3,673 research outputs found
A superconducting qubit with Purcell protection and tunable coupling
We present a superconducting qubit for the circuit quantum electrodynamics
architecture that has a tunable coupling strength g. We show that this coupling
strength can be tuned from zero to values that are comparable with other
superconducting qubits. At g = 0 the qubit is in a decoherence free subspace
with respect to spontaneous emission induced by the Purcell effect. Furthermore
we show that in the decoherence free subspace the state of the qubit can still
be measured by either a dispersive shift on the resonance frequency of the
resonator or by a cycling-type measurement.Comment: 4 pages, 3 figure
Purcell effect with microwave drive: Suppression of qubit relaxation rate
We analyze the Purcell relaxation rate of a superconducting qubit coupled to
a resonator, which is coupled to a transmission line and pumped by an external
microwave drive. Considering the typical regime of the qubit measurement, we
focus on the case when the qubit frequency is significantly detuned from the
resonator frequency. Surprisingly, the Purcell rate decreases when the strength
of the microwave drive is increased. This suppression becomes significant in
the nonlinear regime. In the presence of the microwave drive, the loss of
photons to the transmission line also causes excitation of the qubit; however,
the excitation rate is typically much smaller than the relaxation rate. Our
analysis also applies to a more general case of a two-level quantum system
coupled to a cavity.Comment: Published versio
Tunable coupling in circuit quantum electrodynamics with a superconducting V-system
Recent progress in superconducting qubits has demonstrated the potential of
these devices for the future of quantum information processing. One desirable
feature for quantum computing is independent control of qubit interactions as
well as qubit energies. We demonstrate a new type of superconducting charge
qubit that has a V-shaped energy spectrum and uses quantum interference to
provide independent control over the qubit energy and dipole coupling to a
superconducting cavity. We demonstrate dynamic access to the strong coupling
regime by tuning the coupling strength from less than 200 kHz to more than 40
MHz. This tunable coupling can be used to protect the qubit from cavity-induced
relaxation and avoid unwanted qubit-qubit interactions in a multi-qubit system.Comment: 5 pages, 4 figure
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