2,335 research outputs found
State estimation from pair of conjugate qudits
We show that, for parallel input states, an anti-linear map with respect
to a specific basis is essentially a classical operator. We also consider the
information contained in phase-conjugate pairs , and prove
that there is more information about a quantum state encoded in phase-conjugate
pairs than in parallel pairs.Comment: 4 pages, 1 tabl
Lifshitz transitions in a heavy-Fermion liquid driven by short-range antiferromagnetic correlations in the two-dimensional Kondo lattice model
The heavy-Fermion liquid with short-range antiferromagnetic correlations is
carefully considered in the two-dimensional Kondo-Heisenberg lattice model. As
the ratio of the local Heisenberg superexchange to the Kondo coupling
increases, Lifshitz transitions are anticipated, where the topology of
the Fermi surface (FS) of the heavy quasiparticles changes from a hole-like
circle to four kidney-like pockets centered around . In-between
these two limiting cases, a first-order quantum phase transition is identified
at where a small circle begins to emerge within the large
deformed circle. When , the two deformed circles intersect
each other and then decompose into four kidney-like Fermi pockets via a
second-order quantum phase transition. As increases further, the
Fermi pockets are shifted along the direction () to (),
and the resulting FS is consistent with the FS obtained recently using the
quantum Monte Carlo cluster approach to the Kondo lattice system in the
presence of the antiferrmagnetic order.Comment: 4 pages, 5 figure
Realization of All-or-nothing-type Kochen-Specker Experiment with Single Photons
Using the spontaneous parametric down-conversion process in a type-I phase
matching BBO crystal as single photon source, we perform an all-or-nothing-type
Kochen-Specker experiment proposed by Simon \QTR{it}{et al}. [Phys. Rev. Lett.
\QTR{bf}{85}, 1783 (2000)] to verify whether noncontextual hidden variables or
quantum mechanics is right. The results strongly agree with quantum mechanics.Comment: 3 figure
Electronic control and switching of entangled spin state using anisotropy and exchange in the three-particle paradigm
We explore the control and switching of the entangled spin states of
multi-spin particle qubit coupled to an electron using a three-particle spin
model described by (), in which is an
electron and can have any spin with both exchange coupling and
magnetic anisotropy. We derive a general formula for the existence of a
switching (DJ) resonance for any spin . We further contrast the
entanglement switching mechanisms for the and
spin models. We find that while the onsite magnetic anisotropy in
the case of allows full control of their spin states via
interaction with , in order to achieve acceptable control of a Bloch
vector within the model, additional mechanisms, such as
anisotropic exchange coupling, are required
Optimal entanglement witnesses based on local orthogonal observables
We show that the entanglement witnesses based on local orthogonal observables
which are introduced in [S. Yu and N.-L. Liu, Phys. Rev. Lett. 95, 150504
(2005)] and [O. G\"uhne, M. Mechler, G. T\'oth and P. Adam, Phys. Rev. A 74,
010301 (2006)] in linear and nonlinear forms can be optimized, respectively. As
applications, we calculate the optimal nonlinear witnesses of pure bipartite
states and show a lower bound on the I-concurrence of bipartite higher
dimensional systems with our method.Comment: 6 pages, 1 figure; minor changes, references adde
Comment on "Quantum key distribution without alternative measurements"
In a recent paper [A. Cabello, Phys. Rev. A 61, 052312 (2000)], a quantum key
distribution protocol based on entanglement swapping was proposed. However, in
this comment, it is shown that this protocol is insecure if Eve use a special
strategy to attack.Comment: 2 Pages, 1 Figur
Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons
We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.Comment: 7 pages, 4 figures, new results added, replaced by accepted versio
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