JQI-QuICS-CMTC Seminar

We present an optimal protocol for encoding an unknown qubit state into a multiqubit Greenberger-Horne-Zeilinger-like state and, consequently, transferring quantum information in large systems exhibiting power-law (1/r^α) interactions. For all power-law exponents α between d and 2d+1, where d is the dimension of the system, the protocol yields a polynomial speedup for α>2d and a superpolynomial speedup for α≤2d, compared to the state of the art.

We propose a scheme to create electronic Floquet vortex states by irradiating the circularly-polarized laser light carrying non-zero orbital angular momentum on the two-dimensional semiconductor. We study the properties of the Floquet vortex states analytically and numerically using methods analogous to the techniques used for the analysis of superconducting vortex states, while we exhibit that the Floquet vortex created in the current system has the wider tunability.

We theoretically study the Hofstadter butterfly of a triangular network model in minimally twisted bilayer graphene. The band structure manifests periodicity in energy, mimicking that of Floquet systems. The butterfly diagrams provide fingerprints of the model parameters and reveal the hidden band topology. In a strong magnetic field, we establish that minimally twisted bilayer graphene realizes low-energy Floquet topological insulators (FTIs) carrying zero Chern number, while hosting chiral edge states in bulk gaps.

This talk will introduce generalized Jordan–Wigner transformation on arbitrary triangulation of any simply connected manifold in 2d, 3d and general dimensions. This gives a duality between all fermionic systems and a new class of lattice gauge theories. This map preserves the locality and has an explicit dependence on the second Stiefel–Whitney class and a choice of spin structure on the manifold.

Applying a periodic Hamiltonian to a system of particles allows us to study out-of-equilibrium matter, like the prethermal discrete time crystal (PDTC). One can define a time-independent Hamiltonian that describes the dynamics of the driven system not continuously, but in a stroboscopic manner. This implies energy conservation during the validity window of this approximation.

In this work we explore the energy spectrum of a superconducting circuit consisting of a single fluxonium atom coupled to a long section of 1-D transmission line. Owing to the strong anharmonicity of the fluxonium we uncover a new many-body effect, dressing of photons by photons. Specifically, fluxonium's local non-linearity leads to hybridization between one-photon states and nearly resonant multi-photon states.  Accounting for this effect requires deriving the correct multi-mode light matter coupling model of our circuit.

Caroline Figgatt is an atomic physicist working to develop ion trap quantum computers at Honeywell Quantum Systems. She completed her PhD in physics at the University of Maryland in 2018, where she built a programmable ion trap quantum computer and demonstrated a variety of quantum algorithms on it. For her dissertation, she performed the first parallel 2-qubit operations in a single chain of trapped ion qubits. She will talk about quantum research at the company, highlight what it's like to work at Honeywell, and hold a Q&A.

Quantum error-correction remains a critical component to realizing the full promise of quantum algorithms.  In this talk, I will discuss experimental progress towards creating and controlling logical qubits on a trapped ion quantum computer. Our code of choice is the Bacon-Shor [[9,1,3]] subsystem code, which consists of 9 data qubits, encoding 1 logical qubit, with stabilizer measurements mapped to 4 ancilla qubits capable of correcting any single qubit error.

It is known that the AdS/CFT correspondence is related to approximate quantum error correction codes. However, the exact manner in which gravity can arise in such codes remains largely unexplored. Here we construct an approximate quantum error correction code which can be represented as a holographic tensor network. In the "noiseless" limit, it admits a local log-depth decoding circuit and reproduces certain properties of holography, such as the Ryu-Takayanagi formula and subregion duality, much like other known holographic codes.

The quantized Hall conductivity of integer and fractional quantum Hall (IQH and FQH) states is directly related to a topological invariant, the many-body Chern number. The conventional calculation of this invariant in interacting systems requires a family of many-body wave functions parameterized by twist angles in order to calculate the Berry curvature. In this work, we demonstrate how to extract the Chern number given a single many-body wave function, without knowledge of the Hamiltonian.