Y. Liu

Hardware implementation of quantum stabilizers in superconducting circuits

  1. K. Dodge,
  2. Y. Liu,
  3. A. R. Klots,
  4. B. Cole,
  5. A. Shearrow,
  6. M. Senatore,
  7. S. Zhu,
  8. L.B. Ioffe,
  9. R. McDermott,
  10. and B. L. T. Plourde
Stabilizer operations are at the heart of quantum error correction and are typically implemented in software-controlled entangling gates and measurements of groups of qubits. Alternatively,
qubits can be designed so that the Hamiltonian corresponds directly to a stabilizer for protecting quantum information. We demonstrate such a hardware implementation of stabilizers in a superconducting circuit composed of chains of π-periodic Josephson elements. With local on-chip flux- and charge-biasing, we observe a softening of the energy band dispersion with respect to flux that is exponential in the number of frustrated plaquette elements, in close agreement with our numerical modeling.
arxiv pdf

Continuous quantum nondemolition measurement of the transverse component of a qubit

  1. U. Vool,
  2. S. Shankar,
  3. S. O. Mundhada,
  4. N. Ofek,
  5. A. Narla,
  6. K. Sliwa,
  7. E. Zalys-Geller,
  8. Y. Liu,
  9. L. Frunzio,
  10. R. J. Schoelkopf,
  11. S. M. Girvin,
  12. and M. H. Devoret
Quantum jumps of a qubit are usually observed between its energy eigenstates, also known as its longitudinal pseudo-spin component. Is it possible, instead, to observe quantum jumps
between the transverse superpositions of these eigenstates? We answer positively by presenting the first continuous quantum nondemolition measurement of the transverse component of an individual qubit. In a circuit QED system irradiated by two pump tones, we engineer an effective Hamiltonian whose eigenstates are the transverse qubit states, and a dispersive measurement of the corresponding operator. Such transverse component measurements are a useful tool in the driven-dissipative operation engineering toolbox, which is central to quantum simulation and quantum error correction.
arxiv pdf