Invisible cloaks provide a way to hide an object under the detection of waves. A perfect cloak guides the incident waves through the cloaking shell without any distortion. In most cases, some important quantum degrees of freedom, e.g. electron spin o
r photon polarization, are not taken into account when designing a cloak. Here, we propose to use the temporal steering inequality of these degrees of freedom to detect the existence of an invisible cloak.
When dealing with system-reservoir interactions in an open quantum system, such as a photosynthetic light-harvesting complex, approximations are usually made to obtain the dynamics of the system. One question immediately arises: how good are these ap
proximations, and in what ways can we evaluate them? Here, we propose to use entanglement and a measure of non-Markovianity as benchmarks for the deviation of approximate methods from exact results. We apply two frequently-used perturbative but non-Markovian approximations to a photosynthetic dimer model and compare their results with that of the numerically-exact hierarchy equation of motion (HEOM). This enables us to explore both entanglement and non-Markovianity measures as means to reveal how the approximations either overestimate or underestimate memory effects and quantum coherence. In addition, we show that both the approximate and exact results suggest that non-Markonivity can, counter-intuitively, increase with temperature, and with the coupling to the environment.
Entanglement plays a central role in the field of quantum information science. It is well known that the degree of entanglement cannot be increased under local operations. Here, we show that the concurrence of a bipartite entangled state can be incre
ased under the local PT -symmetric operation. This violates the property of entanglement monotonicity. We also use the Bell-CHSH and steering inequalities to explore this phenomenon.
We propose a scheme to realize entanglement swapping via superradiance, entangling two distant cavities without a direct interaction. The successful Bell-state-measurement outcomes are performed naturally by the electromagnetic reservoir, and we show
how, using a quantum trajectory method, the non-local properties of the state obtained after the swapping procedure can be verified by the steering inequality. Furthermore, we discuss how the unsuccessful measurement outcomes can be used in an experiment of delayed-choice entanglement swapping. An extension of testing the quantum steering inequality with the observers at three different times is also considered
Quantum steering is the ability to remotely prepare different quantum states by using entangled pairs as a resource. Very recently, the concept of steering has been quantified with the use of inequalities, leading to substantial applications in quant
um information and communication science. Here, we highlight that there exists a natural temporal analogue of the steering inequality when considering measurements on a single object at different times. We give non-trivial operational meaning to violations of this temporal inequality by showing that it is connected to the security bound in the BB84 protocol and thus may have applications in quantum communication.
The radiative decay of quantum dot (QD) excitons into surface plasmons in a cylindrical nanowire is investigated theoretically. Maxwells equations with appropriate boundary conditions are solved numerically to obtain the dispersion relations of surfa
ce plasmons. The radiative decay rate of QD excitons is found to be greatly enhanced at certain values of the exciton bandgap. Analogous to the decay of a two-level atom in the photonic crystal, we first point out that such an enhanced phenomenon allows one to examine the non-Markovian dynamics of the QD exciton. Besides, due to the one dimensional propagating feature of nanowire surface plasmons, remote entangled states can be generated via super-radiance and may be useful in future quantum information processing.
The effects of magnetic flux in statistical magnetisms, including Pauli paramagnetism, Landau diamagnetism, and De Hass-van Alphen oscillation, are discussed. It is shown that the diamagnetism could be much increased by the fractional magnetic flux,
and the amplitude of the magnetic oscillation of De Hass-van Alphen can be amplified by the quantum effect of the flux.
