The 2023 American Physical Society (APS) March Meeting drew international leaders in physics to Las Vegas this month, where they shared research and discussed the newest opportunities in industry and academia. The University of Chicago’s Pritzker School of Molecular Engineering (PME) presented cutting-edge research spanning subjects from quantum networking to biosensing, including a critical update on the national state of quantum science and engineering.
The highlights included:
- Nine invited speakers from Pritzker Molecular Engineering
- Twenty-two invited speakers from the University of Chicago
- Quantum Casino
- Chicago Quantum Exchange community room
The APS meeting is a leading venue for presenting the scientific advances that are the basis for novel and improved high-tech devices, imaging instrumentation, and materials. More than 10,000 technical papers are presented at the meeting, covering a broad spectrum of topics.
PME presentation highlights
Influence of Sequence Charge Pattern on Secondary Structures of Bioinspired Polyampholytes
Matthew Tirrell, D. Gale Johnson Distinguished Service Professor and Dean of the Pritzker School of Molecular Engineering
A systematic investigation of the influence of sequence charge pattern on the secondary structure preferences of peptide-based polyampholytes and their responsiveness to external stimuli will be presented. The polyampholyte sequences utilized in this study are composed entirely of ionizable amino acids (charge fraction, f=1), and an equal number of positive and negative charges (f+=f-=0.5) with distinct charge patterns consisting of lysine and glutamic acid monomers. Our work reveals that the sequence charge pattern has a pronounced influence on the secondary structure preferences of polyampholytes at physiological pH. Furthermore, it demonstrates that external stimuli such as pH and ionic strength can be used to modulate the secondary structure of the examined polyampholytes. The observed structural transformations are different from those determined for uniformly charged homo-polypeptides under matching conditions.
Quantum Information Science and Engineering
David D Awschalom, Liew Family Professor of Molecular Engineering and Vice Dean for Research and Infrastructure, the Pritzker School of Molecular Engineering; Senior Scientist, Argonne National Laboratory; Director of the Chicago Quantum Exchange
A special session, devoted to the National Quantum Initiative (NQI), including six talks from the industry, research, education, and government leaders involved in the Quantum Information Science and Engineering (QISE) efforts. Speakers will share their perspectives and vision of QISE in general and NQI in particular and are encouraged to discuss experiences, milestones, results, lessons learned, outlook, and their takes on problems solved and unsolved under the general umbrella of QISE and NQI.
Nancy Kawalek, Professor and Distinguished Fellow in the Arts, Science and Technology
Sunanda Prabhu-Gaunkar, STAGE Director of Science
Engaging, fun, and memorable games that afford a first-hand experience with core principles of quantum mechanics. Concepts such as probability, measurement, superposition, coherence, entanglement, and quantum key distribution are integral to the rules and mechanics of the games, some of which require players to employ many of the same problem-solving strategies as those encountered in the laboratory.
Diamond bullseye antennas for enhanced quantum collection efficiency
Anchita Addhya, PhD student in High Lab
Color centers in wide bandgap materials such as diamond and silicon carbide are excellent candidates for quantum technologies due to their spin initialization, manipulation, and readout. Unfortunately, the host materials for these applications present high intrinsic optical indexes, limiting photon collection due to total internal reflection. In this work, we demonstrate improved collection efficiencies from these color centers with the use of photonic structures, paving the way for efficient communication and sensing protocols. Specifically, we show the fabrication of bullseye antenna resonators etched into thin diamond membranes improve signal collection via Purcell enhancement while simultaneously realizing higher collection efficiency into low NA objectives. The radius and pitch of these structures are numerically optimized to be in resonance with the emission wavelengths of the integrated color centers e.g., nitrogen, silicon, and germanium-vacancy centers. We also experimentally demonstrate that the resonances can be realized across a broad range of wavelengths in the visible and near-infrared. Fabrication of these photonic cavities is shown to be tailorable, enabling flexibility and ease of integration with the chosen emitters.
Mid-circuit readout and error mitigation on a dual-species atom array processor
Hannes Bernien, Assistant Professor of Molecular Engineering
Scaling up invariably error-prone quantum processors is a formidable challenge. While quantum error correction ultimately promises fault-tolerant operation, the required qubit overhead and error thresholds are daunting, and many codes break down under correlated noise. Recent proposals have suggested a complementary approach based on co-located, auxiliary ‘spectator’ qubits. These act as in-situ probes of noise, and enable real-time, coherent corrections of the resulting errors on the data qubits. Here, we use an array of cesium spectator qubits to correct correlated phase errors on an array of rubidium data qubits [1]. Crucially, by combining in-sequence readouts, data processing, and feed-forward operations, these correlated errors are suppressed within the execution of the quantum circuit.
The learnability of Pauli noise
Senrui Chen, PhD student from Jiang Group
Understanding quantum noise is a major challenge for scaling up quantum computing systems. Despite recent developments in quantum noise characterization methods, the fundamental question of what information about gate noise is self-consistently learnable has been unclear even for a single CNOT gate. In this work, we give a precise characterization about the learnability of Pauli noise associated with Clifford gates using graph theoretical tools, showing that the learnable information corresponds exactly to the cycle space of the pattern transfer graph of a given gate set. We show that a modified version of cycle benchmarking can extract all learnable information of Pauli noise. We experimentally demonstrate Pauli noise characterization of IBM’s CNOT gate, where we learn all 14 learnable degrees of freedom and bound the 2 unlearnable degrees of freedom using physical constraints. The implications of these results for quantum error mitigation will be discussed. We will also talk about the possibility to resolve the unlearnability by going beyond qubits and leveraging additional energy levels.
Aashish Clerk, Professor of Molecular Engineering
Evolving an arbitrary initial state of a system described by a Markovian Lindblad master equation requires finding the full Liouvillian eigenvalues and eigenvectors. Recently, Prosen [1] and Prosen and Seligman [CITE] developed third quantization, a technique which allows one to diagonalize the Lindbladian of quadratic fermionic or bosons systems linearly-coupled to a set of baths. However, it is not immediately clear how this approach is connected to other more standard methods.In this work we reformulate third quantization by demonstrating that it is naturally related to other well-known open quantum system formalisms and tools. We first show that all such models exhibit a dissipative symmetry that, once used, allows for a simple diagonalization procedure. We then demonstrate how the Wigner quasi-probability function and Keldysh field theory emerge in our framework. Our reformulation renders third quantization an overall more powerful tool in the study of open quantum systems.
Charge-Pattern Dependent Sequestration of Globular Proteins in Membraneless Organelles
Heyi Liang, postdoctoral researcher in de Pablo Group
Condensation of polyampholytes into coacervates is driven by sequence-dependent charge correlations. It is proposed to be one of the mechanisms underlying the formation of membraneless organelles (MLOs) through liquid-liquid phase separation of intrinsically disordered proteins (IDPs), which are rich in charged residues and lack ordered structures. Unlike IDPs, globular proteins fold into complicated 3d structures and expose their charged residues to the surface to form specific surface charge patterns. We use coarse-grained molecular dynamics simulations to study the role of surface charge patterns in the sequestration of globular proteins in MLOs. In our coarse-grained model, globular proteins are modeled by spherical nanoparticles with patterned surface charges, while MLOs are represented by sequence-controlled polyampholyte coacervates. The free energy landscape of a globular protein partitioning between two MLOs is calculated by umbrella sampling. We have shown that the MLO formed by blocky polyampholytes prefers to uptake globular proteins with patchy surface charge, while the MLO formed by random polyampholytes shows a stronger affinity to globular proteins with random surface charge. Such "like dissolves like" behavior is consistent with the theoretical picture of the sequence/pattern-dependent electrostatic correlation.
Relaxation Mechanisms of Single Dark Spins in Diamond
Jonathan Marcks, PhD student in Awschalom Group
Widespread adoption of the nitrogen vacancy (NV) center is diamond for quantum sensing requires understanding and mitigating spin decoherence. The substitutional nitrogen electron spin (P1 center) bath, introduced into the diamond lattice during NV center synthesis, is a dominant source of NV center decoherence, but an experimental picture of the underlying bath evolution remains incomplete. Here, we present a combined computational and experimental approach to engineer NV-bath interactions and measure the relaxation of individual P1 bath spins. First, cluster correlation expansion (CCE) calculations predict the growth conditions necessary to isolate single bath spin interactions. Furthermore, these calculations allow us to determine the spin bath structure around the NV center, enabling simulations of bath dynamics that account for local disorder. We then use the NV center to measure the evolution of P1 spins with a polarization pump-probe scheme. Time-resolved P1 measurements reveal charge and spin dynamics at the single-spin level.
Interfacing Biomolecules with Coherent Quantum Sensors
Peter Maurer, Assistant Professor of Molecular Engineering
Quantum optics has had a profound impact on precision measurements, and recently enabled probing various physical quantities, such as magnetic fields and temperature, with nanoscale spatial resolution. In my talk, I will discuss the development and application of novel quantum metrological techniques that enable the study of biological systems in a new regime. I will start with a general introduction to quantum sensing and its applications to nanoscale nuclear magnetic resonance (NMR) spectroscopy. In this context, I will discuss how we can utilize tools from single-molecule biophysics to interface a coherent quantum sensor with individual intact biomolecules, and how this could eventually pave the way towards a new generation of biophysical and diagnostic devices.
2D heat, light, and mass transport in engineered 2D systems
Jiwoong Park, Professor of Molecular Engineering
Two-dimensional atomic crystals, including graphene, hBN and TMDs, and their heterostacks have provide excellent platforms for exploring both conventional and correlated electronic phenomena with broad scientific and technological impacts. It is increasingly recognized that the same 2D nature of these systems provide unprecendented opprotunites for designing and controling novel transport phenomena with other fundamental degrees of freedom: phonons, photons, and mass. In this talk, we will present my group's recent efforts to generate large-scale 2D materials and stacked films specifically engineered to realize 2D photonic, photonic and mass transport phenomena. This general picture, which is mostly demonstrated with waferscale TMD monolayers so far, will be also discussed in the context of new molecule based crystals and hybrid systems for further expansion of available 2D systems.
Anion Conduction and Water Percolation Effects in Polynorbornene-based Thin Film Membranes
Shrayesh Patel, Assistant Professor of Molecular Engineering
Anion exchange membranes (AEMs) are at the heart of many electrochemical driven processes such as fuel cells, water electrolysers, reverse electrodialysis, and redox flow batteries. It requires a fundamental understanding of ion transport in AEMs at different hydration states to efficiently operate these systems with long term durability. To allow for better understanding, combining experimental characterizations with targeted simulations reveals new insights on the interplay of water and ion transport in hydrated AEMs. Here, we have synthesized and fabricated polynorbornene-based anion exchange thin films as our model polymers due to their high alkaline stabilities and ionic conductivities via vapor infiltration reactions (VIRs). We customize an in situ ellipsometer to understand thin film expansion at different hydration levels and water uptakes of AEMs has been measured by dynamic water sorption. We investigate bromide ion (Br-) transport by measuring thin film electrochemical impedance as a function of relative humidity and temperature. Br- conductivities show Arrhenius behaviors and activation energy has been extracted as a function of relative humidity. By combining experimental characterizations, percolation theory, and atomistic molecular dynamics simulations, we quantitatively identify two transport regimes (site hopping mechanism and vehicular mechanism) from low to high relative humidity.
Dual-species Rydberg array of rubidium and cesium atoms
Kevin Singh, postdoctoral researcher in Bernien Group
Quantum information processing architectures that leverage multiple modalities of qubits offer compelling strategies for suppressing qubit errors, performing quantum non-demolition measurements, and executing auxiliary-qubit based quantum protocols. In this talk I will present the latest results from our dual-species atom array composed of individually controlled rubidium and cesium atomic qubits. Using species-selective trapping, we demonstrate independent placement of single rubidium and cesium atoms in arbitrary geometries up to 512 trapping sites and observe negligible crosstalk [1]. This negligible crosstalk enables reloading of one set of atomic qubits into the array while maintaining quantum coherence in the other, paving the way towards continuous-mode operation of atom array processors. Furthermore, I will discuss how we use mid-circuit measurements on one atomic species to perform corrections or apply quantum gates on the other species all within the execution of a quantum circuit [2]. Combining these feedforward operations with programmable intraspecies and interspecies Rydberg gates will enable auxiliary-qubit-assisted protocols, as required for quantum error correction and measurement-based state preparation.
Unbounded deterministic entanglement generation by autonomous quantum measurement and feedforward
Yuxin Wang, PhD student in Clerk Group
Entanglement generation is crucial for the implementation of a plethora of quantum information processing tasks. Open quantum dynamics, including dissipation and measurements, provides a versatile approach to producing entanglement. However, standard open-system entangling schemes either require post-selection or conditional feedback, or focus on the stationary state regime, where the maximal amount of entanglement is ultimately set by parameters describing the dissipative process (i.e. the Liouvillian). Here, we propose a class of dissipative protocols, based on autonomous quantum measurement and feedforward, where the entanglement generation is deterministic, and can even grow indefinitely with evolution time in bosonic systems. While such entanglement exhibits a curious tradeoff with purity of the generated states, we also show how pure-state entanglement can be deterministically recovered via a single cycle of local measurement and feedback operations. Our results reveal a pathway for converting measurement-induced conditional entanglement into deterministic entanglement, and also shed new light on the entanglement generation mechanism via correlated dephasing. Furthermore, our feedforward-based approach opens up new possibilities of probing measurement-induced entanglement phase transitions in unconditional dynamics.
Delicate Ferromagnetism in MnBi6Te10
Shuolong Yang, Assistant Professor of Molecular Engineering
Tailoring magnetic orders in topological insulators is critical to the realization of topological quantum phenomena. An outstanding challenge is to find a material where atomic defects lead to tunable magnetic orders while maintaining a nontrivial topology. Here, by combining magnetization measurements, angle-resolved photoemission spectroscopy, and transmission electron microscopy, we reveal disorder-enabled, tunable magnetic ground states in MnBi6Te10. In the ferromagnetic phase, an energy gap of 15 meV is resolved at the Dirac point on the MnBi2Te4 termination. In contrast, antiferromagnetic MnBi6Te10 exhibits gapless topological surface states on all terminations. Transmission electron microscopy and magnetization measurements reveal substantial Mn vacancies and Mn migration in ferromagnetic MnBi6Te10. We provide a conceptual framework where a cooperative interplay of these defects drives a delicate change of overall magnetic ground state energies, and leads to tunable magnetic topological orders. Our work provides a clear pathway for nanoscale defect-engineering towards the realization of topological quantum phases.