arXiv subjects

Yunshan Cao

Publications and source records attributed to Yunshan Cao.

60 records · Page 4Linked to original sources

arXiv2013

Cross-correlations mediated by Majorana bound states

We consider the correlated parallel transport through two quantum dots which are tunnel-coupled to the ends of a semiconductor nanowire where the Majorana bound states (MBSs) may emerge under proper conditions. In terms of the cross-correlation of currents, we reveal unusual behaviors originated from the nonlocal MBSs, including such as the distinct symmetry and antisymmetry of the spectral density in response to the dot-level modulations, and the vanished cross correlation occurred when any of the dot-levels is in resonance with the Majorana zero mode.

cond-mat.mes-hall↗

arXiv2013

Angular and Linear Momentum of Excited Ferromagnets

The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist in the presence of dipole-dipole interactions. However, spin and orbital angular momentum are not conserved separately. We also define the linear momentum of ferromagnetic textures. We illustrate the general principles with special reference to the spin transfer torques and identify the emergence of a non-adiabatic effective field acting on domain walls in ferromagnetic insulators.

cond-mat.mes-hall↗

arXiv2012

Current-oscillator correlation and Fano factor spectrum of quantum shuttle with finite bias voltage and temperature

A general master equation is derived to describe an electromechanical single-dot transistor in the Coulomb blockade regime. In the equation, Fermi distribution functions in the two leads are taken into account, which allows one to study the system as a function of bias voltage and temperature of the leads. Furthermore, we treat the coherent interaction mechanism between electron tunneling events and the dynamics of excited vibrational modes. Stationary solutions of the equation are numerically calculated. We show current through the oscillating island at low temperature appears step like characteristics as a function of the bias voltage and the steps depend on mean phonon number of the oscillator. At higher temperatures the current steps would disappear and this event is accompanied by the emergence of thermal noise of the charge transfer. When the system is mainly in the ground state, zero frequency Fano factor of current manifests sub-Poissonian noise and when the system is partially driven into its excited states it exhibits super-Poissonian noise. The difference in the current noise would almost be removed for the situation in which the dissipation rate of the oscillator is much larger than the bare tunneling rates of electrons.

cond-mat.mes-hall↗

arXiv2012

Probing the existence and dynamics of Majorana fermion via transport through a quantum dot

We consider an experimentally feasible setup to demonstrate the existence and coherent dynamics of Majorana fermion. The transport setup consists of a quantum dot and a tunnel-coupled semiconductor nanowire which is anticipated to generate Majorana excitations under some conditions. For transport under finite bias voltage, we find that a subtraction of the source and drain currents can expose the essential feature of the Majorana fermion, including the zero-energy nature by gate-voltage modulating the dot level. Moreover, coherent oscillating dynamics of the Majorana fermion between the nanowire and the quantum dot is reflected in the shot noise via a spectral dip together with a pronounced zero-frequency noise enhancement effect. Important parameters, e.g. for the Majorana's mutual interaction and its coupling to the quantum dot, can be extracted out in experiment using the derived analytic results.

cond-mat.mes-hall↗

arXiv2012

Non-Markovian Transmission through Two Quantum Dots Connected by a Continuum

We consider a transport setup containing a double-dot connected by a continuum. Via an exact solution of the time-dependent Schrödinger equation, we demonstrate a highly non-Markovian quantum-coherence-mediated transport through this dot-continuum-dot (DCD) system, which is in contrast with the common premise since in typical case a quantum particle does not reenter the system of interest once it irreversibly decayed into a continuum (such as the spontaneous emission of a photon). We also find that this DCD system supports an unusual steady state with unequal source and drain currents, owing to electrons irreversibly entering the continuum and floating there.

cond-mat.mes-hall↗

arXiv2011

Decoherence and the retrieval of lost information

We found that in contrast with the common premise, a measurement on the environment of an open quantum system can {\em reduce} its decoherence rate. We demonstrate it by studying an example of indirect qubit's measurement, where the information on its state is hidden in the environment. This information is extracted by a distant device, coupled with the environment. We also show that the reduction of decoherence generated by this device, is accompanied with diminution of the environmental noise in a vicinity of the qubit. An interpretation of these results in terms of quantum interference on large scales is presented.

cond-mat.mes-hall↗