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High-fidelity feedback-assisted parity measurement in circuit QED

Lars Tornberg (Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik) ; Göran Johansson (Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik)
Physical Review A (1050-2947). Vol. 82 (2010), 1,
[Artikel, refereegranskad vetenskaplig]

We analyze a two-qubit parity measurement based on dispersive readout in circuit quantum electrodynamics. The back action on the qubits has two qualitatively different contributions. One is an unavoidable dephasing in one of the parity subspaces, arising during the transient time of switching on the measurement. The other part is a stochastic rotation of the phase in the same subspace, which persists during the whole measurement. The latter can be determined from the full measurement record using the method of state estimation. Our main result is that the outcome of this phase determination process is independent of the initial state in the state estimation procedure. The procedure can thus be used in a measurement situation where the initial state is unknown. We discuss how this feedback method can be used to achieve a high-fidelity parity measurement for moderate values of the cavity-qubit coupling strength. Finally, we discuss the robustness of the feedback procedure toward errors in the measurement record.

Nyckelord: quantum, state, qubits

Denna post skapades 2010-08-17. Senast ändrad 2014-09-02.
CPL Pubid: 124671


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Institutioner (Chalmers)

Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik



Chalmers infrastruktur