arXiv subjects

Jian Wang

Publications and source records attributed to Jian Wang.

At least 1,315 records · Page 73Linked to original sources

arXiv2006

Quantum secure communication protocols based on entanglement swapping

We present a quantum secure direct communication protocol and a multiparty quantum secret sharing protocol based on Einstein-Podolsky-Rosen pairs and entanglement swapping. The present quantum secure direct communication protocol makes use of the ideal of block transmission. We also point out that the sender can encode his or her secret message without ensuring the security of the quantum channel firstly. In the multiparty quantum secret sharing protocol, the communication parties adopt checking mode or encoding mode with a certain probability. It is not necessary for the protocol to perform local unitary operation. In both the protocols, one party transmits only one photon for each Einstein-Podolsky-Rosen pair to another party and the security for the transmitting photons is ensured by selecting Z-basis or X-basis randomly to measure the sampling photons.

quant-ph↗

arXiv2006

Quantum secure communication scheme with W state

Recently, Cao et al. proposed a new quantum secure direct communication scheme using W state. In their scheme, the error rate introduced by an eavesdropper who takes intercept-resend attack, is only 8.3%. Actually, their scheme is just a quantum key distribution scheme because the communication parties first create a shared key and then encrypt the secret message using one-time pad. We then present a quantum secure communication scheme using three-qubit W state. In our scheme, the error rate is raised to 25% and it is not necessary for the present scheme to use alternative measurement or Bell basis measurement. We also show our scheme is unconditionally secure.

quant-ph↗

arXiv2006

Quantum secure direct communication based on order rearrangement of single photons

Based on the ideal of order rearrangement and block transmission of photons, we present a quantum secure direct communication scheme using single photons. The security of the present scheme is ensured by quantum no-cloning theory and the secret transmitting order of photons. The present scheme is efficient in that all of the polarized photons are used to transmit the sender's secret message except those chosen for eavesdropping check. We also generalize this scheme to a multiparty controlled quantum secret direct communication scheme which the sender's secret message can only be recovered by the receiver under the permission of all the controllers.

quant-ph↗

arXiv2006

Nonequilibrium current driven by a step voltage pulse: an exact solution

One of the most important problems in nanoelectronic device theory is to estimate how fast or how slow a quantum device can turn on/off a current. For an arbitrary noninteracting phase-coherent device scattering region connected to the outside world by leads, we have derived an exact solution for the nonequilibrium, nonlinear, and time-dependent current driven by both up- and down-step pulsed voltages. Our analysis is based on the Keldysh nonequilibrium Green's functions formalism where the electronic structure of the leads as well as the scattering region are treated on an equal footing. A model calculation for a quantum dot with a Lorentzian linewidth function shows that the time-dependent current dynamics display interesting finite-bandwidth effects not captured by the commonly used wideband approximation.

cond-mat.mes-hall↗

arXiv2006

Quantum key distribution protocols using entangled state

We present three quantum key distribution protocols using entangled state. In the first two protocols, all Einstein-Podolsky-Rosen pairs are used to distribute a secret key except those chosen for eavesdropping check, because the communication parties measure each of their particles in an invariable measuring basis. The first protocol is based on the ideal of qubit transmission in blocks. Although it need quantum memory, its theoretic efficiency approximates to 100%. The second protocol does not need quantum memory and its efficiency for qubits can achieve 100%. In the third protocol, we present a controlled quantum key distribution using three-particle entangled state to solve a special cryptographic task. Only with the controller's permission could the communication parties establish their sharing key and the sharing key is secret to the controller. We also analyze the security and the efficiency of the present protocols.

quant-ph↗

arXiv2006

Conservation of spin current

The conventional definition of spin-current, namely spin density multiplied by the group velocity, is not a conserved quantity due to possible spin rotations caused by spin-orbit (SO) interaction. However, in a model with spin-spin interactions, rotation of a spin causes a dynamic response of surrounding spins that opposes the rotation. Such a many-body effect restores the spin-current conservation. Here we prove that the non-conservation problem of spin-current can be resolved if a self-consistent spin-spin interaction is included in the analysis. We further derive a spin-conductance formula which partitions spin-current into different leads of a multi-lead conductor.

cond-mat.mes-hall↗

arXiv2006

Multiparty controlled quantum secret direct communication using Greenberger-Horne-Zeilinger state

Base on the idea of dense coding of three-photon entangled state and qubit transmission in blocks, we present a multiparty controlled quantum secret direct communication scheme using Greenberger-Horne-Zeilinger state. In the present scheme, the sender transmits her three bits of secret message to the receiver directly and the secret message can only be recovered by the receiver under the permission of all the controllers. All three-photon entangled states are used to transmit the secret messages except those chosen for eavesdropping check and the present scheme has a high source capacity because Greenberger-Horne-Zeilinger state forms a large Hilbert space.

quant-ph↗

arXiv2005

Efficient multiparty quantum secret sharing of secure direct communication

In this paper, we present an (n, n) threshold quantum secret sharing scheme of secure direct communication using Greenberger-Horne-Zeilinger state. The present scheme is efficient in that all the Greenberger-Horne-Zeilinger states used in the quantum secret sharing scheme are used to generate shared secret messages except those chosen for checking eavesdropper. In our scheme, the measuring basis of communication parties is invariable and the classical information used to check eavesdropping needs only the results of measurements of the communication parties. Another nice feature of our scheme is that the sender transmit her secret messages to the receivers directly and the receivers recover the sender's secret by combining their results, different from the QSS scheme whose object is essentially to allow a sender to establish a shared key with the receivers. This feature of our scheme is similar to that of quantum secret direct communication.

quant-ph↗

arXiv2005

Quantum secure direct communication without using perfect quantum channel

Most of the quantum secure direct communication protocol needs a pre-established secure quantum channel. Only after insuring the security of quantum channel, could the sender encode the secret message and send them to the receiver through the secure channel. In this paper, we present a quantum secure direct communication protocol using Einstein-Podolsky-Rosen pairs. It is not necessary for the present protocol to insure the security of quantum channel before transmitting the secret message. In the present protocol, all Einstein-Podolsky-Rosen pairs are used to transmit the secret message except those chosen for eavesdropping check.

quant-ph↗

arXiv2005

Quantum signature scheme with single photons

Quantum digital signature combines quantum theory with classical digital signature. The main goal of this field is to take advantage of quantum effects to provide unconditionally secure signature. We present a quantum signature scheme with message recovery without using entangle effect. The most important property of the proposed scheme is that it is not necessary for the scheme to use Greenberger-Horne-Zeilinger states. The present scheme utilizes single photons to achieve the aim of signature and verification. The security of the scheme relies on the quantum one-time pad and quantum key distribution. The efficiency analysis shows that the proposed scheme is an efficient scheme.

quant-ph↗

arXiv2005

Carbon Nanotube Thermal Transport: Ballistic to Diffusive

We propose to use l_0/(l_0+L) for the energy transmission covering both ballistic and diffusive regimes, where l_0 is mean free path and L is system length. This formula is applied to heat conduction in carbon nanotubes (CNTs). Calculations of thermal conduction show: (1) Thermal conductance at room temperature is proportional to the diameter of CNTs for single-walled CNTs (SWCNTs) and to the square of diameter for multi-walled CNTs (MWCNTs). (2) Interfaces play an important role in thermal conduction in CNTs due to the symmetry of CNTs vibrational modes. (3) When the phonon mean free path is comparable with the length L of CNTs in ballistic-diffusive regime, thermal conductivity κgoes as L^α . The effective exponent αis numerically found to decrease with increasing temperature and is insensitive to the diameter of SWCNTs for Umklapp scattering process. For short SWCNTs (<0.1 μm) we find α\approx 0.8 at room temperature. These results are consistent with recent experimental findings.

cond-mat.mes-hall↗

arXiv2005

Energy Transmission across Acoustically Mismatched Solid Junctions

We derive expression for energy flux in terms of lattice normal mode coordinates. Energy transmission across solid junctions from lattice dynamic point of view is given and its relation with atomic masses, lattice constants, and group velocities is clarified. A scattering boundary method (SBM) is proposed for calculating the amplitude transmission across solid junctions. The phonon transmission coefficients and thermal conductance are calculated for two kinds of acoustically mismatched junctions: different chirality nanotubes (11,0) to (8,0), and Si-Ge interface structure. Our calculation shows a mode-dependent transmission in nanotube junction due to the high symmetry vibrating motions for nanotube atoms, indicating its possible important role in nanotube mixture thermal conductance. Energy transmission and Kapitza conductance across the Si-Ge interface [001] are calculated for the Si-Ge diamond-type structure. It is shown that the energy transmission across the Si-Ge interface depends on the incident angle and on the interface mode conversion. A critical incident angle about 42 degrees numerically found for waves incident from Ge to Si. Our numerical result of the Kapitza conductance at temperature T=200K is G_K=4.6x10^8 W/(Km^2) We find numerically scaling law G_K proportional to T^{2.87} for [001] interface at low temperature.

cond-mat.stat-mech↗

arXiv2005

Ballistic Thermal Conduction across Acoustically Mismatched Solid Junctions

We derive expressions for energy flow in terms of lattice normal mode coordinates and energy transmission involving reduced group velocities. With a version of Landauer formula appropriate for lattice dynamic approach, the phonon transmission coefficients and thermal conductance are calculated for two kinds of acoustically mismatched junctions: different chirality nanotubes (11,0) to (8,0), and Si-Ge superlattice structure. Our calculation shows a mode-dependent transmission in nanotube junction and a resonantly modulated ballistic thermal conductance in superlattice. The superlattice result suggests a new interpretation of the experimental data. Our approach provides an atomistic way for the calculation of thermal conduction in nanostructure.

cond-mat.stat-mech↗

arXiv2004

Quantum transport theory for nanostructures with Rashba spin-orbital interaction

We report on a general theory for analyzing quantum transport through devices in the Metal-QD-Metal configuration where QD is a quantum dot or the device scattering region which contains Rashba spin-orbital and electron-electron interactions. The metal leads may or may not be ferromagnetic, they are assumed to weakly couple to the QD region. Our theory is formulated by second quantizing the Rashba spin-orbital interaction in spectral space (instead of real space), and quantum transport is then analyzed within the Keldysh nonequilibrium Green's function formalism. The Rashba interaction causes two main effects to the Hamiltonian: (i) it gives rise to an extra spin-dependent phase factor in the coupling matrix elements between the leads and the QD; (ii) it gives rise to an inter-level spin-flip term but forbids any intra-level spin-flips. Our formalism provides a starting point for analyzing many quantum transport issues where spin-orbital effects are important. As an example, we investigate transport properties of a Aharnov-Bohm ring in which a QD having Rashba spin-orbital and e-e interactions is located in one arm of the ring. A substantial spin-polarized conductance or current emerges in this device due to a combined effect of a magnetic flux and the Rashba interaction. The direction and strength of the spin-polarization are shown to be controllable by both the magnetic flux and a gate voltage.

cond-mat.mes-hall↗

arXiv2003

Gate-controllable spin-battery

We propose a gate-controllable spin-battery for spin current. The spin-battery consists of a lateral double quantum dot under a uniform magnetic field. A finite DC spin-current is driven out of the device by controlling a set of gate voltages. Spin-current can also be delivered in the absence of charge-current. The proposed device should be realizable using present technology at low temperature.

cond-mat.mes-hall↗

arXiv2003

Shot noise of spin current

We report an exact solution for the noise spectrum of spin-current without charge-current in a spin field effect transistor (SFET). For the SFET with two leads, it is found that both auto- and cross-correlation functions are needed to characterize the noise of spin-current. A shot noise is also generated for the charge-current even though the net charge-current is identically zero. The noise spectra of spin-current and charge-current depends on the coupling strength between the SFET and the leads, and they may behave qualitatively differently. We also present results of noise spectra in the adiabatic regime.

cond-mat↗

arXiv2003

A spin-cell for spin current

We propose and investigate a spin-cell device which provides the necessary spin-motive force to drive a spin current for future spintronic circuits. Our spin-cell have four basic characteristics: (i) it has two poles so that a spin current flows in from one pole and out from the other pole, this way a complete spin-circuit can be established; (ii) it has a source of energy to drive the spin current; (iii) it maintains spin coherence so that a sizable spin current can be delivered; (iv) it drives a spin current without a charge current. The proposed spin-cell for spin current should be realizable using technologies presently available.

cond-mat.mes-hall↗

arXiv2003

Spin-current induced electric field

We theoretically predict that a pure steady state spin-current without charge-current can induce an electric field. A formula for the induced electric field is derived and we investigate its characteristics. Conversely, a moving spin is affected by an external electric field and we present a formula for the interaction energy.

cond-mat.mes-hall↗