Faculty

Size and Memory Both Matter in Quantum Computing

With their promise of unimaginable speed and huge capacity, quantum computers stand to revolutionize the world of information processing. They have the potential to be vastly more powerful than our current digital devices, with the ability to solve important computational problems and simulate complex physical systems with unprecedented efficiency.

Quantum computing operates at the subatomic level, where the familiar laws of classical physics don’t apply. A different set of rules—quantum mechanics—comes into play to explain the behavior of matter and energy on the atomic and subatomic scale—in essence, a different reality from the everyday, observable world.

Unlike today’s silicon-based microprocessors that manipulate ones and zeros as bits and bytes, quantum computing uses quantum physics to represent and process information that is stored in quantum bits or “qubits.” A qubit can be a one, a zero, and everything in between, simultaneously, and can be utilized by physical systems as different as the “spin” of an electron in a trapped atom and a semiconductor quantum device.

Quantum Data Storage Breakthrough (Forbes)

A team of researchers from Dartmouth and the University of Sydney has developed a new method to preserve quantum information, reports Forbes.

The inability to preserve information that is error-free has inhibited the development of practical quantum computing, explains Forbes. The new method being developed by scientists at Dartmouth and Sydney could be a breakthrough, the article explains.

Dartmouth’s Lorenza Viola, a professor of physics and astronomy, and Kaveh Khodjasteh Lakelayeh, a research assistant professor, are co-authors of the study, “Designing a Practical High-Fidelity Long-Time Quantum Memory,” published June 19 in Nature Communications.

Forbes notes that in their paper, the researchers write, “Developing techniques for the preservation of arbitrary quantum states—that is, quantum memory—in realistic, noisy physical systems is vital if we are to bring quantum-enabled applications including secure communications and quantum computation to reality.”

Robyn Millan, Dartmouth College

Topic: "Dynamics of Radiation Belt Electrons and the BARREL Experiment" (Video)

Abstract: The intensity of relativistic electrons in Earth's radiation belts is known to be highly variable, but the processes responsible for this variability are still not well understood. Observed rapid depletions and subsequent rebuilding of the trapped particle population imply an efficient energization process, in some cases accelerating electrons to multiple MeV energies on a timescale as short as minutes. NASA's two Van Allen Probes were launched in August 2012 to study the radiation belts. BARREL is a multiple-balloon investigation that works with the Van Allen Probes to study atmospheric loss of radiation belt electrons. The first BARREL balloon campaign was carried out in January-February 2013. Twenty small (~20 kg) balloon payloads were launched from the SANAE IV and Halley VI Antarctic research stations. A second campaign will be carried out next year. This talk will provide an introduction to radiation belt physics, and will summarize early results from BARREL and Van Allen.

Dartmouth Space Physicists Explore Earth’s Radiation Belts

They say that it’s sunspots. That is the typical explanation you hear when your television goes on the fritz or your cellphone quits working or the GPS in your car tells you you’re driving in the middle of the ocean. Certainly, the sun is at the root of your problem, but it’s not simply the sunspots. It’s also the effect that all kinds of solar activity have on the Earth’s magnetosphere.

Yes, Virginia, the Earth has a magnetosphere—which is like a giant magnet with lines of force surrounding our planet. This magnetic field waxes and wanes with surges of activity on the sun, activities that include sunspots as well as more dramatic behavior. Massive bursts of solar wind and magnetic force released by the sun as shock waves into space can wreak havoc on our magnetic environment.

Ryan Hickox, Dartmouth College

Topic: "The beauty of simplicity: Some insights on galaxy and black hole formation"  (Video)

Abstract: Astronomers now have a general picture for how galaxies and supermasive black hole form over cosmic time. However, these objects exhibit a rich and complex phenomenology that can make it challenging to build a clear physical intuition for how this process works in detail. I will give a brief introduction to galaxy and black hole formation, and show that some important aspects of this process can be explained remarkably well with extremely simple physical scenarios based on the underlying growth of dark matter structures and the characteristic timescales for variability. I will focus on the triggering of powerful starburst galaxies, the evolution of the specific star formation rate in galaxies, and the connection between star formation and the growth of black holes, and will present a simple intuitive pictures for these processes that can help us better understand the more complex relevant physics.

A Responsibility to the Next Generation (The New York Times)

In an opinion piece, Stephon Alexander, the Ernest Everett Just 1907 Professor of Natural Sciences and director of Dartmouth’s E.E. Just Program, talks about his responsibility toward younger generations of aspiring scientists who are members of minority groups.

“I feel a deep responsibility to speak and act; I would not be a theoretical physicist today if both black and white scholars had not spoken and acted on my behalf,” Alexander writes.

“All physicists should be on the lookout for talented students who might not have had the best preparation, or whose imaginations might not follow well-trodden paths,” he says. “Many of the greatest minds might not reach their potential without some help from those who have gone before.”

Read the full opinion piece, published 2/4/13 in The New York Times.

Walter E. Lawrence III, Dartmouth College / University of Chicago

Topic: "Quantum Information and the Paradoxes of Physics"  (Video)

Abstract: The paradoxes of Einstein-Rosen-Podolsky (1935), Schrödinger's Cat (1935), and Maxwell's Demon (1867) illustrate how the science of quantum information is changing the way we think about quantum physics, information and the second law. With brief histories of these paradoxes, I will illustrate how all of them became intertwined with quantum information and related advances over the last three decades, and in particular how Schrödinger's Cat and Maxwell's Demon have taken new leases on life.

Lorenza Viola, Department of Physics and Astronomy, Dartmouth College

Topic: "Untangling Entanglement: An Observer-Dependent Perspective"  (Video)

ABSTRACT: Entanglement is one of the most fundamental and yet most elusive properties of quantum mechanics. Not only does entanglement play a central role in quantum information science, it also provides an increasingly prominent bridging notion across different subfields of Physics --- including quantum foundations, quantum gravity, quantum statistical mechanics, and beyond. The property of a state being entangled or not is by no means unambiguously defined. Rather, it depends strongly on how we decide to regard the whole as composed of its part or, more generally, on the restricted ways in which we are able to observe and control the system at hand. I will argue how acknowledging the implications of such an operationally constrained point of view leads to a notion of "generalized entanglement," which is directly based on observables and offers added flexibility in a variety of contexts. Time permitting, I will survey some accomplishments of the generalized entanglement program to date, with an eye towards open problems.

Pages