Eric Holland

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

Cavity State Manipulation Using Photon-Number Selective Phase Gates

  1. Reinier W. Heeres,
  2. Brian Vlastakis,
  3. Eric Holland,
  4. Stefan Krastanov,
  5. Victor V. Albert,
  6. Luigi Frunzio,
  7. Liang Jiang,
  8. and Robert J. Schoelkopf
The large available Hilbert space and high coherence of cavity resonators makes these systems an interesting resource for storing encoded quantum bits. To perform a quantum gate on
this encoded information, however, complex nonlinear operations must be applied to the many levels of the oscillator simultaneously. In this work, we introduce the Selective Number-dependent Arbitrary Phase (SNAP) gate, which imparts a different phase to each Fock state component using an off-resonantly coupled qubit. We show that the SNAP gate allows control over the quantum phases by correcting the unwanted phase evolution due to the Kerr effect. Furthermore, by combining the SNAP gate with oscillator displacements, we create a one-photon Fock state with high fidelity. Using just these two controls, one can construct arbitrary unitary operations, offering a scalable route to performing logical manipulations on oscillator-encoded qubits.
arxiv pdf