Seminar

Quantum error-correcting codes are essential in the realization of a scalable fault-tolerant quantum computation. Traditionally, these codes encodes logical information in a fixed subspace of a many-body quantum system which allow correction of errors by performing commuting measurements to determine appropriate corrections. By allowing non-commuting measurements, one obtain the so called "subsystem’’ code which allow for simpler measurements and the ability to perform universal fault-tolerant computation by switching across logical subspaces.

Quantum information science is a promising, interdisciplinary field focusing on both understanding and utilizing quantum systems. Two major paradigms of quantum mechanics are discrete variable (finite dimensional) systems, such as qubits and qudits, and continuous variable (infinite dimensional) systems,  such as bosonic modes. In this dissertation, we explore the properties, protocols, and applications of both discrete and continuous variable systems.

Robust storage and manipulation of quantum information in realistic quantum devices remains one of the central challenges in realizing practical quantum computation. To resolve this problem, the quantum error correction (QEC) is proposed as a technique to perform robust encoding and operations in noisy and realistic quantum devices. In the quantum realm, two fundamentally different types of particles—fermions and bosons—exhibit distinct behaviors.

Quantum computers have the theoretical potential to solve problems intractable for classical computers. However, realizing this potential requires dealing with the noise inherent in near and far-term devices. One way of doing this is to redundantly encode the quantum information in a quantum error-correcting code and manipulate the encoded states to do computation. Protecting quantum information in this way incurs additional space overhead in the form of extra qubits; this is problematic since qubits are a scarce resource, especially for near-term quantum computers.

Locality constrains the flow of information between different parts of many-body quantum systems. In quantum computers, this affects the ability to perform arbitrary interactions for quantum information processing tasks. A crucial challenge for scalable quantum architectures is thus to minimize the overheads due to locality constraints. Additionally, locality constraints affect the way information and entanglement can be spread in many body quantum systems, and our ability to make predictions about such systems.

Instabilities, where initially small fluctuations seed the formation of large-scale structures, govern the dynamics in wide variety of fluid flows. The Rayleigh-Taylor instability (RTI) is an iconic example that leads to the development of mushroom-shaped incursions when immiscible fluids are accelerated into each other. RTI drives structure formation throughout science and engineering including table-top oil and water mixtures; supernova explosions; and inertial confinement fusion.  Despite its ubiquity, controlled laboratory RTI experiments are technically challenging.

Quantum many-body systems can host exotic phases of matter characterized by their quantum entanglement. Among them are phases with topological order. In this talk we discuss how to explore the toric code model in a field (or equivalently the Fradkin-Shenker lattice gauge theory) — a paradigmatic model hosting a Z2 topologically ordered phase and a trivial phase — on a quantum processor [1]. We then focus on the higher-form symmetries of the model. In contrast to global on-site (0-form) symmetries, higher-from symmetries act on subdimensional manifolds.

Moire superlattices in semiconductors are predicted to exhibit a rich variety of interaction-induced topological states. However, experimental demonstrations of such topological states, apart from MoTe2 superlattices [1–8], have remained scarce [9, 10]. Here, we report the first optical detection of quantum anomalous Hall (QAH) states in twisted WSe2 homobilayer (tWSe2). Specifically, we employ polarization-resolved attractive polaron spectroscopy on a dual-gated, 2degree tWSe2 and observe direct signatures of spontaneous time-reversal symmetry breaking at hole filling ν = 1.

Talk 1: Quantum Wave Atom Transforms
Marianna Podzorova - CS Grad Student

Edge states—localized electronic states at the boundaries of a material—are often attributed to structural defects or topological features in crystalline solids. In finite 𝜋-conjugated systems such as graphene nanoribbons, boron nitride, and short segments of single-walled carbon nanotubes, these edge states can lead to electron scattering and fluorescence quenching. Computational studies have shown that certain chemical modifications, such as tailored edge-passivation and fullerene-end capping, can suppress these states.