Multi-qubit joint measurements in circuit QED: stochastic master equation analysis

Stefan Filipp, Patrick Maurer, Peter Leek +2 more

Anonymous

Ben Criger, Alessandro Ciani, David Peter Divincenzo

We derive a family of stochastic master equations describing homodyne measurement of multi-qubit diagonal observables in circuit quantum electrodynamics. In the regime where qubit decay can be neglected, our approach replaces the polaron-like transformation of previous work, which required a lengthy calculation for the physically interesting case of three qubits and two resonator modes. The technique introduced here makes this calculation straightforward and manifestly correct. Using this technique, we are able to show that registers larger than one qubit evolve under a non-Markovian master equation. We perform numerical simulations of the three-qubit, two-mode case from previous work, obtaining an average post-measurement state fidelity of ∼ 94%, limited by measurement-induced decoherence and dephasing.

Kevin Lalumière, Jay Gambetta, Alexandre Blais

Joint measurements of multiple qubits open new possibilities for quantum information processing. Here we present an approach based on homodyne detection to realize such measurements in the dispersive regime of cavity or circuit QED. By changing details of the measurement, the readout can be tuned from extracting only single-qubit to extracting only multiqubit properties. We obtain a reduced stochastic master equation describing this measurement and its effect on the qubits. As an example, we present results showing parity measurements of two qubits. In this situation, measurement of an initially unentangled state can yield, with near unit probability, a state of significant concurrence.

Vadim Smelyanskiy, Sergio Boixo, Hrant Gharibyan +6 more

Rosanna Migliore, ANTONINO MESSINA