2021 Seminars

Dr. James S. Clarke (Intel Corporation)

"From a Grain of Sand to a Quantum Computer"

Today’s quantum processors are limited to 10’s of entangled quantum bits. If you believe the hype, a commercially relevant system is just around the corner that can outperform our largest supercomputers. The reality, however, is that we are still at mile 1 of a marathon. There are many unanswered fundamental questions. At Intel, our approach is to rely on the continued evolution of Moore’s Law to build qubit arrays with a high degree of process control. Here, we present progress toward the realization of 300mm spin qubit devices in a production environment. This includes (i) isotopically purified 28 Si epi substrates with a compelling substrate quality (ii) design of a custom qubit layout, (iii) integration of spin qubit devices using immersion lithography, moving from classical transistor structures to full spin qubits, and (iv) the realization of quantum dots in a nested gate design novel to a 300mm process line. In addition, this talk will focus on two bottlenecks to moving beyond today’s few-qubit devices. The first bottleneck is in the interconnect design of the quantum circuit. Today’s qubits have personalities. Individual control of each qubit is required. A small quantum processor today has multiple RF and DC wires per qubit. This is a brute force approach to wiring and will not scale to the millions of qubits needed for large applications. The second bottleneck relates to the speed of information turns in quantum development. Fabrication of spin qubits in a silicon substrate bares similarity to conventional transistors from advanced CMOS technologies. One of the above 300mm wafers has over 10,000 individual quantum test structures. Naturally, R&D should be accelerated by the potential volume of statistical data. While automated electrical testing of a CMOS transistor wafer can be completed in less than an hour at room temperature, data collection at cryogenic temperatures is currently limited to a small number of devices with a turnaround of hours to days. Rhetorically speaking, “How can we deliver an exponentially fast compute technology with slow and serial characterization of quantum chips?” Biography: Jim Clarke is the director of the Quantum Hardware research group within Intel’s Components Research Organization. Jim launched Intel’s Quantum Computing effort in 2015, as well as a research partnership with QuTech (TU Delft and TNO). His group’s primary focus is to use Intel’s process expertise to develop scalable qubit arrays. In 2018, Jim worked with industry leaders and the Intel policy group to influence the U.S. National Quantum Initiative Act. Prior to his current role, Jim managed a group focused on interconnect research at advanced technology nodes as well as evaluating new materials and paradigms for interconnect performance. He has co-authored more than 100 papers and has over 50 patents. Prior to joining Intel in 2001, Jim completed a B.S. in chemistry at Indiana University, a Ph.D. in physical chemistry at Harvard University and a post-doctoral fellowship in physical organic chemistry at ETH, Zürich. He is a member of IEEE.

Host: Prof. Sophia Economou

Prof. Pablo Poggi (University of New Mexico)

Errors in NISQ era Quantum Simulators: Theory of Robust observables and instabilities in Trotterized evolution

Quantum simulators are widely seen as one of the most promising near-term applications of quantum technologies. However, it remains unclear to what extent a noisy device can output reliable results in the presence of unavoidable imperfections. In this talk I will talk about some recent work addressing this issue. First, I will describe a recently developed framework that links the robustness to perturbations of the simulated expectation values with the spectral properties of the output observable, which can in turn be associated with the macroscopic or microscopic character of the observable. I will show that, under general assumptions and on average over all states, imperfect simulators are able to reproduce the dynamics of macroscopic observable accurately, while the relative error in the expectation value of microscopic observables is much larger on average. Then, I will discuss gate-based simulation using Trotter - Suzuki decomposition, and describe how the mapping of the simulator dynamics to a driven Floquet system can lead to novel insights into the emergence of errors in the quantum simulation.

Host: Prof. Sophia Economou

Prof. Sunxiang Huang (University of Miami)

The multifaceted physics of correlated topological kagome metals in thin films

Recently, a class of materials known as topological kagome metals (TKMs) are rapidly being recognized as exciting topological materials with rich magnetic ordering and electron correlations. At the heart of TKMs are layered 2D kagome lattices occupied by transition metals (Fe, Mn, Co), which give rise to exotic topological band structure with a coexistence of Weyl/Dirac cones and flat bands. The research on TKMs has mostly centered on bulk compounds. The introduction of high-quality epitaxial films and hetero-structures enables opportunities to achieve properties and functions impossible within parent materials. In this talk, I will describe our realization of high-quality epitaxial thin films of several TKMs (Mn3Sn, Fe3Sn2, FeSn, and CoSn). I’ll then discuss their multifaceted physics in thin films, including Kondo physics in Mn3+xSn1-x [1], spintronic properties of TKMs [2,3], and superconducting proximity effect with potential triplet pairing in the hetero structure between TKMs and the superconductor Nb.

Host: Prof. Shengfeng Cheng

No Seminar

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Dr. Olivia Lanes (IBM Quantum)

" Superconducting Quantum Processors: Hardware & Control"

This talk will largely be an overview of the progress IBM Quantum is making towards a large scale quantum computer. It will begin with a broad overview of qubits, transmons, and quantum information at large. Next, I will discuss IBM's universal gates, including the entangling cross resonance gate, and iSWAP. I will also discuss the processing unit and current hardware challenges we are facing the in the field before moving on to bench marking metrics and the latest results. Lastly, I will demonstrate a newer usage of the IBM Quantum hardware to simulate time evolved Hamiltonian's, and will conclude my introducing the fall Open Science Challenge which is focused on this application.

Host: Prof. Sophia Economou

Yifei Wang (Physics, Virginia Tech)

"Broadband photodetectors based on graphene/semiconductor hetero structures"

Ultra fast,highly sensitive, low cost photodetectors operating at room temperature sensitive from the deep-ultraviolet to mid-infrared region remain a significant challenge in optoelectronics. Achievements in traditional semiconductors using cryogenic operation and complicated growth processes prevent the cost-effective and practical application of broadband detectors. Alternative methods towards high-performance photodetectors, hybrid graphene-semiconductor colloidal quantum dots have been intensively explored. However, the operation of these photodetectors has been limited by the spectral bandwidth and response time.Here, we have demonstrated hybrid photodetectors operating from the deep-ultraviolet to the mid-infrared region with high sensitivity and ultra-fast response based on graphene/semiconductor hetero-structures. The photo detectors achieve a high photo-resistivity (up to 2.5 ´106 A/W), ultra fast rise time (faster than 20 ns), and a specific detectivity (up to ~ 8.5 ´ 1011 Jones). The work provides a method for achieving high-performance optoelectronics operating in the deep-ultraviolet to mid-infrared region.

Host: Prof. Vinh Nguyen

No Seminar (Thanksgiving Holiday)

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Reserved

Host: Prof. Vinh Nguyen

Joint CDM & CSB Seminar

Dr. Sascha Wald (Dresden, Germany)

NON-EQUILIBRIUM DYNAMICS IN MANY-BODY QUANTUM SYSTEMS

We study dynamical transition phenomena in analytically solvable many-body quantum systems. Here, we focus on the quantum spherical model and other closely related models that have proven to be a valuable tool for the study of universal properties where one would usually strictly employ numerical methods. We show how the external constraints that define these models can induce surprisingly rich dynamical behavior, such as chaotic phases and freezing-by-heating transitions, on relatively simple single-body systems. We then discuss a naive Lindblad approach to the many-body dynamics and we pinpoint the shortcomings of such an approach. To overcome these problems, we present a physical motivation of how to formulate sensible many-body quantum dynamics using quantum Langevin equations and we apply this type of dynamics to quench problems in the quantum spherical model

Host: Uwe Tauber

Condensed Matter Seminar

Prof. David Pekker (University of Pittsburgh)

"Simulating the dynamics of braiding of Majorana zero modes on the IBM quantum computer"

Topological quantum computing relies on braiding of non-abelian anyons like Majorana zero modes. While there has been considerable work on Majorana zero modes in engineered superconducting-semiconducting systems, thus far all attempts at observing branding experimentally have failed. Being interested in quantum simulation and braiding, it was natural to attempt to simulate the dynamics of braiding on an IBM quantum computer. Our first attempt failed as we found that the native quantum gates introduce too much noise. In order to overcome this problem, we used Qiskit Pulse to develop scaled two-qubit quantum gates that better match the unitary time evolution operator and enable us to observe braiding. This work demonstrates that quantum computers can indeed be used for simulating non-trivial quantum dynamics and highlights the use of pulse-level control for programming quantum computers. Finally, we remark that as far as we know our work is the first demonstration of braiding in a quantum system.

Host: Ed Barnes

No Seminar

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Condensed Matter Seminar

Prof. Yi-Ting Hsu (University of Notre Dame)

"Inversion-protected Majorana corner modes: A case study of superconducting mono-layer WTe2"

Mono-layer WTe2, an inversion-symmetric transition metal dichalcogenide, has recently been established as a quantum spin Hall insulator and found superconducting upon gating. It is therefore natural to wonder whether this discovered superconductivity is topological. In this talk I will first show that gated mono-layer WTe2 in fact satisfies a general recipe we find for an inversion-protected ``higher-order" topological superconductor. Such a class of 2D superconductors feature Majorana corner modes. Then I will present numerical results demonstrating that corner Majoranas indeed appear throughout the WTe2 superconducting phase diagram self-consistently. Finally, I will discuss the bulk-boundary correspondence and present topological in variants that can diagnose the type of Majorana boundary modes from ab initiation band structures. Our topological in variants could guide future material search for more candidate superconductors hosting corner Majoranas without utilizing proximity effect.

Host: Kyungwha Park

March Meeting-No Seminar

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Joint CDM & CSMB Seminar

Prof. Reza Mirzaeifar (Mechanical Engineering, Virginia Tech)

"Metal-Graphene Composites"

For years, in classic engineering, tremendous amount of work was dedicated to improve the metals properties by utilizing various therm-mechanical post-processing techniques. But at some point, almost everyone was accepting those methods have reached a saturation and modifying these techniques can only make insignificant improvements in mechanical properties. In recent years the idea of using some nano materials (such stenographer) changed the whole story and promised a chance to drastically improve the metals performance. However, in the process of reinforcing metals materialization many challenges evolved when the initial theoretical concepts-were tried to be implemented in practical applications. Although nano materials exhibit ultra-high strength and large recoverable strains (due to the absence of crystalline defects in their structure), when a nano-filler, e.g. graphene,is added to conventional metal matrices to create composites, their exceptional intrinsic mechanical properties cannot be fully harvested. This failure in achieving the intrinsic large elastic strain and high strengths of nano materials, once they are in composite, is commonly dubbed the “valley of death”, pointing to the loss of mechanical performance over two different length scales. In this talk, we review our recent investigations nonmetal-geographer composites and a new concept of matching the large recoverable strain in the transforming metal matrix with the large elastic strain of the graphene. Using the large recoverable strains in the metallic matrix, and the exceptional strength of reinforced composite particles in the composite, this system can make a significant advancement in transferring the exceptional mechanical properties of nano-fillers across larger scales, and can make a substantial progression in overcoming the longstanding strength-ductility trade-off challenge.

Host: Prof. Uwe Tauber

Condensed Matter Seminar

Prof. Shruti Puri (Yale University)

"Quantum Error Correction with Bosonic Qubits"

With fault-tolerant quantum error correction (FTQEC) it is possible to reliably simulate an arbitrarily long quantum circuit using faulty quantum operations as long as the error rate is below a threshold. Unfortunately, this tolerance to errors comes at the cost of dauntingly large overheads in the number of qubits and gates. Therefore, it is essential to develop natively robust qubits and gates to reduce the overheads for FTQEC. Recently, an alternate paradigm of quantum information processing has gained momentum which is based on encoding a qubit in an oscillator. Such qubits are referred to as bosonic qubits and can have some in-built protection against common errors from the environment. In this talk, I will discuss a particularly appealing bosonic qubit called the Kerr-cat qubit. This qubit is engineered to have inherent protection against certain errors which leads to a highly asymmetric or biased noise channel. I will show how the inherent bias in these qubits can be exploited to achieve hardware-efficient FTQEC.

Host: Prof. Ed Barnes

Joint CDM & CSMB Seminar

Dr. Michael Salemo (U.S. Army Research Laboratory)

"Atomistic and Coarse-Grained Polymer Modeling: Applications at the Army Research Laboratory"

Many fundamental and applied research projects at the Army Research Laboratory (ARL) rely on all-atom molecular dynamics (MD) simulations and also need to extend or couple to adjacent length and timescales. I will discuss two relevant modeling problems that link MD to smaller and larger length scales: First, ab-initio results on molecular photo excitation are used to model photo responsive molecules in glassy materials. Results from MD simulations show that the dynamics of photo activated molecules in glassy solids depends critically on local density features. A characteristic power-law wait-time for photo isomerization occurs in samples for densities that vary with photo activemolecule and glass-matrix material. Dynamic behavior is driven by difficult-to-identify local density features, which suggests an opportunity fora machine-learning approach. Second, understanding the shear flow and rheology of polymers like high-molecular-weight polyethylene requires simulations orders of magnitude beyond the lengths and times of atomistic MD.

Host:Prof. Shengfeng Cheng

Condensed Matter Seminar

Dr. Ruslan Shaydulin (Argonne National Lab)

"Classical symmetries and QAOA"

We study the relationship between the Quantum Approximate Optimization Algorithm (QAOA) and the underlying symmetries of the objective function to be optimized. Our approach formalizes the connection between quantum symmetry properties of the QAOA dynamics and the group of classical symmetries of the objective function. The connection is general and includes but is not limited to problems defined on graphs. We show a series of results exploring the connection and highlight examples of hard problem classes where a nontrivial symmetry subgroup can be obtained efficiently. In particular we show how classical objective function symmetries lead to invariant measurement outcome probabilities across states connected by such symmetries, independent of the choice of algorithm parameters or number of layers. We illustrate the power of the developed connection in two ways. First, we apply machine learning techniques towards predicting QAOA performance based on symmetry considerations. We provide numerical evidence that a small set of graph symmetry properties suffices to predict the minimum QAOA depth required to achieve a target approximation ratio on the Max Cut problem, in a practically important setting where QAOA parameter schedules are constrained to be linear and hence easier to optimize. Second, we show a connection between classical symmetries of the objective function and the symmetries of the terms of the cost Hamiltonian with respect to the QAOA energy. We show how by considering only the terms that are not connected by symmetry, we can significantly reduce the cost of evaluating the QAOA energy. <

Host: Prof. Sophia Economou

Condensed Matter Seminar

Dr. Nicholas Frattini (Yale University)

" The Kerr-cat qubit: stabilization, readout and operations "

Schrödinger cat states, super positions of coherent states in an oscillator, encode a noise-biased qubit that is naturally protected against phase-flip errors. To be practical for quantum information processing, these highly excited states must be stabilized to maintain the protection in a way that is simultaneously compatible with fast gates and readout of the encoded information. We experimentally demonstrate a method for the generation and stabilization of Schrödinger cat states--the Kerr-cat qubit--that is based on the interplay between Kerr non-linearity and single-mode squeezing in a superconducting microwave resonator. The realized Kerr-cat qubit exhibits over an order of magnitude increase in the transverse relaxation time over the single-photon Fock-state encoding, and all single-qubit gates were performed sixty times faster than the shortest coherence time. Unlike traditional two-level systems, the Kerr-cat qubit also admits a CNOT gate that preserves its noise-bias. All together, the Kerr-cat qubit is a potentially powerful tool for quantum information processing and even promises significant overhead reduction for quantum error correction in surface-code-style architectures.

Host: Prof. Sophia Economou

Special Time and Date Condensed Matter Seminar

Dr. Antonio Mezzacapo (IBM)

“Measurements of Complex Hamiltonians on Quantum Computers”

We present methods to estimate averages of quantum operators given as linear combination of Pauli operators, on states prepared with quantum computers. The approaches illustrated make use of short depth circuits and are relevant for variational quantum simulations of quantum chemistry. 

Host: Prof. Sophia Economou