7,004 research outputs found
Real time image subtraction and "exclusive or" operation using a self-pumped phase conjugate mirror
Real time "exclusive or" operation with an interferometer using a self-pumped phase conjugate mirror is reported. Also, results of image subtraction and intensity inversion are shown
A quantum analog of Huffman coding
We analyze a generalization of Huffman coding to the quantum case. In
particular, we notice various difficulties in using instantaneous codes for
quantum communication. Nevertheless, for the storage of quantum information, we
have succeeded in constructing a Huffman-coding inspired quantum scheme. The
number of computational steps in the encoding and decoding processes of N
quantum signals can be made to be of polylogarithmic depth by a massively
parallel implementation of a quantum gate array. This is to be compared with
the O (N^3) computational steps required in the sequential implementation by
Cleve and DiVincenzo of the well-known quantum noiseless block coding scheme of
Schumacher. We also show that O(N^2(log N)^a) computational steps are needed
for the communication of quantum information using another Huffman-coding
inspired scheme where the sender must disentangle her encoding device before
the receiver can perform any measurements on his signals.Comment: Revised version, 7 pages, two-column, RevTex. Presented at 1998 IEEE
International Symposium on Information Theor
Getting the Goods on Virtual Items: A Fresh Look at Transactions in Multi-User Online Environments
Insecurity of position-based quantum cryptography protocols against entanglement attacks
Recently, position-based quantum cryptography has been claimed to be
unconditionally secure. In contrary, here we show that the existing proposals
for position-based quantum cryptography are, in fact, insecure if entanglement
is shared among two adversaries. Specifically, we demonstrate how the
adversaries can incorporate ideas of quantum teleportation and quantum secret
sharing to compromise the security with certainty. The common flaw to all
current protocols is that the Pauli operators always map a codeword to a
codeword (up to an irrelevant overall phase). We propose a modified scheme
lacking this property in which the same cheating strategy used to undermine the
previous protocols can succeed with a rate at most 85%. We conjecture that the
modified protocol is unconditionally secure and prove this to be true when the
shared quantum resource between the adversaries is a two- or three- level
system
Physical transformations between quantum states
Given two sets of quantum states {A_1, ..., A_k} and {B_1, ..., B_k},
represented as sets of density matrices, necessary and sufficient conditions
are obtained for the existence of a physical transformation T, represented as a
trace-preserving completely positive map, such that T(A_i) = B_i for i = 1,
..., k. General completely positive maps without the trace-preserving
requirement, and unital completely positive maps transforming the states are
also considered
Two-way quantum communication channels
We consider communication between two parties using a bipartite quantum
operation, which constitutes the most general quantum mechanical model of
two-party communication. We primarily focus on the simultaneous forward and
backward communication of classical messages. For the case in which the two
parties share unlimited prior entanglement, we give inner and outer bounds on
the achievable rate region that generalize classical results due to Shannon. In
particular, using a protocol of Bennett, Harrow, Leung, and Smolin, we give a
one-shot expression in terms of the Holevo information for the
entanglement-assisted one-way capacity of a two-way quantum channel. As
applications, we rederive two known additivity results for one-way channel
capacities: the entanglement-assisted capacity of a general one-way channel,
and the unassisted capacity of an entanglement-breaking one-way channel.Comment: 21 pages, 3 figure
Understanding Three Hydration-Dependent Transitions of Zwitterionic Carboxybetaine Hydrogel by Molecular Dynamics Simulations
In this work, molecular dynamics simulations were
performed to study a carboxybetaine methacrylate (CBMA) hydrogel under various swelling states. The water content in this study ranged from 28% to 91% of the total weight of the hydrogel. Three transitions of the CBMA hydrogel were observed as the water content increased. The first transition occurs when the water content increases from 33%
to 37%. The observed kink in the self-diffusion coefficient of water indicates that the hydration of the polymer network of the hydrogel is saturated; the further added water is in a less confined state. The second transition was found to be related to the physical cross-links of
the polymer network. As the water content rises to above 62%, the lifetime of the physical cross-links decreases significantly. This abrupt change in the lifetime indicates that the transition represents the equilibrium swelling state of the hydrogel. Finally, the third transition was observed when the water content goes above 81%. The significant increases in the bond and angle energies of the
polymer network indicate that the hydrogel reaches its upper limit swelling state at this transition. These results are comparable to previously published experimental studies of similar zwitterionic hydrogels
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