Daria Kowsari

Universal Hamiltonian control in a planar trimon circuit

  1. Vivek Maurya,
  2. Daria Kowsari,
  3. Kumar Saurav,
  4. S.A. Shanto,
  5. R. Vijay,
  6. Daniel A. Lidar,
  7. and Eli M. Levenson-Falk
Multimode circuits provide an avenue for flexible control of single and multi-qubit gates. In this work we implement a multimode circuit known as a trimon integrated in a planar geometry.
The trimon features three transmon-like modes with strong all-to-all ZZ coupling. We demonstrate high fidelity operations on the trimon, achieving flexible control of its rich state space. This includes qubit rotations conditioned on one or both other qubits, unconditional single-qubit rotations, and both excitation-conserving and double-excitation two-qubit entangling gates. Through multi-tone driving we are able to implement all 16 two-qubit Pauli operators in the two-qubit space. We further demonstrate using the trimon as a qudit with up to 8 states and higher coherence than typical transmon-based implementations. Our results show a compact, highly controllable device that can potentially replace transmons in standard superconducting processor architectures.
arxiv pdf

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

Observing Parity Time Symmetry Breaking in a Josephson Parametric Amplifier

  1. Chandrashekhar Gaikwad,
  2. Daria Kowsari,
  3. Weijian Chen,
  4. and Kater W. Murch
A coupled two-mode system with balanced gain and loss is a paradigmatic example of an open quantum system that can exhibit real spectra despite being described by a non-Hermitian Hamiltonian.
We utilize a degenerate parametric amplifier operating in three-wave mixing mode to realize such a system of balanced gain and loss between the two quadrature modes of the amplifier. By examining the time-domain response of the amplifier, we observe a characteristic transition from real-to-imaginary energy eigenvalues associated with the Parity-Time-symmetry-breaking transition.
arxiv pdf