265 research outputs found
Eavesdropping on the "ping-pong" quantum communication protocol
The proposed eavesdropping scheme reveals that the quantum communication
protocol recently presented by Bostrom and Felbinger [Phys. Rev. Lett. 89,
187902 (2002)] is not secure as far as quantum channel losses are taken into
account
Experimental demonstration of four-party quantum secret sharing
Secret sharing is a multiparty cryptographic task in which some secret
information is splitted into several pieces which are distributed among the
participants such that only an authorized set of participants can reconstruct
the original secret. Similar to quantum key distribution, in quantum secret
sharing, the secrecy of the shared information relies not on computational
assumptions, but on laws of quantum physics. Here, we present an experimental
demonstration of four-party quantum secret sharing via the resource of
four-photon entanglement
Interaction of light with a single atom in the strong focusing regime
We consider the near-resonant interaction between a single atom and a focused
light mode, where a single atom localized at the focus of a lens can scatter a
significant fraction of light. Complementary to previous experiments on
extinction and phase shift effects of a single atom, we report here on the
measurement of coherently backscattered light. The strength of the observed
effect suggests combining strong focusing with the well-established methods of
cavity QED. We consider theoretically a nearly concentric cavity, which should
allow for a strongly focused optical mode. Simple estimates show that in a such
case one can expect a significant single photon Rabi frequency. This opens new
perspectives and a possibility to scale up the system consisting of many
atom+cavity nodes for quantum networking due to a significant technical
simplification of the atom--light interfaces.Comment: 7 pages, 6 figures, followup of workshop "Single photon technologies"
in Boulder, CO, 200
Tailoring Single and Multiphoton Probabilities of a Single Photon On-Demand Source
As typically implemented, single photon sources cannot be made to produce
single photons with high probability, while simultaneously suppressing the
probability of yielding two or more photons. Because of this, single photon
sources cannot really produce single photons on demand. We describe a
multiplexed system that allows the probabilities of producing one and more
photons to be adjusted independently, enabling a much better approximation of a
source of single photons on demand.Comment: 4 pages, LaTex, 2 figures, twocolumn and RevTex Style for PR
Secure communication with a publicly known key
We present a scheme for direct and confidential communication between Alice and Bob, where there is no need for establishing a shared secret key first, and where the key used by Alice even will become known publicly. The communication is based on the exchange of single photons and each and every photon transmits one bit of Alice's message without revealing any information to a potential eavesdropper
Quantum time of flight distribution for cold trapped atoms
The time of flight distribution for a cloud of cold atoms falling freely
under gravity is considered. We generalise the probability current density
approach to calculate the quantum arrival time distribution for the mixed state
describing the Maxwell-Boltzmann distribution of velocities for the falling
atoms. We find an empirically testable difference between the time of flight
distribution calculated using the quantum probability current and that obtained
from a purely classical treatment which is usually employed in analysing time
of flight measurements. The classical time of flight distribution matches with
the quantum distribution in the large mass and high temperature limits.Comment: 6 pages, RevTex, 4 eps figure
Single Qubit Quantum Secret Sharing
We present a simple and practical protocol for the solution of a secure
multiparty communication task, the secret sharing, and its experimental
realization. In this protocol, a secret message is split among several parties
in a way that its reconstruction require the collaboration of the participating
parties. In the proposed scheme the parties solve the problem by a sequential
communication of a single qubit. Moreover we show that our scheme is equivalent
to the use of a multiparty entangled GHZ state but easier to realize and better
scalable in practical applications.Comment: 5 pages, 2 figures, submitted December 29, 200
Full-field implementation of a perfect eavesdropper on a quantum cryptography system
Quantum key distribution (QKD) allows two remote parties to grow a shared
secret key. Its security is founded on the principles of quantum mechanics, but
in reality it significantly relies on the physical implementation.
Technological imperfections of QKD systems have been previously explored, but
no attack on an established QKD connection has been realized so far. Here we
show the first full-field implementation of a complete attack on a running QKD
connection. An installed eavesdropper obtains the entire 'secret' key, while
none of the parameters monitored by the legitimate parties indicate a security
breach. This confirms that non-idealities in physical implementations of QKD
can be fully practically exploitable, and must be given increased scrutiny if
quantum cryptography is to become highly secure.Comment: Revised after editorial and peer-review feedback. This version is
published in Nat. Commun. 8 pages, 6 figures, 1 tabl
- …