3,106 research outputs found
Quantum plateau of Andreev reflection induced by spin-orbit coupling
In this work we uncover an interesting quantum plateau behavior for the
Andreev reflection between a one-dimensional quantum wire and superconductor.
The quantum plateau is achieved by properly tuning the interplay of the
spin-orbit coupling within the quantum wire and its tunnel coupling to the
superconductor. This plateau behavior is justified to be unique by excluding
possible existences in the cases associated with multi-channel quantum wire,
the Blonder-Tinkham-Klapwijk continuous model with a barrier, and lattice
system with on-site impurity at the interface.Comment: 6 pages, 3 figures
Revisit the spin-FET: Multiple reflections, inelastic scattering, and lateral size effects
We revisit the spin-injected field effect transistor (spin-FET) by simulating
a lattice model based on recursive lattice Green's function approach. In the
one-dimensional case and coherent regime, the simulated results reveal
noticeable differences from the celebrated Datta-Das model, which motivate thus
an improved treatment and lead to analytic and generalized result. The
simulation also allows us to address inelastic scattering (using B\"uttiker's
fictitious reservoir approach) and lateral confinement effects on the control
of spins which are important issues in the spin-FET device.Comment: 9 pages, 4 figure
Qubit state tomography in superconducting circuit via weak measurements
The standard method of "measuring" quantum wavefunction is the technique of
{\it indirect} quantum state tomography. Owing to conceptual novelty and
possible advantages, an alternative {\it direct} scheme was proposed and
demonstrated recently in quantum optics system. In this work we present a study
on the direct scheme of measuring qubit state in the circuit QED system, based
on weak measurement and weak value concepts. To be applied to generic parameter
conditions, our formulation and analysis are carried out for finite strength
weak measurement, and in particular beyond the bad-cavity and weak-response
limits. The proposed study is accessible to the present state-of-the-art
circuit-QED experiments.Comment: 7 pages,5figure
Transport probe of nonadiabatic transition caused by Majorana moving
We propose a transport probe scheme to detect the nonadiabatic transition
caused by Majornana moving, which is relevant to the braiding operations in
topological quantum computation. The scheme is largely based on a time
dependent single-electron-wavefunction approach to quantum transport. Applying
the Kitaev model, we simulate the time dependent Andreev-reflection current and
examine the feasibility of using the current to infer the nonadiabatic
transition. We design a scheme to determine the Landau-Zener tunneling ratio in
the context of transport, and compare it with the result obtained from the
isolated quantum wire. Desirable agreements are demonstrated for the proposed
scheme.Comment: 8 pages, 6 figure
Revisit the non-locality of Majorana zero modes and teleportation: Bogoliubov-de Gennes equation based treatment
The nonlocal nature of the Majorana zero modes implies an inherent
teleportation channel and unique transport signatures for Majorana
identification. In this work we make an effort to eliminate some
inconsistencies between the Bogoliubov-de Gennes equation based treatment and
the method using the associated regular fermion number states of vacancy and
occupation within the `second quantization' framework. We first consider a
rather simple `quantum dot--Majorana wire--quantum dot' system, then a more
experimentally relevant setup by replacing the quantum dots with transport
leads. For the latter setup, based on the dynamical evolution of electron-hole
excitations, we develop a single-particle-wavefunction approach to quantum
transport, which renders both the conventional quantum scattering theory and
the steady-state nonequilibrium Green's function formalism as its stationary
limit. Further, we revisit the issue of Majorana tunneling spectroscopy and
consider in particular the two-lead coupling setup. We present comprehensive
discussions with detailed comparisons, and predict a zero-bias-limit
conductance of (for symmetric coupling to the leads),which is a half of
the popular result of the zero-bias-peak, or, the so-called Majorana quantized
conductance (). The present work may arouse a need to reexamine some
existing studies and the proposed treatment is expected to be involved in
analyzing future experiments in this fast developing field.Comment: 12 pages, 4 figure
Quantum transfer through a continuum under continuous monitoring
In this work we extend our previous studies on the quantum transfer of a
particle through a finite-bandwidth continuum under frequent detections, by
replacing the assumed frequent measurements with a genuine continuous
monitoring by a point-contact detector. We present a quantitative comparison
between the two types of measurement. We also propose possible measurements,
based on the state-of-the-art experiments, to test the `scaling' property
between the measurement rate and the bandwidth of the reservoir, rooted in the
transfer dynamics under continuous monitoring.Comment: 8 pages, 4 figure
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