IQUIST at March Meeting: basic science to novel applications | Part 1

In Minneapolis, no snow was in sight as over 10,000 attendees – physicists and others alike – descended on the city’s convention center for the annual March Meeting, held in the first full week of the eponymous month. The American Physical Society (APS) organizes the March Meeting, the largest conference of its kind in the United States. It focuses on a selection of physics subdomains, including condensed matter physics, materials science, and quantum information theory. These fields encompass the interdisciplinary nature of IQUIST, making the March Meeting the perfect venue for presentations highlighting a selection of the center’s broad research portfolio.

Quantum foundations from condensed matter physics to cryptography

The conference started with several presentations by collaborations involving Fox Family Professor in Engineering Peter Abbamonte. The Abbamonte group studies “elementary collective phenomena in condensed matter [physics].” This work is funded by the DOE-EFRC center on Quantum Sensing and Quantum Materials (QSQM), of which Abbamonte is the Center Director. One goal of QSQM is to “develop and apply nontrivial quantum sensing methods to measure and unravel mysteries associated with three families of quantum materials.” These quantum materials include strange metals (metals with high electrical resistance, a property usually associated with insulators) and topological crystalline insulators (crystal materials in which electrons move only along its surface and not its interior).   

In this context, Abbamonte group graduate student Xuefei Guo presented his talk “Low Energy Charge Fluctuations in a Strange Metal” on Monday. “We presented our measurements on the density response to a strange metal in the low-energy region, which serves as a crucial testbed for theories addressing this complex problem,” Guo explains. Fellow group member and post-doctoral scholar Dipanjan Chaudhuri presented the recently proposed topological crystalline insulator bismuth (“Charge dynamics in elemental bismuth measured with momentum-resolved EELS”).

 

Also supported by QSQM were two additional talks by graduate students Henry Amir and Jack Zwettler, members of the group of Assistant Professor of Physics  Fahad Mahmood. The talks, jointly titled “Development of 2e-ARPES to Measure Correlated Electron Pairs in Unconventional Superconductors,” built on each other.

2e-ARPES is an acronym for two-electron coincidence photoemission spectroscopy. This technique allows the group “to directly probe correlated pairs of electrons to study the internal structure of Cooper pairs in superconductors and other macroscopic quantum phenomena,” says Amir. Cooper pairs are pairs of electrons, which – acting together – are responsible for the phenomenon of superconductivity in certain materials (superconductors) at low temperatures. This, in turn, “will be able to shed a new experimental light on many physical systems of interest, such as unconventional superconductors and strange metals,” Amir adds.

 

Superconductors make great qubits, an area of focus for Assistant Professor of Physics  Wolfgang Pfaff. One of the group’s presentations, “Driven-dissipative preparation of remote entanglement in chiral waveguide quantum electrodynamics,” presented by Abdullah Irfan, focuses on stabilizing entanglement between remote qubits. Entanglement is a critical quantum resource and refers to strong correlations between quantum particles. The phenomenon is a key ingredient for essentially every quantum protocol of interest, but creating and maintaining it is often challenging.

A new approach to stabilizing entanglement, building upon internal and external collaborations, uses driven-dissipative quantum systems, which include repeated excitations of the system and lossy interactions of the qubit with its environment. Specifically, the collaboration “studied how loss affects a driven-dissipative entanglement protocol and used this understanding to extend the protocol to better protect the entangled qubits,” says Irfan. While theoretical, key to the research is its application of the real-life constraints of superconducting qubits and a “fundamental interest in understanding driven-dissipative entanglement.”

 

Entanglement can be investigated across all quantum systems, including in anyons. Anyons are quasiparticles that appear in two- (as opposed to three-) dimensional systems and were first detected experimentally in 2020. This recent discovery has renewed interest in the subject, including work by Professor of Physics Smitha Vishveshwara, who has previously worked on this subject for many years. Vishveshwara’s student Preethi Basani presented at the March Meeting about the “Dynamics and Entanglement Properties of Anyons in the Quantum Hall Bulk.”

In their work, the researchers “were able to quantitatively describe the motion of two anyons in a quadratic potential by borrowing ideas from quantum information theory,” Basani explains. “This work makes connections between the field of quantum information and condensed matter physics and gives new ways of looking at both fields.”

 

Another side of quantum information science research concerns how successful quantum technology can be implemented for cryptographic tasks, that is, to secure communication and information. This work is part of the focus of the group of Associate Professor of Electrical and Computer Engineering  Eric Chitambar, whose graduate student Ian George also presented at the conference. Their international collaboration (“Time-Constrained Local Quantum State Discrimination”) set out to “help with the development of new quantum cryptographic technology,” so George.

Specifically, the researchers examined the “task of quantum state discrimination using local operations and simultaneous classical or quantum communication.” This is the setting of real-life quantum applications like quantum position verification, in which two parties try to verify the position of a third using quantum resources while limited to the operations enumerated above. A successful protocol relies on the verifying parties to send the third messages (either classical or quantum), to which the third party needs to reply accurately and for which it is necessary to distinguish between different quantum states. George explains that his research “developed new methods for analyzing this task.”

 

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End of Part 1. For more reporting on the APS March Meeting be on the look out for Part 2 of this article, as well as other articles.