B. Abdo

Quantum back-action of variable-strength measurement

  1. M. Hatridge,
  2. S. Shankar,
  3. M. Mirrahimi,
  4. F. Schackert,
  5. K. Geerlings,
  6. T. Brecht,
  7. K. M. Sliwa,
  8. B. Abdo,
  9. L. Frunzio,
  10. S. M. Girvin,
  11. R. J. Schoelkopf,
  12. and M. H. Devoret
Measuring a quantum system can randomly perturb its state. The strength and nature of this back-action depends on the quantity which is measured. In a partial measurement performed
by an ideal apparatus, quantum physics predicts that the system remains in a pure state whose evolution can be tracked perfectly from the measurement record. We demonstrate this property using a superconducting qubit dispersively coupled to a cavity traversed by a microwave signal. The back-action on the qubit state of a single measurement of both signal quadratures is observed and shown to produce a stochastic operation whose action is determined by the measurement result. This accurate monitoring of a qubit state is an essential prerequisite for measurement-based feedback control of quantum systems.
arxiv pdf

Experimental demonstration of a resonator-induced phase gate in a multi-qubit circuit QED system

  1. Hanhee Paik,
  2. A. Mezzacapo,
  3. Martin Sandberg,
  4. D. T. McClure,
  5. B. Abdo,
  6. A. D. Corcoles,
  7. O. Dial,
  8. D. F. Bogorin,
  9. B. L. T. Plourde,
  10. M. Steffen,
  11. A. W. Cross,
  12. J. M. Gambetta,
  13. and Jerry M. Chow
The resonator-induced phase (RIP) gate is a multi-qubit entangling gate that allows a high degree of flexibility in qubit frequencies, making it attractive for quantum operations in
large-scale architectures. We experimentally realize the RIP gate with four superconducting qubits in a three-dimensional (3D) circuit-quantum electrodynamics architecture, demonstrating high-fidelity controlled-Z (CZ) gates between all possible pairs of qubits from two different 4-qubit devices in pair subspaces. These qubits are arranged within a wide range of frequency detunings, up to as large as 1.8 GHz. We further show a dynamical multi-qubit refocusing scheme in order to isolate out 2-qubit interactions, and combine them to generate a four-qubit Greenberger-Horne-Zeilinger state.
arxiv pdf