20,609 research outputs found
Engineering asymmetric steady-state Einstein-Podolsky-Rosen steering in macroscopic hybrid systems
Generation of quantum correlations between separate objects is of
significance both in fundamental physics and in quantum networks. One important
challenge is to create the directional "spooky action-at-a-distanc" effects
that Schr\"{o}dinger called "steering" between two macroscopic and massive
objects. Here, we analyze a generic scheme for generating steering correlations
in cascaded hybrid systems in which two distant oscillators with effective
masses of opposite signs are coupled to a unidirectional light field, a setup
which is known to build up quantum correlations by means of quantum back-action
evasion. The unidirectional coupling of the first to the second oscillator via
the light field can be engineered to enhance steering in both directions and
provides an active method for controlling the asymmetry of steering. We show
that the resulting scheme can efficiently generate unconditional steady-state
Einstein-Podolsky-Rosen steering between the two subsystems, even in the
presence of thermal noise and optical losses. As a scenario of particular
technological interest in quantum networks, we use our scheme to engineer
enhanced steering from an untrusted node with limited tunability (in terms of
interaction strength and type with the light field) to a trusted, highly
tunable node, hence offering a path to implementing one-sided
device-independent quantum tasks.Comment: 11 pages, 8 figure
Convergence of Adaptive Finite Element Approximations for Nonlinear Eigenvalue Problems
In this paper, we study an adaptive finite element method for a class of a
nonlinear eigenvalue problems that may be of nonconvex energy functional and
consider its applications to quantum chemistry. We prove the convergence of
adaptive finite element approximations and present several numerical examples
of micro-structure of matter calculations that support our theory.Comment: 24 pages, 12 figure
On Neutralization of Charged Black Holes
For non-spinning, charged (Reissner–Nordström) black holes, the particles with an opposite sign of charge with respect to that of the black hole will be pulled into the black hole by the extra electromagnetic force. Such a hole will be quickly neutralized so that there should not exist significantly charged, non-spinning black holes in the universe. The case of spinning, charged (Kerr–Newmann, KN) black holes is more complicated. For a given initial position and initial velocity of the particle, an oppositely charged particle does not always more easily fall into the black hole than a neutral particle. The possible existence of a magnetosphere further complicate the picture. One therefore cannot straightforwardly conclude that a charged spinning black hole will be neutralized. In this paper, we make the first step to investigate the neutralization of KN black holes without introducing a magnetosphere. We track the particle trajectories under the influence of the curved space–time and the electromagnetic field carried by the spinning, charged black hole. A statistical method is used to investigate the neutralization problem. We find a universal dependence of the falling probability into the black hole on the charge of the test particle, with the oppositely charged particles having a higher probability of falling. We therefore conclude that charged, spinning black holes without a magnetosphere should be quickly neutralized, consistent with people’s intuition. The neutralization problem of KN black holes with a corotating force-free magnetosphere is subject to further studies
Role of thermal noise in tripartite quantum steering
The influence of thermal noise on bipartite and tripartite quantum steering
induced by a short laser pulse in a hybrid three-mode optomechanical system is
investigated. The calculation is carried out under the bad cavity limit, the
adiabatic approximation of a slowly varying amplitude of the cavity mode, and
with the assumption of driving the cavity mode with a blue detuned strong laser
pulse. Under such conditions, explicit expressions of the bipartite and
tripartite steering parameters are obtained, and the concept of collective
tripartite quantum steering, recently introduced by He and Reid [Phys. Rev.
Lett. 111, 250403 (2013)], is clearly explored. It is found that both bipartite
and tripartite steering parameters are sensitive functions of the initial state
of the modes and distinctly different steering behaviour could be observed
depending on whether the modes were initially in a thermal state or not. We
find that the initial thermal noise is more effective in destroying the
bipartite rather than the tripartite steering which, on the other hand, can
persist even for a large thermal noise. For the initial vacuum state of a
steered mode, the tripartite steering exists over the entire interaction time
even if the steering modes are in very noisy thermal states. When the steered
mode is initially in a thermal state, it can be collectively steered by the
other modes. There are thresholds for the average number of the thermal photons
above which the existing tripartite steering appears as the collective
steering. Finally, we point out that the collective steering may provide a
resource in a hybrid quantum network for quantum secret sharing protocol.Comment: 13 pages, 9 figure
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