JQI-QuICS-CMTC Seminar

Confinement is a ubiquitous mechanism in nature, whereby particles feel an attractive force that increases without bound as they separate. A prominent example is color confinement in particle physics, in which baryons and mesons are produced by quark confinement. Analogously, confinement can also occur in low-energy quantum many-body systems when elementary excitations are confined into bound quasiparticles. We report the observation of magnetic domain wall confinement in an interacting spin chain with a trapped-ion quantum simulator.

The field of quantum Hamiltonian complexity lies at the intersection of quantum many-body physics and computational complexity theory, with deep implications to both fields. The main object of study is the LocalHamiltonian problem, which is concerned with estimating the ground-state energy of a local Hamiltonian. A major challenge in the field is to understand the complexity of the LocalHamiltonian problem in more physically natural parameter regimes.

The field of quantum Hamiltonian complexity lies at the intersection of quantum many-body physics and computational complexity theory, with deep implications to both fields. The main object of study is the LocalHamiltonian problem, which is concerned with estimating the ground-state energy of a local Hamiltonian. A major challenge in the field is to understand the complexity of the LocalHamiltonian problem in more physically natural parameter regimes.

Junctions of more than two superconducting terminals are required for implementing braiding operations on Majorana fermions. Moreover, such multi-terminal Josephson Junctions (JJ) were predicted to support topological state and host zero-energy quasiparticles. Unlike conventional two-terminal JJs where the value of critical current is a number, the multi-terminal JJs exhibit a novel feature – the critical current contour (CCC).

The standard circuit model for quantum computation presumes the ability to directly perform gates between arbitrary pairs of qubits, which is unlikely to be practical for large-scale experiments. Power-law interactions with strength decaying as 1/r^α in the distance r provide an experimentally realizable resource for information processing, whilst still retaining long-range connectivity. We leverage the power of these interactions to  implement a fast quantum fanout gate with an arbitrary number of targets.

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. We perform extensive numerical simulations involving IQH and FQH states to validate these methods.

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.

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.

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.

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.