4,779 research outputs found
Synchronization of Coupled Boolean Phase Oscillators
We design, characterize, and couple Boolean phase oscillators that include
state-dependent feedback delay. The state-dependent delay allows us to realize
an adjustable coupling strength, even though only Boolean signals are
exchanged. Specifically, increasing the coupling strength via the range of
state-dependent delay leads to larger locking ranges in uni- and bi-directional
coupling of oscillators in both experiment and numerical simulation with a
piecewise switching model. In the unidirectional coupling scheme, we unveil
asymmetric triangular-shaped locking regions (Arnold tongues) that appear at
multiples of the natural frequency of the oscillators. This extends
observations of a single locking region reported in previous studies. In the
bidirectional coupling scheme, we map out a symmetric locking region in the
parameter space of frequency detuning and coupling strength. Because of large
scalability of our setup, our observations constitute a first step towards
realizing large-scale networks of coupled oscillators to address fundamental
questions on the dynamical properties of networks in a new experimental
setting.Comment: 8 pages, 8 figure
Preparation and manipulation of a fault-tolerant superconducting qubit
We describe a qubit encoded in continuous quantum variables of an rf
superconducting quantum interference device. Since the number of accessible
states in the system is infinite, we may protect its two-dimensional subspace
from small errors introduced by the interaction with the environment and during
manipulations. We show how to prepare the fault-tolerant state and manipulate
the system. The discussed operations suffice to perform quantum computation on
the encoded state, syndrome extraction, and quantum error correction. We also
comment on the physical sources of errors and possible imperfections while
manipulating the system.Comment: Typo corrected, title changed as suggested by the editors of Phys.
Rev. B, references adde
Quantum Logic between Remote Quantum Registers
We analyze two approaches to quantum state transfer in solid-state spin
systems. First, we consider unpolarized spin-chains and extend previous
analysis to various experimentally relevant imperfections, including quenched
disorder, dynamical decoherence, and uncompensated long range coupling. In
finite-length chains, the interplay between disorder-induced localization and
decoherence yields a natural optimal channel fidelity, which we calculate.
Long-range dipolar couplings induce a finite intrinsic lifetime for the
mediating eigenmode; extensive numerical simulations of dipolar chains of
lengths up to L=12 show remarkably high fidelity despite these decay processes.
We further consider the extension of the protocol to bosonic systems of coupled
oscillators. Second, we introduce a quantum mirror based architecture for
universal quantum computing which exploits all of the spins in the system as
potential qubits. While this dramatically increases the number of qubits
available, the composite operations required to manipulate "dark" spin qubits
significantly raise the error threshold for robust operation. Finally, as an
example, we demonstrate that eigenmode-mediated state transfer can enable
robust long-range logic between spatially separated Nitrogen-Vacancy registers
in diamond; numerical simulations confirm that high fidelity gates are
achievable even in the presence of moderate disorder.Comment: 15 pages, 10 figure
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