Fall 2020

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.

ABSTRACT

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.

Entanglement is a critical resource for a useful quantum computer. There is a not a consensus on whether large-scale entanglement is physically possible, and entanglement on mixed states at non-zero temperature is poorly understood.  We discuss theoretical and computable bounds on how much entropy a quantum system can tolerate and still be useful for computation, and some directions for further exploration.  This is not a research talk, but rather a review of interesting results.

Finding ways to connect quantum systems in a controlled and flexible fashion lies at the core of constructing quantum information processing systems. Superconducting quantum circuits present a particularly promising platform for engineering quantum systems from the ground up: the strong light-matter interactions in these circuits can readily be used to realize interactions between different components. There remain interesting questions, however, about what types of interactions we can realize.

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 computations promise the ability to solve problems intractable in the classical setting. Restricting the types of computations considered often allows to establish a provable theoretical quantum advantage, and later demonstrate it experimentally.  I will discuss space-restricted computations, where input is a read-only memory and only one (qu)bit can be computed on. We show that any n-bit symmetric Boolean function can be implemented exactly through the use of quantum signal processing as a space-restricted quantum computation using O(n^2) gates.

A linear optical approach to quantum computing offers highly coherent qubits, high fidelity single qubit gates, and probabilistic entangling operations that can be implemented using well-known quantum optical methods.