Michael J. Hatridge

A quantum memory with near-millisecond coherence in circuit QED

  1. Matthew Reagor,
  2. Wolfgang Pfaff,
  3. Christopher Axline,
  4. Reinier W. Heeres,
  5. Nissim Ofek,
  6. Katrina Sliwa,
  7. Eric Holland,
  8. Chen Wang,
  9. Jacob Blumoff,
  10. Kevin Chou,
  11. Michael J. Hatridge,
  12. Luigi Frunzio,
  13. Michel H. Devoret,
  14. Liang Jiang,
  15. and Robert J. Schoelkopf
Significant advances in coherence have made superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent
quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by qubits, while maintaining superior coherence. We demonstrate a novel superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for near-millisecond storage of quantum states in a resonator while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. The observed coherence times constitute an improvement of almost an order of magnitude over those of the best available superconducting qubits. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing with Josephson junction-based quantum circuits.
arxiv pdf

Confining the state of light to a quantum manifold by engineered two-photon loss

  1. Zaki Leghtas,
  2. Steven Touzard,
  3. Ioan M. Pop,
  4. Angela Kou,
  5. Brian Vlastakis,
  6. Andrei Petrenko,
  7. Katrina M. Sliwa,
  8. Anirudh Narla,
  9. Shyam Shankar,
  10. Michael J. Hatridge,
  11. Matthew Reagor,
  12. Luigi Frunzio,
  13. Robert J. Schoelkopf,
  14. Mazyar Mirrahimi,
  15. and Michel H. Devoret
Physical systems usually exhibit quantum behavior, such as superpositions and entanglement, only when they are sufficiently decoupled from a lossy environment. Paradoxically, a specially
engineered interaction with the environment can become a resource for the generation and protection of quantum states. This notion can be generalized to the confinement of a system into a manifold of quantum states, consisting of all coherent superpositions of multiple stable steady states. We have experimentally confined the state of a harmonic oscillator to the quantum manifold spanned by two coherent states of opposite phases. In particular, we have observed a Schrodinger cat state spontaneously squeeze out of vacuum, before decaying into a classical mixture. This was accomplished by designing a superconducting microwave resonator whose coupling to a cold bath is dominated by photon pair exchange. This experiment opens new avenues in the fields of nonlinear quantum optics and quantum information, where systems with multi-dimensional steady state manifolds can be used as error corrected logical qubits.
arxiv pdf