R. W. Heeres

A Schrodinger Cat Living in Two Boxes

  1. Chen Wang,
  2. Yvonne Y. Gao,
  3. Philip Reinhold,
  4. R. W. Heeres,
  5. Nissim Ofek,
  6. Kevin Chou,
  7. Christopher Axline,
  8. Matthew Reagor,
  9. Jacob Blumoff,
  10. K. M. Sliwa,
  11. L. Frunzio,
  12. S. M. Girvin,
  13. Liang Jiang,
  14. M. Mirrahimi,
  15. M. H. Devoret,
  16. and R. J. Schoelkopf
Quantum superpositions of distinct coherent states in a single-mode harmonic oscillator, known as „cat states“, have been an elegant demonstration of Schrodinger’s
famous cat paradox. Here, we realize a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states. We present full quantum state tomography of this complex cat state over a Hilbert space exceeding 100 dimensions via quantum non-demolition measurements of the joint photon number parity. The ability to manipulate such multi-cavity quantum states paves the way for logical operations between redundantly encoded qubits for fault-tolerant quantum computation and communication.
arxiv pdf

Single-photon Resolved Cross-Kerr Interaction for Autonomous Stabilization of Photon-number States

  1. E. T. Holland,
  2. B. Vlastakis,
  3. R. W. Heeres,
  4. M. J. Reagor,
  5. U. Vool,
  6. Z. Leghtas,
  7. L. Frunzio,
  8. G. Kirchmair,
  9. M. H. Devoret,
  10. M. Mirrahimi,
  11. and R. J. Schoelkopf
Quantum states can be stabilized in the presence of intrinsic and environmental losses by either applying active feedback conditioned on an ancillary system or through reservoir engineering.
Reservoir engineering maintains a desired quantum state through a combination of drives and designed entropy evacuation. We propose and implement a quantum reservoir engineering protocol that stabilizes Fock states in a microwave cavity. This protocol is realized with a circuit quantum electrodynamics platform where a Josephson junction provides direct, nonlinear coupling between two superconducting waveguide cavities. The nonlinear coupling results in a single photon resolved cross-Kerr effect between the two cavities enabling a photon number dependent coupling to a lossy environment. The quantum state of the microwave cavity is discussed in terms of a net polarization and is analyzed by a measurement of its steady state Wigner function.
arxiv pdf