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Wednesday, September 17, 2025 (Special start time: 10:45 AM, instead of the usual 11:00 AM)
Hoang Van Do (UMass Boston)

Rydberg atom arrays for quantum information science and quantum sensing

Neutral atom arrays have rapidly emerged as a versatile platform for advancing quantum technologies. By combining the programmable arbitrary geometry with the strong, controllable interactions of Rydberg atoms, these systems enable new opportunities for quantum information science, quantum simulation, and precision measurement. In this talk, I will outline the broad potential of Rydberg arrays as a quantum technology platform: from exploring fundamental many-body physics to developing novel protocols for sensing and metrology. I will also discuss how integrating atom array experiments with complementary approaches in atomic, molecular, and optical physics can open pathways toward next-generation quantum devices that address both scientific and practical challenges

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Wednesday, September 24, 2025
No colloquium: Departmental Meeting 

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Wednesday, October 1, 2025
Liwen Ko (Harvard University)

Title: Input-output formulation of quantum light spectroscopy 

In the first part of the talk, I will introduce an input-output formulation of quantum light spectroscopy. This formalism combines the input-output theory, traditionally used in the quantum optics community, with the perturbative expansion method for nonlinear spectroscopy, traditionally used in the chemical physics community. The new input-output approach provides a unified framework for analyzing optical signals in both the perturbative and non-perturbative regimes. Using this formalism, we show that a class of quantum light spectroscopy can be emulated by classical-like coherent light pulses. In the second part of the talk, I will share our development of a normal-ordered perturbative expansion method, which describes the time evolution of the reduced matter system state under the influence of non-classical light pulses. Using the normal-ordered expansion, we are able to accurately simulate the reduced system dynamics under a cat state excitation in a regime where the conventional perturbative expansion fails.  

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Wednesday, October 8, 2025
Nikolay Gnezdilov (Dartmouth)

Dynamic thermalization on noisy quantum hardware

Emulating thermal observables on a digital quantum computer is essential for quantum simulation of many-body physics. However, thermalization typically requires a large system size due to incorporating a thermal bath, whilst limited resources of near-term digital quantum processors allow for simulating relatively small systems. We show that thermal observables and fluctuations may be obtained for a finite-sized system without emulating a thermal bath. Thermal observables occur upon classically averaging quantum mechanical observables over randomized variants of their time evolution under a Hamiltonian falling into a class of Gaussian unitary ensembles (GUE) of random matrix theory. Each variant of the time evolution runs independently on a quantum computer. The energy of the initial state defines the resulting temperature. Using an IBM quantum computer, we experimentally find thermal occupation probabilities with finite positive and negative temperatures [1]. Averaging over random evolutions facilitates error mitigation, with the noise contributing to the temperature in the simulated observables. This result fosters probing the dynamical emergence of equilibrium properties of matter at finite temperatures on noisy intermediate-scale quantum hardware.

[1] H. Perrin, T. Scoquart, A. I. Pavlov, and N. V. Gnezdilov, Communications Physics 8, 95 (2025)

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Wednesday, October 15, 2025
Mathieu Beau (UMass Boston)

Context-Dependent Time in Quantum Mechanics: From Quantum Control to Time of Arrival

In quantum mechanics, time is not represented by an operator but only as an external parameter, which complicates the definition of observables such as arrival times or transition durations. We present a unifying framework where time is understood contextually, through statistical time-of-flow (TF) distributions reconstructed from projective measurements. This framework applies to both discrete systems, such as multi-level transitions, and continuous systems, where it recovers and generalizes the time-of-arrival (TOA) distribution. It naturally leads to a new time-energy uncertainty relation, offering experimentally accessible tools for quantum control and diagnostics.

In the context of quantum control, we show how the TF distribution can be used to analyze and optimize protocols such as driven two- and three-level systems, as well as the Hadamard gate under dephasing. We also apply the approach to TOA in free fall, predicting a measurable quantum delay relative to classical fall times and deriving a novel TOA-position uncertainty relation.

These results suggest that quantum time should be regarded not as a universal observable but as a context-dependent statistical variable, with implications for both foundational studies and quantum technologies.

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Wednesday, October 22, 2025
No colloquium: Departmental Meeting

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Wednesday, October 29, 2025
Thomas Videbaek (Brandeis University)

Title: Arts-and-crafts inspired self-assembly: folding, cutting, and coloring triangulated sheets to make tubules and toroids

Self-assembly is one of the most promising strategies for making functional materials at the nanoscale. Typically, synthetic self-assembly has been limited to spatially unbounded periodic lattice structures. In contrast, many biological systems have developed the ability to create complex self-closing structures, such as viral capsids (shells) and microtubules (cylinders), where preferred binding angles between subunits allow for the accumulation of curvature that results in a finite global size. How does one go about trying to design a synthetic system that can make such self-closing, finite-size assemblies? In this talk, I will discuss how to use triangular subunits that interact at their edges with programmable binding angles to create such self-closing structures. To begin, we will look at how to create a cylindrical tubule and how to realize its assembly in experiment using DNA origami. When we assemble tubules using a single type of subunit, we find that thermal fluctuations drive the system to access nearby, off-target states with slightly different widths and helicities. To eliminate these off-target geometries, we impose a coloring pattern on the triangles, which limits the number of ways in which the assembly can close and reduces the density of off-target states, thereby increasing the selectivity of our particular target geometry. We find that when the length scale for the periodicity of the coloring pattern matches the length scale of thermal fluctuations, only a single tubule type can form. Emboldened by the ability to place unique subunits in particular locations within the tubules, we attempt to create more complex geometries by also encoding spatially varying curvatures. More specifically, I will discuss a kirigami-inspired design strategy, which excises patches from our cylindrical sheets and stitches them back together to produce new edge-connectivity graphs. This design scheme allows us to assemble surfaces with varying Gaussian curvature, including toroids, achiral serpentine assemblies, and both right- and left-handed helical tubules. Taken together, these examples demonstrate how controlling both the geometry and the specificity of interactions between self-assembling subunits can be used to create both highly specific and complex structures.

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Wednesday, November 5, 2025
Joel Fish (UMB Math)

The State of Math Instruction and Education at UMB: A forum for questions, concerns, and tough conversations 

A departmental forum to discuss the current state of math instruction and education at UMass Boston. This session will provide space for physics faculty to raise questions, share concerns, and engage in open and constructive conversations about challenges and opportunities in math education as it relates to our programs. 

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Wednesday, November 12, 2025
Nobuyuki Matsumoto (Boston University)

Extending the scope of lattice calculations to further probe the non-perturbative dynamics of quantum field theory

The expressibility of quantum field theory (QFT) as a theoretical framework is immeasurable. On one end, weak coupling allows one to use perturbation theory that provides an intuitive picture of interacting particles in a simple diagrammatic form, while on the other end, strong nonlinear effects give rise to phenomena such as confinement in quantum chromodynamics (QCD) that completely change the low-energy effective degrees of freedom from the original field variables. Intriguingly, nature blends the two ends of QFT in the Standard Model in a subtle way, and therefore it is valuable to scrutinize QFTs in a fully non-perturbative manner and be prepared to tackle beyond-Standard-Model (BSM) physics and grand unification, not only for a theoretical perspective but also for phenomenology. Today, in studying strongly interacting systems, the lattice method has established its status as a systematically improvable way to perform first-principles calculations through its applications to QCD, as exemplified in the recent success of enumerating the hadronic contributions to muon g-2 with the precision comparable to the experiments. In this talk, I first discuss the effectiveness of the lattice method by using the g-2 example [1], and move on to the ongoing works to apply the method for BSM physics in the cosmological context and derive a possible gravitational wave signal from the early universe [2] and further to extend its scope to curved manifolds [3], by which we can address even more interesting questions such as conformal field theories in higher dimensions.

[1] T. Blum, NM, et al. [RBC/UKQCD], “Update of Euclidean windows of the hadronic vacuum polarization,'' Phys. Rev. D108, no.5, 054507 (2023) [2301.08696 [hep-lat]].

[2] In preparation. For proceedings: V. Ayyar, NM, A. S. Meyer, S. Park [LSD Collaboration], “Finite Temperature Transition in Hyper Stealth Dark Matter using Möbius Domain Wall Fermions,” PoS LATTICE2024, 148 (2025) [2502.00331 [hep-lat]].

[3] P. A. Boyle, R. C. Brower, G. T. Fleming, E. Katz, NM, R. Misra, "Studying QED3​ with radial quantization on the lattice -- I. Free limit," 2510.03085 [hep-lat].

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Wednesday, November 19, 2025
Hidenori Tanaka (Harvard University)

Title: TBA

Abstract: TBA

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Wednesday, November 26, 2025
No colloquium -- Thanksgiving

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Tuesday, December 02, 2025 (Special Date)
Avadh Saxena (LANL) 

Hopfions in Condensed Matter and Field Theory 

TBA Nontrivial topological defects such as knotted solitons called hopfions have been observed in a variety of materials including chiral magnets, nematic liquid crystals and even in ferroelectrics as well as studied in other physical contexts such as Bose-Einstein condensates.  These topological entities can be modeled using the relevant physical variable, e.g., magnetization, polarization or the director field.  Specifically, we find exact static soliton solutions for the unit spin vector field of an inhomogeneous, anisotropic three-dimensional (3D) Heisenberg ferromagnet and calculate the corresponding Hopf invariant H analytically and obtain an integer, demonstrating that these solitons are indeed hopfions [1]. The invariant H is a product of two integers, the first being the usual winding number of a skyrmion in two dimensions, while the second integer encodes the periodicity in the third dimension. We also study the underlying geometry of H, by mapping the 3D unit vector field to tangent vectors of three appropriately defined space curves. Our analysis shows that a certain intrinsic twist is necessary to yield a nontrivial topological invariant, i.e., a linking number [2]. We also focus on the formation energy of hopfions to study their properties for potential applications. Finally, we investigate the dynamics of hopfions interacting with an array of line defects resulting in a toron under certain conditions. In addition, we find that an asymmetric array of defects leads to a hopfion ratchet effect [3].

[1] R. Balakrishnan, R. Dandoloff, and A. Saxena, Phys. Lett. A 480 128975 (2023).

[2] R. Balakrishnan, R. Dandoloff and A. Saxena, Phys. Lett. A 493, 129261 (2024). 

[3] J.C.B. Souza et al., Scientific Reports 15, 16802 (2025).

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Wednesday, December 10, 2025
No colloquium: Departmental Meeting

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