## CQRT Seminars

The Atomic, Molecular and Optical (AMO) and Condensed Matter (CM) physics groups are hosting a joint seminar as part of the Center for Quantum Research and Technology (CQRT). This endowed seminar series brings in experts from across the country as well as across campus to discuss the latest in research advances in quantum science.

Seminars in Spring 2022 will be conducted over Zoom and will be held on Tuesdays from 1:15-2:15pm or Fridays from 2:30-3:30pm, depending upon speaker availability. If you wish to attend a seminar and are not on our mailing list, please contact either Kieran Mullen (kieran@ou.edu) or Robert Lewis-Swan (lewisswan@ou.edu) to obtain a link.

### Spring 2022 (virtual Zoom series)

**Title: Site-specific spectroscopic measurement of spin and charge in (LuFeO _{3})_{m}/(LuFe_{2}O_{4})_{1} multiferroic superlattices**

Janice Musfeldt, University of Tennessee

*Tuesday, February 22, 2022
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO_{3})_{m}/(LuFe_{2}O_{4})_{1} superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the *m* = 3 member. In particular, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ → Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe_{2}O_{4} layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.

**Title: Searches for New Physics with Quantum Sensors in the Laboratory and in Space**

**Marianna Safranova, University of Delaware**

*Tuesday, March 1, 2022
1:15-2:15pm (Zoom link will be announced)
*

Abstract: The extraordinary advances in quantum control of matter and light have been transformative for atomic and molecular precision measurements enabling probes of the most basic laws of Nature to gain a fundamental understanding of the physical Universe. Exceptional versatility, inventiveness, and rapid development of precision experiments supported by continuous technological advances and improved atomic and molecular theory led to rapid development of many avenues to explore new physics. I will give an overview of atomic and molecular physics searches for physics beyond the standard model and focus of dark matter searches with atomic and nuclear clocks. Recent ideas on dark matter searches and test of general relativity with clocks in space will be discussed. I will also briefly discuss new ideas and prototype experiments in gravitational wave detection with atomic quantum sensors.

**Title: Bridging Few- And Many-Body Physics in Fermi Gases**

**Yangqian Yan, The Chinese University of Hong Kong**

*Friday, March 4, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: The strongly interacting Fermi gas with large scattering lengths constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear and particle physics. Such a model applies to the core of nuclei, the crust of a neutron star, and the highly controllable ultracold atoms with tunable scattering lengths. Whereas it is challenging to theoretically tackle strongly interacting Fermi gases, the virial expansion serves as a powerful tool to bridge few- and many-body physics. With the help of Richard Feynman’s path integral, we used classical computers to simulate few-body systems and obtained the viral coefficients for many-body systems. In particular, I will discuss how to extract the so-called contact, the central quantity controlling dilute quantum systems, using the virial expansion.

Including multiple flavors in interacting Fermi gases provides physicists with an even richer playground. In a recent collaboration with Prof. Gyu-Boong Jo’s group at HKUST, we have theoretically predicted and experimentally verified that the contact of a 3D SU(N) Fermi gas approaches spinless bosons via a particular scaling law at finite temperatures. This provides a rigorous proof of the bosonization of 3D SU(N) fermions and also opens the door to a new framework of manipulating quantum statistics in many-body systems.

**Title: A Direct View into Optical Lattices: Dynamics, Topology and Dissipation**

Klaus Sengstock, University of Hamburg

*Friday, March 11, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: Ultracold atoms in optical lattices act as powerful systems for quantum technologies, including quantum simulation, quantum information and quantum computing, as well as for precision experiments and as fully new model systems. I will report on recent developments from our lab to image 3D optical lattice systems with better than single-site resolution (Nature 599, 571 (2021)) allowing for a direct view into dynamics, thermalization and further properties within the optical lattices. We could observe the spontaneous build-up of a density waves (PRX, in print, arXiv:2108.11917) and study topological properties of quantum gases in lattices (Nature Physics, 15, 449 (2019)).

**Title: Using Computational Methods to Improve and Design Energy Materials**

MIchelle Johannes, Naval Research Lab

*Tuesday, March 22, 2022
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Although batteries and fuel cells are generally considered electrochemical systems, a surprising amount of their performance stems from the physics of the materials that make up their basic components:anode, cathode and electrolyte. Ionic conduction, electronic conductivity, chemical stability and voltage can all be traced back to intrinsic materials properties which are governed by fundamental physics.

In this talk, I will discuss how computational simulation can be used to analyze, develop and improve energy materials, such as Li-ion batteries, supercapacitors, and fuel cells. I will specifically discuss how seemingly small details of the electronic structure can make or break performance. I will further discuss some of the safety concerns that are currently driving battery research and development and how computational screening can determine in advance how stable a material will be during charging. Finally, I will discuss the use of nanoscale materials and how they can be stabilized against degradation by judicious oxide coating.

**Title: Photons, plasmons, and polaritons: optical phenomena in quantum materials**

Stephanie Law, University of Delaware

*Tuesday, March 29, 2022
1:15-2:15pm (Zoom link will be announced)
*

Abstract: When light interacts with quantum materials, we can excite a variety of modes including plasmon polaritons and optical phonons. In layered materials, these modes can interact with each other to produce hybrid excitations resulting in novel optical phenomena such as negative refraction, extreme light confinement, and preferential thermal emission. In this talk, I will first discuss our work on the growth of topological insulator thin films and heterostructures by molecular beam epitaxy. Topological insulators have two-dimensional surface states that house massless electrons, and the plasmon polaritons in these materials show unusual properties. I will discuss the dispersion of these modes and show record high mode indices and extremely long polariton lifetimes. Using MBE, we can then grow layered structures comprising multiple topological and normal insulators, resulting in hybrid coupled plasmon modes. We can also grow self-assembled topological insulator quantum dots, which could be used as qubits. I will close by discussing our work on semiconductor hyperbolic metamaterials, which are layered materials comprising alternating metallic and dielectric materials. I will show our work demonstrating strong coupling between the volume plasmon polariton modes and quantum well intersubband transitions.

**Title: Emergence and quantum complexity in mono element solids**

G. Baskaran, Matscience, IITMadras, Chennai, India

*Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: We are witnessing gradual understanding of myriads of materials, synthetic quantum matter and ever growing number of phenomena and surprises. Emergence and quantum complexity are smiling at us. I will point to some of our works and briefly discuss two families: allotropes of carbon and solid hydrogen. Emergence creates a web of unexpected connections and new insights. For example, graphene offers [1,2] relativistic analogue of time dilation, Kaluza Klein collapse, zitterbewegung, parity anomaly, emergent gauge fields, Majorana Fermions etc. Small twists in bilayer graphene produces superconductor or Mott insulator ! Solid hydrogen under pressure takes us through a series of unexpected structures and Mott insulating phases, before becoming a metal that Wigner and Huntington envisaged in 1935.

[1] G. Baskaran, Quantum Complexity in Graphene, Mod. Phys. Lett., B25, 605 (2011)

[2] G. Baskaran, Physics of Quanta and Fields in Graphene,

in `Graphene: Synthesis, Properties and Phenomena,

Editors: C.N.R. Rao and A.K. Sood (Wiley)

**Title: Connecting the dots**

Michael Scheibner, University of California, Merced

*Friday, April 15, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: How many straight lines connect two dots? The answer: That depends on the dots and their environment. By placing two quantum dots near each other we can probe fundamental quantum mechanical properties of the semiconductor system and its interactions. Equipped with that knowledge we can start to tailor the quantum states to develop novel quantum-enhanced applications. In doing so, we make use of an enhanced versatility and functionality that arises from the superposition of states of the two dots. For example, their discrete electronic states and optical transitions can be tuned *in-situ* over tens of meV. As a result, it is possible to control and realize coupling between varieties of excitations of the solid-state system, ranging from different spin states, phonons to the mechanical motion of the system. In this seminar I will review the unique properties of coupled quantum dots and discuss their advantages as tools in quantum technologies, such as quantum photonics and quantum sensing.

**Title: Representing many-body quantum states with neural networks**

Martin Gärttner, University of Heidelberg

*Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: I will discuss the idea of using neural networks a variational ansatz for the quantum many-body wave function. These neural network quantum states have recently been employed for variational ground state search, quantum dynamics, and quantum state tomography. I will report on two contribution of our group on using neural network representations of mixed quantum states for simulating the dynamics of open quantum systems and for quantum state tomography.

**Title: TBA**

Henri Lezec, NIST

*Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: TBA

**Title: TBA**

David Ebert, OU

*Tuesday, March 29, 2022*

*1:15-2:15pm (Zoom link will be announced)*

Abstract: TBA

**Title: Representing many-body quantum states with neural networks**

Martin Gärttner, University of Heidelberg

*Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)
*

Abstract: I will discuss the idea of using neural networks a variational ansatz for the quantum many-body wave function. These neural network quantum states have recently been employed for variational ground state search, quantum dynamics, and quantum state tomography. I will report on two contribution of our group on using neural network representations of mixed quantum states for simulating the dynamics of open quantum systems and for quantum state tomography.

**Title:Quantum fluctuations in nonlinear Schrödinger breathers**

O. V. Marchukov, Institut für Angewandte Physik, Technical University of Darmstadt, Germany

*Monday May 16, 2022
SPECIAL TIME: 9:00-10:00am (Zoom link will be announced)
*

Abstract: Solitons are nonlinear waves that show up in many different fields of physics: From solitary water waves to Langmuir waves in plasmas, the formation of solitons attracts the interest of theoreticians and experimentalists alike. In this talk, we focus on the two-soliton breathers – nonlinear superposition of two bright solitons – in one-dimensional Bose gases that were recently obtained experimentally [2,4]. We present the linearization approach that allows one to evaluate quantum fluctuations of the parameters that define the solitonic solutions.

Furthermore, we demonstrate the uncertainty relations of the parameters for both the fundamental soliton and breather. We also discuss the dissociation of breather under both the influence of an external perturbation [1] and the quantum fluctuations of relative velocity. The former allows us to evaluate the breather dissociation time, i.e. the time it takes for the constituent solitons to be significantly separated. Without an external perturbation, the dissociation does not occur in the mean-field regime, thus making the dissociation time a potentially observable manifestation of quantum effects [3].

**References**

[1] O. V. Marchukov et al., Phys. Rev. A 99, 063623 (2019).

[2] A. Di Carli et al., Phys. Rev. Lett. 123, 123602 (2019).

[3] O. V. Marchukov et al., Phys. Rev. Lett. 125, 050405 (2020).

[4] D. Luo et al., Phys. Rev. Lett. 125, 183902 (2020).

**Title: Probing Fundamental Physics with Precision Molecular Spectroscopy**

Samuel Meek, Max Planck Institute for Multidisciplinary Sciences, Gaettingen

*Monday May 23, 2022
SPECIAL TIME: 9:00-10:00am (Zoom link will be announced)
*

Abstract: Precise measurements of molecular transition frequencies can provide a means to test fundamental physical questions, such as whether there are additional forces between the nuclei that are not predicted by the standard model or if the masses of elementary particles vary over time. Such measurements can also help determine physical constants more precisely and provide data that can be used to better interpret astronomical spectra. In my lab, we have developed an apparatus for determining vibrational and electronic transition frequencies of isolated small molecules with high precision. The central component of this apparatus is a precision laser system containing narrow-linewidth reference and spectroscopy lasers linked to each other and to an atomic clock reference using an optical frequency comb. So far, we have used this apparatus to investigate electronic transitions in OH, OD, and SH, as well as vibrational transitions in HD and D₂. In all of these measurements, we have been able to determine the absolute transition frequencies with orders of magnitude higher precision than previously reported and, in some cases, detect systematic errors in earlier, less precise measurements. In future measurements, trapping the molecules and applying quantum techniques can help to achieve narrower transition linewidths and improve the precision further.

### Fall 2021 (virtual Zoom series)

**Title: High-precision physics and chemistry with ultracold molecules**

**Tanya Zelevinsky, Columbia University**

*Tuesday, August 24, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Techniques for controlling the internal quantum states and motion of atoms have led to extremely precise metrology and studies of degenerate gases. Extending such techniques to various types of molecules further enriches the understanding of fundamental physics, basic chemical processes, and many-body science. Samples of diatomic molecules can be created by binding laser-cooled atoms, or by direct molecular laser cooling. We explore both approaches and demonstrate high-precision metrology with an optical-lattice based molecular clock as well as chemistry in the highly nonclassical domain.

**Title: Topological physics: from photons to electrons**

**Mohammad Hafezi, University of Maryland**

*Friday, September 3, 2021
12:15-1:15pm (Zoom link will be announced)
*

Abstract: here are many intriguing physical phenomena that are associated with topological features --- global properties that are not discernible locally. The best-known examples are quantum Hall effects in electronic systems, where insensitivity to local properties manifests itself as conductance through edge states which are insensitive to defects and disorder. In the talk, we first discuss how similar physics can be explored with photons; specifically, how various topological models can be simulated in various photonics systems, from ring resonators to photonic crystals. We then discuss that the integration of strong optical nonlinearity can lead to unique bosonic phenomena, such as topological frequency combs, topological source of quantum light, and chiral quantum optics. These results may enable the development of classical and quantum optical devices with built-in protection for next-generation optoelectronic and quantum technologies. In the end, we discuss an emerging field at the interface of quantum optics and correlated electron systems, with the goal of creating and manipulating many-body states of light-matter hybrids with new functionalities, such as high-Tc superconductors.

**Title: Synthetic dimensions in ultracold quantum matter**

**Kaden Hazzard, Rice University**

*Tuesday, September 7, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: A synthetic dimension is a degree of freedom where motion in space is mimicked by motion through other states, such as hyperfine states of atoms or rotations of molecules. These states act as lattice sites in extra spatial dimensions, and can be used alone or in combination with any real spatial dimensions. The superb control of internal degrees of freedom opens a vast new frontier in quantum science, both for simulating phenomena in condensed matter (such as topological band structures or fracton matter) and for studying phenomena that don't occur elsewhere in nature, such as fluctuating quantum strings, embranes, and even 3-branes that fluctuate in 4D.

In this talk I will discuss our theoretical understanding of synthetic dimensions, and the rapid experimental progress exploring synthetic dimensions made with three types of ultracold matter: Rydberg atoms, molecules, and momentum-space lattices.

**Title: Simulating many-body physics using quantum tensor networks**

*Michael Foss-Feig, Honeywell*

*Friday, September 17, 2021
12:15-1:15pm (Zoom link will be announced)
*

Abstract: Tensor network techniques exploit the structure of entanglement to dramatically reduce the difficulty of simulating quantum systems on classical computers. But these techniques have limitations, and many problems in many-body quantum physics, for example simulating dynamics, remain intractable despite decades of effort to solve them. Quantum computers offer an alternative route to simulating quantum systems that is in principle efficient, but their small size and limited fidelities have so far prevented solution of problems of real practical interest that cannot be solved classically. Here we discuss prospects for combining these two techniques by directly representing tensor-network states as quantum circuits, and show that recent developments in quantum hardware make it possible to carry out quantitatively accurate simulations of quantum dynamics directly in the thermodynamic (infinite system size) limit using a small number of qubits.

**Title: Entangled Bose-Einstein condensates in momentum space**

*Carsten Klempt, Leibniz University Hannover*

*Tuesday, September 21, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: The generation and application of entangled many-particle states is a central goal of the second quantum revolution. In our work, we employ spin-changing collisions to create spin entanglement in atomic Bose-Einstein condensates. I will present our work towards transferring this entanglement towards external degrees of freedom. The successful transfer of spin entanglement to momentum states presents an important step towards the operation of future atom interferometers with a sensitivity beyond the Standard Quantum Limit.

**Title: Dipolar Quantum Gases of Magnetic Lanthanide Atoms: achievements and future opportunities**

*Francesca Ferlaino, University of Innsbruck*

*Tuesday, September 28, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Since its creation, the field of ultracold atoms has been through fantastic developments. Some of the most recent include the development of quantum-gas microscopes, atom tweezers, and various forms of interaction engineering. Each of these experimental advances has allowed new quantum phenomena to be accessed and observed. A further important development is based on the use of more exotic atomic species, whose peculiar atomic properties have allowed to broaden the horizons of investigation.

This talk aims to retrace the new opportunities that have emerged from the use of quantum gases composed of the strongly magnetic erbium and dysprosium atoms from the perspective of the Innsbruck experiments.

Thanks to their large magnetic moment, these species exhibit a large dipolar interaction that has allowed us to observe rotonic excitations, quantum droplets, and supersolid states. Moreover, their dense atomic spectrum has also made possible to implement new optical manipulation schemes, and more recently the observation of an Hz-wide transition in the telecom frequency region promises new possibilities in quantum optics.

**Title: Observation of a Transition between Dynamical Phases in a Quantum Degenerate Fermi Gas**

*Joseph Thywissen, University of Toronto*

*Tuesday, October 5, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: I will discuss collective dynamics of ultracold fermions, in two contexts. First, I will discuss a study of spin dynamics near the non-interacting point of an s-wave Feshbach resonance. The collective enhancement of weak interactions allows for an interesting range of behaviors, including a non-equilibrium phase transition. Second, I will discuss a proposal to study collective orbital dynamics of spin-polarized fermions in an optical lattice.

A proposed paradigm for out-of-equilibrium quantum systems is that an analogue of quantum phase transitions exists between parameter regimes of qualitatively distinct time-dependent behavior. We present evidence of such a transition between dynamical phases in a cold-atom quantum simulator of the collective Heisenberg model. Our simulator encodes spin in the hyperfine states of ultracold fermionic potassium. Atoms are pinned in a network of single-particle modes, whose spatial extent emulates the long-range interactions of traditional quantum magnets. We find that, below a critical interaction strength, magnetization of an initially polarized fermionic gas decays quickly, while above the transition point, the magnetization becomes long-lived, due to an energy gap that protects against dephasing by the inhomogeneous axial field. Our quantum simulation reveals a non-equilibrium transition predicted to exist but not yet directly observed in quenched s-wave superconductors.

In the second part of the talk, I discuss non-equilibrium orbital dynamics of spin-polarized ultracold fermions in the first excited band of an optical lattice. A specific lattice depth and filling configuration is designed to allow the px and py excited orbital degrees of freedom to act as a pseudo-spin. Bragg dressing can reduce single-particle dispersion rates, such that a collective many-body gap is opened with only moderate Feshbach enhancement of p-wave interactions. Time permitting, I will discuss the first experimental steps towards realizing this proposal.

**Title: A quick visit to the world of quantum graphs**

*Alejandro Chávez-Domínguez, OU Mathematics*

*Friday, October 15, 2021*

* 12:15-1:15pm (Zoom link will be announced)
*

Abstract: A classical graph consists of a set of vertices, some pairs of which are joined by edges. In contrast, a quantum graph is a linear space of square matrices with complex entries, containing the identity matrix and closed under taking the conjugate transpose. This seemingly strange notion has its origins in Quantum Information Theory, where such objects play a role that in classical Information Theory is occupied by a classical graph.

In the talk I will explain the analogy relating classical and quantum graphs, and will present a couple of examples of recently-developed quantum versions of some geometric notions from classical graph theory. Based on joint works with Andrew Swift.

**Title: Site-specific spectroscopic measurement of spin and charge in (LuFeO _{3})_{m}/(LuFe_{2}O_{4})_{1} multiferroic superlattices**

Janice Musfeldt, University of Tennessee

*Tuesday, October 26, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: TBA

**Title: Heralded Noiseless Amplification and Attenuation for Quantum Communications**

*Todd Pittman, UMBC*

*Tuesday, November 2, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Although quantum optical signals cannot be deterministically amplified without adding noise, it has recently been shown that non-deterministic (heralded) noiseless amplification is possible. Somewhat surprisingly, the inverse process of heralded noiseless attenuation has also been shown to be useful in the context of quantum communications*. *Here we review our group’s recent work in these areas, including the counterintuitive use of an Optical Parametric Amplifier (OPA) as an attenuator, and methods of combining heralded amplifiers and attenuators to reduce the amount of “which path” information left behind in a quantum communications channel. Many of these interesting effects result from the probabilistic nature of the heralding process, and are closely related to the idea that the “annihilation” operator, â, can actually increase the average number of photons for certain states.

**Title: The Quantum Neutron**

**Charles Clark, NIST, JQI and Univ. of Maryland**

*Date: Friday, November 5, 2021
12:15-1:15pm LH 105
*

Abstract: I present a simple overview of the particle and wave properties of the neutron, with emphasis on their parallels in light, electrons and atoms. Neutron interferometry enables one to realize the quantum limit of the Young double slit experiment, when no mor that only neutron is ever present in the interferometer. How can only one neutron go through both slits? We have used neutron interferometry and holography to address some of the questions of structured waves of light and matter that have been studied with photons, electrons and atoms.

**Title: Lattice resonances: a collective response of periodic arrays of nanostructures**

Alejandro Manjavacas, Instituto de Óptica ( CSIC)/University of New Mexico.

*Tuesday, November 9, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Periodic arrays are an exceptionally interesting arrangement for nanostructures due to their ability to support strong collective lattice resonances, which arise from the coherent multiple scattering enabled by the array periodicity. Thanks to these exceptional properties, periodic arrays are being exploited in a wide variety of applications, including ultrasensitive biosensing, nanoscale light emission, and color printing, to cite a few.

*
*The goal of this seminar is to provide an instructive introduction to this topic. To that end, we will start by discussing how the interplay between the response of the individual constituents of the array and their collective interaction determines the ultimate limits of the field enhancement provided by a periodic array. We will also discuss the response of arrays with multi-particle unit cells using an analytical approach based on hybridization theory, which provides a simple and efficient way to design periodic arrays with engineered properties. We will pay particular attention to bipartite arrays and show how, depending on the relative position of the particles within the unit cell, these systems can support super- or subradiant lattice resonances with very different optical responses.

**Title: Unsupervised Machine Learning of Quantum Phase Transitions**

* Zhe-Xuan Gong, Colorado School of Mines*

*Tuesday, November 16, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Experimental quantum simulators have become large and complex enough that discovering new physics from the huge amount of measurement data can be quite challenging, especially when little theoretical understanding of the simulated model is available. Unsupervised machine learning methods are particularly promising in overcoming this challenge. I will review typical unsupervised learning methods and show that they generally only work for learning simple symmetry-breaking quantum phase transitions. I will then show that a more advanced method known as diffusion map, which performs nonlinear dimensionality reduction and spectral clustering of the measurement data, has much better potential for unsupervised learning of complex phase transitions, such as topological phase transitions and many-body localization. This method is readily applicable to many experimental quantum simulators as it only requires measuring each particle in a single and local basis.

Reference: A. Lidiak and Z.-X. Gong, Phys. Rev. Lett. 125, 225701 (2020).

**Title: Quantum Control with Spinor Bose-Einstein Condensates **

*Hillary Hurst, San Jose State University*

*Friday, November 19, 2021
12:15-1:15pm (Zoom link will be announced)*

Quantum Control with Spinor Bose-Einstein Condensates

Abstract: Understanding and controlling many-body quantum systems in noisy environments is paramount to developing robust quantum technologies. An external environment can be thought of as a "measurement reservoir" which extracts information about the quantum system. Cold atoms are well suited to examine system-environment interaction via weak (i.e. minimally destructive) measurement techniques, wherein the measurement probe acts as the environment and also provides a noisy record of system dynamics. The measurement record can then be used in a feedback scheme, opening the door to real time control of quantum gases. In this talk I discuss our theoretical proposal to use weak measurement and feedback to engineer new phases in spin-1/2 Bose-Einstein condensates. First, I will discuss the formalism we developed to describe condensates undergoing weak measurement via phase-contrast imaging. We then show that measurement and feedback alters the effective Hamiltonian governing system dynamics, thereby driving phase transitions reminiscent of a quantum quench for the closed system. We also develop a feedback cooling protocol which prevents runaway heating of the condensate due to measurement backaction. Our results show that measurement and feedback can alter condensate dynamics in a stable, controllable manner and provides a route toward Hamiltonian engineering in many-body systems.

HMH, S. Guo, and I. B. Spielman, Physical Review Research, 2(4), 043325 (2020), HMH and I. B. Spielman, Physical Review A 99.5, 05361 (2019)

**Title: Formation and Evolution of Single Molecule Junctions Containing ransition Metal Atoms**

Maria Kamanetska, Boston University

*Tuesday, November 30, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: Untangling structure-function relationships on the nano-scale is critical to understanding biological molecular machinery and to engineering human-made nano-devices. In this talk I will give an overview of my lab’s approaches to probing and controlling sub-nanometer atomic arrangements in biological and synthetic systems. I will focus on our combined Scanning Tunneling Microscope-based Break Junction measurements and Density Functional Theory studies of the formation and evolution of molecular junctions incorporating transition metal atoms. Such junctions can increase the scope of observable phenomena due to incorporation of metal centers with new degrees of freedom. Overall, our methods allow a comprehensive, atomic picture of junction structure and electronic properties. Interestingly, we find that transition metal centers can be wired into single molecule junctions by coordinating to organic linkers during junction elongation. These *in situ* assembled coordination complexes present a new approach for creating molecular junctions with potential for non-trivial electronic and spin functionality.

**Title: Quantum Error Correction Now!**

Kenneth Brown, Duke University

*Tuesday, December 7, 2021
1:15-2:15pm (Zoom link will be announced)
*

Abstract: The power of quantum computers requires reliable and robust quantum systems. It is widely believed that quantum error correction will be critical to make quantum operations with errors less than one part per billion. In this talk, I will explain the basics of quantum error correction and then discuss recent experimental demonstrations showing that the time for quantum error correction is now.