85,186 research outputs found
Gr\"obner-Shirshov bases for categories
In this paper we establish Composition-Diamond lemma for small categories. We
give Gr\"obner-Shirshov bases for simplicial category and cyclic category.Comment: 20 page
Perturbational approach to the quantum capacity of additive Gaussian quantum channel
For a quantum channel with additive Gaussian quantum noise, at the large
input energy side, we prove that the one shot capacity is achieved by the
thermal noise state for all Gaussian state inputs, it is also true for
non-Gaussian input in the sense of first order perturbation. For a general case
of copies input, we show that up to first order perturbation, any
non-Gaussian perturbation to the product thermal state input has a less quantum
information transmission rate when the input energy tend to infinitive.Comment: 5 page
Quantum correlations in the collective spin systems
Quantum and classical pairwise correlations in two typical collective spin
systems (i.e., the Dicke model and the Lipkin-Meshkov-Glick model) are
discussed. These correlations in the thermodynamical limit are obtained
analytically and in a finite-size system are calculated numerically. Large-size
scaling behavior for the quantum discord itself is observed, which has never
been reported in another critical system. A logarithmic diverging behavior for
the first derivative of the quantum discord is also found in both models, which
might be universal in the second-order quantum phase transition. It is
suggested that the pronounced maximum or minimum of first derivative of quantum
discord signifies the critical point. Comparisons between the quantum discord
and the scaled concurrence are performed. It is shown that the quantum discord
is very small in one phase and robust in the other phase, while the scaled
concurrence shows maximum at the critical point and decays rapidly when away
from the the critical point.Comment: 8 pages, 4 figure
Spin-Orbit Coupling and Tunneling Current in a Parabolic Quantum Dot
We propose a novel approach to explore the properties of a quantum dot in the
presence of the spin-orbit interaction and in a tilted magnetic field. The
spin-orbit coupling within the quantum dot manifest itself as anti-crossing of
the energy levels when the tilt angle is varied. The anti-crossing gap has a
non-monotonic dependence on the magnitude of the magnetic field and exhibits a
peak at some finite values of the magnetic field. From the dependence of the
tunneling current through the quantum dot on the bias voltage and the tilt
angle, the anti-crossing gap and most importantly the spin-orbit strength can
be uniquely determined
- …