## Upcoming Seminars

UMass Boston Physics Colloquia

Talks are on Thursdays, 12:45 pm (new time, this semester only), at S(cience)-3-126, unless stated otherwise

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Thursday, Feb 8, 12:45pm
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Bryan Spring
Northeastern U
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Selective treatment and imaging of cancer micrometastases using biophysical approaches
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Molecular-targeted, activatable probes are emerging for optical biopsy of cancer. An unexplored potential clinical use of this approach is to monitor and treat residual cancer micrometastases that escape surgery and chemotherapy. This talk will introduce a new platform for activatable phototherapy and in vivo imaging of residual metastases that enables high-fidelity imaging and treatment of cancer cells. Optically active nanomaterials--that use light as both a drug release mechanism and as a cytotoxic modality-are an emerging component of this approach and will also be introduced. These developments stem from the cross--fertilization of biophysical imaging and quantum photophysics with cancer research.

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Thursday, Feb 15, 12:45pm
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Vladan Vuletic
MIT
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Very attractive photons
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Photons, if colorful, are somewhat boring: they all move at one speed and do not interact with one another. I will present an unusual optical medium that is nonlinear at the quantum scale: In this medium, photons travel slowly, acquire mass, and exhibit strong mutual attraction, so strong that two photons can even form a bound state. Furthermore, I will discuss a new method how to directly optically cool an atomic gas to form a Bose-Einstein condensate.

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Thursday, Feb 22, 12:45pm
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Christopher Fuchs
UMass Boston
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The Search for a QBist Formulation of Quantum Theory
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Some time ago, Steven Weinberg wrote an article for the New York Review of Books with the title, "Symmetry: A `Key to Nature's Secrets'." So too, I would like to say of the quantum theory itself: Only by identifying Hilbert space’s most hidden symmetries will we be able to unlock quantum theory’s deepest secrets and greatest potential. In this talk, I introduce the "symmetric informationally complete" (SIC) sets of quantum states as a candidate for such a symmetry. When these structures exist—and it seems they do for all finite dimensions, though in 18 years, with immense effort, no one has proven it!—one can use them to re-express a quantum state as a single, simple probability distribution and a unitary transformation as a doubly stochastic matrix. Most importantly, this formalism gives an insightful way to rewrite the Born rule so that it too is in purely probabilistic terms, never once making mention of quantum states or operators on a complex vector space. This sort of thing is music to the ears of a recent contender in the debate over quantum theory’s interpretation—namely, QBism. In particular, it gives hope that all the mathematical structure of quantum theory might be derivable from a single, very basic physical scenario to do with how one should organize probabilities for complementary experiments in terms of each other. It’s not the double-slit experiment that Feynman argued for in his Feynman Lectures, but one that might still appeal to his intuition that, "In reality, [this scenario] contains the only mystery [of quantum mechanics]."

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Thursday, Mar 1, 12:45pm
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John Doyle
Harvard U
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Ultracold Polyatomic Molecules--- N Atoms Too Many
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Control of molecules is greatly aided by cooling their external degrees of freedom. Exquisite quantum state control has already been achieved with atomic species, leading to great progress in quantum computation, simulation, searches for physics beyond the Standard Model, and novel collisions and chemical reactions. Molecules are now a current frontier in cold matter science, with diatomic molecules taking center stage at the moment. Moving to the next frontier, the creation of ultracold polyatomic molecules presents new laboratory challenges. One of our key long-term scientific goals is to achieve for polyatomic molecules the kind of single-state control now available with atoms with a very wide variety of polyatomic structures. We believe that this will open up important new scientific opportunities.

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Thursday, Mar 8, 12:45pm
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Srivalleesha Mallidi
Wellman Center for Photomedicine, MGH
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Photoacoustic imaging for treatment guidance, dosimetry and tumor recurrence prediction
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For personalizing effective treatment strategies it is paramount to understand the dynamic changes in the microenvironment as the tumor adapts or surrenders to a therapeutic insult. Towards this goal, we present the utility of non-invasive 3D ultrasound guided photoacoustic imaging (PAI) to understand the tumor functional and molecular heterogeneity in addition to predicting local recurrence. Photoacoustic imaging, as a nomenclature suggests, involves generation of acoustic signals by irradiating tissue with nanosecond laser pulses and it offers functional information with high sensitivity on par with optical imaging at deeper penetration depths. In the first part of the talk, I will present utility of PAI for monitoring photodynamic therapy (PDT), a photochemistry-based treatment modality, with 3D atlas of the changes in tumor blood oxygen saturation (endogenous contrast) and its correlation to tumor recurrence. In the second part of the talk, I will present utility of PAI in obtaining molecular maps of cancer biomarkers such as epidermal growth factor receptor (EGFR), with molecular targeted gold nanoparticles and drug antibody conjugates(exogenous contrast). Finally I will present long term strategy and directions on pushing the envelope of ultrasound-guided PAI as an important preclinical and clinical tool in tumor diagnosis, selection of customized patient-specific treatment, monitoring the therapeutic progression and overall treatment outcome.

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Thursday, Mar 15
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NO SEMINAR SPRING VACATION
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Thursday, Mar 22, 12:45pm
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Mareike Haberichter
UMass Amherst
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Solitons: From Tsunamis to Skyrmions
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Topological solitons are stable, finite energy solutions to nonlinear field equations found in a variety of physical systems. Examples include vortices in superconductors, baby Skyrmions in condensed matter systems and the infamous Skyrmions of nuclear physics. In this talk, I will provide an introduction to topological solitons, with a particular focus on the solitons of the sine-Gordon and Skyrme models. We will also discuss some of the nuclear physics applications of the Skyrme model.

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Thursday, Mar 29, 12:45pm
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Matthew Bell
UMass Boston
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Symmetry Protected Quantum Bits through Fluxon Pairing
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Over the past decade, the performance of superconducting quantum bits (qubits) have improved tremendously with coherence times routinely reaching many 10s of microseconds. The much-improved coherence, lithographic scalability, and compatibility with microwave control, place superconducting qubits in the forefront in the race amongst several quantum technologies towards the realization of a gate-based quantum computer. Despite this progress in qubit performance, it is still a formidable challenge to realize a highly coherent single logical qubit based on conventional physical qubits - the number of faulty physical qubits required to run the necessary error correction protocols is very large and the control of these numerous physical qubits is very complex. Practical implementation of a suitable logical qubit still requires further development of physical qubits with a higher degree of coherence.

In this talk I will present our efforts toward implementing transformative ideas of improving the qubit coherence through symmetry-protection of a quantum state encoded in the parity of fluxons in a superconducting circuit. It is expected that such circuits will demonstrate very long coherence in the protected state (the protection will have to be removed only during measurement of the quantum state). Even more important, the fault-tolerant gate operations can be performed on such qubits. The focus of this work is to realize a fluxon-pairing qubit (FPQ) whose logical states are encoded in the parity of very stable fluxons in a superconducting loop formed by a two-junction Cooper-pair box (CPB) and a large inductor. Through the Aharanov-Casher (AC) effect the single-fluxon tunneling through the weak CPB junctions is suppressed and the parity of fluxons in the loop is preserved. The suppression of energy relaxation due to parity protection in the prototype of this qubit has already been demonstrated in our recent experiments. If the rate of double-fluxon tunneling in the CPB is sufficiently high, the wavefunctions of the two lowest-energy states of the qubit corresponding to even and odd number of fluxons in the loop become indistinguishable, resulting in the suppression of decoherence. The physical qubit layout allows for scaling in a planar geometry without the materials or strict RF design restrictions found in state-of-the-art approaches.

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Thursday, Apr 3, 2pm, ISC-1200
(Joint with the Quantum Technologies meeting, unusual time/place)
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Boris Malomed
Tel Aviv U
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Probing quasi-integrability of the Gross-Pitaevskii equation in a harmonic-oscillator potential
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Previous simulations of the one-dimensional Gross-Pitaevskii equation (GPE) with repulsive nonlinearity and a harmonic-oscillator trapping potential hint towards the emergence of quasi-integrable dynamics, in the sense of quasi-periodic evolution of a moving dark soliton without any signs of ergodicity, although this model does not belong to the list of integrable equations. To investigate this problem, we replace the full GPE by a suitably truncated expansion over harmonic-oscillator eigenmodes (the Galerkin approximation), which accurately reproduces the full dynamics, and then analyze the system's spectrum. The analysis enables us to interpret the observed quasi-integrability as the fact that the Galerkin approximation's fi nite-mode dynamics always produces a quasi-discrete power spectrum, with no visible continuous component, the presence of the latter being a necessary manifestation of ergodicity. Undertaking, for the comparison's sake, the same analysis in a potential box with zero boundary conditions, we conclude that it leads, instead, to a clearly continuous power spectrum.

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Thursday, Apr 5, 12:45pm
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Anushya Chandran
Boston U
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Schrodinger's clowder: entanglement in many-body physics
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Nearly 80 years after Schrodinger introduced his famous cat, quantum entanglement has fuelled a conceptual revolution in many-body quantum physics. What Einstein, Podolsky and Rosen once found anathema, we now understand as a quantitative tool for classifying the allowed quantum phases of matter, analyzing the performance of quantum simulations and diagnosing thermalization. In this talk, I will re-introduce you to entanglement from this many-body point of view. We will see how the entanglement entropy organizes quantum phases of matter in the absence of local order parameters and how the entanglement spectrum probes the bulk-boundary correspondence in such quantum phases. Finally, we will turn to the dynamics of entanglement and how it has offered a phenomenological understanding of the newly discovered many-body localized phase.

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Thursday, Apr 12, 12:45pm (moved from Apr 26)
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Mohamed Gharbi
UMass Boston
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Directed assembly of biomaterials and functional nanomaterials: A toolkit to fabricate advanced materials
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The opportunities for guiding assembly using energy stored in soft matter are wide open. The emerging scientific frontiers in this field show an exceptional promise for significant new applications. Since soft materials can be readily reconfigured, there are unplumbed opportunities to make responsive devices with tunable properties. Liquid crystals (LCs) constitute a fascinating class of soft matter characterized by the counterintuitive combination of fluidity and long-range order. These materials are known for their exceptionally successful applications in displays, smart windows, and biosensing applications. When the order of molecules in some local regions of LCs is not well defined, topological defects form. These defects are strong trapping sites for colloidal inclusions and have been widely used to control their assembly. In this talk, I will introduce few examples where I use defects in LCs as a platform to directed assembly of colloidal inclusions. I will present recent progress in understanding the mechanisms that govern the formation of different assemblies in ordered fluids and will report how defects in soft matter can inspire strategies for making a new generation of advanced materials.

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Thursday, Apr 19, 12:45pm
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Shabnam Beheshti
Queen Mary U
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Three (and a half) Integrable Equations of Mathematical Physics
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The study of partial differential equations was transformed dramatically with the discovery of "integrability" nearly half a century ago. We shall motivate the broad reach of this concept through the study of several concrete examples whose associated equations appear in physical contexts ranging from fluid dynamics to general relativity. Our investigation will send us through seemingly disparate areas of mathematics including combinatorics, differential geometry, graph theory, analysis and algebraic geometry, to name a few. Recent work and open questions will be toured lightly along the way, with an emphasis on the rich interactions between the physics and mathematics yet to be discovered. This talk is welcomes non-specialists, graduate and undergraduate students.

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Thursday, Apr 26, 12:45pm (M. Gharbi's seminar moved to Apr 12th)
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Prof. Alexander D. Cronin
University of Arizona, Tucson, AZ
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More Power to Atom Interferometry
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TBA

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Thursday, May 3, 12:45pm
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George Kaminski
WPI
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Accurate and efficient calculations of protein acidity constants: From polarizable to coarse-grain methods
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TBA

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Thursday, May 24, 2 pm, ISC-1200 (unusual time and venue)
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Vladimir Yurovsky
Tel Aviv U
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Dissociation of one-dimensional matter-wave breathers due to quantum
many-body effects
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We use the ab initio Bethe Ansatz dynamics to predict the dissociation of one-dimensional cold-atom breathers that are created by a quench from a fundamental soliton. We find that the dissociation is a robust quantum many-body effect, while in the mean-field (MF) limit the dissociation is forbidden by the integrability of the underlying nonlinear Schrodinger equation. The analysis demonstrates the possibility to observe quantum many-body effects without leaving the MF range of experimental parameters. We find that the dissociation time is of the order of a few seconds for a typical atomic-soliton setting.

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