Xingrui Song

Entanglement assisted probe of the non-Markovian to Markovian transition in open quantum system dynamics

  1. Chandrashekhar Gaikwad,
  2. Daria Kowsari,
  3. Carson Brame,
  4. Xingrui Song,
  5. Haimeng Zhang,
  6. Martina Esposito,
  7. Arpit Ranadive,
  8. Giulio Cappelli,
  9. Nicolas Roch,
  10. Eli M. Levenson-Falk,
  11. and Kater W. Murch
We utilize a superconducting qubit processor to experimentally probe the transition from non-Markovian to Markovian dynamics of an entangled qubit pair. We prepare an entangled state
between two qubits and monitor the evolution of entanglement over time as one of the qubits interacts with a small quantum environment consisting of an auxiliary transmon qubit coupled to its readout cavity. We observe the collapse and revival of the entanglement as a signature of quantum memory effects in the environment. We then engineer the non-Markovianity of the environment by populating its readout cavity with thermal photons to show a transition from non-Markovian to Markovian dynamics, reaching a regime where the quantum Zeno effect creates a decoherence-free subspace that effectively stabilizes the entanglement between the qubits.
arxiv pdf

Quantum process inference for a single qubit Maxwell’s demon

  1. Xingrui Song,
  2. Mahdi Naghiloo,
  3. and Kater Murch
While quantum measurement theories are built around density matrices and observables, the laws of thermodynamics are based on processes such as are used in heat engines and refrigerators.
The study of quantum thermodynamics fuses these two distinct paradigms. In this article, we highlight the usage of quantum process matrices as a unified language for describing thermodynamic processes in the quantum regime. We experimentally demonstrate this in the context of a quantum Maxwell’s demon, where two major quantities are commonly investigated; the average work extraction ⟨W⟩ and the efficacy γ which measures how efficiently the feedback operation uses the obtained information. Using the tool of quantum process matrices, we develop the optimal feedback protocols for these two quantities and experimentally investigate them in a superconducting circuit QED setup.
arxiv pdf