17,088 research outputs found
Constructing Functional Braids for Low-Leakage Topological Quantum Computing
We discuss how to significantly reduce leakage errors in topological quantum
computation by introducing an irrelevant error in phase, using the construction
of a CNOT gate in the Fibonacci anyon model as a concrete example. To be
specific, we construct a functional braid in a six-anyon Hilbert space that
exchanges two neighboring anyons while conserving the encoded quantum
information. The leakage error is for a braid of 100
interchanges of anyons. Applying the braid greatly reduces the leakage error in
the construction of generic controlled-rotation gates.Comment: 5 pages, 4 figures, updated, accepeted by Phys. Rev.
Mixed Qubit Cannot Be Universally Broadcast
We show that there does not exist any universal quantum cloning machine that
can broadcast an arbitrary mixed qubit with a constant fidelity. Based on this
result, we investigate the dependent quantum cloner in the sense that some
parameter of the input qubit is regarded as
constant in the fidelity. For the case of constant , we establish the
optimal symmetric dependent cloner with a fidelity 1/2. It is also
shown that the optimal quantum cloning machine for pure qubits is also
optimal for mixed qubits, when is the unique parameter in the
fidelity. For general broadcasting of mixed qubits, the situation is
very different.Comment: 5 pages, Revte
Topological Dirac states beyond orbitals for silicene on SiC(0001) surface
The discovery of intriguing properties related to the Dirac states in
graphene has spurred huge interest in exploring its two-dimensional group-IV
counterparts, such as silicene, germanene, and stanene. However, these
materials have to be obtained via synthesizing on substrates with strong
interfacial interactions, which usually destroy their intrinsic
()-orbital Dirac states. Here we report a theoretical study on the
existence of Dirac states arising from the orbitals instead of
orbitals in silicene on 4H-SiC(0001), which survive in spite of the strong
interfacial interactions. We also show that the exchange field together with
the spin-orbital coupling give rise to a detectable band gap of 1.3 meV. Berry
curvature calculations demonstrate the nontrivial topological nature of such
Dirac states with a Chern number , presenting the potential of realizing
quantum anomalous Hall effect for silicene on SiC(0001). Finally, we construct
a minimal effective model to capture the low-energy physics of this system.
This finding is expected to be also applicable to germanene and stanene, and
imply great application potentials in nanoelectronics.Comment: 6 Figures , Accepted by Nano Letter
Enhanced transmission of optically thick metallic films at infrared wavelengths
For an optically thick metallic film, the transmission for both s- and
p-polarized waves is extremely low. If the metallic film is coated on both
sides with a finite dielectric layer, light transmission for -polarized
waves can be enhanced considerably. This enhancement is not related to surface
plasmon-polaritions. Instead, it is due to the interplay between Fabry-Perot
interference in the coated dielectric layer and the existence of the Brewster
angle at the dielectric/metallic interface. It is shown that the coated
metallic films can act as excellent polarizers at infrared wavelengths.Comment: 3 pages, 4 figures. Submitted to Appl. Phys. Let
Distillable entanglement in dimension
Distillable entanglement () is one of the acceptable measures of
entanglement of mixed states. Based on discrimination through local operation
and classical communication, this paper gives for two classes of
orthogonal multipartite maximally entangled states.Comment: 6 page
Comparison of Power Dependence of Microwave Surface Resistance of Unpatterned and Patterned YBCO Thin Film
The effect of the patterning process on the nonlinearity of the microwave
surface resistance of YBCO thin films is investigated. With the use of a
sapphire dielectric resonator and a stripline resonator, the microwave of
YBCO thin films was measured before and after the patterning process, as a
function of temperature and the rf peak magnetic field in the film. The
microwave loss was also modeled, assuming a dependence of
on current density . Experimental and modeled results
show that the patterning has no observable effect on the microwave residual
or on the power dependence of .Comment: Submitted to IEEE Trans. MT
Quantum coherence and entanglement induced by the continuum between distant localized states
It is demonstrated that two distant quantum wells separated by a reservoir
with a continuous spectrum can possess bound eigenstates embedded in the
continuum. These represent a linear superposition of quantum states localized
in the wells. We show that such a state can be isolated in the course of free
evolution from any initial state by a null-result measurement in the reservoir.
The latter might not be necessary in the many-body case. The resulting
superposition is regulated by ratio of couplings between the wells and the
reservoir. In particular, one can lock the system in one of the wells by
enhancing this ratio. By tuning parameters of the quantum wells, many-body
entangled states in distant wells can be produced through interactions and
statistics.Comment: small modifications, one reference is added, to appear in Phys. Rev.
Disorder driven collapse of the mobility gap and transition to an insulator in fractional quantum Hall effect
We study the nu=1/3 quantum Hall state in presence of the random disorder. We
calculate the topologically invariant Chern number, which is the only quantity
known at present to unambiguously distinguish between insulating and current
carrying states in an interacting system. The mobility gap can be determined
numerically this way, which is found to agree with experimental value
semiquantitatively. As the disorder strength increases towards a critical
value, both the mobility gap and plateau width narrow continuously and
ultimately collapse leading to an insulating phase.Comment: 4 pages with 4 figure
Trade-off between multiple-copy transformation and entanglement catalysis
We demonstrate that multiple copies of a bipartite entangled pure state may
serve as a catalyst for certain entanglement transformations while a single
copy cannot. Such a state is termed a "multiple-copy catalyst" for the
transformations. A trade-off between the number of copies of source state and
that of the catalyst is also observed. These results can be generalized to
probabilistic entanglement transformations directly.Comment: Essentially the journal version. 7 pages, no figures. Minor
correction
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