Margaret G. Panetta

Manybody Interferometry of Quantum Fluids

  1. Gabrielle Roberts,
  2. Andrei Vrajitoarea,
  3. Brendan Saxberg,
  4. Margaret G. Panetta,
  5. Jonathan Simon,
  6. and David I. Schuster
Characterizing strongly correlated matter is an increasingly central challenge in quantum science, where structure is often obscured by massive entanglement. From semiconductor heterostructures
and 2D materials to synthetic atomic, photonic and ionic quantum matter, progress in preparation of manybody quantum states is accelerating, opening the door to new approaches to state characterization. It is becoming increasingly clear that in the quantum regime, state preparation and characterization should not be treated separately – entangling the two processes provides a quantum advantage in information extraction. From Loschmidt echo to measure the effect of a perturbation, to out-of-time-order-correlators (OTOCs) to characterize scrambling and manybody localization, to impurity interferometry to measure topological invariants, and even quantum Fourier transform-enhanced sensing, protocols that blur the distinction between state preparation and characterization are becoming prevalent. Here we present a new approach which we term ‚manybody Ramsey interferometry‘ that combines adiabatic state preparation and Ramsey spectroscopy: leveraging our recently-developed one-to-one mapping between computational-basis states and manybody eigenstates, we prepare a superposition of manybody eigenstates controlled by the state of an ancilla qubit, allow the superposition to evolve relative phase, and then reverse the preparation protocol to disentangle the ancilla while localizing phase information back into it. Ancilla tomography then extracts information about the manybody eigenstates, the associated excitation spectrum, and thermodynamic observables. This work opens new avenues for characterizing manybody states, paving the way for quantum computers to efficiently probe quantum matter.
arxiv pdf

Chiral Cavity Quantum Electrodynamics

  1. John Clai Owens,
  2. Margaret G. Panetta,
  3. Brendan Saxberg,
  4. Gabrielle Roberts,
  5. Srivatsan Chakram,
  6. Ruichao Ma,
  7. Andrei Vrajitoarea,
  8. Jonathan Simon,
  9. and David Schuster
Cavity quantum electrodynamics, which explores the granularity of light by coupling a resonator to a nonlinear emitter, has played a foundational role in the development of modern quantum
information science and technology. In parallel, the field of condensed matter physics has been revolutionized by the discovery of underlying topological robustness in the face of disorder, often arising from the breaking of time-reversal symmetry, as in the case of the quantum Hall effect. In this work, we explore for the first time cavity quantum electrodynamics of a transmon qubit in the topological vacuum of a Harper-Hofstadter topological lattice. To achieve this, we assemble a square lattice of niobium superconducting resonators and break time-reversal symmetry by introducing ferrimagnets before coupling the system to a single transmon qubit. We spectroscopically resolve the individual bulk and edge modes of this lattice, detect vacuum-stimulated Rabi oscillations between the excited transmon and each mode, and thereby measure the synthetic-vacuum-induced Lamb shift of the transmon. Finally, we demonstrate the ability to employ the transmon to count individual photons within each mode of the topological band structure. This work opens the field of chiral quantum optics experiment, suggesting new routes to topological many-body physics and offering unique approaches to backscatter-resilient quantum communication.
arxiv pdf