35 research outputs found
High-frequency suppression of inductive coupling between flux qubit and transmission line resonator
We perform theoretical calculations to investigate the naturally occurring
high-frequency cutoff in a circuit comprising a flux qubit coupled inductively
to a transmission line resonator (TLR). Our results agree with those of past
studies that considered somewhat similar circuit designs. In particular, a
decoupling occurs between the qubit and the high-frequency modes. As a result,
the coupling strength between the qubit and resonator modes increases with mode
frequency as at low frequencies and decreases as
at high frequencies. We derive expressions for the
multimode-resonator-induced Lamb shift in the qubit's characteristic frequency.
Because of the natural decoupling between the qubit and high-frequency modes,
the Lamb-shift-renormalized qubit frequency remains finite.Comment: 24 pages (preprint), 5 figure
Using Superconducting Qubit Circuits to Engineer Exotic Lattice Systems
We propose an architecture based on superconducting qubits and resonators for
the implementation of a variety of exotic lattice systems, such as spin and
Hubbard models in higher or fractal dimensions and higher-genus topologies.
Spin systems are realized naturally using qubits, while superconducting
resonators can be used for the realization of Bose-Hubbard models. Fundamental
requirements for these designs, such as controllable interactions between
arbitrary qubit pairs, have recently been implemented in the laboratory,
rendering our proposals feasible with current technology.Comment: 7 pages (two-column), 3 figure
Rabi oscillations in a qubit coupled to a quantum two-level system
We consider the problem of a qubit driven by a harmonically oscillating external field while it is coupled to a quantum two-level system (TLS). We perform a systematic numerical analysis of the problem by varying the relevant parameters. The numerical calculations agree with the predictions of a simple intuitive picture, namely one that takes into consideration the four-level energy spectrum, the simple principles of Rabi oscillations and the basic effects of decoherence. Furthermore, they reveal a number of other interesting phenomena. We provide explanations for the various features that we observe in the numerical calculations and discuss how they can be used in experiment. In particular, we suggest an experimental procedure to characterize an environment of TLSs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49057/2/njp6_6_103.pd
Nonclassicality of open circuit QED systems in the deep-strong coupling regime
We investigate theoretically how the ground state of a qubit-resonator system
in the deep-strong coupling (DSC) regime is affected by the coupling to an
environment. We employ as a variational ansatz for the ground state of the
qubit-resonator-environment system a superposition of coherent states displaced
in qubit-state-dependent directions. We show that the reduced density matrix of
the qubit-resonator system strongly depends on how the system is coupled to the
environment, i.e., capacitive or inductive, because of the broken rotational
symmetry of the eigenstates of the DSC system in the resonator phase space.
When the resonator couples to the qubit and the environment in different ways
(for instance, one is inductive and the other is capacitive), the system is
almost unaffected by the resonator-waveguide coupling. In contrast, when the
two couplings are of the same type (for instance, both are inductive), by
increasing the resonator-waveguide coupling strength, the average number of
virtual photons increases and the quantum superposition realized in the
qubit-resonator entangled ground state is partially degraded. Since the
superposition becomes more fragile with increasing the qubit-resonator
coupling, there exists an optimal coupling strength to maximize the
nonclassicality of the qubit-resonator system.Comment: 24 pages, 11 figure