Colloquia This Term

Neutral atom arrays coupled to optical cavities are a promising platform for quantum information science. Optical cavities enable fast and non-destructive readout of individual atomic qubits; however, scaling up to arrays of qubits remains challenging. We recently addressed this by using locally controlled excited-state Stark shifts to achieve site-selective hyperfine-state cavity readout across a 10-site array. To further speed up array readout, we demonstrated adaptive search strategies utilizing global/subset checks, paving the way for faster quantum error correction cycles. As a step toward fault tolerance, we demonstrated repeated rounds of classical error correction, showing exponential suppression of logical error and extending logical memory fivefold beyond the single-bit idling lifetime. In addition to these experimental results, I will present my recent theoretical work on fault-tolerantly linking atom arrays using cavity-based photonic interconnects. By tailoring our quantum error correction scheme to the strengths of the neutral atom array + cavity platform, we can lower the bar for communication fidelity, bringing fault-tolerant connection of error-corrected modules within reach of existing neutral atom technology.

Quantum-controlled molecules are powerful sensors for physics beyond the Standard Model such as symmetry-violating interactions involving TeV-scale particles and the temporal variation of fundamental constants induced by ultralight dark matter. Furthermore, laser cooling of molecules provides an avenue for precision spectroscopy with large samples, long coherence times, and mitigation of systematic errors, which all optimize the sensitivity to signatures of new physics. Until a few years ago, the only molecules to be directly laser-cooled and trapped were diatomic species isoelectronic to alkali atoms (CaF, SrF, and YO). More complex molecules—including those with more than two atoms as well as those with fundamentally different electronic structures—can possess unique features that provide critical experimental tools such as the ability to easily orient the molecules in the laboratory and to populate pairs of low-energy, near-degenerate states. I will describe our recent achievement capturing >104 SrOH molecules in a magneto-optical trap at millikelvin temperatures. This brings SrOH into the realm of full quantum control, the fundamental step toward measurements of the electron electric dipole moment and proton-to-electron mass ratio variation. I will also outline experimental and theoretical evidence that nonlinear molecules with two-fold rotational symmetry (e.g., SrNH2) are ideal candidates for future precision measurements with even greater sensitivity. Finally, I will present a new direction in ultracold molecules: quantum control of highly magnetic species with large angular momentum, such as DyO, which promises to enable probes of beyond-Standard Model particles with masses greater than 100 TeV.

Recently, our lab realized the first BEC of polar molecules. By eliminating two- and three-body collisional losses via double microwave shielding, gases of sodium-cesium molecules are evaporatively cooled to quantum degeneracy. The BEC reveals itself via a bimodal momentum distribution when the phase-space density exceeds one. In this talk, I will share our latest insights into controlling the dipolar interactions in the BEC. Notably, we find that as dipolar interactions increase, their characteristic length scale exceeds the interparticle separation, signifying the onset of strong interactions.

Optical atomic clocks are exemplary quantum sensors, combining robust environmental decoupling with exquisite laser phase sensitivity. By leveraging new quantum engineering techniques, today’s optical clocks now realize a staggering 19 digits of accuracy and precision. Beyond timekeeping, this new level of performance promises novel tests of fundamental physics, from general relativity to dark matter. Motivated by these advances, I will show how carefully controlling ensembles of neutral atoms tightly confined within optical lattices continues to push the limits of frequency metrology. I will first introduce optical lattice clocks (OLCs), which set precision records by leveraging thousands of trapped alkaline-earth-like atoms. Using strontium in a shallow lattice regime allows us to control atomic interactions and realize unprecedented measurement capability, resolving the gravitational redshift within our millimeter-scale atomic sample. In ytterbium we have developed and employed multiple ultracold ensembles within a standard OLC to measure accuracy-limiting differential atomic polarizabilities. Recently we have even operated OLCs outside the lab, with plans for measuring gravitational redshifts atop nearby mountains. Looking forward, the OLC architecture can be extended beyond alkaline-earth-like atoms, enabling a single-species clock network to explore new frontiers in both quantum metrology and fundamental physics.

Advanced quantum optical techniques are revolutionizing our
ability to observe and understand the universe. Two well-established
catalogs of quantum optical states — squeezed states and single-photon
states — are critical in this advancement. For squeezed light, I will
discuss how squeezing has significantly enhanced the sensitivity of 4km
gravitational-wave detectors, the largest quantum metrology experiment
in the world. I will also explain the demonstration of quantum
correlations in LIGO detectors, showcasing 40kg human-scale macroscopic
quantum phenomena. For photon interferometry, I will describe how
two-photon states sense Earth's rotation under a non-inertial frame,
followed by how entangled photons in an interferometer sensitive to
1E-16 strain can probe the interface between gravitational fields and
quantum mechanics. This work also extends to potential applications in
dark matter detection. Ultimately, all these achievements pave the way
to create unprecedented quantum optical states, offering a novel
platform not only for precision quantum measurements to address
fundamental questions about our universe, but also for expanding the
Hilbert space of quantum information processing.

Modern computing and communication technologies such as supercomputers and the internet are based on optically linked networks of information processors operating at microwave frequencies. An analogous architecture has been proposed for quantum networks using optical photons to distribute entanglement between remote superconducting quantum processors. Here I will discuss our recent demonstration of a chip-scale source of entangled optical and microwave photonic qubits, an essential milestone towards realizing such an architecture. Our device platform integrates a piezo-optomechanical transducer with a superconducting resonator which is robust under optical illumination. We drive a photon-pair generation process and employ a dual-rail encoding to prepare entangled states of microwave and optical photons. This entanglement source can directly interface telecom wavelength time-bin qubits and GHz frequency superconducting qubits, two well-established platforms for quantum communication and computation, respectively.

Established in 1954, the “Conseil Européen pour la Recherche Nucléaire” or “CERN” has been the leading European laboratory for accelerator-based studies of the fundamental particles and their interactions.  CERN has hosted several large particle colliders, including LEP and HL-LHC, leading to the discoveries of the W, Z, and Higgs bosons.  The ongoing European Strategy Update will decide CERN’s next large facility.  In this talk, I’ll describe the leading candidate, the Future Circular Collider program, centered around a new large tunnel, allowing an electron-positron collider followed by a proton-proton collider.  I’ll talk about its exciting physics program and its potential impact on the unanswered questions of fundamental physics. 

The discovery in 1983 by the European Muon Collaboration (EMC) that quark distributions in nuclei are modified relative to the free proton and neutron was surprising and had implications for what physicists thought they knew about the role of quarks in the nucleus.  After more than 40 years of intense theoretical and experimental study, there is still no consensus on the origin of this so-called EMC Effect.  However, an exciting program of measurements at Jefferson Lab inspired by recent theoretical predictions and experimental observations provides hope that this long-running question will soon be answered.  In this talk, I will discuss this program and discuss some recent results that will provide important information about the origin of the EMC Effect.

My Ph.D. in Physics followed an applied mathematics undergraduate degree, and my interest in computing started with summer undergraduate experiences punching holes in cards and carrying the daily jobs from Cambridge to London to the IBM 7094 data center. My Ph.D. adviser wisely told me, “Geoffrey, nobody looks at data.” In those days, High Energy Physics was the Big Data leader, and I taught myself statistics from DOE laboratory memos and Kolmogorov. Some of my papers, such as “Veni, Vidi, Vici Regge Theory,”  described large-scale Regge+Resonance data analyses. I learned modeling from Feynman, worked with the particle data group at LBL, and participated in experiments to get more reliable data. Meanwhile, working with Wolfram on the early version, SMP, of Mathematica, I stumbled into computer science through parallel hardware, software, and algorithms for Quantum Chromodynamics and other simulations. However, I was always termed the physicist, and my training in this field was very useful as it taught me about systems. Computing is itself a complex system that produces discoveries in other complex systems. Since then, computing has continued to advance through the Internet and distributed systems and, most recently, Artificial Intelligence, AI, and a situation where “Geoffrey, everybody only looks at data.” Every ten years, I have noted that computing has been successful, but the next ten years look even more promising. Today, AI for Science has incredible promise, and I finish with some of these opportunities.

Condensed matter physics has witnessed emergent quantum phenomena driven by electron correlation and topology. In this talk, I will introduce a family of synthetic quantum materials, based on crystalline multilayer graphene, as a new platform to engineer and study emergent phenomena driven by many-body interactions. This system hosts flat-bands in highly ordered conventional crystalline materials and dresses them with proximity effects enabled by rich structures in 2D van der Waals heterostructures. As a result, a rich spectrum of emergent phenomena including correlated insulators, spin/valley-polarized metals, integer and fractional quantum anomalous Hall effects, as well as chiral superconductivities have been observed in our experiments.

References: [1] Han, T., Lu, Z., Scuri, G. et al. Nat. Nanotechnol. 19, 181–187 (2024). [2] Han, T., Lu, Z., Scuri, G. et al. Nature 623, 41–47 (2023). [3] Han, T., Lu, Z., Yao, Y. et al. Science 384,647-651(2024). [4] Lu, Z., Han, T., Yao, Y. et al. Nature 626, 759–764 (2024). [5] Lu, Z., Han, T., Yao, Y. et al. Nature 2025. https://arxiv.org/abs/2408.10203 [6] Yang, J., Chen, G., Han, T. et al. Science, 375(6586), pp.1295-1299. (2022)

In 1964, when Thorne was a student, there were hints that our universe might have a Warped Side:  Objects and phenomena made from warped space and warped time instead of from matter.  Thorne and his colleagues have spent these past sixty years turning those hints into clear understanding.  They have explored the Warped Side through theory (using mathematics and computer simulations to probe what the laws of physics predict) and through astronomical observations (primarily with gravitational waves). In this lecture he will describe what they have learned about Warped-Side phenomena:  black holes, wormholes, gravitational waves, our universe’s big-bang birth, and the possibility of time travel.

Since Phil Anderson's "More is Different" or perhaps since Landau's conceptualization of quantum liquids, condensed matter physicists have modeled the emergent behavior of complex matter by boiling it down to the relevant emergent degrees of freedom, symmetries and interaction. What if we could invert that approach? Instead of developing Hamiltonians that conceptualize unusual phenomena seen in materials found serendipitously in nature, we could create artificial materials deliberately for exotic emergent behaviors. That was the perhaps ambitious goal of artificial spin ices (arrays of interacting, magnetic frustrated nano-islands representing binary magnetic variables) since its inception in 2006. Since then, advances in fabrication and characterization have allowed to push that envelope to show magnetic monopoles, ordering of magnetic charges, and a wealth of emergent phenomena. We shall discuss two of the most recent results: a system that orders by raising its entropy [1] and another one showing a topological crossover in its kinetics [2].

[1] SAGLAM, Hilal, et al. Entropy-driven order in an array of nanomagnets. Nature Physics, 2022, 18.6: 706-712.

[2] ZHANG, Xiaoyu, et al. Topological kinetic crossover in a nanomagnet array. Science, 2023, 380.6644: 526-531.

On December 25, 2021, the James Webb Space Telescope was launched from Earth towards its ultimate destination at the L2 Lagrange Point, 1.5 million kilometers away from Earth. The culmination of decades of planning, construction, execution, and transport all came down to a critical few minutes, which led to our newest flagship observatory in space. Science operations began in July of 2022, with the past 2+ years bringing about a number of scientific revolutions: both expected, such as the discovery of a number of record-breaking galaxies and other cosmic objects, and unexpected, such as new features in star and planet-formation, and big surprises about the earliest supermassive black holes in our Universe. Come learn what we've discovered and how it's altered our cosmic perspective, and explore what's inside the speaker's first National Geographic book, Infinite Cosmos: Visions from the James Webb Space Telescope.

TBA