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We are a theoretical research group working at the interface of quantum optics, quantum information science, and condensed matter physics.
Postdoc and graduate student positions available: email av[group leader's last name]@gmail.com
New Approach to Information Transfer Reaches Quantum Speed Limit
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.
Two (Photons) is Company, Three’s a Crowd
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.