4,018 research outputs found
Digital-Analog Quantum Simulations with Superconducting Circuits
Quantum simulations consist in the intentional reproduction of physical or
unphysical models into another more controllable quantum system. Beyond
establishing communication vessels between unconnected fields, they promise to
solve complex problems which may be considered as intractable for classical
computers. From a historic perspective, two independent approaches have been
pursued, namely, digital and analog quantum simulations. The former usually
provide universality and flexibility, while the latter allows for better
scalability. Here, we review recent literature merging both paradigms in the
context of superconducting circuits, yielding: digital-analog quantum
simulations. In this manner, we aim at getting the best of both approaches in
the most advanced quantum platform involving superconducting qubits and
microwave transmission lines. The discussed merge of quantum simulation
concepts, digital and analog, may open the possibility in the near future for
outperforming classical computers in relevant problems, enabling the reach of a
quantum advantage.Comment: Review article, 26 pages, 4 figure
Entanglement creation in circuit QED via Landau-Zener sweeps
A qubit may undergo Landau-Zener transitions due to its coupling to one or
several quantum harmonic oscillators. We show that for a qubit coupled to one
oscillator, Landau-Zener transitions can be used for single-photon generation
and for the controllable creation of qubit-oscillator entanglement, with
state-of-the-art circuit QED as a promising realization. Moreover, for a qubit
coupled to two cavities, we show that Landau-Zener sweeps of the qubit are well
suited for the robust creation of entangled cavity states, in particular
symmetric Bell states, with the qubit acting as the entanglement mediator. At
the heart of our proposals lies the calculation of the exact Landau-Zener
transition probability for the qubit, by summing all orders of the
corresponding series in time-dependent perturbation theory. This transition
probability emerges to be independent of the oscillator frequencies, both
inside and outside the regime where a rotating-wave approximation is valid.Comment: 12 pages, 7 figure
Quantum information processing with superconducting qubits in a microwave field
We investigate the quantum dynamics of a Cooper-pair box with a
superconducting loop in the presence of a nonclassical microwave field. We
demonstrate the existence of Rabi oscillations for both single- and
multi-photon processes and, moreover, we propose a new quantum computing scheme
(including one-bit and conditional two-bit gates) based on Josephson qubits
coupled through microwaves.Comment: 7 pages, 1 figur
One qubit and one photon -- the simplest polaritonic heat engine
Hybrid quantum systems can often be described in terms of polaritons. These
are quasiparticles formed of superpositions of their constituents, with
relative weights depending on some control parameter in their interaction. In
many cases, these constituents are coupled to reservoirs at different
temperatures. This suggests a general approach to the realization of
polaritonic heat engines where a thermodynamic cycle is realized by tuning this
control parameter. Here we discuss what is arguably the simplest such engine, a
single qubit coupled to a single photon. We show that this system can extract
work from feeble thermal microwave fields. We also propose a quantum
measurement scheme of the work and evaluate its back-action on the operation of
the engine.Comment: 8 pages, 4 figures, new contents adde
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