11/17/2023
By Tristan Brown

The Kennedy College of Sciences, Department of Physics and Applied Physics, invites you to attend a Ph.D. Dissertation defense by Tristan Brown on "Dissipation-Engineered State Stabilization in Parametric Circuit Quantum Electrodynamics."

Degree: Doctor of Philosophy in Physics
Defense Date: Tuesday, Nov. 21, 2023
Defense Time: 3 p.m. EST
Location: Olney 218, North Campus
Dissertation Title: Dissipation-Engineered State Stabilization in Parametric Circuit Quantum Electrodynamics

Committee Members:​

  • Chair,Professor Archana Kamal, Department of Physics and Applied Physics, Kennedy College of Science, University of Massachusetts Lowell
  • Leonardo Ranzani, Raytheon BBN Technologies
  • Professor Nishant Agarwal, Department of Physics and Applied Physics, Kennedy College of Science, University of Massachusetts Lowell
  • Professor Wei Guo, Department of Physics and Applied Physics, Kennedy College of Science, University of Massachusetts Lowell

Abstract: Dissipation engineering is a powerful framework for controlling quantum systems that offers critical functionalities such as deterministic quantum state preparation and autonomous error correction. The key idea rests on tailoring the dissipation seen by a system via controlled couplings to an engineered environment, such that the system’s long-time dynamics relax towards a preferred subspace or quantum state. In addition to being immune to initialization and measurement errors, such protocols employ continuous-wave drives precluding the need of complicated pulse engineering such as that employed in gate-based quantum control paradigms. Several dissipation engineering protocols proposed and implemented to date realize a form of "approximate" state stabilization, an approach which leads to a trade-off between the state preparation fidelity and stabilization rate. In this dissertation, I will first discuss the design principles, advantages and implementation of exact stabilization protocols which have no intrinsic error and stabilize the target state with unit fidelity in the absence of local decoherence.

Then, I will discuss an implementation that employs strong parametric drives to engineer dissipation on a qutrit-qubit circuit QED system, comprising two transmon qubits coupled to a common lossy resonator that acts as an engineered reservoir. In this protocol, we engineer a purely dissipative channel for population transfer into the target Bell state via parametric coupling to the third level of the transmon, and without any direct coherent coupling into or out of it, making the Bell state an eigenstate of the drive Hamiltonian and also a dark state of the engineered dissipation. Given the absence of any intrinsic error, our scheme attains a steady-state fidelity of 84\% with a time-constant of 339 nanoseconds, leading to the smallest error-time product of 55 nanoseconds reported in solid state quantum information platforms. Furthermore, we verify that the steady state error and preparation time are linearly correlated with engineered dissipation rate, confirming the trade off-free behavior. Notably, the reported protocol is the minimal instance of exact stabilization physics that employs only unconditional driving and linear engineered dissipation.

I will then present ideas for extending and implementing such exact protocols for stabilizing multipartite entanglement, beginning with a discussion of a theoretical proposal for exact 3-qubit W-state stabilization using purely parametric interactions. I will then discuss the experimental challenges and considerations informing our ongoing efforts in developing both all-to-all and modular multi-qubit architectures to this end.