a laser packed with many photons.  In the experiment, the researchers examined how photons in a laser beam can interact through atomic intermediaries so that most photons are scattered out of the beam and only a single photon is transmitted at a time. They also developed an improved model that makes better predictions for more intense levels of light than previous research focused on. The new results reveal details about the work to be done to conquer the complexities of interacting photons. 

When it comes to quantum physics, light and matter are not so different. Under certain circumstances, negatively charged electrons can fall into a coordinated dance that allows them to carry a current through a material laced with imperfections. That motion, which can only occur if electrons are confined to a two-dimensional plane, arises due to a phenomenon known as the quantum Hall effect.Researchers, led by Mohammad Hafezi, a JQI Fellow and assistant professor in the Department of Electrical and Computer Engineering at the University of Maryland, have made the first direct measurement that characterizes this exotic physics in a photonic platform. The research was published online Feb. 22 in Nature Photonics. These techniques may be extended to more complex systems, such as one in which strong interactions and long-range quantum correlations play a role.