31,212 research outputs found
Single carbon nanotubes as ultrasmall all-optical memories
Performance improvements are expected from integration of photonic devices
into information processing systems, and in particular, all-optical memories
provide a key functionality. Scaling down the size of memory elements is
desirable for high-density integration, and the use of nanomaterials would
allow for devices that are significantly smaller than the operation
wavelengths. Here we report on all-optical memory based on individual carbon
nanotubes, where adsorbed molecules give rise to optical bistability. By
exciting at the high-energy tail of the excitonic absorption resonance,
nanotubes can be switched between the desorbed state and the adsorbed state. We
demonstrate reversible and reproducible operation of the nanotube optical
memory, and determine the rewriting speed by measuring the molecular adsorption
and desorption times. Our results underscore the impact of molecular-scale
effects on optical properties of nanomaterials, offering new design strategies
for photonic devices that are a few orders of magnitude smaller than the
optical diffraction limit.Comment: 8 pages, 6 figure
From quantum circuits to adiabatic algorithms
This paper explores several aspects of the adiabatic quantum computation
model. We first show a way that directly maps any arbitrary circuit in the
standard quantum computing model to an adiabatic algorithm of the same depth.
Specifically, we look for a smooth time-dependent Hamiltonian whose unique
ground state slowly changes from the initial state of the circuit to its final
state. Since this construction requires in general an n-local Hamiltonian, we
will study whether approximation is possible using previous results on ground
state entanglement and perturbation theory. Finally we will point out how the
adiabatic model can be relaxed in various ways to allow for 2-local partially
adiabatic algorithms as well as 2-local holonomic quantum algorithms.Comment: Version accepted by and to appear in Phys. Rev.
Decoherence in a superconducting flux qubit with a pi-junction
We consider the use of a pi-junction for flux qubits to realize degenerate
quantum levels without external magnetic field. On the basis of the
Caldeira-Leggett model, we derive an effective spin-Boson model, and study
decoherece of this type of qubits. We estimate the dephasing time by using
parameters from recent experiments of SIFS junctions, and show that high
critical current and large subgap resistance are required for the pi-junction
to realize a long coherent time.Comment: 5 pages, 2 figure
Quasi Periodic Oscillations (QPOs) and frequencies in an accretion disk and comparison with the numerical results from non-rotating black hole computed by the GRH code
The shocked wave created on the accretion disk after different physical
phenomena (accretion flows with pressure gradients, star-disk interaction etc.)
may be responsible observed Quasi Periodic Oscillations (QPOs) in ray
binaries. We present the set of characteristics frequencies associated with
accretion disk around the rotating and non-rotating black holes for one
particle case. These persistent frequencies are results of the rotating pattern
in an accretion disk. We compare the frequency's from two different numerical
results for fluid flow around the non-rotating black hole with one particle
case. The numerical results are taken from our papers Refs.\refcite{Donmez2}
and \refcite{Donmez3} using fully general relativistic hydrodynamical code with
non-selfgravitating disk. While the first numerical result has a relativistic
tori around the black hole, the second one includes one-armed spiral shock wave
produced from star-disk interaction. Some physical modes presented in the QPOs
can be excited in numerical simulation of relativistic tori and spiral waves on
the accretion disk. The results of these different dynamical structures on the
accretion disk responsible for QPOs are discussed in detail.Comment: 13 figures, added reference, accepted for publication in Modern
Physics Letters
Perturbative Gadgets at Arbitrary Orders
Adiabatic quantum algorithms are often most easily formulated using many-body
interactions. However, experimentally available interactions are generally
two-body. In 2004, Kempe, Kitaev, and Regev introduced perturbative gadgets, by
which arbitrary three-body effective interactions can be obtained using
Hamiltonians consisting only of two-body interactions. These three-body
effective interactions arise from the third order in perturbation theory. Since
their introduction, perturbative gadgets have become a standard tool in the
theory of quantum computation. Here we construct generalized gadgets so that
one can directly obtain arbitrary k-body effective interactions from two-body
Hamiltonians. These effective interactions arise from the kth order in
perturbation theory.Comment: Corrected an error: U dagger vs. U invers
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