Professors Jain and Sochnikov received NSF research grant entitled “New Quantum Elastocaloric Demagnetization Refrigeration for the Millikelvin Range”. A major focus of their research will be the cooling of quantum chips. For this purpose, their teams will study ‘spin liquids’, which can be harnessed to achieve millikelvin temperatures without magnetic fields. At such low temperatures, […]
Associate Professor of Physics Menka Jain and the Institute of Materials Science is co-organizing a workshop-28th International Workshop on Oxide Electronics (IWOE) in Maine next month. The IWOE series has become an important venue to discuss recent advances and emerging trends in this developing field. The aim of the workshop is to provide an interdisciplinary […]
The James Webb Space Telescope released its first science observations on July 12 with much fanfare and excitement across the globe. UConn Physics Professor Jonathan Trump is part of the Cosmic Evolution Early Release Science collaboration that was awarded some of the first observations on the transformative new space telescope. Prof. Trump was interviewed by several local media outlets, […]
Professor Cara Battersby has been awarded an NSF CAREER grant! “The Faculty Early Career Development (CAREER) Program is a Foundation-wide activity that offers the National Science Foundation’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the […]
UConn is now home to tools that have played an instrumental role in mapping the universe — 10 large aluminum plates used as part of the Sloan Digital Sky Survey (SDSS). Measuring 32 inches across, one-eighth of an inch thick, and with thousands of tiny holes drilled in them, these plates may not be the […]
UConn’s collaboration with the Department of Defense Air Force Research Laboratory (AFRL) is launching a new project. It is titled Multiscale Modeling and Characterization of Metamaterials, Functional Ceramics and Photonics. This is a $4.7 M contract with $1M for Physics. The project’s goal is to explore and advance the understanding of electronic, photonic, magnetic, and […]
The article The Largest Suite of Cosmic Simulations for AI Training Is Now Free to Download; Already Spurring Discoveries describe research of a team of astrophysicists that includes UConn Professor of Physics Daniel Anglés-Alcázar. “Machine learning is revolutionizing many areas of science, but it requires a huge amount of data to exploit,” says Anglés-Alcázar. “The […]
UConn Physics Professor Jonathan Trump is part of a group of scientists who will be the first to conduct research using the James Webb space telescope. The local Fox News TV station conducted an interview with Prof. Trump.
On Friday December 3rd, a group of U.S. Senators, Richard Blumenthal (D-CT), Edward J. Markey (D-MA), Marco Rubio (R-FL), Elizabeth Warren (D-MA), and Rick Scott (R-FL) introduced a bipartisan a resolution to recognize the significant scientific, educational, and economic contributions made by the Arecibo Observatory telescope. “The telescope at Puerto Rico’s Arecibo Observatory was a […]
Chiara Mingarelli, Assistant Professor of Physics at UConn, is the lead researcher on a $650,000 Collaborative Research Grant from the National Science Foundation, half of which is earmarked for UConn, to conduct an experiment to prove the existence of supermassive black hole binaries. This grant will combine, for the first time, traditional astronomy with gravitational […]
UConn Physics graduate student Mohammed (Mo) Akhshik works on data gathered using the Hubble Space Telescope (HST) and has led to exciting discoveries, some while he served as the science Principle Investigator of the REQUIEM HST program from which he is co-author on two publications, one in Nature and one in Nature Astronomy. Akhshik is also […]
At the center of galaxies, like our own Milky Way, lie massive black holes surrounded by spinning gas. Some shine brightly, with a continuous supply of fuel, while others go dormant for millions of years, only to reawaken with a serendipitous influx of gas. It remains largely a mystery how gas flows across the universe […]
Prof. Emeritus Winthrop Smith and former student Prof. Douglas Goodman (Quinnipiac University) Edit Special Issue of Open Access Journal Atoms, on Low Energy Interactions between Ions and Ultracold Atoms The Special Issue of the online journal Atoms is a collection of current peer-reviewed articles by experts in the field of ultracold collisions and reactions involving […]
The Physics Department welcomes our newest faculty member, Dr. Anh-Thu Le, although he prefers to be called simply AT. AT worked for many years at the well-known James R. Macdonald Laboratory, rising to the rank of Research Professor. He worked alongside a world-known theorist, Dr. Chii-Dong Lin. Dr. Le went on to become an Assistant […]
Professor Andrew Puckett’s research group is currently leading, as part of a collaboration of approximately 100 scientists from approximately 30 US and international institutions, the installation in Jefferson Lab’s Experimental Hall A of the first of a series of planned experiments known as the Super BigBite Spectrometer (SBS) Program, with beam to Hall A tentatively […]
Physics major Nicole Khusid, a rising senior at UConn, was featured in a UConn Today article about her research. Nicole has been working on gravitional lensing of distant sources of gravitational waves, seeking to understand their multimessenger signals and detectability by future astrophysics facilities. Nicole was awarded a SURF (Summer Undergraduate Research Fund) award to […]
It seems that the muon, a heavier partner of the electron, may be breaking what have been understood as the laws of physics. The findings announced on April 7th were met with excitement and speculation at what this might mean. UConn physics researchers Professor Thomas Blum and Assistant Professor Luchang Jin helped pioneer the theoretical physics behind the findings.
Professor Cara Bettersby’s research is featured in the article “The Study of Big Data: How CLAS Researchers Use Data Science” published by UConn Today. Prof. Battersby’s work focuses on describing and studying the center of the Milky Way galaxy, which she calls an “experimental playground” for the distant cosmos. Her work described the spectroscopy of […]
New Physics PhD graduate Yasaman Homayouni is featured in a story on the class of 2021 from the College of Liberal Arts and Sciences (CLAS). For the full story of what inspired Yasaman and other students during their time at UConn, see the article in UConn Today.
Mark Rayner/CERN The Fermilab E989 experiment announced the first new result on the muon’s anomalous magnetic moment in almost 20 years. The new measurement, combined with Brookhaven’s E821, has increased the discrepancy with the Standard Model value to 4.2 standard deviations. UConn Professors Tom Blum and Luchang Jin explain the theory calculations in a feature […]
I will discuss experiments and calculations that demonstrate long lived electronic coherences in molecules using a combination of measurements with shaped octave spanning ultrafast laser pulses, 3D velocity map imaging and calculations of the light matter interaction. Our pump-probe measurements prepare and interrogate entangled nuclear-electronic wave packets whose electronic phase remains well defined despite vibrational motion along many degrees of freedom. The experiments and calculations illustrate how coherences between excited electronic states survive even when coherence with the ground state is lost, and may have important implications for light harvesting, electronic transport and attosecond science.
Fully Consistent NLO Calculation of Forward Single-Inclusive Hadron Production in Proton-Nucleus Collisions
We study the single-inclusive particle production from proton-nucleus collisions in the dilute-dense framework of the color glass condensate (CGC) at next-to-leading order (NLO) accuracy. In this regime, the cross section factorizes into hard impact factors and dipole-target scattering amplitude describing the eikonal interaction of the partons in the target color field. For the first time, we combine the NLO impact factors with the dipole amplitude evolved consistently using the NLO Balitsky-Kovchegov (BK) equation with the initial conditions fitted to HERA structure function data.
The resulting neutral pion cross section with all parton channels included are qualitatively consistent with the recent LHCb measurement. In particular, the NLO evolution coupled to the leading order impact factor is shown to produce a large Cronin peak that is not visible in the data, demonstrating the importance of consistently including NLO corrections to all the ingredients. Furthermore, the transverse momentum spectrum is found to be sensitive to the resummation scheme and the running coupling prescription in the BK evolution. This demonstrates how additional constraints for the initial condition of the BK evolution can be obtained from global analyses including both the HERA and LHC data. In light of the upcoming upgrades to the LHC, the dependence of our results on rapidity will also be discussed.
Scattering amplitudes are the arena where quantum field theory meets particle experiments, for example at the Large Hadron Collider where the copious scattering of quarks and gluons in quantum chromodynamics (QCD) produces Higgs bosons and many backgrounds to searches for new physics. Particle scattering in QCD and other gauge theories is far simpler than standard perturbative approaches would suggest. Modern approaches based on unitarity and bootstrapping dramatically simplify many computations previously done with Feynman diagrams. Even so, the final results are often highly intricate, multivariate mathematical functions, which are difficult to describe, let alone compute. In many cases, the functions have a “genetic code” underlying them, called the symbol, which reveals much of their structure. The symbol is a linear combination of words, sequences of letters analogous to sequences of DNA base pairs. Understanding the alphabet, and then reading the code, exposes the physics and mathematics underlying the scattering process, including new symmetries. For example, the two scattering amplitudes that are known to the highest orders in perturbation theory (8 loops) are related to each other by a mysterious antipodal duality, which involves reading the code backwards as well as forwards. A third scattering amplitude, which contains both of these as limits, has an antipodal self-duality which “explains” the other duality. However, we still don’t know `who ordered’ antipodal (self-)duality, or what it really means.
Multimode cavity control of ferroelectric fluctuations
Electromagnetic cavities and metamaterials have been used to great effect in the field of AMO physics and electrical engineering. By shaping the spatial, spectral, or polarization characteristics of the electromagnetic environment, the coherent interaction between light and matter can be focused and amplified, leading to phenomena such as lasing, the Purcell effect, the Casimir effect, and superradiance. In this talk I will show how these ideas may be extended and applied to solid state quantum materials. In particular, I will consider polarization fluctuations in a quantum paraelectric insulator, and consider their coupling to a Fabry-Perot type optical cavity. By using the full multimode continuum description of the system, I will show how the ferroelectric fluctuations respond in a local, spatially resolved manner. The presence of the cavity indeed is shown to renormalize the soft-mode frequency, with effects primarily confined to the surface, and thus for thin films this effect can be pronounced. The temperature dependence shows this effect only onsets at low temperatures, indicating its origin from quantum electrodynamics effects – in close analogy with the Casimir effect.
The field of circuit QED has emerged as a rich platform for both quantum computation and quantum simulation. These systems exhibit a high degree of both spatial and temporal control which can be used to create synthetic lattice systems. Spatial lattices can be formed using periodic arrays of resonators. Combined with strong qubitphoton interactions, these systems can be used to study dynamical phase transitions, many-body phenomena, and spin models in driven-dissipative systems. I will show that lattices of coplanar waveguide (CPW) resonators permit the creation of unique devices which host photons in curved spaces, gapped flat bands, and novel forms of qubit-qubit interaction [1,2]. I will show that graph theory is the natural language for describing these microwave photonic systems and present preliminary data on the development of a new generation of CPW lattice devices with unconventional band structures. Periodic modulation in superconducting-qubit systems also provides a route to Floquet systems with topological band structures. I will present preliminary experimental steps toward the realization of a topological energy pump which can “boost” smaller non-clalssical states of light into larger ones [3].
[1] A. J. Koll´ar et al., Nature 45, 571 (2019).
[2] A. J. Koll´ar et al., Comm. Math. Phys. 376, 1909 (2020).
[3] D. Long et al., Phys. Rev. Lett. 128, 183602 (2022).
The continuously improving performance of quantum sensors is enabling the exploration of fundamental physics with unprecedented precision. Notable examples of these systems include optical atomic clocks and atom interferometers, which are among the most precise devices ever invented by humankind. As a result, they are increasingly utilized in the search for new physics. The application of Atomic, Molecular, and Optical (AMO) Physics techniques to such inquiries in the realm of nuclear physics has been gaining attention in the current decade. The level of control and precision achievable in AMO tabletop experiments, especially with ultracold atoms, enhances the measurement capabilities in complex experimental systems that pursue tests of fundamental physics and symmetries, the search for the electron electric dipole moment (eEDM), and physics beyond the standard model. In this talk, I will explain how incorporating entanglement into these systems can further improve their measurement capabilities. Additionally, I will discuss several proposals that employ laser-cooled atoms and molecules in the search for physics beyond the Standard Model.
Prof. Tigran Sedrakyan, University of Massachusetts Amherst
Moat-band physics and emergent excitonic topological order in correlated electron-hole bilayers”
The role of the particle-particle interaction becomes increasingly important if the spectral band structure of a free system has increasing degeneracy. Ultimately, it will be the role of interactions to choose the state of the system. Examples include the systems with the lowest band having a degenerate minimum along a closed contour in the reciprocal space – the Moat. Any weak perturbation can set a new energy scale describing the state with qualitatively different properties in such a limit of infinite degeneracy. In this talk, I will discuss the general principles behind the universal properties of correlated bosons on moat bands, which host topological order with long-range quantum entanglement. In particular, I will discuss moat-band phenomena in shallowly inverted InAs/GaSb quantum wells, where we observe an unconventional time-reversal-symmetry breaking excitonic ground state under imbalanced electron and hole densities. I will show that the strong frustration of the system leads to a moat band for excitons, resulting in a time-reversal-symmetry breaking excitonic topological order, which explains all our experimental observations.
Daniel Norman, Department of Physics, University of Connecticut
The Complex Analytic Properties of Bandwidth Limited Signals and their Application to Conformal Cosmology and Signal Processing
Conformal gravity is an alternative theory of gravity derived from the conformally invariant Weyl squared action as opposed to the standard Einstein-Hilbert action. The general equations of conformal gravity were applied to the cosmological scale to create a theory of Conformal Cosmology where the geometry of space-time is described by first order fluctuations on a conformal-to-flat background of constant negative curvature. The differential equations of this cosmological model have solutions in terms of Legendre functions with complex degree and order. In order to calculate the multipole expansion of Cosmic Background Radiation (CMB) anisotropy within this model, it is necessary to integrate the Legendre function solutions with respect to their complex degree. An analytic method for solving this integration problem was developed which makes use of the fact that the Legendre functions are Bandwidth Limit Signals (BLS’s) which are functions with a finite domain in frequency space. A general analysis of the properties of BLS’s in the complex plane was done which has yielded new theorems and expansion formulas applicable to all BLS’s as well as to other related families of complex functions. These results have both specific applications to Conformal Cosmology as well as broader applications to the field of signal processing. The methods of complex integration developed in this work, initially for the purpose of computing the CMB anisotropy in Conformal Cosmology, have been used to provide a novel solution to the infamous Borweinn integral as well as a novel proof of the Nyquist-Shannon sampling theorem.
Post-Nobel Award on attosecond Science – Challenges and opportunities in the field going forward
It is an exciting month for the attosecond and strong-field physics communities after the announcement of the three Nobel Laureates earlier. How will this field evolve going forward? While it is very attractive to talk about the shortest light pulses to the general public, and even to the physical science community, the field still faces great challenges but also opportunities. I will “talk” about the challenges and will share with you some of the recent progress toward developing theories that can be compared to experiments.
Prof. Cyrus Dreyer, Stony Brook University and Flatiron Institute
Nonadiabatic lattice dynamics in metals and magnets
In electronic structure theory, lattice vibrations are usually treated under the Born-Oppenheimer approximation, where electronic degrees of freedom are assumed to be fast compared to nuclear dynamics. However, going beyond this adiabatic approximation is necessary in many situations for an accurate description of phonons, and their effects on materials properties. I will discuss two such cases. The first case involves Born effective charges, which are crucial to understanding, e.g., ferroelectric polarization, phonon dispersions in ionic insulators, electron-phonon scattering, dielectric screening, electromechanical coupling, and optical spectra in the IR/THz regime. Via density-functional perturbation theory (DFPT) calculations, I will show that going beyond the adiabatic approximation extends the definition of Born effective charges from insulators to conducting systems and relates them to a seemingly unrelated fundamental property of metals: the Drude weight. The second case I will discuss is the coupling of magnetism and phonons in materials. Specifically, I will demonstrate a DFT-based methodology for including the velocity-dependence of interatomic forces, which explicitly accounts for time-reversal symmetry breaking in the nuclear equations of motion. I will show that in some magnetic materials, such as CrI3, the assumption of adiabatic separation between electron and nuclear dynamics breaks down completely due to the role of (slow) spin dynamics in the coupling between phonons and the magnetic order.
Dr. Romain Vasseur, University of Massachusetts Amherst
Learning global charges from local measurements
Monitored random quantum circuits (MRCs) exhibit a measurement-induced phase transition between area-law and volume-law entanglement scaling. In this talk, I will review the physics of such entanglement transitions, and discuss the current status of this field as well as recent experimental realizations. I will argue that MRCs with a conserved charge additionally exhibit two distinct volume-law entangled phases that cannot be characterized by equilibrium notions of symmetry-breaking or topological order, but rather by the non-equilibrium dynamics and steady-state distribution of charge fluctuations. These include a charge-fuzzy phase in which charge information is rapidly scrambled leading to slowly decaying spatial fluctuations of charge in the steady state, and a charge-sharp phase in which measurements collapse quantum fluctuations of charge without destroying the volume-law entanglement of neutral degrees of freedom. I will present some statistical mechanics description of such charge-sharpening transitions, and relate them to the efficiency of classical decoders to “learn” the global charge of quantum systems from local measurements.
Dr. Sandra Beauvarlet, UConn and PULSE, SLAC National Laboratory
Attosecond X-ray pulse pair generation at SLAC- LCLS X-ray Free Electron Laser and application to probe ultrafast electron dynamics in aminophenol
I will present in this AMO seminar general notions about how Free Electron Laser (FEL) work and will present some of the characteristics and more recent developments at the SLAC X-ray FEL light source. I will discuss the key advances to reach the sub-fs timescale enabling the production of isolated attosecond X-ray pulses but also the generation of attosecond X-ray pulse pairs with controllable delays. These pulses open the way to pump-probe measurements of ultrafast dynamics with attosecond temporal resolution and angstrom spatial resolution due to the X-ray nature of the light produced. Going from a more technical development perspective to an experimentalist vision, I will report on two examples of attosecond X-ray pump - attosecond X-ray probe measurements conducted on gas phase Aminophenol molecules (C _{6} H _{7} NO). The first one relies on carbon K-shell ionization and the effect of post-collision interaction (PCI). The second one relies on X-ray absorption spectroscopy to probe charge migration across the molecules on a sub-10 fs timescale.
The search for Majoranas in the context of topological quantum computing has led to remarkable progress in quantum materials and measurement technologies over a short period of just over a decade. Although topological Majoranas remain to be definitively observed, Majorana-like quantum states derived from part-semiconductor/part-superconductor parents already exist and feature sophisticated control and measurement capabilities. While this research is heavily motivated and driven by its potential applications, most notably by Microsoft, I will focus on how these new quantum platforms can help answer fundamental physics questions. I will discuss how the development of the planar Josephson junction platform for topological superconductivity allowed novel physics discoveries such as the Josephson diode effect [1], Andreev rectification [2], and phase-controlled Josephson vortices [3] - all by designing experiments that are impossible in conventional Josephson junctions. Surprisingly (or not), all these effects have topological counterparts, producing distinctive signatures in the topological regime. Careful study of these signatures in over 10 devices provide support for intermediate-disorder topological superconductivity [4]. Although not mature enough for a topological quantum processor, these relatively disordered devices may help solve open physics problems from the detection of Cooper pair entanglement to non-abelian quantum statistics on the road towards the dream of pristine topological superconductivity.
Filming ultrafast chemical reactions in real-time – from coherent motion to roaming dynamics
Upon photoexcitation, molecules can undergo different types of transformations such as simple vibrations or rotations, but also migrations, or dissociations. Due to the required combination of ultrafast time-scales and ultra-small length-scales involved, specific tools are required to follow such reactions in real-time. Here, we are using time-resolved Coulomb explosion imaging (CEI) as the ultrafast tool to image such dynamics. With CEI, we can not only image coherent molecular dynamics such as proton migration in acetylene; it also works for various dissociation pathways, even if they occur differently from one molecule to another.
In the formaldehyde molecule, we can see fragments following the direct, conventional dissociation path, as well as fragments deviating from this minimum energy path. So-called roaming fragments or “roamers” explore the potential energy landscape in a statistical manner and were directly captured in real-time, despite the signal’s statistical character. This is possible due to the single-molecule sensitivity of CEI. In addition to the first direct observation of roaming fragments undergoing dynamics, we could show that the onset of roaming occurs actually several orders of magnitude earlier than previously expected. We thus show that CEI provides the means to extract new, unexpected pathways, which would otherwise remain hidden underneath a strong background.
Provakar Datta, Department of Physics, University of Connecticut
Probing the Neutron’s Internal Structure via High-Q2 Electromagnetic Form Factor Measurements
The electromagnetic form factors (EMFFs) are among the most basic observables sensitive to the nucleon’s internal structure. Knowing their values with high precision in a wide range of squared four-momentum transfer (Q2) is essential for the advancement of QCD. The high Q ^{2} precision data of the nucleon EMFFs are scarce due to the challenges associated with such measurements. However, the Super BigBite Spectrometer (SBS) collaboration is currently running multiple experiments in Jefferson Lab’s experimental Hall A to precisely measure the proton and neutron EMFFs with unprecedented Q ^{2} reach, which will vastly improve the situation. In this talk, I will give an overview of the SBS high Q ^{2} program with a focus on the SBS-GMn experiment. SBSGMn, the very first SBS experiment, was completed during Oct. 2021 - Feb. 2022 running period to measure the neutron magnetic form factor (GnM) up to Q ^{2} = 13.6 (GeV/c) ^{2} using “ratio” method. I will briefly discuss the underlying theory, measurement technique, associated technical challenges, and present our progress of physics analysis including preliminary data/MC comparisons. I will also show realistic projections of the final uncertainties on GnM, emphasizing the high-Q ^{2} data points.
Condensed-matter systems provide alternative “vacua” exhibiting emergent low-energy properties dramatically different from those of the standard model. A case in point is the emergent quantum electrodynamics (QED) in the family of magnetic materials known as quantum spin ice. The emergent QED possesses many features familiar from our universe, such as charges, anti-charges and photons, but also
many unfamiliar one, such as magnetic monopoles. Thus these magnetic insulators provide a laboratory for exploring effective QED in regimes quite inaccessible to traditional Maxwell electromagnetism.
In this talk, I will review the beautiful picture of how QED emerges in these frustrated magnets when quantum fluctuations cause the spins to fractionalize into spinons – and what this has to do with ice and pyrochlore materials. We will then turn to several results regarding its fine structure. We will see that the fine structure constant – the dimensionless coupling which controls the interactions between
emergent light and charges – generically takes values ~0.1 in quantum spin ice, much larger than the \(\alpha\) ~ 1/137 of our universe [1]. This leads to a variety of predictions regarding the coherent dynamics of the spinons which we expect can be probed by neutron scattering [2]. Finally, we will consider how true electric fields couple into this magnetic insulator – and may permit the indirect observation of
the emergent magnetic monopole and a curious inverted Lorentz force [3].
Entanglement measures in scattering and the S-matrix Bootstrap
Quantum information theory has been instrumental in offering new
insights into old physics problems. In this talk, I shall use it to
study 2-2 scattering in quantum field theories[1], defining the
Entanglement entropy and the relative entropy in this setting. I will
evaluate these measures for theories like φ4, chiral perturbation
theory ( χP T ), etc. Using known bounds on the differential elastic
cross section, I will argue a general bound on relative entropy at
high energy. I will also find definite sign properties of relative
entropy that shall help constrain the S-matrix Bootstrap. Reviving the
old 1960s effort to study Quantum field theory using S-matrices, the
S-matrix bootstrap is a recent attempt to study S-matrices
numerically. I will briefly describe the bootstrap methods and how
relative entropy becomes helpful in this study. These constraints help
isolate S-matrices, which have leading Regge trajectory compatible
with experiments[2].
[1] A. Bose, P. Haldar, A. Sinha, P. Sinha, and S. S. Tiwari,
“Relative entropy in scattering and the
S-matrix bootstrap,” SciPost Phys. 9, 081 (2020),arXiv:2006.12213 [hep-th]
[2]A. Bose, A. Sinha, and S. S. Tiwari, “Selection rules for the
S-Matrix bootstrap,” SciPost Phys. 10, 122 (2021),arXiv:2011.07944
[hep-th].
From driven nanoscale dynamics to macroscopic properties in quantum materials
In quantum materials, coexistent degrees of freedom such as spin, charge, and lattice respond in concert to various external stimuli including light and electrical current. Understanding the interactions between these degrees of freedom and stimuli promises advances in technology from next-generation electronics to energy storage. From coexistent emergent phases and far-from-equilibrium states to topological defects and nanomaterial morphology, nanostructural heterogeneities in space and time connected to crystal lattice commonly underpin the material behavior. Breakthrough coherent X-ray scattering techniques at novel X-ray sources capture nanoscale changes in lattice in-situ to connect them to macroscopic properties. Precise control over lattice dynamics by photoexcitations on sub-picosecond timescales sheds light on interaction between lattice dynamics and electronic order in chromium, an archetypal density wave material. In Mott insulators, nanoscale measurements reveal novel hierarchy and transition behavior of heterogeneities during metal-insulator transitions. Unique capabilities of coherent X-ray science offer us glimpses into the physics of phase transition in quantum materials and future design possibilities.
Prof. George Gibson, Department of Physics, University of Connecticut
The influence of molecular structure on strong-field interactions and the problem of coupling three electrons
1D 1-electron models explain a surprising amount of phenomena in the strong-field interaction with atoms and molecules, such as ionization rates, enhanced ionization at a critical internuclear separation, and high-harmonic generation. 1D 2-electron models predict multielectron phenomena, such as enhanced multiphoton susceptibilities leading to strong multiphoton excitation. In this talk, we examine 1D 3-electron systems to address the possibility of direct inner-orbital ionization. Indeed, an old question of excitation through inner-orbital ionization, versus a two-step process, in which ionization is followed by excitation can finally be answered. Based on symmetry arguments, we show unambiguously that direct inner-orbital ionization is possible.
Prof. P. Mannheim, Department of Physics, University of Connecticut
Normalization of the vacuum and the ultraviolet completion of Einstein gravity
Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Minkowski path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be PT-symmetric. And when one continues the theory into the complex plane and uses the PT-symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Minkowski path integral now is well behaved, and the theory now can serve as a low energy effective theory. Consequently, the theory can now be offered as a fully consistent, unitary, and renormalizable theory of quantum gravity.
Graduate student Phi-Hung Tran, Department of Physics, University of Connecticut
An accurate semiclassical method for constructing photoelectron momentum distribution for atoms and molecules in intense lasers
We propose a version of the semiclassical method based on the Herman-Kluk propagator combined with the strong-field approximation for atoms and molecules in intense lasers. Here we illustrate the application of the method for calculation of photoelectron momentum distribution (PMD) for different atoms (H, Ar, Ne, and Xe) in intense few-cycle laser pulses. We show that the constructed PMDs agree very well with the exact numerical solutions of the time-dependent Schrödinger equation. We further show that our method provides a clear physical interpretation for the validity of the factorization of the recollision process. In contrast to the common belief that there are two paths, so-called long and short trajectories, we found that there are typically multiple trajectories that lead to a given final momentum in the high-energy region. Accurate phases of those trajectories are needed to obtain correct interference patterns in the PMD. Our method can be used to extend current capabilities of laser-induced electron diffraction and other ultrafast imaging and strong-field spectroscopic techniques.
Prof. Michael Lublinsky, Department of Physics, Ben-Gurion University
Magnetic monopole in chiral plasma
Chiral anomaly induces qualitatively new transport phenomena in finite temperature plasma of massless fermions. In the first part of the talk, we will explore the effect of a magnetic monopole inserted into chiral plasma. Next, we will present various novel anomaly induced phenomena discovered in a holographically defined model.
Fatma Aslan, University of Connecticut
Basics of factorization in a scalar Yukawa field theory
The factorization theorems of QCD apply equally well to most simple quantum field theories that require renormalization but where direct calculations are much more straightforward. Working with these simpler theories is convenient for stress testing the limits of the factorization program and for examining general properties of the parton density functions or other correlation functions that might be necessary for a factorized description of a process. With this view in mind, we review the steps of factorization in a real scalar Yukawa field theory for both deep inelastic scattering and semi-inclusive deep inelastic scattering cross sections. In the case of semi-inclusive deep inelastic scattering, we illustrate how to separate the small transverse momentum region, where transverse momentum-dependent parton density functions are needed, from a purely collinear large transverse momentum region, and we examine the influence of subleading power corrections. We also review the steps for formulating transverse momentum-dependent factorization in transverse coordinate space, and we study the effect of transforming to the well-known scheme. Within the Yukawa theory, we investigate the consequences of switching to a generalized parton model approach and compare it with a fully factorized approach. Our results highlight the need to address similar or analogous issues in QCD.
Dr. Leonardo Civale, Los Alamos National Laboratory How to improve the critical currents in REBa_{2}Cu_{3}O_{7} films and coated conductors by tailoring pinning centers Superconductivity was discovered more than a century ago. The possibility to carry electrical currents without dissipation immediately suggests attractive technological opportunities, but in practice, the very low temperatures required to operate conventional superconductors limited their use to rather limited applications. Three properties of a superconductor that are obviously desirable for applications are high critical temperature (T_{c}), large upper critical field (H_{c2}), and strong pinning. The arrival of the cuprate high T_{c} superconductors represented a huge improvement in the first two conditions. However, the large influence of thermal fluctuations in these materials (orders of magnitude stronger than in conventional superconductors) produces new vortex liquid phases where vortex pinning vanishes, reducing the magnetic field range useful for applications, and induces fast detrimental dynamics in the solid phases (flux creep) that effectively reduces the critical current density (J_{c}). In this talk, I will focus on REBa_{2}Cu_{3}O_{7} films and coated conductors (where RE=Y, rare earth, or a combination of them). These systems exhibit the highest J_{c} in any known superconductor, making the study of their vortex matter relevant both from fundamental and technological perspectives. Large efforts from many research groups have succeeded in enhancing Jc even further, either by the incorporation of non-superconducting second phases (in the form of self-assembled nanorods or randomly dispersed nanoparticles) or by particle irradiation. I will present our studies aimed at tuning the pinning landscapes for in-field J_{c} optimization. Finally, I will discuss the effects of thermal fluctuations. Research supported by US DOE, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering
Dr. Nobuyuki Matsumoto, Brookhaven National Lab
Possible use of trivializing maps as a coarse-graining map
In lattice calculation of quantum field theory, we encounter the infamous critical slowing down when approaching the continuum limit. Luscher in 2009 proposed to use a trivializing map in numerical simulations that map a gauge theory to its strong coupling limit. As the gauge configurations can be generated efficiently in the strong coupling, this method can potentially resolve the critical slowing down. However, the original algorithm was tested and asserted to have a fair amount of overhead eliminating the gain [Engel-Schaefer 2011]. This work considers how we can redesign the map so that one overcomes this practical difficulty. In this talk, I report an exploratory effort to use local trivializing maps as a coarse-graining map. The coarse-graining map allows us to use the effective action we obtain after integrating local degrees of freedom. The method is applied to a toy model of 2D U(1) pure gauge theory, for which we can see the gain at least in the unit of Monte Carlo steps.
Dr. En-Hung Chao, Columbia University
The anomalous magnetic moment of the muon from Lattice QCD with coordinate-space formalisms
The discrepancy between the experimentally measured value for the anomalous magnetic moment of the muon (\(a_\mu\)) and the Standard Model prediction is a long-standing puzzle in modern particle physics. As of the theory consensus reached in 2020, the tension lies at the 4.2-\(\sigma\) level. Currently, the theory uncertainty is dominated by hadronic contributions. The two most relevant categories of such contributions are the Hadronic Vacuum Polarization (HVP) and the Hadronic Light-by-Light (HLbL), starting at the second and third order in the fine structure constant respectively. Over the past years, Lattice Quantum Chromodynamics (LQCD) has been successfully applied to determine the HVP and the HLbL contributions and the estimates are being continuously improved. With these updates, tensions emerge between LQCD and the data-driven methods, based on which the leading-order HVP contribution of the 2020 theory consensus is given.
In this talk, I will present two \(a_\mu\)-related LQCD activities of the Mainz group. Firstly, I will discuss a recent publication on the calculation of the intermediate window quantity of the HVP [arXiv:2211.15581], where precise comparisons between LQCD and the data-driven methods can be made. Our calculation is done in a covariant coordinate-space framework and performed at an unphysical reference pion mass with a careful treatment for the finite-volume effects. Our result is consistent with the Mainz 2022 result based on another more conventional formalism, the time-momentum representation, interpolated to the same reference pion mass. Secondly, I will review the Mainz endeavor on the direct calculation of the HLbL contribution to \(a_\mu\) [arXiv: 2006.16224, 2104.02632, 2204.08844], where the QED effects are treated in the continuum and infinite volume. This effort includes many different lattice spacings and heavier-than-physical pion masses, allowing for a robust extrapolation to the physical point for the up-, down- and strange-quark contributions. An estimate for the charm quark contribution is also given based on a partially-quenched calculation at the SU(3)-flavor symmetric limit.
Dr. Johnny Pelliciari, Brookhaven National Laboratory Resonant Inelastic X-Ray Scattering to study ultrathin quantum materials The comprehension of the interactions leading to the properties of strongly correlated systems requires the investigation of their elementary excitations in energy and momentum space. In this context, Resonant Inelastic X-ray Scattering (RIXS) has emerged as a powerful probe the electronic (spin, orbital, and charge) and lattice degrees of freedom. Thanks to recent developments RIXS has been employed in the investigation of many different systems, including cuprates, Fe-based superconductors, and low dimensional magnets. One of the latest interests has been the investigation of ultrathin films and materials where the properties are markedly different than the bulk. In my talk, I will present our recent RIXS investigations in the field of ultrathin films [1,2]. I will focus on two different cases, the effect of confinement on the spin excitations of metallic iron [1], and the evolution of the spin fluctuations in FeSe from the bulk down to the monolayer [2]. I will show how RIXS can identify the elementary excitations in samples as thin as a single unit cell and by comparison with the respective bulk materials, I will discuss how the limited thickness affects the spin excitations and the consequences in the description of the interactions of those systems. In the case of ultrathin FeSe grown on SrTiO_{3} the spin excitations are strongly hardened and flattened by the thickness. This can be explained thanks to Fermiology arguments accounting for the topological transition of the Fermi surface from the bulk to the monolayer. In the second case of metallic Fe the decrease of thickness affects anisotropically the three-dimensional spin excitations of the bulk ferromagnet. In the out-of-plane direction, the spin excitations are gradually softened whereas the in-plane spin excitations persist and retain their dispersion. This evolution can be explained by conventional Heisenberg models accounting for the number of broken magnetic bonds in the proximity of the interface. References: [1] J. Pelliciari et al. Nat. Mat. 20, 188 (2021) [2] J. Pelliciari et al. Nat. Comm. 12, 3122 (2021)
Prof. Pouyan Ghaemi, City College of New York Quantum algorithm to realize and study fractional Hall states and their dynamics on near term quantum computers: A tabletop experiment on quantum gravity Intermediate-scale quantum technologies provide unprecedented opportunities for scientific discoveries while posing the challenge of identifying important problems that can take advantage of them through algorithmic innovations. Fractional Hall systems which are one class of correlated electron systems with many interesting and puzzling properties. In this talk, I present an efficient quantum algorithm to generate an equivalent many-body state to Laughlin’s ν=1/3 fractional quantum Hall state on a digitized quantum computer. Our algorithm only uses quantum gates acting on neighboring qubits in a quasi-one-dimensional setting, and its circuit depth is linear in the number of qubits. I then present another quantum algorithm to generate and study out-of-equilibrium properties of the fractional Hall state. Such features reveal novel geometric aspects of fractional Hall states which mimics gravitons. References PRX Quantum 1, 020309 (2020) Phys. Rev. Lett. 129, 056801 (2022)
Connor Occhialini, Massachusetts Institute of Technology Non-collinear magnetism and multiferroic order in atomically-thin van der Waals materials The recent discovery of magnetic order down to the single-layer limit of van der Waals (vdW) materials has launched substantial interest in realizing functional properties associated to magnetoelectric or topological magnetic phases in two-dimensions (2D). One approach to realize such properties is through non-collinear magnetism, including spiral (e.g. helical/cycloidal) or skyrmionic spin textures. Here, I will discuss our recent work on the nickel dihalides (NiX_{2}, X = Cl, Br, I) which are semiconducting triangular-lattice vdW magnets with frustrated exchange interactions from which non-collinear magnetic phases are stabilized in the bulk. In particular, NiI_{2} hosts an incommensurate helimagnetic ground state (Q = 0.138a* + 1.457c*) alongside a spin-induced ferroelectric order and is therefore a type-II multiferroic with TN ~ 60 K. We identified multiple optical signatures, including optical linear dichroism, second harmonic generation and Raman spectroscopy, which reflect the characteristic symmetry-breaking attributed to polar magnetism and allow us to track the multiferroic phase transition in atomically-thin samples. Our results provide evidence for the persistence of type-II multiferroic order down to the single-layer limit of NiI_{2} with a transition temperature of T_{N} ~ 21 K. We conclude a helimagnetic order in the single-layer that is stabilized by anisotropic symmetric exchange and enhanced by a dimensionality-tuned interlayer interaction in multilayers. I will also discuss complementary optical and X-ray diffraction measurements at high-pressures which reveal a significant pressure enhancement of the multiferroic transition temperature in the bulk at a rate of 14.4 K/GPa. This observation is in quantitative agreement with first-principles calculations of the exchange interactions which reveal a stabilized helimagnetic order from pressure-enhanced interlayer and third-nearest neighbor intralayer exchange. These results provide a generalized route to realize intrinsic multiferroic order in 2D materials with high transition temperature. References: - Qian Song, Connor A. Occhialini, Emre Ergeçen, and Batyr Ilyas et al, “Evidence for a single-layer van der Waals multiferroic”, Nature 602, 601-605 (2022). - Connor A. Occhialini, Luiz G. P. Martins et al, “Pressure-stabilized magnetic phase transitions in van der Waals multiferroic NiI_{2}” (In preparation, 2023).
Zachary Harris, Department of Physics, University of Connecticut
Resurgence in QED: Probing the Schwinger effect in inhomogeneous fields
The structure of the QED vacuum is a subject of great interest, especially as experiments begin to more directly probe the non-linear regime of the theory. One of the most striking features of the vacuum is its polarization in the presence of an electric field — a non-perturbative phenomenon that leads to pair production. Detailed information about this non-perturbative structure is contained in the divergence of perturbation theory, which is more generally described by the theory of resurgence. We study the one-loop QED effective action for an exactly solvable, inhomogeneous background field configuration and use Borel summation to illustrate the connection between perturbative and non-perturbative regimes. Using only 15 terms in the weak magnetic field perturbative expansion, we extrapolate to both strong magnetic field and electric field configurations and obtain a pair-production rate that agrees with the exact effective action to remarkable precision.
Zachary Harris, Department of Physics, University of Connecticut
Resurgence in QED: Probing the Schwinger effect in inhomogeneous fields
The structure of the QED vacuum is a subject of great interest, especially as experiments begin to more directly probe the non-linear regime of the theory. One of the most striking features of the vacuum is its polarization in the presence of an electric field — a non-perturbative phenomenon that leads to pair production. Detailed information about this non-perturbative structure is contained in the divergence of perturbation theory, which is more generally described by the theory of resurgence. We study the one-loop QED effective action for an exactly solvable, inhomogeneous background field configuration and use Borel summation to illustrate the connection between perturbative and non-perturbative regimes. Using only 15 terms in the weak magnetic field perturbative expansion, we extrapolate to both strong magnetic field and electric field configurations and obtain a pair-production rate that agrees with the exact effective action to remarkable precision.