Generation of entangled states in circuit QED

Start date 01/01/2008


Entanglement is thought to be one of the purely quantum effects behind the power of quantum computing. Thus it is important to show the possibility to generate and sustain entangled states in any good candidate for a physical qubit implementation. In this work read-out methods for the preparation and detection of entangled multi-qubit states in circuit quantum electrodynamics are proposed and analyzed. Here, three superconducting qubits are coupled to a photon cavity made from a co-planar wave guide. Due to the coherent interaction between the qubits and cavity, information about the joint state of the three qubits can be inferred by measuring the signal coming from the cavity. We show that a joint readout of several qubits can be utilized for the probabilistic production of high-fidelity entangled states of the three qubits. This method is suitable for the demonstration of violation of local hidden variable (LHV) theories.

The top picture shows the ideal probability distribution for the signal S corresponding to the qubit states indicated within each peak. If a signal is detected within the region (ν1, ν2), the measurement postulate in quantum mechanics tells us that the post-measurement state is given by a superposition of the states (↓↓↑) and (↑↑↓), which is a highly entangled state of three qubits. The bottom picture shows a corresponding histogram from a quantum trajectory simulation including the effect of relaxation and dephasing errors.

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Swedish Research Council (VR)
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