20,436 research outputs found
Secure direct communication using step-split Einstein-Podolsky-Rosen pair
We presen a secure direct communication protocol by using step-split
Einstein-Podolsky-Rosen (EPR) pair. In this communication protocol, Alice first
sends one qubit of an EPR pair to Bob. Bob sends a receipt signal to Alice
through public channel when he receives Alice's first qubit. Alice performs her
encoding operations on the second qubit and sends this qubit to Bob. Bob
performs a Bell-basis measurement to draw Alice's information. The security of
this protocol is based on `High fidelity implies low entropy'. If Eve want to
eavesdrop Alice's information, she has to attack both qubits of the EPR pair,
which results in that any effective eavesdropping attack can be detected. Bob's
receipt signal can protect this protocol against the eavesdropping hiding in
the quantum channel losses. And this protocol is strictly secure to perform a
quantum key distribution by using Calderbank-Shor-Steane codes.Comment: PACS:03.67.Hk,03.65.U
Deterministic Secure Direct Communication Using Ping-pong protocol without public channel
Based on an EPR pair of qubits and allowing asymptotically secure key
distribution, a secure communication protocol is presented. Bob sends either of
the EPR pair qubits to Alice. Alice receives the travel qubit. Then she can
encode classical information by local unitary operations on this travel qubit.
Alice send the qubit back to Bob. Bob can get Alice's information by
measurement on the two photons in Bell operator basis. If Eve in line, she has
no access to Bob's home qubit. All her operations are restricted to the travel
qubit. In order to find out which opeartion Alice performs, Eve's operation
must include measurements. The EPR pair qubits are destroyed. Bob's measurement
on the two photons in Bell operator basis can help him to judge whether Eve
exist in line or not. In this protocal, a public channel is not necessary.Comment: 3 figure
Measurement, Trace, Information Erasure and Entropy
We show that both information erasure process and trace process can be
realized by projective measurement. And a partial trace operation consists to a
projective measurement on a subsystem. We show that a nonunitary operation will
destroy the wave-behavior of a particle. We give a quantum manifestation of
Maxwell's demon and give a quantum manifestation of the second law of
therodynamics. We show that, considering the law of memontum-energy
conversation, the evolution of a closed system should be unitary and the von
Neumann entropy of the closed quantum system should be least.Comment: 8pages. Reported on the Conference of Chinese Physics Society (2003
autumn):Quantum information conncil hous
Eavesdropping on the Bostroem-Filbinger Communication Protocol in Noisy Quantum Channel
We show an eavesdropping scheme on Bostr\UNICODE{0xf6}m-Felbinger
communication protocol (called ping-pong protocol) [Phys. Rev. Lett. 89, 187902
(2002)] in an ideal quantum channel. A measurement attack can be perfectly used
to eavesdrop Alice's information instead of a most general quantum operation
attack. In a noisy quantum channel, the direct communication is forbidden. We
present a quantum key distribution protocol based on the ping-pong protocol,
which can be used in a low noisy quantum channel. And we give a weak upper
bound on the bit-error ratio that the detection probability should be lower
than 0.11, which is a requirement criterion when we utilize the ping-pong
protocol in a real communication.Comment: 4 pages; PSCA, 03.67.Hk, 03.65.U
Optimal Experimental Scheme for Bennett-Brassard 1984 Quantum Key Distribution Protocol with Weak Coherent Sources, Noisy and Lossy Channel
It is the first scheme which allows the detection apparatus to achieve both
the photon number of arriving signals and quantum bit error rate of the
multiphoton pulses precisely. We show that the upper bound of the fraction of
the tagged multiphoton pulses counts is , which is independent of the
channel loss and the intensity of the decoy source. Such upper bound is
and cannot be reduced any longer as long as the weak coherent
scouces and high lossy channel are used. We show that our scheme can be
implemented even if the channel loss is very high. A stronger intensity of the
pulse source is allowable to improve the rate of quantum key distribution. Both
the signal pulses and decoy pulses can be used to generate the raw key after
verified the security of the communication. We analyze that our scheme is
optimal under today's technology.
PACS: 03.67.DdComment: RevTex, 2figures, submitted for publication on 30 March 200
Deterministic Secure Direct Communication Using Mixed state
We show an improved ping-pong protocol which is based on the protocol showed
by Kim Bostrom and Timo Felbinger [Phys. Rev. Lett. 89, 187902 (2002);
quant-ph/0209040]. We show that our protocol is asymptotically secure key
distribution and quasisecure direct communication using a single photon
resource. And this protocol can be can be carried out with great efficiency and
speed using today's technology
An one-time-pad key communication protocol with entanglement
We present an one-time-pad key communication protocol that allows secure
direct communication with entanglement. Alice can send message to Bob in a
deterministic manner by using local measurements and public communication. The
theoretical efficiency of this protocol is double compared with BB84 protocol.
We show this protocol is unconditional secure under arbitrary quantum attack.
And we discuss that this protocol can be perfectly implemented with current
technologies.Comment: 4 pages;PACS: 03.67.Hk, 03.65.U
Generation of magnetic skyrmions through pinning effect
Based on analytical estimation and lattice simulation, a proposal is made
that magnetic skyrmions can be generated through the pinning effect in 2D
chiral magnetic materials, in absence of an external magnetic field or magnetic
anisotropy. In our simulation, stable magnetic skyrmions can be generated in
the pinning areas. The properties of the skyrmions are studied for various
values of ferromagnetic exchange strength and the Dzyaloshinskii-Moriya
interaction strength.Comment: 22 pages, 15 figure
Shape of a skyrmion
We propose a method of determining the shape of a two-dimensional magnetic
skyrmion, which can be parameterized as the position dependence of the
orientation of the local magnetic moment, by using the expansion in terms of
the eigenfunctions of the Schr\"{o}dinger equation of a harmonic oscillator. A
variational calculation is done, up to the next-to-next-to-leading order. This
result is verified by a lattice simulation based on Landau-Lifshitz-Gilbert
equation. Our method is also applied to the dissipative matrix in the Thiele
equation as well as two interacting skyrmions in a bilayer system.Comment: 25 pages, 11 figure
Paley type group schemes from cyclotomic classes and Arasu-Dillon-Player difference sets
In this paper, we present constructions of abelian Paley type group schemes
by using multiplicative characters of finite fields and Arasu-Dillon-Player
difference sets. The constructions produce many new Paley type group schemes
that were previous unknown in our classification of Paley type group schemes in
finite fields of small orders
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