Seminar

With the development of delegated quantum computation, clients will want to ensure confidentiality of their data and algorithms, and the integrity of their computations. In this talk, I present recent work on two directions of research related to blind and verified quantum computing.

Theoretical models of quantum computation usually assume that 2-qubit gates can be performed between arbitrary pairs of qubits. However, in practice, scalable quantum architectures have qubit connectivity constraints, which can introduce polynomial depth overheads. Compiling quantum algorithms to work on scalable architectures therefore requires optimizing arrangements of gates and qubits to minimize these overheads.

In this special Friday Quantum Seminar, Dr. Allyson O'Brien, a Quantum Technology Scientist at Leidos, will share stories from her career path and a broader perspective on the field.

Pizza and drinks served after the talk.

Understanding whether dissipation in an open quantum system is truly quantum is a question of both fundamental and practical interest. We consider a general model of n qubits subject to correlated Markovian dephasing, and present a sufficient condition for when bath-induced dissipation can generate system entanglement and hence must be considered quantum. Surprisingly, we find that the presence or absence of time-reversal symmetry (TRS) plays a crucial role: broken TRS is required for dissipative entanglement generation.

In typical quantum systems with conservation laws, the approach to equilibrium at finite temperature is governed by classical hydrodynamics in which charge and energy diffuse. In this talk, I will discuss some one dimensional quantum systems with anomalous hydrodynamic behavior — that is, systems where diffusion of charge is replaced by subdiffusion or superdiffusion.

The foundations of classical Algebraic Geometry and Real Algebraic Geometry are the Nullstellensatz and Positivstellensatz.  Over the last two decades the basic analogous theorems for matrix and operator theory (noncommutative variables) have emerged.  In this talk I'll discuss commuting operator strategies for nonlocal games, recall NC Nullstellensatz which are helpful, and then apply them to a very broad collection of nonlocal games.

A Physical Unclonable Function (PUF) is a device with unique behaviour that is hard to clone due to the imperfections and natural randomness during the manufacturing procedure, hence providing a secure fingerprint. A variety of PUF structures and PUF-based applications have been explored theoretically as well as being implemented in practical settings. Recently, the inherent unclonability of quantum states has been exploited to derive the quantum analogue of PUF as well as new proposals for the implementation of PUF.

To realize a digital quantum processor based on superconducting qubits, gate error rates must be further reduced by raising coherence times and increasing anharmonicity. I report our group's progress in improving coherence and control of fluxonium superconducting qubits by optimizing the circuit's spectrum and enhancing fabrication methods.

In this talk I will give an overview of various strategies we have developed for suppressing the inevitable errors occurring during quantum computations. These tools work at the gate level and thus can be effective even through a cloud API exposing only elementary gates to the end-user. I will demonstrate the effectiveness of these tools with experimental results across multiple hardware architectures.

Variational quantum algorithms are proposed to solve relevant computational problems on near term quantum devices. Popular versions are variational quantum eigensolvers and quantum approximate optimization algorithms that solve ground state problems from quantum chemistry and binary optimization problems, respectively. They are based on the idea of using a classical computer to train a parametrized quantum circuit. We show that the corresponding classical optimization problems are NP-hard.