38,544 research outputs found
Storage of light: A useful concept?
We show both analytically and numerically that photons from a probe pulse are
not stored in several recent experiments. Rather, they are absorbed to produce
a two-photon excitation. More importantly, when an identical coupling pulse is
re-injected into the medium, we show that the regenerated optical field has a
pulse width that is very different from the original probe field. It is
therefore, not a faithful copy of the original probe pulse.Comment: 5 pages, 3 figures. Correct LaTEX listings of reference
Quantum secret sharing between m-party and n-party with six states
We propose a quantum secret sharing scheme between -party and -party
using three conjugate bases, i.e. six states. A sequence of single photons,
each of which is prepared in one of the six states, is used directly to encode
classical information in the quantum secret sharing process. In this scheme,
each of all members in group 1 choose randomly their own secret key
individually and independently, and then directly encode their respective
secret information on the states of single photons via unitary operations, then
the last one (the th member of group 1) sends of the resulting qubits
to each of group 2. By measuring their respective qubits, all members in group
2 share the secret information shared by all members in group 1. The secret
message shared by group 1 and group 2 in such a way that neither subset of each
group nor the union of a subset of group 1 and a subset of group 2 can extract
the secret message, but each whole group (all the members of each group) can.
The scheme is asymptotically 100% in efficiency. It makes the Trojan horse
attack with a multi-photon signal, the fake-signal attack with EPR pairs, the
attack with single photons, and the attack with invisible photons to be
nullification. We show that it is secure and has an advantage over the one
based on two conjugate bases. We also give the upper bounds of the average
success probabilities for dishonest agent eavesdropping encryption using the
fake-signal attack with any two-particle entangled states. This protocol is
feasible with present-day technique.Comment: 7 page
Efficient quantum cryptography network without entanglement and quantum memory
An efficient quantum cryptography network protocol is proposed with
d-dimension polarized photons, without resorting to entanglement and quantum
memory. A server on the network, say Alice, provides the service for preparing
and measuring single photons whose initial state are |0>. The users code the
information on the single photons with some unitary operations. For preventing
the untrustworthy server Alice from eavesdropping the quantum lines, a
nonorthogonal-coding technique (decoy-photon technique) is used in the process
that the quantum signal is transmitted between the users. This protocol does
not require the servers and the users to store the quantum state and almost all
of the single photons can be used for carrying the information, which makes it
more convenient for application than others with present technology. We also
discuss the case with a faint laser pulse.Comment: 4 pages, 1 figures. It also presented a way for preparing decoy
photons without a sinigle-photon sourc
Circular quantum secret sharing
A circular quantum secret sharing protocol is proposed, which is useful and
efficient when one of the parties of secret sharing is remote to the others who
are in adjacent, especially the parties are more than three. We describe the
process of this protocol and discuss its security when the quantum information
carrying is polarized single photons running circularly. It will be shown that
entanglement is not necessary for quantum secret sharing. Moreover, the
theoretic efficiency is improved to approach 100% as almost all the instances
can be used for generating the private key, and each photon can carry one bit
of information without quantum storage. It is straightforwardly to utilize this
topological structure to complete quantum secret sharing with multi-level
two-particle entanglement in high capacity securely.Comment: 7 pages, 2 figure
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