5,312 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
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
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
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
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
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
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
Hawking radiation as tunneling from the Kerr and Kerr-Newman black holes
Recent work, which treats the Hawking radiation as a semi-classical tunneling
process at the horizon of the Schwarzschild and Reissner-Nordstrom spacetimes,
indicates that the exact radiant spectrum is no longer pure thermal after
considering the black hole background as dynamical and the conservation of
energy. In this paper, we extend the method to investigate Hawking radiation as
massless particles tunneling across the event horizon of the Kerr black hole
and that of charged particles from the Kerr-Newman black hole by taking into
account the energy conservation, the angular momentum conservation, and the
electric charge conservation. Our results show that when self-gravitation is
considered, the tunneling rate is related to the change of Bekenstein-Hawking
entropy and the derived emission spectrum deviates from the pure thermal
spectrum, but is consistent with an underlying unitary theory.Comment: 10 pages, no figure, Revtex4, typos removed, final version to appear
in PR
Hawking Radiation of Dirac Particles in a Variable-mass Kerr Black Hole
Hawking effect of Dirac particles in a variable-mass Kerr space-time is
investigated by using method of the generalized tortoise coordinate
transformation. The location and the temperature of event horizon of the
non-stationary Kerr black hole are derived. It is shown that the temperature
and the shape of event horizon depend not only on the time but also on the
polar angle. However, our results demonstrate that the Fermi-Dirac spectrum
displays a new spin-rotation effect which is absent from that of Bose-Einstein
distribution.Comment: 6 pages, revtex (12pt), no figure. Chin. Phys. Lett. 18 (2001) 485
(in press
Hawking Radiation of Weyl Neutrinos in a Rectilinearly Non-uniformly Accelerating Kinnersley Black Hole
Quantum thermal effect of Weyl neutrinos in a rectilinearly non-uniformly
accelerating Kinnersley black hole is investigated by using the generalized
tortoise coordinate transformation. The equation that determines the location,
the Hawking temperature of the event horizon and the thermal radiation spectrum
of neutrinos are derived. Our results show that the location and the
temperature of the event horizon depend not only on the time but also on the
angle.Comment: 9 pages, no figure, Latex 2.09, accepted for Chinese Physics Vol. 11,
No. 7 (2002
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