227 research outputs found
Controllable Operations of Edge States in Cross-One-dimensional Topological Chains
Topological edge states are recently attracting intense interest due to their
robustness in the presence of disorder and defects. However, most approaches
for manipulating such states require global modulations of the system's
Hamiltonian. In this work, we develop a method to control edge states using
local interactions of a four-node junction between cross-one-dimensional
topological atomic chains. These junction interactions can give rise to tunable
couplings between the hybridized edge states within different geometric
symmetry, allowing us to implement robust quantum state transfer and SWAP gate
between the two topological chains, where the edge states are pair-encoded as a
single qubit. Moreover, when the atoms are precisely positioned to couple
waveguides, the correlated decay caused by the environment enables the
anti-symmetric edge states to present subradiant dynamics and thus show
extremely long coherence time. These findings open up new possibilities for
quantum technologies with topological edge states in the future.Comment: 7 pages, 4 figure
Ultrastrong coupling phenomena beyond the Dicke model
We study effective light-matter interactions in a circuit QED system
consisting of a single resonator, which is coupled symmetrically to
multiple superconducting qubits. Starting from a minimal circuit model, we
demonstrate that in addition to the usual collective qubit-photon coupling the
resulting Hamiltonian contains direct qubit-qubit interactions, which have a
drastic effect on the ground and excited state properties of such circuits in
the ultrastrong coupling regime. In contrast to a superradiant phase transition
expected from the standard Dicke model, we find an opposite mechanism, which at
very strong interactions completely decouples the photon mode and projects the
qubits into a highly entangled ground state. These findings resolve previous
controversies over the existence of superradiant phases in circuit QED, but
they more generally show that the physics of two- or multi-atom cavity QED
settings can differ significantly from what is commonly assumed.Comment: 11 pages, 8 figure
A universal time-dependent control scheme for realizing arbitrary bosonic unitaries
We study the implementation of arbitrary unitary transformations between two
sets of stationary bosonic modes, which are connected through a photonic
quantum channel. By controlling the individual couplings between the modes and
the channel, an initial -partite quantum state in register A can be released
as a multi-photon wavepacket and, successively, be reabsorbed in register B.
Here we prove that there exists a set of control pulses that implement this
transfer with arbitrarily high fidelity and, simultaneously, realize a
pre-specified unitary transformation between the two sets of modes.
Moreover, we provide a numerical algorithm for constructing these control
pulses and discuss the scaling and robustness of this protocol in terms of
several illustrative examples. By being purely control-based and not relying on
any adaptions of the underlying hardware, the presented scheme is extremely
flexible and can find widespread applications, for example, for boson-sampling
experiments, multi-qubit state transfer protocols or in continuous-variable
quantum computing architectures.Comment: 7 pages, 4 figures + Supplementary material (4 pages, 1 figure
Coherent Resonant Coupling between Atoms and a Mechanical Oscillator Mediated by Cavity-Vacuum Fluctuations
We show that an atom can be coupled to a mechanical oscillator via quantum
vacuum fluctuations of a cavity field enabling energy transfer processes
between them. In a hybrid quantum system consisting of a cavity resonator with
a movable mirror and an atom, these processes are dominated by two
pair-creation mechanisms: the counter-rotating (atom-cavity system) and
dynamical Casimir interaction terms (optomechanical system). Because of these
two pair-creation mechanisms, the resonant atom-mirror coupling is the result
of high-order virtual processes with different transition paths well described
in our theoretical framework. We perform a unitary transformation to the
atom-mirror system Hamiltonian, exhibiting two kinds of multiple-order
transitions of the pair creation. By tuning the frequency of the atom, we show
that photon frequency conversion can be realized within a cavity of multiple
modes. Furthermore, when involving two atoms coupled with the same mechanical
mode, a single vibrating excitation of the mechanical oscillator can be
simultaneously absorbed by the two atoms. Considering recent advances in strong
and ultrastrong coupling for cavity optomechanics and other systems, we believe
our proposals can be implemented using available technology.Comment: 18 pages, 13 figur
Hybrid quantum device based on NV centers in diamond nanomechanical resonators plus superconducting waveguide cavities
We propose and analyze a hybrid device by integrating a microscale diamond
beam with a single built-in nitrogen-vacancy (NV) center spin to a
superconducting coplanar waveguide (CPW) cavity. We find that under an ac
electric field the quantized motion of the diamond beam can strongly couple to
the single cavity photons via dielectric interaction. Together with the strong
spin-motion interaction via a large magnetic field gradient, it provides a
hybrid quantum device where the dia- mond resonator can strongly couple both to
the single microwave cavity photons and to the single NV center spin. This
enables coherent information transfer and effective coupling between the NV
spin and the CPW cavity via mechanically dark polaritons. This hybrid
spin-electromechanical de- vice, with tunable couplings by external fields,
offers a realistic platform for implementing quantum information with single NV
spins, diamond mechanical resonators, and single microwave photons.Comment: Accepted by Phys. Rev. Applie
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