Today marks the 110th birthday of C. S. Wu, who won the Wolf Prize in Physics for her discovery of parity breaking.

We had a length piece on the blog for her birthday last year: https://lecdem.physics.umd.edu/tools-and-resources/lecdem-blog/621-celebrating-the-birthday-of-chien-shiung-wu.html

And another nice article was published today by the Linda Hall Library https://www.lindahall.org/about/news/scientist-of-the-day/chien-shiung-wu

AIP Hisotry has a teaching guide about her work https://www.aip.org/history-programs/physics-history/teaching-guides/chien-shiung-wu-chinese-nuclear-physicist

Demonstration P4-04, the Cosmic Ray Detector, has recently been upgraded. PhD student Liz Friedman shows it in action in this video.

When energetic particles from space hit the upper atmosphere, they create a cascade of particles in the air around us. Even a single cosmic ray might create a whole shower of particles in our atmosphere. They’re invisible, but with the right apparatus we can detect them. Each of the two dark blocks in this device is a scintillator. When a particle passes through one scintillator, it makes a tiny spark of light, which is picked up by a sensitive photodetector. By checking for correlations between the two paddles, we can spot which sparks are being caused by particles passing straight through from space.

These particles stream around and through us all the time, harmlessly; but it’s pretty amazing that we can build a tabletop device that can measure them!

You can read more about Liz’s adventures in physics, hunting neutrinos in Antarctica, in last summer’s Odyssey magazine https://cmns.umd.edu/news-events/features/4642

Lit up on a billboard so everyone sees them in neon

-In Neon, Elton John

For a century, neon lights have been synonymous – even metonymous – with marketing, entertainment, and nightlife. This month marks the 105^th anniversary of neon lighting being patented in the US, so it seems like a good time to explore the physics behind the lights.

Gas discharge lighting uses the ionization of a gas to produce light. An electric field is created in the tube that strips some of the outer electrons from the atoms of the gas in the tube. These free electrons flow towards the positively charged anode on one end of the tube, while the now positively charged atoms flow towards the negatively charged cathode. They collide with other neutrally-charged atoms, exchanging charge and gaining energy from the collisions; when these now higher-energy atoms release this excess energy, they produce light. The color of this light is determined by the structure of the atoms; each produces a distinctive spectrum.

When first created as an experiment, these tubes were filled with a variety of gases, and often burned out quickly. French scientist Georges Claude discovered that using noble gases like neon and argon, which do not react with most other materials, greatly extended their lifespan; and also developed better ways of keeping the electrical power steady in the tube. This made them practical for lighting and signage, and he was able to patent the device;  a patent was approved in the US on January 19, 1914.

Lights like this have been used for many other purposes in the past, as well – many outdoor lamps use gas discharge lighting, though this is now being replaced in many places by more energy-efficient LED lighting. So soon we may only see gas discharge lighting in the laboratory and in artistic applications like these.

We often use straight tubes with a single gas in them in the classroom to demonstrate the spectrum of an element or compound. Many classes have used these when introducing the concept of spectroscopy or when discussing the structure of atoms; check out demonstration N2-05: Diffraction Spectra, which can be used with lightweight diffraction gratings to let every student see the spectrum of some common or popular elements. This has consistently been one of our more popular demonstrations. Less often used, though, are these classic discharge tubes (sometimes called Geissler tubes) found at P3-24. They can be a fun addition to any discussion of ionization and atomic structure.

Despite the common name, many of these signs today aren’t actually filled with neon, but argon; other gases can be used as well. In the pictures here, only one light has the distinctive red glow of neon. Colloquially, though, they tend to all be referred to as “neon lights,” if only because “gas discharge tube light” is hard to fit into a rock lyric.

Welcome back to the Physics Demonstrations Blog! We’re back from the winter deep freeze and here to share more fun ideas about physics. This week, a brief look into the quantum world with electron beams!

The electron is a fundamental particle, one of the earliest discovered in modern physics, which has a small but finite rest mass and carries a negative electrical charge.
However, quantum mechanics has taught us that, under certain circumstances, the electron, which we conventionally think of as a particle, can also behave like a wave.

A stream of electrons traveling through space means a stream of charges is traveling through space – this is, in effect, what an electrical current is. And an electrical current can be deflected by a magnet – so, too, can a beam of electrons. If you hold a magnet near a beam of electrons, like the one in this cathode ray tube, the beam will deflect in a direction perpendicular to the magnetic field.

Likewise, if you run two electrical currents parallel to each other, the electric field of each will deflect the other slightly, which can be seen in either two wires running parallel, or by running a wire parallel to the electron beam.

This beam is made up of electrons; the glow in the screen behind it is made when a few individual electrons passing by interact with the phosphors in the screen.

But what happens if we take that beam and pass it through a narrow opening? Conventionally, if you throw a bunch of particles at a hole, either they pass through in a straight line, or they miss and bounce off. But instead, look what happens when we do it with electrons:

The electrons are not passing through in a straight line, but instead are diffracting, forming a pattern of rings. This is an interference pattern formed by the interaction of the peaks of a wave. We can see this frequently when light passes through a narrow opening, forming such a pattern.

But here, it is being formed by electrons – very small particles, but particles nonetheless. Thus, here we see an electron behaving as a wave.

We love our demonstrations, but there are some things you can’t easily demonstrate in the classroom, either because the physics isn’t compatible with that environment, or because the scale is beyond what we can practically see. This is where simulations can be valuable, in letting us go beyond what we can do on the tabletop and look inside the black boxes. 

The quantum nature of the hydrogen atom is a good example. We can demonstrate the emission spectrum of hydrogen with the Balmer Series demonstration P3-51, and we have simple models of electron orbitals for more complex atoms, but how can we look at the structure of the hydrogen atom itself?

Here are some simulations available for looking inside our smallest atom.

• Falstad offers this illustration of the energy levels of the hydrogen atoms, which allows you to switch the view between the Bohr and Dirac models within a single active diagram https://www.falstad.com/nw/hydrogen.html

• The PhET model hydrogen atom lets you compare different historical models of the atom to simulated experimental results https://phet.colorado.edu/sims/cheerpj/hydrogen-atom/latest/hydrogen-atom.html?simulation=hydrogen-atom

• Andrew Duffy’s Emission Spectra simulator lets you compare the hydrogen spectrum with other visible spectra side-by-side with the full white light spectrum, for orientation http://physics.bu.edu/~duffy/HTML5/emission_spectra.html

• This more complex Falstad simulator lets you display the wave functions/orbitals in either real or complex modes, and to take slices along the axes as well as viewing them in three dimensions. This is potentially valuable for upper level courses analyzing the orbital structure. http://www.falstad.com/qmatom/

This spring brings another development in AMO physics. A German research team reports successfully carrying out atom interferometry in a Bose-Einstein Condensate in a microgravity environment using sounding rockets.

 Interferometry uses the interaction of waveforms to make ultrafine measurements. We do this routinely in demonstrations using light waves, but atom interferometry uses the wavelike characteristics of atoms themselves.

Read more:

Lachmann et al (2021), Ultracold atom interferometry in space, Nature Communications 12

https://www.nature.com/articles/s41467-021-21628-z

Padavic-Callaghan (2021), Ultracold Quantum Collisions Have Been Achieved in Space for the First Time, Scientific American

https://www.scientificamerican.com/article/ultracold-quantum-collisions-have-been-achieved-in-space-for-the-first-time/

Dataset for the manuscript "Ultracold atom interferometry in space" at Leibniz Universität Hannover

https://data.uni-hannover.de/dataset/08b693d2-bf35-4d6b-8914-d3a7c41f5489

Alicia Kollár, Assistant Professor of Physics and JQI Fellow, has received the National Science Foundation’s Faculty Early Career Development Award. This NSF program recognizes scientists making important advances in both research and education.

Kollár’s research will be studying photon behaviour in superconductor circuits, a potential part of quantum computing systems. She will also be developing online outreach programs to introduce more people to the wonders of quantum physics.

Read More:

• news at UMD Physics https://umdphysics.umd.edu/about-us/news/department-news/1715-kollar-career.html

• news at JQI https://jqi.umd.edu/news/kollar-receives-national-science-foundation-career-award

• Kollár Research Group at JQI https://groups.jqi.umd.edu/kollar/

On September 22, Prof. Bill Phillips and Dr. Laurie Loccascio will present a virtual fireside chat, “Quantum Basics for the Curious.” This event, hosted by the Mid-Atlantic Quantum Alliance, will explore Prof. Phillips’ research and how he came to win the Nobel Prize, an introduction to quantum mechanics, and the future of quantum physics and technology.

The Mid-Atlantic Quantum Alliance launched in January with a ceremony in Annapolis; and focuses on cross-disciplinary collaborations in quantum technology. The MQA consortium includes UMD and other USM institutions, and other academic, government, and industrial research centers.

Read more:

• Event announcement: “Quantum Basics for the Curious” September 22

• Mid-Atlantic Quantum Alliance Homepage

• MQA launch announcement, January 2020

A new article in the National Academy of Inventors journal Technology and Innovation highlights commercial spin-offs of UMD research. The article explores both new exploratory startups, and some already fully active and profitable, and talks about the strategies behind their success. Among the firms profiled is IonQ, the quantum computing company cofounded by UMD Physics’ own Prof. Chris Monroe

The authors, Julie Lenzer and Piotr Kulczakowicz, are respectively UMD’s Chief Innovation Officer and UM Ventures’ Senior Innovation Manager.

Read more

• news release from the UMD Division of Research

• “Fueling Spin-offs” at Technology & Innovation