RQS Seminar

Studying high-energy collisions of composite particles, such as hadrons and nuclei, is an outstanding goal for quantum simulators. However, the preparation of hadronic wave packets has posed a significant challenge, due to the complexity of hadrons and the precise structure of wave packets. This has limited demonstrations of hadron scattering on quantum simulators to date. Observations of confinement and composite excitations in quantum spin systems have opened up the possibility to explore scattering dynamics in spin models.

Ab initio simulations of the Standard Model will require thousands of qubits and millions of gates. Developing efficient quantum simulation algorithms for such settings, which will only be feasible in the era of fault-tolerant quantum computing, necessitates principles entirely different from those used in the near term.

In this talk, I will first provide an overview of an ongoing project on symmetric quantum circuits and then discuss two related recent results from this year. The overarching goal of this project is to investigate the properties of quantum circuits constructed from k-local gates that all respect a global symmetry, such as U(1) or SU(d). It turns out that general unitary transformations respecting a global symmetry cannot be realized by composing local gates with the same symmetry, which contrasts with the universality of 2-local gates in the absence of symmetries.

Quantum states can quickly decohere due to their interaction with the environment and imperfections in the applied quantum controls. Quantum error correction promises to preserve coherence by encoding the state of each qubit into a multi-qubit state with a high-degree of symmetry. Perturbations are first detected by measuring the symmetries of the quantum state and then corrected by applying a set of gates based on the measurements.

Gauge theory is a powerful theoretical framework for understanding the fundamental forces in the standard model. Simulating the real time dynamics of gauge theory, especially in the strong coupling regime, is a challenging classical problem. Quantum computers offer a solution to this problem by taking advantage of the intrinsic quantum nature of the systems. The Schwinger model, that is the 1+1 dimensional U(1) gauge theory coupled to fermions, has served as a testbed for different methods of quantum simulation.

How to write successful grant proposals, pushing your writing skills to the next level. Our speaker will provide an overview of grant writing and discuss successful strategies. Come prepared with your questions.

You can send your questions in advance to rqs-seed@umiacs.umd.edu.

Lunch will be provided.

Quantum devices hold promise to outperform classical computers in performing some physical simulations in the nearest future, making them a valuable tool for physics research. In this talk, Oles will focus on quantum simulation of the topological states of matter hosting Majorana modes – the exotic “half-electron” states. He will show the results obtained from noisy quantum hardware provide us with accurate prediction of Majorana mode wavefunctions. This experiment also allows us to verify the topological nature of observed modes.

This presentation introduces a family of identities that express general linear non-unitary evolution operators as a linear combination of unitary evolution operators, each solving a Hamiltonian simulation problem. This formulation can exponentially enhance the accuracy of the recently introduced linear combination of Hamiltonian simulation (LCHS) method [An, Liu, and Lin, Physical Review Letters, 2023].

Noise is widely regarded as a major obstacle to quantum computing. Fortunately, this problem can be solved efficiently due to the existence of the threshold theorem. It states that under sufficiently weak noise and universal assumptions, there always exists an active quantum error correction protocol with only logarithmic hardware overhead. One may ask: can a similar result be obtained for autonomous (passive) error correction, where noise is suppressed by natural or engineered dissipation?

Noncommuting conserved quantities have recently launched a subfield of quantum thermodynamics. In conventional thermodynamics, a system of interest and an environment exchange quantities—energy, particles, electric charge, etc.—that are globally conserved and are represented by Hermitian operators. These operators were implicitly assumed to commute with each other, until a few years ago. Freeing the operators to fail to commute has enabled many theoretical discoveries—about reference frames, entropy production, resource-theory models, etc.