Entanglement Generated by the Dispersive Interaction: The Dressed Coherent State

Abstract

In the dispersive regime of qubit-cavity coupling, classical cavity drive populates the cavity, but leaves the qubit state unaffected. However, the dispersive Hamiltonian is derived after both a frame transformation and an approximation. Therefore, to connect to external experimental devices, the inverse frame transformation from the dispersive frame back to the lab frame is necessary. In this work, we show that in the lab frame the system is best described by an entangled state known as the dressed coherent state, and thus even in the dispersive regime, entanglement is generated between the qubit and the cavity. Also, we show that further qubit evolution depends on both the amplitude and phase of the dressed coherent state, and use the dressed coherent state to calculate the measurement contrast of a recently developed dispersive readout protocol.

9 pages, 3 figures

References in corpus (4)

• Resolving photon number states in a superconducting circuit
• Dispersive regime of circuit QED: photon-dependent qubit dephasing and relaxation rates
• High-fidelity qubit measurement with a microwave photon counter
• Scalable two- and four-qubit parity measurement with a threshold photon counter

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• Parallel tomography of quantum non-demolition measurements in multi-qubit devices
• Entangling distant solid-state spins via thermal phonons
• Nonadiabatic corrections to fast dispersive multiqubit gates involving Z control
• Generating entangled states from coherent states in circuit-QED
• Measurement-induced state transitions in dispersive qubit readout schemes
• Quantum phase transitions in the driven dissipative Jaynes-Cummings oscillator: from the dispersive regime to resonance
• Complete physical characterization of QND measurements via tomography
• Towards a heralded eigenstate preserving measurement of multi-qubit parity in circuit QED
• Gradual partial-collapse theory for ideal nondemolition measurements of qubits in circuit QED
• Direct measurement of atomic entanglement via cavity photon statistics