1,532 research outputs found
Overcoming a limitation of deterministic dense coding with a non-maximally entangled initial state
Under two-party deterministic dense-coding, Alice communicates (perfectly
distinguishable) messages to Bob via a qudit from a pair of entangled qudits in
pure state |Psi>. If |Psi> represents a maximally entangled state (i.e., each
of its Schmidt coefficients is sqrt(1/d)), then Alice can convey to Bob one of
d^2 distinct messages. If |Psi> is not maximally entangled, then Ji et al.
[Phys. Rev. A 73, 034307 (2006)] have shown that under the original
deterministic dense-coding protocol, in which messages are encoded by unitary
operations performed on Alice's qudit, it is impossible to encode d^2-1
messages. Encoding d^2-2 is possible; see, e.g., the numerical studies by Mozes
et al. [Phys. Rev. A 71, 012311 (2005)]. Answering a question raised by Wu et
al. [Phys. Rev. A 73, 042311 (2006)], we show that when |Psi> is not maximally
entangled, the communications limit of d^2-2 messages persists even when the
requirement that Alice encode by unitary operations on her qudit is weakened to
allow encoding by more general quantum operators. We then describe a
dense-coding protocol that can overcome this limitation with high probability,
assuming the largest Schmidt coefficient of |Psi> is sufficiently close to
sqrt(1/d). In this protocol, d^2-2 of the messages are encoded via unitary
operations on Alice's qudit, and the final (d^2-1)-th message is encoded via a
(non-trace-preserving) quantum operation.Comment: 18 pages, published versio
Deterministic dense coding and entanglement entropy
We present an analytical study of the standard two-party deterministic
dense-coding protocol, under which communication of perfectly distinguishable
messages takes place via a qudit from a pair of non-maximally entangled qudits
in pure state |S>. Our results include the following: (i) We prove that it is
possible for a state |S> with lower entanglement entropy to support the sending
of a greater number of perfectly distinguishable messages than one with higher
entanglement entropy, confirming a result suggested via numerical analysis in
Mozes et al. [Phys. Rev. A 71 012311 (2005)]. (ii) By explicit construction of
families of local unitary operators, we verify, for dimensions d = 3 and d=4, a
conjecture of Mozes et al. about the minimum entanglement entropy that supports
the sending of d + j messages, j = 2, ..., d-1; moreover, we show that the j=2
and j= d-1 cases of the conjecture are valid in all dimensions. (iii) Given
that |S> allows the sending of K messages and has the square roof of c as its
largest Schmidt coefficient, we show that the inequality c <= d/K, established
by Wu et al. [ Phys. Rev. A 73, 042311 (2006)], must actually take the form c <
d/K if K = d+1, while our constructions of local unitaries show that equality
can be realized if K = d+2 or K = 2d-1.Comment: 19 pages, 2 figures. Published versio
Scotin, a novel p53-inducible proapoptotic protein located in the ER and the nuclear membrane
p53 is a transcription factor that induces growth arrest or apoptosis in response to cellular stress. To identify new p53-inducible proapoptotic genes, we compared, by differential display, the expression of genes in spleen or thymus of normal and p53 nullizygote mice after γ-irradiation of whole animals. We report the identification and characterization of human and mouse Scotin homologues, a novel gene directly transactivated by p53. The Scotin protein is localized to the ER and the nuclear membrane. Scotin can induce apoptosis in a caspase-dependent manner. Inhibition of endogenous Scotin expression increases resistance to p53-dependent apoptosis induced by DNA damage, suggesting that Scotin plays a role in p53-dependent apoptosis. The discovery of Scotin brings to light a role of the ER in p53-dependent apoptosis
Conformal dimension and random groups
We give a lower and an upper bound for the conformal dimension of the
boundaries of certain small cancellation groups. We apply these bounds to the
few relator and density models for random groups. This gives generic bounds of
the following form, where is the relator length, going to infinity.
(a) 1 + 1/C < \Cdim(\bdry G) < C l / \log(l), for the few relator model,
and
(b) 1 + l / (C\log(l)) < \Cdim(\bdry G) < C l, for the density model, at
densities .
In particular, for the density model at densities , as the relator
length goes to infinity, the random groups will pass through infinitely
many different quasi-isometry classes.Comment: 32 pages, 4 figures. v2: Final version. Main result improved to
density < 1/16. Many minor improvements. To appear in GAF
On Convergence to the Denjoy-Wolff Point
For holomorphic selfmaps of the open unit disc U that are not elliptic automorphisms, the Schwarz Lemma and the Denjoy-Wolff Theorem combine to yield a remarkable result: each such map φ has a (necessarily unique) Denjoy-Wolff point ..
Description of \u3ci\u3eHydrosmectomorpha\u3c/i\u3e Klimaszewski and Webster, a new subgenus of \u3ci\u3eAtheta\u3c/i\u3e C. G. Thomson, with three new Canadian species (Coleoptera: Staphylinidae: Aleocharinae)
A new subgenus, Hydrosmectomorpha Klimaszewski and Webster, of the genus Atheta C. G. Thomson (Coleoptera: Staphylinidae: Aleocharinae) is erected to accommodate three new species and Atheta newfoundlandica (Klimaszewski and Langor). The new species are: Atheta (Hydrosmectomorpha) meduxnekeagensis Webster and Klimaszewski, new species; Atheta (Hydrosmectomorpha) quebecensis Webster and Klimaszewski, new species, Atheta (Hydrosmectomorpha) vincenti Webster and Klimaszewski, new species. The new species are described, illustrated, and a key is provided. Atheta newfoundlandica (Klimaszewski and Langor), was recently transferred from Hydrosmecta C.G. Thomson to an unspecified subgenus of Atheta. New habitat/collection data are presented for the treated species
The augmented message-matrix approach to deterministic dense coding theory
A method is presented for producing analytical results applicable to the
standard two-party deterministic dense coding protocol, wherein communication
of K perfectly distinguishable messages is attainable with the aid of K
selected local unitary operations on one qudit from a pair of entangled qudits
of equal dimension d in a pure state. The method utilizes the properties of a
(d^2)x(d^2) unitary matrix whose initial columns represent message states of
the system used for communication, augmented by sufficiently many additional
orthonormal column vectors so that the resulting matrix is unitary. Using the
unitarity properties of this augmented message-matrix, we produce simple proofs
of previously established results including (i) an upper bound on the value of
the square of the largest Schmidt coefficient, given by d/K, and (ii) the
impossibility of finding a pure state that can enable transmission of K=d^2-1
messages but not d^2. Additional results obtained using the method include
proofs that when K=d+1 the upper bound on the square of the largest Schmidt
coefficient (i) always reduces to at least (1/2)[1+sqrt{(d-2)/(d+2)}], and (ii)
reduces to (d-1)/d in the special case that the identity and shift operators
are two of the selected local unitaries.Comment: 16 page
A hypercyclic finite rank perturbation of a unitary operator
A unitary operator and a rank operator acting on a Hilbert space
\H are constructed such that is hypercyclic. This answers affirmatively
a question of Salas whether a finite rank perturbation of a hyponormal operator
can be supercyclic.Comment: published in Mathematische Annale
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