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We all know that diamonds can hold great sentimental (and monetary) value. As luck may have it, diamonds—particularly defective ones, with little errors in their crystal structure—also hold great scientific value. The defects have properties that can only be described by quantum mechanics, and researchers are working on harnessing these properties to pick up on tiny signals coming from individual biological cells. In this episode of Relatively Certain, Dina sits down with defective diamond expert Ronald Walsworth, the founding director of the Quantum Technology Center at the University of Maryland (UMD), as well as Minta Martin professor of electrical and computer engineering and professor of physics at the UMD. Walsworth is also a member of the Institute for Research in Electronics & Applied Physics and a Fellow of the Joint Quantum Institute. Walsworth explains how diamond defects can be used as superb magnetic field sensors and discusses recent strides toward using them to image the insides of individual cells. More details on these advances can be found in two recent publications from Walsworth’s lab. This episode of Relatively Certain was produced by Dina Genkina, Chris Cesare and Emily Edwards. Music featured in this episode includes Picturebook by Dave Depper, The Jitters and Apogee by Metre and Examples by Ketsa, with sound effects by Brian Little. Relatively Certain is a production of the Joint Quantum Institute, a research partnership between the University of Maryland and the National Institute of Standards and Technology, and you can find it on iTunes, Google Play, Soundcloud or Spotify.

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. For instance, sunlight is a mixture of many different colors of light, each bobbing up and down with their own characteristic frequency. But taken together the colors merge into a uniform yellowish glow. A prism, or something like it, can also undo this splitting, mixing a rainbow back into a single beam. Back in the late 1970s, scientists figured out how to generate many colors of light, evenly spaced in frequency, and mix them together—a creation that became known as a frequency comb because of the spiky way the frequencies lined up like the teeth on a comb. They also overlapped the crests of the different frequencies in one spot, making the colors come together to form short pulses of light rather than one continuous beam. As frequency comb technology developed, scientists realized that they could enable new laboratory developments, such as ultra-precise optical atomic clocks, and by 2005 frequency combs had earned two scientists a share of the Nobel Prize in physics. These days, frequency combs are finding uses in modern technology, by helping self-driving cars to “see” and allowing optical fibers to transmit many channels worth of information at once, among others. Now, a collaboration of researchers at the University of Maryland (UMD) has proposed a way to make chip-sized frequency combs ten times more efficient by harnessing the power of topology—a field of abstract math that underlies some of the most peculiar behaviors of modern materials. The team, led by JQI Fellows Mohammad Hafezi and Kartik Srinivasan, as well as Yanne Chembo, an associate professor of electrical and computer engineering at UMD and a member of the Institute for Research in Electronics and Applied Physics, published their result recently in the journal Nature Physics.

Even though quantum computers are a young technology and aren’t yet ready for routine practical use, researchers have already been investigating the theoretical constraints that will bound quantum technologies. One of the things researchers have discovered is that there are limits to how quickly quantum information can race across any quantum device. These speed limits are called Lieb-Robinson bounds, and, for several years, some of the bounds have taunted researchers: For certain tasks, there was a gap between the best speeds allowed by theory and the speeds possible with the best algorithms anyone had designed. It’s as though no car manufacturer could figure out how to make a model that reached the local highway limit. But unlike speed limits on roadways, information speed limits can’t be ignored when you’re in a hurry—they are the inevitable results of the fundamental laws of physics. For any quantum task, there is a limit to how quickly interactions can make their influence felt (and thus transfer information) a certain distance away. The underlying rules define the best performance that is possible. In this way, information speed limits are more like the max score on an old school arcade game than traffic laws, and achieving the ultimate score is an alluring prize for scientists. Now a team of researchers, led by JQI Fellow Alexey Gorshkov, have found a quantum protocol that reaches the theoretical speed limits for certain quantum tasks. Their result provides new insight into designing optimal quantum algorithms and proves that there hasn’t been a lower, undiscovered limit thwarting attempts to make better designs. Gorshkov, who is also a Fellow of the Joint Center for Quantum Information and Computer Science (QuICS) and a physicist at the National Institute of Standards and Technology, and his colleagues presented their new protocol in a recent article published in the journal Physical Review X. 

In this episode of Relatively Certain, JQI Adjunct Fellow Marianna Safronova and JQI Fellow Charles Clark return to discuss the limits of our understanding of gravity, and how new experiments with atom interferometers may be the key to not only a higher-precision understanding of gravity but also possible new physics.